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Tribologie und Schmierungstechnik HERAUSGEGEBEN VON RÜDIGER KRETHE UND MANFRED JUNGK 69. JAHRGANG eOnly SONDERAUSGABE 1 _ 22 Organ der Gesellschaft für Tribologie Organ der Österreichischen Tribologischen Gesellschaft Organ der Swiss Tribology Editorial 1 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0024 Ladies and Gentlemen, Lubricants help to keep our systems running: They protect our machine elements from wear and corrosion and in this way ensure a long service life and smart operation. As diverse as our machines are, as diverse the lubricants must be to optimally fulfil the specific requirements of a particular machine system. Today’s machines are becoming more and more powerful thanks to permanent research and development. Thus, even the constantly growing demands on lubricants cannot be met without well-founded scientific research. Kurt Lewin, German social psychologist, put it in a nutshell: Nothing is more practical than a good theory. In other words: Science and practice belong together. No progress without science, no real progress without putting the knowledge gained into practice, and no money for further research without economic success in practice. Our journal, starting from the editorial team, the editor, the publisher, the many authors, and advertisers are committed to the transfer of scientific knowledge into practice. And of course, you, dear reader: You are a very important element in this chain, because lubrication does not happen by itself. Without you, the final step is missing. Lubrication must be organised and done. Best of all, on a solid basis. In this special edition, we present a selection of expert papers from the OilDoc Conference 2021. The international conference and technical exhibition, which has been taking place every two years since 2011, also aims to bring together all those involved: Scientists, designers, oil experts, manufacturers of lubrication systems, testing technology and sensors, maintenance specialists and the service companies that support them, for example for oil monitoring and oil care. The special profile of the conference is the mix of expert lectures, the high level of practical relevance and the direct contact with leading experts and companies from the various specialist areas during the breaks, at the exhibition and the evening events. Therefore, our invitation: Stay tuned so that your machines run better and better. And perhaps we will see you - at the next OilDoc Conference in May 2023! Petra Bots & Rüdiger Krethe OilDoc Akademie Reliable machine lubrication means lifelong learning Veranstaltungen 2 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 Supported by Gears • Turbines • Engines • Hydraulic systems • Rolling and plain bearings • Special applications Condition Monitoring & Maintenance 4.0 Analysis methods for oils / greases / coolants • Sampling • Evaluation and Interpretation • Oil Sensors • Troubleshooting • Success Stories • On-site Measurement • Digitalization • Artificial intelligence Fluid Condition Monitoring - Online • On-Site • Offline Asset & Lubrication Management • Lubrication Schedules & Programs • Professional Oil Maintenance • Lubricators • Lubricant Storage, Transport & Handling • Disposal • Lubrication Methods • Lubrication systems • Sustainability Asset & Fluid Management - Innovative & Sustainable Base oils • Additives • Lubricating greases & pastes • Bonded coatings • Solid lubricants • Dry lubrication Lubricants - Latest developments Engines • Sewage gas, biogas and wood gas engines • Gears • Hydraulics • Bearings • Turbines • Wind energy plants • Compressors • Fuel & Energy economy • Sustainability Lubricants - Design to Application Water based and water free fluids • Multifunctional lubricants • Minimum quantity lubrication and dry processing • Modular systems in lubricant formulation Metal working and forming lubrication Environmental and health aspects of lubrication • Vacuum lubrication • Biodegradable fluids • Food grade lubricants • Fire resistant lubricants • High or low temperature lubrication Lubrication in Special Environments Insulating oils • Heat transfer fluids • Coolants • Corrosion protection • Cleaning agents Functional fluids - Everything but lubrication Friction and wear • Materials, surface engineering, contact mechanics • Tribometry • Hydrodynamic and elasto-hydrodynamic Lubrication • Minimal quantity lubrication • Dry lubrication • Tribology of machine parts and components Tribology - Research targeting Experience Lubricants & Lubrication for E-Mobiles / powertrain / bearings • Coolants • Concepts & Solutions • Energy Efficiency E-Drive Lubrication T O P I C S Sign up for more info at: www.oildoc-conference.com The trend-setting event - established 2011 - on the topics of sustainable lubrication, lubricants, and condition monitoring will again take place as a presence event on site in Rosenheim from May 9-11, 2023! At the OilDoc Conference & Exhibition an ambitious program awaits you: On the first two days, you will benefit from numerous presentations by renowned speakers , two evening events (e.g. the famous Baverian Evening ) and a large accompanying exhibition . On the third day, you have the choice to participate in various handson workshops or excursions in the surroundings of Rosenheim (50 km south of Munich). Don‘t miss the next OilDoc Conference & Exhibition in the Bavarian Spring Season! Until 30.11.2022 you can still register at the Extra Early Bird rate! Extra Early Bird Rate: 799 € + VAT (Regular Rate: 995 € + VAT) You want to be an active part of the Event? Register for the international OilDoc Exhibition or submit an abstract and become a speaker at the Conference! We also offer Sponsorship Packages for every budget. O i l D o c C o n f e r e n c e SAFE THE BEST PRICE! DEADLINE: Nov. 30, 2022 EXTRA EARLY BIRD Inhalt 3 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 4 Neil Conway, Carsten Giebeler, Benjamin Wiesent How to get Lab Equivalent Oil Analysis 24/ 7 11 Thomas Emmrich, Klaus Herrmann, Michael Guenther Pre-ignition phenomena in the tension field between operating agents and thermodynamic boundary conditions 19 Frank Reichmann A practical Approach to predict Service Life and Re-lubrication Rate of Grease in Rolling Bearings 25 Tobias Schick, Jochen Hörer, Karl-Heinz Blum, Klaus Ellenrieder, Katharina Schmitz Sensitivity analysis of operating parameters in hydraulic systems with respect to the aging of hydraulic fluids 30 Govind Khemchandani Development of Next Generation EV Coolant 34 Tomas Klima, Wojciech Majka How to commission the turbine oil system that was over years out of operation? Can heavily corroded and deposited turbine oil systems be restored 1 Editorial Reliable machine lubrication means lifelong learning Aus Wissenschaft und Forschung Vorab Tribologie und Schmierungstechnik Organ der Gesellschaft für Tribologie Organ der Österreichischen Tribologischen Gesellschaft Organ der Swiss Tribology 69. Jahrgang, eOnly Sonderausgabe 1 November 2022 Veröffentlichungen Die Autoren wissenschaftlicher Beiträge werden gebeten, ihre Manuskripte direkt an den Herausgeber, Dr. Jungk, zu senden (Checkliste und Formatvorgaben siehe Umschlagseite hinten). Authors of scientific contributions are requested to submit their manuscripts directly to the editor, Dr. Jungk (see inside back cover for formatting guidelines). IHR ONLINE-ABONNEMENT DER TuS Ab dem Jahrgang 2019 können Sie die aktuellen Hefte der Tribologie und Schmierungstechnik im Online-Abonnement beziehen. Die Hefte der vergangenen Jahrgänge werden kontinuierlich integriert. Unsere eLibrary bietet Ihnen einen qualitativ hochwertigen und benutzerfreundlichen Zugang zum digitalen Buch- und Zeitschriftenprogramm der Verlage expert, Narr Francke Attempto und UVK. Nutzen Sie mit uns die Chancen der Digitalisierung: https: / / elibrary.narr.digital/ journal/ tus Der Online-Zugang ist in Kombination mit dem Print-Abo oder als e-only-Abo erhältlich. Abo-Service: Tel: +49 (0)7071 97 97 10 Fax: +49 (0)7071 97 97 11 eMail: abo@narr.de Weitere Inhalte zu den Themen Schmierung, Reibung und Verschleiß finden Sie unter www.narr.de/ technik. ric constant or impedance of the oil, but these types of parameters are never found in any oil analysis report and are therefore very difficult to interpret without having expert knowledge. In general, these sensors work well in controlled environments. In real world applications where the oil undergoes many changes in parallel (base number reduction, oxidation, water, soot, additive depletion etc) and not to forget temperature changes, all these individual parameters will have an influence on the sensor output, and it is impossible to extract the root cause of the observed sensor changes. Aus Wissenschaft und Forschung 4 1 Introduction Oils and lubricants play a critical role in industry and in the operation of plant equipment such as gas engines, and turbines (steam, gas, hydro) for power generation, large gas compressors, gearboxes (on wind turbines for example), hydraulic systems, steel and metal working applications and industrial automotive engines like excavators, diggers and large trucks. Oil condition monitoring forms a critical part of the lubrication management and maintenance programme and it provides important information to ensure that the asset is operated correctly. Conventionally, plant engineers operating and maintaining high value assets rely on taking oil samples periodically and sending them to a laboratory for analysis. It can take up to 5 days from sampling to receiving the oil report and introduces a large time lag in the reporting of the oil condition. This process is shown in figure 1. The benefit of having real-time monitoring of the oil condition is vast. Customers will not only have the satisfaction of being in complete control of their asset, but the Cost of Ownership (COO) will also decrease as: • potential failure modes can be spotted in the data and can be corrected immediately. • a more effective maintenance and service process can be established as the status of the oil/ engine will be known at the time of sending out an engineer. • oil change intervals can be confidently extended and moved from time based to condition-based intervals. Obviously, real time oil condition monitoring is not new and over recent years a number of different sensor technologies have been used and tested, namely inline dielectric or impedance sensors. These sensors measure physical properties of the oil sample, such as the dielect- DOI 10.24053/ TuS-2022-0025 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 How to get Lab Equivalent Oil Analysis 24/ 7 Neil Conway, Carsten Giebeler, Benjamin Wiesent* The established process for oil condition monitoring is to periodically take a sample and have it analysed in an oil laboratory. These laboratory measurements are governed by various technical standards (ASTM,DIN etc) and customers rely on this periodic data to react to oil condition trends and/ or step functions, to plan servicing and maintenance and to reduce asset downtime from failure. Real-time oil condition monitoring systems based on dielectric or impedance analysis of the oil have been available for some time but they only provide summary parameters that are hard to interpretate as they do not correlate with the laboratory oil analysis. In this paper we discuss the development of Spectrolytic’s Oil Condition Monitoring systems (Fluid- InspectIR ® ) and how, by working closely with our customers, we have developed a robust and affordable range of oil condition monitoring systems that gives our clients meaningful and understandable real time data of the same parameters and in the same units as they are commonly receive it from their oil laboratory analysis. These systems provide the customer the comfort of having quantitative and accurate key oil condition data at the touch of a button, while still utilising their standard practices through oil laboratory measurement to validate the predicted key oil parameters by the inline system. Keywords oil condition monitoring, technical standards, Realtime oil condition monitoring, FluidInspectIR ® , laboratory measurements Abstract * Neil Conway Dr. Carsten Giebeler Spectrolytic, Edinburgh, Scotland, UK. Dr.-Ing. Benjamin Wiesent Spectrolytic, Wackersdorf, Germany Based on customer feedback and the clear need for a real time sensor that provides meaningful data, Spectrolytic developed a unique range of oil analysers that measures the most relevant oil degradation and contamination parameters like oxidation, nitration, sulphation, water, soot, additives. The systems also use advanced chemometrics to extract TAN (total Acid Number), TBN (Total Base Number), ipH, viscosity and other chemical changes from the data. For the inline analyser additional modules can be added to house a particle or wear sensor or any sensor that the customer wishes to use to merge with the data stream. A short overview of the next generation of FluidInspectIR ® inline and portable analysers are shown in figure 2. 2 Oil Condition Sensor Platform The sensor platform developed by Spectrolytic utilises the powerful analytical technique of mid-infrared spectroscopy to measure a variety of relevant degradation parameters in an oil sample. With each measurement the sensor determines the changes of the oil at a molecular level using the same analytical technique and data extraction as employed by oil laboratories around the world. The laboratories carry out an oil analysis on customer samples by applying various ASTM and/ or DIN standards to determine Oxidation, Nitration, Sulphation, additive changes and contamination levels of the oil. This common baseline of using mid-infrared spectroscopy as the analytical tool not only allows our sensor to provide real time data with the same units and accuracy as the oil laboratories, but it also provides the option, by employing sophisticated mathematical algorithms, to predict more complex oil parameters such as Total Acid Numbers (TAN), Total Base numbers (TBN) or ipH. Another factor that should not be underestimated is the simplicity of generating calibration files for any given oil/ application. We have developed and designed the systems in such a way that allows the customer to monitor most parametric data from the day of install. There is no need for having old oil samples, shipping oil samples around the world or having to artificially age the oils. 3 Analyser Hardware Spectrolytic’s FluidInspectIR ® Inline oil condition monitoring system allows seamless inline installation. The Aus Wissenschaft und Forschung 5 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0025 Figure 1: Typical oil analysis process in an industrial environment and the positive effects of at-line or real time oil analysis Figure 2: FluidInspectIR ® Inline and Portable Oil Condition Analysers ratio. Typically the SNR ratios for these system are 10000: 1 but it all depends on the sample type, film thickness etc. 4 Application Analysis The sensor extracts, in real time, multiple parameters from the chemical changes in the oils’ infra-red absorption using the same analytical technique as employed in an oil laboratory. The sensor is configured and set-up in such a way that it applies ASTM and DIN standards to determine oxidation, nitration, sulphation etc in real time so that the sensor output is directly proportional to these oil degradation parameters. The table in figure 5 provides a good summary of the parameters that have been measured and analysis with our oil analyser systems. The table not only lists the parameters but also provides the units in which the parameters are reported which correspond exactly to those reported by the oil analysis laboratories. Field Application Engineers are well versed in analysing and interpreting reference reports of oil samples and having the sensor data presented in the same format as in the oil reference report significantly lowers the barrier for adapting real time and/ or at line oil condition monitoring sensor technologies. Today’s oil formulations are complex and depend largely on the application (engine, hydraulic, gearbox etc) as regards to the base oil and additive package. Base oils from Group I-III are predominately mineral oils (some Group III base oils are classed in terminology as ‘synthetic’) and Group IV (PolyAlphaOelfins) and Group V (PolyAlkyGylcol, Polyolesters, Phosphate Ester, siloxanes) are classed as synthetic oils. Aus Wissenschaft und Forschung 6 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0025 kit installation is plug and play and can be carried out remotely with the support of our Field Service Engineers. The Inline Analyser can be integrated into the main oil flow of the asset via a bypass or alternatively oil can be extracted from an oil sump or oil tank using an integrated pump. If required for the application the analyser can be configured to include particle and wear sensors, viscosity sensors or other sensor that might provide additional information. The generation 2 system as seen in figure 3 has a much smaller footprint and has functionality improvements. Housed inside the kit, amongst other hardware, is an innovative inline mid infrared (MIRS8-T) sensor that extracts the relevant oil condition information from chemical changes in the oils’ infra-red absorbance signature. The MIRS device contains a multi-level array of infrared emitters, sensors and a transmission flow-cell ( see figure 4). The customer can choose the number of pay-load channels depending on the number of parameters that need to be measured. The emitters and sensors are orientated in such a way to avoid any undesired interference effects caused by certain microcavity effects but at the same time to provide the best possible Signal to Noise Figure 3: Installations of Generation 1 Inline Analyser on gas engines Figure 4: MIRS8-T sensor used for inline oil measurements in transmission mode Recent advancements in the sensor technology has opened up the industrial markets for disruptive measurements. The inline systems can measure the chemical degradation involved in polyolester and phosphate ester oils and key parameters in steel plants and metal working industry (aluminium sheet milling). 5 Sensor Accuracy There is an excellent agreement between predicted sensor data and reference analysis as shown in plot below. The plot also displays ‘rogue’ measurements from reference analysis that the sensor does not display. This is likely some error in sample taking or sample measurement. The sensor therefore removes all human involvement from the oil analysis process as there is no sample taking process, no storage/ shipment required Aus Wissenschaft und Forschung 7 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0025 Figure 5: Summary of relevant oil degradation parameters that have been measured with our in-line or at-line oil analysers Figure 6: Sensor vrs Oil Lab data for gas engine installation The user can define and set the limits for each parameter to flag any trends or step changes in the behaviour of the oil condition. 7 Conclusion In this paper we have outlined the working principles and the benefits of a real time oil condition monitoring sensor that provides customers with easy to understand and meaningful data. The sensor output data are presented to the user in the same, familiar units that they know from laboratory oil analysis reports and are therefore easy to understand and to interpret. Moreover, our virtual sensor enables the customer to first test the device performance and the usefulness of the sensor in their specific application without having to spend any money on hardware or design-in activities. The sensors can be customised for oil type and application and easily installed with several options for streaming data. Aus Wissenschaft und Forschung 8 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0025 or no lab technician carrying out measurements. The results are reliable and consistent reference analysis with minimum effort. The sensor provides customers with accurate , understandable and actionable oil analysis data 24/ 7. 6 Real time Sensor Data As we move more and more towards the realms of Industry 4.0, it’s critical that the plant asset user has access to the full data stream at the touch of a button. For the Inline system, the Data can be sent to Spectrolytic’s cloud and there is an option to view/ download data via a dashboard. We support customer’s cloud (Azure, AWS) via MQTT or Web API protocols Direct integration available with on-site controller systems From the cloud web portal (example in figure 7), the user can access the process control charts from all the sensors to get a complete picture of the oil condition. Figure 7: Dashboard viewer example of oil parameters Aus Wissenschaft und Forschung 9 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 Aus Wissenschaft und Forschung 10 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 Eine Zeitschrift des Verband Schmierstoff-Industrie e. V. SCHMIERSTOFF SCHMIERUNG www.sus.expert Hier können Sie die Zeitschrift kostenlos abonnieren. E R S C H E I N T V I E R M A L I M J A H R 1 Definition of pre-ignition and phenomenology Pre-ignition is a self-ignition phenomenon in highly supercharged gasoline engines, which is characterized by incipient combustion even before the external ignition source (e.g. electric ignition spark). Because of the early combustion, strong knocking usually occurs subsequently. Pre-ignition occurs spontaneously primarily at high mean pressures and low engine speeds and is stochastically distributed. Pre-ignition events often occur in sequences if no countermeasures are taken. These sequences are thermodynamically driven. If PI events are caused by oil droplets or particles, they are usually single events, which are also distributed in the combustion chamber, stochastically. The energy conversion is rapid and leads to significantly higher combustion chamber pressures (see Graphic 1), which can reach 2 to 3 times the regular combustion chamber pressures. Acoustically, pre-ignition is audible as a distinct metallic-sounding noise (thump), which is due to the high pressure gradients. In the p-V diagram, pre-ignition can be clearly detected by the characteristic pressure rise (see Graphic 1). The occurring maximum pressures often exceed the measuring range of the pressure transducers, which is why usually only a qualitative statement about the events can be made. The consequence of these significant pressure overshoots is often damage to the piston. Typical damages are: • Fractures at ringland 1/ at the ringlands (see Graphic 2) • Fractures/ cracks/ washouts at the top land (due to blowby) • Fractures of the piston pin hub • Hot and cold tight piston rings • Piston ring fractures These damages may occur after single, violent events (force fractures) or may develop after several pre-ignition events (endurance/ fatigue fractures). In addition to the mechanical robustness of the piston, the magnitude of the pressure surge or the severity of the PI event is decisive. The further the heat release moves away from the ignition point towards the early combustion position, Aus Wissenschaft und Forschung 11 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0026 Pre-ignition phenomena in the tension field between operating agents and thermodynamic boundary conditions Thomas Emmrich, Klaus Herrmann, Michael Guenther* Against the background of EU legislation with regard to CO 2 emissions, a development trend towards higher geometric compression is emerging for gasoline engines. In principle, this leads - especially in combination with high mean pressure at low engine speed - to a higher pre-ignition tendency, well known as low speed pre-ignition (LSPI). The worldwide use of engine families with different fuel and oil quality represents an additional challenge, which has to be ensured within the scope of series development. IAV has extensive expertise and methodical approaches to minimize the risk of pre-ignition starting in the preliminary development through to series application and to avoid engine damage in the field. The definition and phenomenology of pre-ignition are presented. The presentation highlighted thermodynamic aspects as well as influences from operating agents and engine design. By using the IAV enthalpy approach, it is possible to evaluate designed engines objectively. This knowledge can also be used in the development of new engines concepts. Finally, a test method is presented which is used for the final assurance of the operational stability even in the case of stochastically occurring pre-ignition. Keywords LSPI, Pre-ignition, enthalpy-approach, endurancetest, oil impact, fuel impact, thermodynamics Abstract * Dr.-Ing. Thomas Emmrich Dipl.-Ing. Klaus Herrmann Dipl.-Ing. Michael Guenther IAV GmbH, Chemnitz, Germany 2 Influencing factors on pre-ignition 2.1 Dependence on operating point/ thermodynamics 2.1.1 Engine speed influence Generally, the risk of pre-ignition is greatest at the lowend torque (LET) point. This point marks the point of maximum mean pressure (= maximum engine torque) at minimum engine speed. In addition to the high load at low speed the knocking impact shifts the center of combustion heat release to a very late position and increases the time for generation of pre ignition conditions. Below the engine speed of the LET, the maximum mean pressure (proportional to the boost pressure) is not reached, or above this engine speed the time for the necessary chemical pre-reactions in the combustion chamber decreases. Both conditions therefore have a reducing effect on the risk of pre-ignition. 2.1.2 Mean effective pressure impact Assuming a stoichiometric fuel-air ratio (λ = 1), the increase in mean effective pressure (BMEP) is achieved by a higher degree of charging (increase in boost pressure) of the engine. Thus, the higher the boost pressure, the greater the internal energy (enthalpy) of the fresh gas at constant displacement. For a given compression ratio, the work of volume change during compression remains almost constant (neglecting wall heat exchange), meaning the enthalpy change of the working gas at TDC is proportional to the change in boost pressure. Graphic 4 shows this relationship for 2 operating points. 2.1.3 Charge air temperature impact The temperature characterizes the internal kinetic energy of a substance, i.e. a high charge air temperature indica- Aus Wissenschaft und Forschung 12 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0026 the higher the pressure peaks. This results from the combination of the pressure increase due to energy release with simultaneous compression as a result of the volume reduction caused by the upward movement of the piston (compression) and the high-frequency pressure components from knocking combustion. Damage to the cylinder bore of the affected cylinder can remain minor if detected in time. Such pre-ignition damage can be detected by measuring the blowby or monitoring the crankcase pressure. Slight or incipient damage can only be reliably detected with high sensitivity of the measuring section and a great deal of experience. Since the resulting increase in crankcase pressure or blowby is only very slight or lies within the permissible tolerance, very narrow monitoring limits on the engine test bench are essential. In field operation without monitoring, PI damage is usually only detectable in the event of severe damage to the piston as a result of the loss of power that occurs. In multi-cylinder engines, compression measurement can be used to determine the affected cylinder. Graphic 1: Pressure curve for PI at n = 1500 rpm and BMEP = 22 bar Graphic 2: Typical damage pattern after several pre-ignitions Graphic 3: Schematic representation of the preignition risk in the engine map tes a higher enthalpy state. The charge air temperature characterizes the starting conditions of the thermodynamic process. If we disregard the wall heat losses during compression, we find the enthalpy increase due to the increase of the charge air temperature at TDC (end of compression) (Graphic 5). accelerates the propagation speed of this flame front and minimizes the risk of unwanted self-ignition (knocking), which is why the Otto combustion process is referred to as a turbulence-driven combustion process. As already stated in (Dahns, Han, & Magar, 2009), a low-knock combustion process also results in a lower risk of preignition. DI/ MPI mixture preparation: The advantage of the duct-injected MPI process is the excellent homogenization of the fuel-air mixture in the intake manifold and the avoidance of lubricant film wash-off and wall wetting when the engine is warm (Brandt, et al., 2010). In addition to using fuel evaporation enthalpy for internal cooling, the DI process still offers the possibility of optimizing the effect of internal cooling via different injection patterns. The effect of these mechanisms is explained in more detail in section 3. 2.2.2 Influence of the residual gas fraction Because the combustion gases are not completely expelled from the combustion chamber, the mixing temperature of the fresh gas charge is raised as a function of the residual gas content. High fresh gas temperatures in the cylinder lead to an increased tendency to pre-ignition. In addition, depending on the mixture quality of the fuel grade and the oil composition, there are radicals in the exhaust gas, which increase the tendency to self-ignition. Especially at critical operating points, high residual gas contents in the cylinder and unfavorable residual gas composition due to incomplete combustion must be avoided. In particular, acetone and high NOx contents in the residual gas can have a catalytic effect on spontaneous combustion (Hoffmeyer, et al., 2009). 2.2.3 Constructive design for oil balance Since the number of possible influencing factors is very large, some typical causes are listed, but they do not claim to be exhaustive: • Washing off of liner (fuel wall buildup) • Entry into fresh gas (blowby recirculation in intake tract, ATL storage) • Storage in crevices or deposits (oil carbon in the top land, oil carbon, combustion residues) • Cylinder wall temperature (depending on coolant temperature) • Pockets/ sinks in the intake section, where oil emulsion can accumulate • Lubricant film thickness (e.g. depending on the tangential force of the piston rings) Aus Wissenschaft und Forschung 13 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0026 Graphic 4: Mean effective pressure influence Graphic 5: charge air temperature impact 2.2 Dependence on the designed engine 2.2.1 Constructional design - combustion process Internal cylinder flow: Starting from an external initialization of combustion, e.g. by an ignition spark, combustion progresses concentrically around this starting point in a flame front. The combustion causes the pressure and temperature in the combustion chamber to rise sharply, which shifts the thermodynamic framework conditions in the combustion chamber toward the self-ignition limit of the fresh gas. However, the chemical reactions are time-dependent, which is why pre-ignition only occurs at low engine speeds. Turbulence (kinetic energy of the particles) Market-specific quality criteria for fuels require adapted test cycles to ensure the operational reliability of the engine. PI-fuels are used specifically for the calibration of pre-ignition protection functions in the control unit and their escalation stages. On the other hand, the mechanical robustness of the engine with regard to pre-ignition can be checked within a reasonable time frame. Aus Wissenschaft und Forschung 14 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0026 In Graphic 6, the influence of crankcase pressure is shown as an example of these influencing factors. The increase in pressure was achieved externally via a pressure source and corresponds approximately to the doubling of the blowby value in the test engine (simulation lifetime). The 50 % change in PI frequency shows the relationship well. An increase in crankcase pressure can occur on the engine practically due to several causes: • Natural wear on the engine (wear of the piston rings - reduction of the tangential force) • Breakage of one or more piston rings • Wear on the liner • Fault in the crankcase ventilation system 2.3 Influence of operating agents 2.3.1 Influence of fuel Fuel quality has a very great influence on pre-ignition behavior. Within the EU, fuel quality is regulated in DIN EN 228 (Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit, 2020). This standardization prescribes, according to the fuel quality, a certain minimum octane number, which characterizes the knocking behavior. As mentioned in (Spicher & Rothe, 2007), conclusions about the pre-ignition behavior can be drawn from the octane number. Fuels with a high octane number cause a lower risk of pre-ignition than fuels with a low octane number. The admixture of diesel fuel, which reduces the octane number and thus the knock resistance and increases the ignition readiness, relies on this effect. Various mineral oil companies offer special fuels (referred to here as PI-fuel) that are specifically formulated to increase the tendency to self-ignition several times over compared with standard fuels (e.g. RON 95). A comparison of the components of PI-fuel and standard fuel RON 95 shows the differences with the same antiknock properties (see Graphic 7). The PI-fuel used for the tests contains approx. 1/ 3 more aromatics. Particularly long-chain and thus high-boiling aromatics are knock-resistant and thus realize the same octane number as in the standard fuel RON 95, but participate only to a limited extent in the mixture formation. The comparison of the boiling lines (see Graphic 9) for both fuels reflects this fact. The fuel components that really participate in mixture formation exhibit lower knock resistance and thus cause the significant increase in pre-ignition frequency (see Graphic 8). Evaporation behavior of the fuel is closely related to the fuel spray. The higher boiling point of PI-fuel prolongs the liquid phase of the spray. This increases the risk of wall wetting resulting in fuel ingress into the oil. Graphic 6: Influence of crankcase pressure Graphic 8: Influence of fuel quality on pre-ignition behavior Graphic 7: Composition of PI-fuel and standard fuel RON 95 E10 2.3.2 Lubricating oil influence Engine oil is a formulation of long-chain hydrocarbons of mineral or synthetic origin. Additives are added to the basic formulation depending on the manufacturer and properties, which makes it very difficult to make a generalized statement regarding the influence of pre-ignition. In principle, however, engine oil has a high boiling point due to its components and thus poor evaporation properties. However, oil vapor mixed with air is very ignitable. Parallels can be drawn here with diesel fuel. It has been shown that the pre-ignition effect caused by the use of a particular oil can be engine-specific. In general, the focus is on oil consumption and certain additive components (Yasueda, Takasaki, & Tajima, 2011). From the large number of possible factors influencing engine oil on pre-ignition frequency, 4 typical representatives are presented: • In (Takeuchi, Fujimoto, Hirano, & Yamashita, 2012), the influence of calcium salt compounds as a typical D/ D additive component on pre-ignition tendency is presented. Particles and combustion residues bind to this salt and are thus kept in suspension. This property prevents the deposition of these particles in the engine and thus has a positive influence on cleanliness and mechanical function. However, as the content of this salt compound in the oil increases, so does the tendency of the engine to pre-ignite. In Graphic 10, this influence is illustrated on a turbocharged 2-liter gasoline engine. Calcium was added in the form of calcium stearate. The experiment showed that doubling the calcium content from 1000 ppm to 2000 ppm led to a doubling of the pre-ignition frequency. The reason given by (Takeuchi, Fujimoto, Hirano, & Yamashita, 2012) for this behavior is that oil droplets/ oil vapor enter the combustion chamber through the wiping action of the piston rings and can oxidize there with oxygen from the fresh gas. This reaction provides the ignition source for pre-ignition. • As a 2 nd influencing factor, oil dilution was investigated. This process is found in vehicles which are primarily operated in urban and short-distance traffic. In the case of under-stoichiometric engine operation as a result of cold-start enrichment, a certain amount of fuel is introduced into the engine oil via the wall wetting, depending on the engine. When the engine is at operating temperature, most of this added fuel evaporates again. If the engine is not at operating temperature, higher molecular weight compounds remain in the engine oil and cause the engine oil level to rise. Due to lower viscosity and the lower boiling point of fuel, a risk potential can be derived here. In the test, 20 % fuel was added directly to the fresh engine oil. However, the test shows that oil dilution has no demonstrable influence on the pre-ignition risk. However, the high-boiling components that end up in the engine oil via the wall wetting due to a higher boiling point cannot increase the pre-ignition risk either, because these components have a high knock resistance (see section 2.3.1). Aus Wissenschaft und Forschung 15 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0026 Graphic 9: Boiling line comparison of PI-fuel and standard fuel RON 95 E10 Graphic 11: Influence of oil dilution with fuel Graphic 10: Effect of calcium compounds on preignition behavior • Graphic 12 shows that the additive packages generally do not have a negative influence. A near-series oil quality and its Group IV base oil are compared here. Despite an increase in the aromatics content and thus in the reactivity to auto-ignition, the pre-ignition index drops significantly. In this particular case, this is possibly due to the reduced lubricating oil concentration as a result of lubricant film height (reduction of surface tension by surfactants) or positively acting oil-fuel interactions. • The different influence of the reaction kinetics of different base oil formulations is confirmed by Graphic 13. Group V base oils are suspected of being more reactive than Group III and IV oils. The polyethylene glycol used here reduces the tendency to pre-ignition by more than 50 %. Even if the hydroscopically acting glycol is not used for lubrication in the basic engine, it clearly shows the influence of the lack of reaction kinetics. The reason for this can be, among other things, the lubricating film thickness with improved sealing effect as well as the non-existent fluctuation of residual gas nests. 2.4 Classification of pre-ignitions According to the theories formulated in public releases and the influences presented, the following classification of influences on pre-ignition (see Graphic 14) is made: 3 Evaluation of pre-ignition behavior with the IAV enthalpy approach As mentioned in section 1, to date there is no clear theory on the origin and mechanisms of pre-ignition. Neverthe- Aus Wissenschaft und Forschung 16 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0026 Graphic 13: Pre-ignition frequency of additivated engine oil and glycol in comparison Graphic 12: Influence of additives in oil on preignition frequency Graphic 14: Main factors influencing pre-ignition behavior less, new engines with higher mean effective pressures are being built all the time. Here, it is important to have an objective evaluation criterion for the pre-ignition problem at hand. For the characterization of thermodynamically based pre-ignition, the internal energy of the charge is a suitable criterion, as described in section 2.1.2. The IAV model approach (Günther, Tröger, Kratzsch, & Zwahr, 2011) is based on the consideration of the operating point-dependent variables of charge pressure, charge temperature and air ratio. Here, the enthalpy H describes the energy contained in the working gas, which is formed by • the enthalpy of the fresh gas • the enthalpy of the residual gas • the enthalpy of the fuel at the time ‘inlet closes’. For the ‘inlet closes’ to ‘FTDC’ interval, energy is supplied to the fresh gas by the volume change work, an energy exchange occurs via the wall heat transfer, and energy is supplied via the injected fuel (DI) and removed again by its evaporation. The calculated enthalpy at TDC is proportional to the reaction kinetics. Relating the enthalpy to the displacement makes it possible to compare different engines. All corresponding formulas are presented in Graphic 15. The enthalpy approach is based on purely thermodynamic factors. For the evaluation, the thermodynamic parameter enthalpy H at a specific operating point is assigned to the associated number of pre-ignitions, which is a result of all factors influencing the pre-ignition. The limit enthalpy derived from this represents the pre-ignition limit (tolerable statistical frequency of pre-ignitions at a specific operating point, e.g. x/ 10000 ASP or x/ h). This limit enthalpy is to be determined in the engine test by parameter variation. The enthalpy curve for a charge air temperature variation on a 4-cylinder engine is shown in Graphic 16. If one pre-ignition per cylinder and hour is declared permissible, the limit enthalpy can be read from this diagram. 4 Measuring pre-ignition, evaluation parameters and limit values In contrast to knock analysis, unfiltered signals are analyzed and the absolute peak pressure is used as a measure. Since the absolute peak pressure is composed of lowfrequency and high-frequency components, it is extremely important to record all components as unaltered as possible. The threshold of combustion chamber pressure, above which pre-ignition must be assumed, can be determined as follows: For the counting and evaluation of the pre-ignition phenomenon, only damage-relevant pre-ignitions are used, which exceed the designed reciprocating strength of the piston. This criterion is defined individually for each engine variant. In Graphic 17, an analysis of the pre-ignition tendency is shown as an example. Here, the lower pressure class _ = _ + 20 Pressure maximum of regular combustion incl. maximum cycle fluctuation Detection distance Aus Wissenschaft und Forschung 17 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0026 Graphic 16: Determination of the enthalpy limit using the example of a charge air temperature variation Graphic 17: Statistical evaluation of pre-ignition with pressure classification Graphic 15: Collection of formulas for the IAV enthalpy approach Robustness test run: Objective: • Verification of mechanical robustness • Generation of many PI’s in a reasonable amount of time • Achievement of the engine-specific number of PI’s according to manufacturer’s specifications related to each cylinder or engine as a whole Fuel qualities: • PI-fuel Components: • Stationary test at LET speed + 100 rpm (safety reserve to prevent signs of aging during the test) • Dynamic engine speed change • Dynamic load change References Brandt, S., Knoll, G., Schlerege, F., Pischinger, S., Wittler, M., Stein, C., . . . Gohl, M. (2010). Beeinflussung der Schmierölemission durch die Gemischbildung im Brennraum von Verbrennungsmotoren. 19.Aachener Kolloquium Fahrzeug- und Motorentechnik, (S. 571-592). Aachen. Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit. (06 2020). Von https: / / www.bmu.de/ themen/ luft-laerm-verkehr/ verkehr/ kraftstoffe/ kraftstoffqualitaet/ abgerufen Dahns, C., Han, K.-M., & Magar, M. (2009). Vorentflammung bei Ottomotoren. Frankfurt/ M: FVV-Forschungsbericht zum Vorhaben 931. Günther, M., Tröger, R., Kratzsch, M., & Zwahr, S. (2011). Enthalpiebasierter Ansatz zur Quantifizierung und Vermeidung von Vorentflammungen. MTZ - Motortechnische Zeitschrift 72 (04), 296-301. Hoffmeyer, H., Montefrancesco, E., Beck, L., Willand, J., Ziebart, F., & Mauss, F. (2009). Catalytic Reformeated Exhaust Gases in Turbocharged DISI-Engines. SAE Paper 2009-01-0503. Spicher, U., & Rothe, M. (2007). Extremklopfer - Ursachenforschung nach schadensrelevanten klopfenden Arbeitsspielen. Frankfurt/ Main: FVV e.V., Abschlussbericht FVV-Vorhaben 816. Takeuchi, K., Fujimoto, K., Hirano, S., & Yamashita, M. (2012). Investigation of engine oil effect on abnormal combustion in turbochargesd direct injection - spark ignition engines. SAE Int. J. Fuel Lubr. 5 (3) 2012-01-1615. Yasueda, S., Takasaki, K., & Tajima, H. (2011). The abnormal combustion caused by lubrication oil on high BMEP gas engines. 13. Tagung ‘Der Arbeitsprozess des Verbrennungsmotors’, (S. 324 - 336). Graz. Aus Wissenschaft und Forschung 18 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0026 for PI detection was set at 135 bar. The distribution of peak pressures detected for this fuel variation shows that the vast majority of PI events are above 215 bar peak pressure. This information can be used as an indication for the mechanical design of the piston. 5 Proposal of an endurance run for the evaluation of the application and mechanical robustness with regard to pre-ignition Defined acceptance methods are useful for the final acceptance of the engine, but also for the evaluation of asbuilt conditions. An endurance run covering all relevant load points that can occur in the field is particularly important for the pre-ignition problem. As already worked out, pre-ignition occurs in special load situations and is stochastically distributed. Therefore, these load points must be approached in a targeted manner in the endurance run. In order to set statistically stable conditions, PI-fuels are used in some cases. For this purpose, the following subdivision of the endurance program was made: Graphic 18: subdivision of endurance test run Calibration test run: Objective: • Verification of the PI protection function  Detection of PI  Response to PI → prevention of sequences • Synthetic replication of field-relevant extreme situations Fuel qualities: • Spec. Fuel (RON95/ 98) • PI-fuel Components: • Stationary test at LET speed + 100 rpm (safety reserve to prevent signs of aging during the test) • Dynamic engine speed change • Dynamic load change • Cold sooting followed by transient operation (low engine speed+high load) 1 Motivation and Background Lubrication is a key technology for sustainability as it is requested in the Brundtland Report [1]: „Humanity has the ability to make development sustainable - to ensure that it meets the needs of the present without compromising the ability of future generations to meet their own needs.“ Lubrication reduces friction and, therefore, saves energy. This reduces the carbon footprint of any mechanical operation. Even more important is the reduction of wear. This enhances the lifetime of any lubricated machine part and, therefore, saves the resources required for production of the lubricated part. At the same time lubricants require resources themselves. Lubricants are mostly based on petroleum oils, a very precious resource. Oil production, refining and processing requires energy. The carbon footprint of mineral based lubricants may very roughly be assumed to be approx. two kg of CO 2 per kg of lubricant. Therefore, the application of lubricants should always be sustainable itself, lubricants should never be wasted. They should not be exchanged long before the service life is over and the re-lubrication rate should not over-lubricate the machine part. This requires methods to predict the service life and the re-lubrication rate. Aus Wissenschaft und Forschung 19 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0027 A practical Approach to predict Service Life and Re-lubrication Rate of Grease in Rolling Bearings Frank Reichmann* Lubrication is crucial for a sustainable operation of any machinery. A sustainable application of lubricants requires the avoidance of any waste, lubricants should not be exchanged long before their service life has ended. This refers especially to those applications where high operation temperatures are reducing the service life and require a huge consumption of lubricants. Therefore, to fulfil the requirement of sustainability a prediction of the service life at elevated temperatures is crucial. At elevated temperatures the service life of lubricants is limited by thermal aging. This results from a chemical reaction of components of the grease with the oxygen of the ambient air. Such a process follows the Arrhenius equation of chemical kinetics and is given by a straight line in a so-called Arrhenius plot. The slope of the line in the Arrhenius plot is given by the activation energy E A . The FAG FE9 test run is a typical method to assess the service life of a lubricating grease in bearings at elevated temperatures. The test is performed at the upper temperature limit of the grease and gives the service life at this maximum temperature. Once the activation energy E A is available the service life at any other temperature may be calculated. Since the temperature of Abstract * Frank Reichmann CARL BECHEM GMBH, Hagen, Germany the FE9 test run is usually the upper temperature limit the operation temperature is usually lower. Once the calculation start from a high temperature in direction a lower temperature low figures of activation energy E A are resulting in conservative service lives, as it is displayed in in this paper. In case of high figures of the activation energy E A the calculated service life becomes too high what may result in bearing failures. With FE9 test runs at different temperatures an activation energy E A = 75 kJ/ mol was found for a reference grease. Laboratory methods to determine the activation energy do usually result is much higher figures. For example, HP-DSC test with this reference grease resulted in an activation energy E A > 100 kJ/ mol, mostly it was even E A > 120 kJ/ mol. Such a result will lead to unrealistic high calculated service lives. An activation energy of E A = 75 kJ/ mol is basically a proper assumption for the calculation of service life of most greases. Generally it is always recommended to estimate a low activation energy. Keywords thermal aging, Arrhenius equation of chemical kinetics, FAG FE9 test run 3 Aging Aging may occur as mechanical aging or thermal aging. Mechanical aging is the continuous degradation of the lubricant due to shear stresses. Thermal aging results from a chemical reaction of components of the grease with the oxygen of the ambient air. This reaction is temperature-driven. 3.1 Mechanical Aging Many bearing manufacturers have published charts [2, 3] where the service life or re-lubrication rate of greases is a function of the so-called speed factor. The speed factor results from the speed and the size of the bearing and may additionally include a factor representing the type of bearing. Another approach [4] suggests the calculation of service life based on the shelf life of the grease, its speed limit and a simple inverse proportional equation depending on the speed factor. The speed limit may be measured on an adequate test rig such like the FAG WS22 spindle bearing test rig. 3.2 Long Term Temperature ϑ LT All the above mentioned approaches have in common to exclude thermal effects on aging since they represent aging processes at a lower temperature level only. Usually an upper temperature limit for the validity is defined. Once the operation temperature of the bearing exceeds this temperature limit a drastic reduction of the service life needs to be considered. Only an operation below this temperature limit allows a long term service of the grease. Therefore, the temperature limit introduced here shall be called long term temperature ϑ LT from now on. Bearing manufacturers [2, 3] often suggest to consider half of the service life of the grease for each 15 K above the long term temperature. This is a significant impact on the service live. Only 45 K above the long term temperature will leave just 12.5 % of the service life. 3.3 Chemical Kinetics The thermal aging of greases is a chemical reaction and, therefore, should follow the Arrhenius equation of chemical kinetics. According to the common approaches [5] the Arrhenius equation gives the dependence of the rate constant k of a chemical reaction on the temperature T of the reaction. (1) In equation (1) k 0 is the pre-exponential factor and a constant for each chemical reaction. E A is the activation enerk = k 0 exp RT E A - Aus Wissenschaft und Forschung 20 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0027 This refers especially to applications where short service life requires high consumption rates. Typically, high operation temperatures are the key factor to shorten the service life of lubricants drastically. Therefore, to fulfil the requirements of sustainability a prediction of the service life at elevated temperatures is crucial. Only very rough procedures are available to predict the service life of greases in rolling bearings. These procedures do often include a number of parameters that are to be estimated only. Therefore, based on the estimations almost any result may be achieved. Furthermore, basic data to follow these procedures are not available and there are no references given how to generate them. Lately there have been a lot of activities to investigate the physical and chemical influences on service life of lubricants in general. Some approaches include the Arrhenius equation that is widely applied in chemical kinetics. Herewith a simple approach for prediction of service life of greases in rolling bearing is introduced, that considers the latest results of these activities. 2 Mechanisms limiting Service Life It is usually the limit of the service life that is asking for re-lubrication. Therefore, usually the re-lubrication rate is given by the service life of the lubricant. The following mechanisms may limit the service life of greases in rolling bearings: • Loss • Contamination • Aging Loss may be evaporation but is rather more likely leakage. Contamination may occur from the ingress of dust. The particles are often abrasive and, therefore, may reduce the service life. Loss and contamination may occur simultaneously, for example in cases of water wash-out, when the water enters the bearing, contaminates the grease and washes it out at the same time. Nevertheless, in any way re-lubrication rates are to be selected to compensate losses and to avoid contamination. Mostly the required re-lubrication rates are high enough to ensure aging is not determining for the service life at all. However, for perfectly sealed bearings there will be neither loss nor contamination. Under the aspects of sustainability this situation is definitely preferable since this will allow an application of the grease until it has aged. This will reduce any waste of grease to the minimum since, as mentioned above, aging is supposed to be the most lengthy mechanism limiting the service life of bearings. gy for the reaction and R is universal gas constant with Depending on the rate constant k the time t required for a certain reaction will be longer or shorter. It is (2) and with equation (1) this results in: (3) C includes several constants introduced so far. In a so-called Arrhenius plot the natural logarithm of the time required for a chemical reaction ln t is dispayed versus the inverse temperature 1/ T. According to equation (3) this should follow a straight line. 3.4 Arrhenius Plots for Grease Aging According to Matzke et al [6] the aging of greases may be well described by the Arrhenius equation. Matzke has carried out experiments with the RapidOxy tester from Anton Paar GmbH. Grease samples of about 0.5 g are heated in an autoclave under pure oxygen to the testing temperature. With the heat the pressure increases inside of the closed chamber. Afterwards a steady decrease of the pressure was observed which is assumed to result from a chemical reaction between grease and oxygen. At a certain point of time the pressure drops drastically. Matzke assumes this point to correspond to the nearly full depletion of the antioxidant and the beginning oxidation of base oil and thickener. This was repeated with different temperatures and the variables of temperature and time to the pressure drop were displayed in an Arrhenius plot. This was matching quite well a straight line. Therefore, it is proven that thermal aging of greases follows an Arrhenius equation. From the slope of the line the activation energy E A of the aging reaction may be found. 4 FAG FE9 Test Run According to DIN 51825 [7] the FAG FE9 test defines the upper service temperature of greases for bearings in a temperature range from 120 °C upwards. Therefore, this test is quite common and results are available for most greases for bearings. 4.1 Test Run and Results For the FE9 Test 5 rolling bearings are operated with the tested grease at a pre-set temperature. The time of operation until the bearings fail is measured. For each test run there are now 5 times of operation until failure of the bearings. k . t = const ln t = + C RT E A R = 8.314 J/ (mol K). The statistic according to Weibull [8] is rather common to analyse lifetimes. Here an exponential function is applied to describe the statistical distribution of lifetimes. By variation of parameters the function may be adjusted to match the measured lifetimes as good as possible. Once adjusted, the failure probability after any time of operation may be found from the function. In the same way any time to reach a certain failure probabability may be found with the function. Typically the statistical operation time to reach the failure probability of 10 %, this is the F10 value, or to reach the statistical failure probability of 50 %, the F50 value is considered. 4.2 Upper Service Temperature ϑ u According to DIN 51825 [7] the upper service temperature ϑ u for greases in bearings is the highest temperature where a 50 % failure probability is not reached before an operation time of 100 hours. This refers to upper service temperatures ϑ u ≥ 120 °C and corresponds to the following condition: (4) with Typically the upper service temperature is defined in discrete steps of 20 °C starting from 120 °C. FE9 tests ask for a certain effort. To reach F50(ϑ u ) ≥ 100 h some of the bearings may operate more than a week. Therefore, FE9 test runs are usually only conducted at the upper service temperature of the corresponding grease. Higher temperatures are usually not relevant since the lifetime of the grease becomes too short for any technical application. Lower temperatures are of strong technical relevance but the time for each test will increase drastically for lower temperatures. Remembering the suggestion of bearing manufacturers [2, 3] to consider half of the service life of the grease for each 15 K above the long term temperature we finally end up with a figure of F50 ≥ 800 h for a test at 45 °C below the upper service temperature. 4.3 Activation Energy from FE9 Test For one grease of Messrs. Carl Bechem GmbH there have been several FE9 test results available over a temperature range of 60 °C. These test result are to be found below in Table 1. Based on the figures of table 1 an Arrhenius plot with F10 and F50 values is given in Figure 1. According to this plot the thermal aging of greases in rolling bearings is well described by the common Arrhenius equation. u ) 100 h u 120 °C Aus Wissenschaft und Forschung 21 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0027 Arrhenius equation with E A = 75 kJ/ mol at lower temperatures close to the temperature the long term temperature ϑ LT the calculation starts from. Going to higher temperatures the difference increases and becomes huge. In any way the 10 K rule results in lower lifetimes and, therefore, is more conservative compared to the 15 K rule or E A = 75 kJ/ mol. However, using the Arrhenius equation with much higher activation energy of E A = 120 kJ/ mol for example will lead to even more conservative results. Nevertheless, mostly the calculation will follow the other direction from high temperature to low temperature. As mentioned earlier the upper service temperature ϑ u is tested rather frequently and, therefore, results from FE9 runs at these high temperatures should be available. For our reference grease where the activation energy was found to be E A = 75 kJ/ mol Figure 3 gives the example of a calculation from from high temperatures to low temperatures. In this case we may even start our calculation from a testing temperature above the upper service temperature ϑ u where the lifetime of the grease was Aus Wissenschaft und Forschung 22 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0027 From the slopes in figure 1 an average activation energy of approximately E A = 75 kJ/ mol may be found. 5 Grease Life at elevated Temperatures Elevated temperatures are temperatures ϑ ≥ ϑ LT where the equation (3) of Arrhenius is valid or the rough 15 K rule suggested by the bearing manufacturers [2, 3] may be applied. Once the service life of the grease at any particular elevated temperature is known and, furthermore, the activation energy E A of the grease is available the service live at any other temperature ϑ ≥ ϑ LT may be calculated. In Figure 2 the example of a calculation is given once a low temperature, probably the long term temperature ϑ LT , is known. This example refers to the previously introduced reference grease where an activation energy of E A = 75 kJ/ mol was found from several FE9 runs. The Arrhenius equation with this activation energy differs quite clearly from the commonly recommended 15 K rule. Once a 10 K rule is applied this comes rather close to the Table 1: Results of FE9 test [4] Figure 1: Arrhenius plot from FE9 results [4] Figure 2: Calculation from low to high temperature only F50 = 24 h. Now a rather good matching between Arrhenius with E A = 75 kJ/ mol and the 15 K rule is found. Furthermore, both approaches are providing much more conservative figures compared to the 10 K rule that appeared to be better before once we discussed the other direction. A much higher activation energy of E A = 120 kJ/ mol, that used to result in the most conservative figures before, now leads to the highest lifetimes. Therefore, in this example the 15 K rule appears to be a proper tool for a rough assumption of the service life of greases under elevated temperatures. Furthermore, the Arrhenius equation with E A = 75 kJ/ mol matches quite well with this commonly suggested 15 K rule based on long experience. Using the more scientific approach of the Arrhenius equation it is recommendable to calculate with a low activation energy of E A = 75 kJ/ mol or even lower. 6 Determination of the Activation Energy The activation energy that has been found from several FE9 tests seems to match quite well with the common and long established 15 K rule. Nevertheless, characteristics of greases may vary and, therefore, a more scientific approach with a variable parameter should be preferred. Such an approach is given with the Arrhenius equation with a specific activation energy for every grease. To find activation energies from FE9 test runs as it has been demonstrated above seems to provide reliable figures but is an enormous effort and, therefore, not practicable. This is why recently there have been severals attempts to find activation energy of greases in lab scale test with less effort. 6.1 Activation Energy from HP-DSC Tests The Differential Scanning Calorimeter (DSC) is a fundamental tool in thermal analysis and uses a feedback loop to maintain a sample material at a set temperature while measuring the power needed to do this against a reference furnace [9]. It may be applied to assess the reactivity of a material under a reactive gas, mostly oxygen or air. For activation of this reaction the test is running at temperatures of 190 to 240 °C. To avoid evaporation of volatile matter from the material and to shorten the testing time the tests are often conducted under high gas pressure. This is called High Pressure DSC (HP-DSC). To measure the activation energy with a HP-DSC the sample is heated to the testing temperature under an inert gas, generally nitrogen. Afterwards the sample is flushed with reactive gas, oxygen or air, and after a certain time an exothermal reaction of sample and gas is detected by a lower energy demand to keep the testing temperature. Running this test at different temperatures creates pairs of temperature and time that may be displayed in an Arrhenius plot. As it was discussed earlier already, the activation energy E A is to be found from the slope in the plot. 6.2 Comparison of Results In section 4.3 an activation energy of E A = 75 kJ/ mol has been found from FE9 tests for a reference grease. Two samples of the same product have been taken to detect the activation energy in the HP-DSC as well. Both samples have been tested with pure oxygen under a pressure of p Ox = 5 bar and p Ox = 10 bar. The results of the tests are to be found in Table 2. Generally, the results are in a range of 120 to 130 kJ/ mol. Only the 1 st test under p Ox = 5 bar is clearly lower with an activation energy of E A = 87.8 kJ/ mol. In the 2 nd test under p Ox = 5 bar an activation energy of E A = 127.7 kJ/ mol is found what is very close to the result under p Ox = 10 bar. Therefore, it may be assumed Aus Wissenschaft und Forschung 23 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0027 Figure 3: Calculation from high to low temperature Table 2: Activation energy from HP-DSC Most probably this correlation will refer to only one temperature. Therefore, it is suggested to search for a correlation between activation energies from lab tests and bearing tests to cover a wider range of temperatures. 8 Reference [1] United Nations: Report of the World Commission on Environment and Development, Note by the Sectretary- General General Assembly, Fourty-second session, 4 th of August, 1987 [2] Schaffler Technologies GmbH & Co. KG: Rolling Bearing, Issued: 2014, April [3] SKF: Hauptkatalog, Druckschrift 6000/ 2 DE, November 2012, SKF Gruppe, 2012 [4] Frank Reichmann: Vorstellung eines allgemeinen Verfahrens zur Bestimmung der Gebrauchsdauer von Schmierfetten in Wälzlagern, Tribologie und Schmierungstechnik, 67. Jahrgang, 5-6/ 2020 [5] Manfred Baerns, Hans Hofmann, Albert Renken: Chemische Reaktionstechnik, Georg Thieme Verlag Stuttgart, New York, 1987 [6] Markus Matzke, Gerd Dornhöfer, Jörg Schöfer: Quantitatively-accelerated testing of grease oxidation - a parameter study with the RapidOxy, 60. Tribologie-Fachtagung der Gesellschaft für Tribologie e.V., Göttingen, September 2019 [7] DIN 51825: Schmierstoffe, Schmierfette K - Einteilung und Anforderungen, DIN Deutsches Institut für Normung e.V., Beuth Verlag GmbH, Berlin, 2004 [8] Dubbel, Taschenbuch für den Maschinenbau: 16. Auflage, Springer Verlag Berlin, Heidelberg, New York, London, Paris, Tokyo, 1987 [9] PerkinElmer, Inc.: 20 Common Questions about DSC, PerkinElmer, Inc., 2013 [10] In-Sik Rhee: Prediction of high temperature grease life using a decomposition kinetic model, 76 th NLGI annual meeting, Tucson, AZ, 2009 Aus Wissenschaft und Forschung 24 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0027 that the single low figure of E A = 87.8 kJ/ mol is a mismeasurement. Finally, it may be concluded that the activation energies found from the HP-DSC are significantly higher compared to the activation energy found from the FE9 test. 7 Conclusion and Outlook Currently there is no way known for a fast and simple measurement of a reliable figure of the activation energy E A . The only reliable procedure is to run FE9 tests at different temperatures. This, of course, is laborious and time-consuming. Therefore, a conservative assumption of the activation energy is the best way at present. Based on experience a figure of E A = 75 kJ/ mol or lower appears to be a good guess. Nevertheless, guessing this important parameter should not be the standard in future since more accurate calculations are required to optimise sustainability of the lubrication. Therefore, the efforts should be continued to find proper lab method to detect activation energies for grease aging. A very promising approach is the introduction of a formula to transfer the activation energy measured by means of RapidOxy tester or HP-DSC test to the conditions of a bearing. Such an approach has been introduced by Rhee [10]. Rhee has applied a thermogravimetric analyser (TGA) to analyse the kinetic properties of ten greases and calculated the grease life at 180 °C. The lifetime of the greases in the bearing test acc. to ASTM D3527 was also tested at 180 °C a huge difference to the calculated lifetime was found. This confirms the findings published in this paper. However, Rhee found a correlation between calculated and measured lifetime. 1 Introduction Hydraulic fluids play a decisive role on the wear and tear of hydraulic components and therefore the service life of the hydraulic system. The trend toward an everincreasing demand such as compact hydraulic systems, higher power density, lower tank volume, high oil circulation and lifetime filling requires a deeper understanding of the aging behavior and aging stability of hydraulic fluids. The current standard requirements such as DIN 51524 [1] for mineral oils include test standards such as the DIN EN ISO 4263-1 (Tost-Test) [2] for the aging of hydraulic fluids. This static test is based on thermal aging with the addition of air, water and copper. There are many other common oxidation tests for accelerated artificial oil aging [3 - 6]. Similar approaches can also be found in literature [7 - 9]. Parameters from real hydraulic systems such as high operating pressures or shear stress are not covered by these tests. A test method for the determination of oxidation stability in a highpressure piston pump is described in the JCMAS P045 Aus Wissenschaft und Forschung 25 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0028 Sensitivity analysis of operating parameters in hydraulic systems with respect to the aging of hydraulic fluids Tobias Schick, Jochen Hörer, Karl-Heinz Blum, Klaus Ellenrieder, Katharina Schmitz* In dieser Arbeit wird ein neuer Ölalterungsprüfstand vorgestellt, der auf einem realen hydraulischen System basiert. Dieser Prüfstand ermöglicht eine beschleunigte Fluidalterung unter einer hohen hydraulischen Belastung. Des Weiteren ist es möglich, die Betriebsparameter zu variieren und somit die verschiedenen Einflussfaktoren auf das Alterungsverhalten von Hydraulikflüssigkeiten zu bewerten. Unter verschiedenen Bedingungen gealterte Ölproben werden mittels FTIR analysiert. Anhand der Ergebnisse wird die jeweilige Alterungsrate des Fluids am Beispiel des Abbaus des Additivs Zink-Dialkyldithiophosphat (ZDDP) berechnet. Die Ergebnisse zeigen deutlich den Zusammenhang zwischen dem Alterungsverhalten und den verschiedenen Betriebsparametern des Prüfstands. Neben dem Abbau von ZDDP kann der Abbau des phenolischen Antioxidans (AO) und die Bildung von Varnish bedingt durch verschiedene Alterungsprodukte auf metallischen Oberflächen festgestellt werden. Schlüsselwörter Ölalterung, ZDDP, ZnDDP, FTIR, Fluidprüfstand, Hydraulik, Spektroskopie In this work, a novel oil aging test-rig based on a real hydraulic system is introduced. This device allows an accelerated fluid-aging rate under high hydraulic loads. Furthermore, it is possible to vary the operating parameters to evaluate the different factors that influence the aging behavior of hydraulic fluids. Oil samples, which are aged under different conditions, are analyzed using FTIR to estimate the rate of aging using the degradation process of Zinc dialkyl dithiophosphate (ZDDP). The results show a clear aging behavior dependent on different operating parameters in hydraulics. In addition to the degradation of ZDDP, the depletion of the phenolic antioxidant (AO) and the formation of a varnish film on metallic surfaces can be observed. Keywords Oil aging, ZDDP, ZnDDP, FTIR, fluid test rig, hydraulic, oil degradation, spectroscopy Kurzfassung Abstract * Tobias Schick Orcid-ID: https: / / orcid.org/ 0000-0002-2586-5401 Bosch Rexroth AG, Glockeraustraße 2 89275 Elchingen, Germany Jochen Hörer Karl-Heinz Blum Bosch Rexroth AG, 72160 Horb, Germany Klaus Ellenrieder Bosch Rexroth AG, 89275 Elchingen, Germany Univ.-Prof. Dr.-Ing. Katharina Schmitz Orcid-ID: https: / / orcid.org/ 0000-0002-1454-8267 Institute for Fluid Power Drives and Systems (ifas) RWTH Aachen University, 52074 Aachen, Germany relevant for oil aging can be identified and modelled in a practical manner. This data provide valuable insights into the design of new hydraulic systems in terms of high durability and low oil change intervals. 2 Experimental setup Figure 2 shows the schematic structure of the test-rig RFT-OA. The Rexroth A2FO10 bent-axis axial piston pump (1) is driven by a variable speed electric motor with up to 3000 rpm. Optionally, air (2) can be added to the test medium in the suction line with high precision. A Rexroth relief valve DBDS 10 K1X/ 400V (3) serves as a load and regulates the pressure up to 400 bar. After the valve, the hydraulic fluid flows back into the tank via a 10 µm filter (4) and a cooler (5). In addition, a polished copper sheet (7) which is a good catalyst for some aging reactions, can be placed in the tank. The system operates with a total volume between 8 to 16 l of hydraulic fluid. During the test, a special sampling-device, (9) automatically extracts oil samples at pre determined times. This enables uninterrupted operation of the test bench and ensures highly comparable and reproducible results. Depending on the choice of parameters, the RFT-OA shows the highest demands on the aging stability of a hydraulic fluid in a real hydraulic system. As much as possible, all hydraulic components of the test rig are constructed of stainless steel. The stainless steel is particularly effective for the oil tank, cooler and the piping. As we can see in Figure 3 the aging process is not only measurable by serveral chemical analysing techniques but also visible for the naked eye. The degradation products of additives and base oil generate molecules with a high specific mass, which are known as varnish. Varnish is not soluable in unpolar oils and forms an orangecolored film on all metal surfaces. This effect can lead to problems such as sticking valves, especially when the system is switched off and cooled down. Prior to each new experiment we clean our RFT-OA test-rig by adding a special varnish-removing additive and run the system for several hours. The system is then flushed three times with fresh oil. 3 Evaluation method We use a fully formulated API group I, ISO VG 32 mineral oil with a zinc-based and phenolic antioxidant containing additive system for our experiments. Mineral oils cover about 75 % of the market share of hydraulic fluids [11]. One of the most important additives in this formulation is the anti-wear (AW) additive zinc dialkyl dithiophosphate (ZDDP). ZDDP is not only reducing friction and wear by forming a protective tribo-film on metal surfaces but also ZDDP acts as extreme pressure (EP) additive and additionally offers antioxidant properties [12]. For these reasons, we focus our attention on the de- Aus Wissenschaft und Forschung 26 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0028 [10]. In this test method, the hydraulic fluids are aged and assessed in a practical hydraulic circuit comprising a Rexroth A2FO10 bent-axis pump, a load valve, a filter unit and an oil cooler as well as a copper catalyst in the tank and the addition of air. In addition to the requirements of the JCMAS P045, the aging test rig RFT-OA “Rexroth-Fluid-Test-Oil-Aging” (Figure 1) developed by Bosch Rexroth allows the variation of all operating parameters, such as operating pressure, pump speed, oil temperature as well as accurately defined contamination with air and water. As a result, all influence parameters Figure 1: Test-rig RFT-OA Figure 2: Schematic structure of the RFT-OA test-rig Figure 3: Formation of a varnish film on the metal surfaces inside the tank during the aging test pletion of ZDDP to calculate an oil-aging rate with respect to the different hydraulic parameters. The degeneration of ZDDP occurs in several steps (Figure 4). During the first reaction, an oxygen atom replaces one sulfur of the dithiophosphate, which leads to a monothio molecule. This monothiophosphate still has some helpful AW-properties. During the second oxidation step the monothio molecules were oxidized to phosphates. In our work we use Fourier-transform infrared spectroscopy (FTIR) to measure the content of AO, ZDDP and its degradation products. A dataset with several FTIR measurements of our reference experiment (350 bar, 1500 rpm, 80 °C, 16 l, air 1 l/ h) is shown in Figure 5. We can identify the degeneration of ZDDP using the IRabsorption spectra evaluated at 654 cm -1 . For the monothiophosphate species, the same method is used at 1018 cm -1 . The concentration of phosphates correlates to the absorption band at 1800 cm -1 . Initially the ZDDP is consumed, which leads to the formation of the monthiophosphate species during the first 300 hours of the test. Once this process is completed, the monothio species reach a maximum content and begin to deplete to phosphates. After 500 h of test time, there is no ZDDP present. Large quantities of phosphates have been produced, and a residual amount of monothiophosphates can also be detected. There are characteristic points which are important: the maximum concentration of monothio species at 250 hours and the (nearly) complete ZDDP decomposition at 300 hours. All these points in time correlate with the rate of oil aging. The second additive to consider is the phenolic antioxidant which appears at 3650 cm -1 in the IR-absorption spectra. In general, the antioxidant is designed to protect the other oil components from oxidative aging. At the beginning of the experiment, only a small amount of AO is consumed. At 250 h, this changes abruptly. In the second half of the experiment, the concentration of antioxidant drops significantly faster. After 500 h, approx. 70 % of the original amount is still available. Aus Wissenschaft und Forschung 27 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0028 Figure 4: Degeneration process of ZDDP Oil volume [l] Pump speed [rpm] Load pressure [bar] Temperature (Tank) [°C] Coppercatalyst Air supply [l/ h] Time max. Monothiophosphates [h] Time max. Monothiophosphates volume compensated [h/ l] 16 1500 350 80 Yes 0 400 25 8 1500 350 80 Yes 0 200 25 13 3000 350 80 Yes 0 200 15,4 13 1500 175 80 Yes 0 >500 >38,5 16 1500 350 100 No 0 300 18,8 13 1500 350 80 No 0 400 30,8 16 1500 350 80 Yes 1 250 15,7 Table 1: Overview of the performed experiments Figure 5: Results of FTIR-analysis during the oil aging process at the RFT-OA test-rig Load pressure In this aging test, the load pressure has an unusually large influence on the aging behavior. At half the pressure, the maximum of the monothiophosphates is no longer reached within 500 h. At constant tank temperature, the point of the highest temperature in the system at the load valve is mainly influenced by the set pressure, which is the reason for the strong influence. Temperature The oil temperature also has a decisive influence on aging behavior. However, the expectation of an arrhenius equation is not met even if the missing copper catalyst in the fifth experiment is considered. One possible reason for this effect could be that an oil formulation is a complex mixture of substances in which many different reactions take place simultaneously which influences each other. Copper Catalyst The copper catalyst in the tank has a comparatively lower but still measurable influence on the aging rate. In the sixth test without the catalytic converter, the time until the maximum monothiophosphate content is reached increases to 30,8 l/ h. Air supply The oxygen content in the oil is increased by the addition of air, which leads to a significantly higher degradation rate of ZDDP. 5 Conclusion Oil samples were aged in a hydraulic test-rig under different operating parameters. The experiments show that the aging of hydraulic fluids is dependent on many different factors. Using the example of the degradation of ZDDP, the individual influences can be evaluated more accurately. This process cannot be fully covered by artificial aging methods. References [1] DIN 51524-3: 2017-06, Pressure fluids - Hydraulic oils -Part 3: HVLP hydraulic oils, Minimum requirements [2] DIN EN ISO 4263-1: 2004, Petroleum and related products - Determination of the ageing behavior of inhibited oils and fluids - TOST test -Part 1: Procedure for mineral oils (ISO 4263-1: 2003) Aus Wissenschaft und Forschung 28 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0028 4 Results and discussion In this work, several experiments with different operating parameters were carried out at the test-rig RFT-OA. During the experiments, oil samples were taken at 50 hours intervals and evaluated using the previously described methods. Table 1 shows an overview of the tests performed with the various parameters. The point in time of maximum concentration of the monothiophosphates is selected as evaluation criterion for the measure of ZDDP depletion. A high value until the maximum concentration is reached means a slower aging rate and vice versa. Due to the different oil quantities in the experiments, it is necessary to compensate the results accordingly. Figure 6 shows the course of the monothiophosphate concentration with different oil volumes and otherwise identical parameters on the test rig. If the oil quantity is halved from 16 l to 8 l with otherwise constant parameters, the time until the maximum of the monothiophosphates is reached, is also cut in half from 400 h to 200 h. This result shows that in both cases an identical aging rate is present during the degradation process of the ZDDP. By standardizing the results for the oil quantity, all other experiments can be made comparable. The value of 25 l/ h for the first two tests is used as reference. Pump speed If the speed and thus the flow rate are increased, each molecule in the oil passes a critical tribological juncture, with high temperature or a narrow shear gap more often. This significantly increases the depletion rate of the ZDDP, which leads to a low value of 15,5 h/ l until the maximum monothiophosphate concentration is reached. Figure 6: Results of FTIR-analysis of two different experiments with different oil quantities [3] ASTM International. D6186-19 Standard Test Method for Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry (PDSC). West Conshohocken, PA; ASTM International (2019) [4] ASTM International. D2272-14a Standard Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel. West Conshohocken, PA; ASTM International (2014) [5] ASTM International. D6514-03(2019)e1 Standard Test Method for High Temperature Universal Oxidation Test for Turbine Oils. West Conshohocken, PA; ASTM International (2019) [6] ASTM International. D5846-07(2017) Standard Test Method for Universal Oxidation Test for Hydraulic and Turbine Oils Using the Universal Oxidation Test Apparatus. West Conshohocken, PA; ASTM International (2017) [7] Dörr, N., Brenner, J., Ristić, A. et al. Correlation Between Engine Oil Degradation, Tribochemistry, and Tribological Behavior with Focus on ZDDP Deterioration. Tribol Lett 67, 62 (2019). [8] Besser, C., Agocs, A., Ronai, B. et al. Generation of engine oils with defined degree of degradation by means of a large scale artificial alteration method. Tribology International, Volume 132 (2019), Pages 39-49 [9] Vito Tič, Tadej Tašner, Darko Lovrec, Enhanced lubricant management to reduce costs and minimise environmental impact. Energy, Volume 77 (2014), Pages 108-116 [10] JCMAS P 045: 2004, Hydraulic Fluids for Construction Machinery - Test Method for Indicating Oxidation Stability in High Pressure Piston Pump [11] Bauer G. (2011) Druckflüssigkeiten. In: Ölhydraulik. Vieweg+Teubner [12] Spikes, H. The History and Mechanisms of ZDDP. Tribology Letters 17, 469-489 (2004) Aus Wissenschaft und Forschung 29 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0028 Aus Wissenschaft und Forschung 30 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0029 1 Introduction The vehicles of the future will require higher voltages of 400 volts than current models need of 12 volts and 40 volts. The global fluids market[1] for electric vehicles(EVs) encompasses three major types of electric vehicles which are hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). These vehicle types are present in the form of both passenger cars and commercial vehicles. Battery electric vehicle (BEV), is set to dominate the EV fluids market as it is powered solely by the battery systems in the vehicle, which makes it more crucial for automotive OEMs to ensure that the fluids in the EVs are able to optimize the thermal management and driving system. The prominent types of fluids which are being adapted for enhanced application in electric vehicles are greases, heat transfer fluids, driver system fluids, and brake fluids. The Heat transfer fluids market is anticipated to be the largest as the need for coolants in electric vehicles is very critical to cool the battery and increase its driving range. Many prominent EV manufacturers have adopted indirect liquid cooling for example Tesla, and GM in North America. Currently, shelf coolants used for ICE are being used in many EV vehicles for indirect cooling. One of the challenges is absence of ASTM test methods for evaluating EV coolants. This has led to many coolant manufacturers to use modified current ASTMD1384 methods and develop some in-house test methods. Moreover, these fluids need several other characteristics that distinguish them from products in ICE vehicles: compatibility with copper coiling, aluminum and polymer coating and ability to withstand electrical currents. These fluids must dissipate the large amounts of heat generated by EV batteries. The EV coolant formulation should also have electrical properties like electrical conductivity in certain range depending upon the battery configuration of particular EV. Author’s Lab, has been engaged in the unique and ongoing research current in engine coolant technology sin- Development of Next Generation EV Coolant Govind Khemchandani* Research indicates that there are two approaches to Electric Vehicle (EV) liquid cooling: direct and indirect. Direct liquid cooling involves direct contact between the coolant and the battery pack. Indirect liquid cooling requires a medium in between the battery pack and the coolant, preventing direct contact. Many prominent EV manufacturers have adopted indirect liquid cooling for example Tesla, and GM in North America. Currently, shelf coolants used for Internal Combustion Engines (ICE) are being used in many EV vehicles for indirect cooling. One of the challenges is absence of ASTM test methods for evaluating EV coolants. Some operators have used copper wires for generating deposits by employing voltage to test low conductivity EV coolants. Dober long ago realized that copper and aluminum will be the main components of EV engines hence used copper wire under high temp and pressure to show differentiation among coolants. The present paper focuses on Dober-in-house test Parr reactor methodology for comparing electrical conductivities, pH and additive depletion of various coolants thereby showing meaningful trends with time and temperature. This ultimately helps in developing new generation EV coolants. It is concluded that low electrical conductivity along with robust corrosion inhibition package is needed for optimum performance of EV coolants. Keywords Electric Vehicle, EV coolants, liquid cooling, shelf coolants, Combustion Engines Abstract * Govind Khemchandani, Ph. D. Dober Chemical, Woodridge, IL, USA https: / / www.dober.com/ performance-fluids Figure 1: Parr Set Up left & copper wire on cooling coil right ce last 30 years. Much of the work focuses on coolants suitable for engine coolant system components used in ICE [2] and EV engines. Dober in-house Parr Reactor method is used in this paper for comparing indirect EV coolants. 2 Experimental Five coolant samples were chosen which are currently being used in EV indirect cooling. These are coded as 1. D1 EG Premix50/ 50 2. G1 EG Premix50/ 50 3. J1 EG Premix50/ 50 4. V1 EG Premix50/ 50 5. D2 EG Premix50/ 50 Experimental set up is shown in Figure 1. The test conditions used are as below: • Temperature: 150 °C (302 °F) • Pre-charge of Air: 90 PSI • 10 feet copper wire • Duration: 2 weeks • Sample withdrawal intervals: 7,14, and 20 days • Measurement parameters: pH, conductivity, and color change These parameters were considered since earlier [2] authors from Fleetguard and Dober developed this method to model primarily the thermal stability of heavy-duty coolants in 300 K to 400 K miles of actual service. Three bench methods viz. Modified Reaction Kettle [3], ASTM D 2272 and Modified 4340 test [4] were chosen for comparison with Parr method. Parr tests were able to differentiate the quality of coolants and glycols. Results were consistent with field experiences and it was found to be the best of the four tests studied in this paper. Our aim is to study how corrosion inhibitor package used in these five coolants affect electrical conductivity and changes occurring in pH with time and temperature. 3 Description of the Method A total of 1,200 mL EG 50/ 50 Premix solution was added into the Parr reactor cylinder. A ten feet copper wire was wrapped around the cooling coils so that the copper wire would be in contact with the test solution. The reactor head was placed on top of the reactor cylinder and the reactor split ring collar was tightened. The type J thermocouple was placed into the reactor head’s thermowell. To start the test, the display, motor, and heater were turned on. The motor speed was set to 40 % maximum for good mixing and the temperature was set to 150 °C (302 °F). Air pressure is about 25 psi, generated from the heating of the coolant. The test lasted for 20 days. Samples were collected at 163, 331 and 482 hours. Samples were measured for pH per ASTM D 1287, electrical conductivity (CY) per ASTM D 1125, copper, and glycol degradation acids (formic and glycolic). After each sample collection, heat was stopped, and the test solution was cooled with cold water to 25 C. Subsequently, the reactor was refilled with air by pumping air through the reactor for 20 minutes before the heat was turned back on to continue the test. Measurement results of pH and CY are shown in Table1. Table 1 shows the experimental data collected during this investigation for the five coolants. During this investigation coolants J1 and D1 were also sent to an external lab for testing by so called copper wire test [5]. Both samples passed the copper wire precipitate test. However, J1 was claimed to be approved by OEM due to the lowest electrical conductivity of 116.3 µS/ cm while D1 is being used by buses successfully despite higher conductivity. It was reported that there were corrosion issues during the field trials of J1. Method used was as below: 1. Remove the rubber cover of electric wire 2. Put it in liquid to be tested 3. Apply 50V for 15 minutes 4. Check for precipitation on wire Both samples J1 and D1 were tested for glassware corrosion per ASTM D 1384. Comparison of the test results is shown in Table 2. Aus Wissenschaft und Forschung 31 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0029 D1 G1 J1 V1 D2 Hrs. CY (μS/ cm) pH CY (μS/ cm) pH CY (μS/ cm) pH CY (μS/ cm) pH CY (μS/ cm) pH 0 3,370 8.22 3,540 8.00 116.3 7.33 2,667 8.79 1,967 8.33 163 3,470 6.40 3,530 7.13 239.0 3.99 2,767 6.70 2,042 5.99 331 3,560 5.97 3,610 6.43 290.1 3.70 2,998 6.01 2,119 5.26 482 3,690 5.74 3,720 5.98 636.0 3.63 3,130 6.01 2,275 4.76 Table 1: Electrical Conductivity & pH Aus Wissenschaft und Forschung 32 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0029 4 Results and Discussions Figure 3 and Figure 4 shows electrical conductivity and pH data of all the five samples. The electrical conductivity of the liquid coolant becomes important in a direct cooling application because of the contact between the coolant and the electronics [6]. However, in indirect cooling applications the electrical conductivity can be important if there are leaks and/ or spillage of the fluids onto the electronics. In the indirect cooling applications where water- Figure 2: Copper wire Deposit Test Type of Metal Sample J1 Sample D1 ASTM D Limits MAX Copper 35.47 1.27 10 Solder 50.20 0.88 30 Brass 56.72 2.07 10 Steel 329.33 -0.07 10 Cast Iron 686.67 -1.00 10 Cast Aluminum -4.72 9.27 30 Table 2: comparison Metal corrosion ASTM D 1384 -100,00% 0,00% 100,00% 200,00% 300,00% 400,00% 500,00% 0 100 200 300 400 500 Percent Change in Conductivity Hours Percent Change in Conductivity G1 D1 J1 V1 D2 Figure 3: Percent change in conductivity based fluids with corrosion inhibitors are generally used, the electrical conductivity of the liquid coolant mainly depends on the ion concentration in the fluid stream. Higher the ionic concentration, larger is the electrical conductivity of the fluid. The increase in the ion concentration in a closed loop fluid stream may occur due to ion leaching from metals and nonmetal components that the coolant fluid is in contact with. During operation, the electrical conductivity of the fluid may increase to a level which could be harmful for the cooling system. Comparison of J1 and D1: CY of J1 starts increasing immediately during the start of the Parr reactor test and by the end of 450 hours it attains the highest CY of 450 %. Under the same test conditions D1 and other coolants CY remains below 25 %. All these coolants are being used as indirect coolants and corrosion issues were reported by users of J1. It is interesting to note that initial pH of J1 is lower than all other coolants. However, after 482 hours it has the highest drop in pH. Simultaneously ASTM D 1384 test data for J1 show high failure rate with respect to copper, brass, solder, cast iron and steel. ICP analysis of J1 and D1 has shown differences in copper and iron wear indicators. Copper in J1 was found to be 206 mg/ l vs. D1 of 8.2 mg/ l. In D1 iron was absent while J1 showed 90 mg/ l. Parr reactor experiment clearly indicates that an increase in the electrical conductivity of the coolant fluid is contributed by ion leaching of both metals. On the other hand, G1 has the lowest drop in pH and lowest rise in CY. It can be hypothesized that there exists some correlation between pH and stability of CY besides the individual robust corrosion package quantity and quality used in these formulations. Authors lab has done further research using parr and developed lowest CY coolant for fuel cell application. These findings will be the part of next series of this project. References [1] Global Fluids and lubricants market for electric vehicles, BIS research,2020 [2] Yu-Sen Chen et al., Comparisio of bench test methods to evaluate heavy duty coolant thermal stability, Journal of Testing and Evaluation, May 2006, ASTM [3] Alkesei V. Gresham et al., Predictive tool for coolant development, ASTM STP 1335,R.E. Beal, ED. [4] Edward et al., A chemical base for engineering coolant/ antifreeze with improved thermal stability properties, SAE Technical Paper Series, 2001-01-1182 SAE,PA, 1996 [5] Internal communication, Chulwoo Park, Bullsone Co. [6] Bojanna Shantheyanda et al., Tech Brief - Low Electrical Conductivity Liquid Coolants for Electronics Cooling, www.electronics-cooling.com, 2015 Aus Wissenschaft und Forschung 33 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0029 -60,00% -50,00% -40,00% -30,00% -20,00% -10,00% 0,00% 0 100 200 300 400 500 Percent Change in pH Hours Percent Change in pH G1 D1 J1 V1 D2 Figure 4: Percent Change in pH checked by videoendoscopy, is usually neglected. Proper preparation of the oil system, comprehensive cleaning done by machine overhaul, new builds and modernization is crucial element for long term machine reliability. What one can do when severe deposits, sludge, varnish or rust formation has occurred in the responsible oil system of turbo-machinery? How to clean newly assembled oil system that is corroded, contaminated with chemical preservatives or machining debris? Moreover, what can be done with big quantities of wear debris inside the oil system after severe seizure and breakdown of the bearing? How to clean it effectively? Aus Wissenschaft und Forschung 34 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0030 1 Introduction Besides the common repairs and maintenance, modernization of the machine usually takes place with strategy of efficiency increase. Other reasons are change of steam parameters where machine is modified following the need of steam parameters in production area of the plant. The expected machine availability is in all cases high and oil system cleanliness plays big role in machine reliability. It seems that the role of oil analyses in industry is understood and proper condition of the oil based on applied analyses program is monitored and maintained. Oil systems are being equipped with different types of purification units where customer nowadays is lost which technology to choose and employ. Turbine oils are highly refined and hydrocracked which leads to higher thermal and oxidation stability on one hand, but tends to produce and built Varnish during operation on the other hand. The level of oil system maintenance is in many cases improved, the oil monitoring usually applied. Oil manufactures offer high quality turbine oils and there are variety of technologies in oil conditioning. However, the cleanliness of the oil system itself, cleanliness of pipes How to commission the turbine oil system that was over years out of operation? Can heavily corroded and deposited turbine oil systems be restored Tomas Klima, Wojciech Majka* Preparation of rotating machinery oil system plays very important role in commissioning process and defines if commissioning process of the turbine brings some troubles. Moreover, future maintenance and operation is very much affected if oil system cleanliness is underestimated and machine commissioned without following complex cleaning procedure. Only standard displacement flush is not effective when system is corroded, where Varnish is agglomerated, pipe assembly done on site with lack of proper care. However, high machine availability and zero breakdowns is nowadays the main goal in every industry sectors! How to restore heavily corroded and Varnished turbine oil system after 10 years out of operation will be presented in this presentation. Keywords rotating machinery oil system, turbine, maintenance, cleaning, corrosion, varnished Abstract * Tomas Klima, MSc Eng Ecol Industrial s.r.o. (sister company of Ecol Sp. z o.o.) Czech Republic Wojciech Majka, MSc Eng. Ecol Sp. z o.o., Rybnik, Poland Figure 1: Uncleaned oil system causing journal bearing overheat, vibration and wear Contaminants must be removed from oil systems for trouble free operation. However, in many cases the standard method of oil flushing is not effective enough and usually takes a lot of time when flushing is performed properly (high flow rate, change of temperature and flowrate, absence of large particles in the oil and on metal meshes, target cleanliness). It is recommended to plan and schedule comprehensive check of the oil system interiors by employing videoendoscope, visual check, shooting photographs and its combination. It is very useful to do it with a certain frequency in order to monitor the level of contamination or corrosion process and also evaluate the uncertain results from oil analyses. Highly recommended is to schedule videoendoscopy check also before closing the bearings and installation of repaired components to avoid oil system contamination from dust, machining particles, insulation and other material. Flushing them out before machine commissioning may takes weeks if this fact is underestimated. of the particular turbine/ compressor for the next long period of operation with the focus on maximum reliability. 2 Problem of dirty oil systems Despite of wide application of high quality filters, developed oil analyses programs, high performance lube oils, there are still problems causing bearing failures, inappropriate working hydraulic systems and changes of physical parameters of the oil especially after the oil exchange. Impurities enter the oil system either during the new assembly as well as execution of overhauls (metal debris from machining, welding slag, sealants and other materials used for assembly/ repairs) or simply from the ambient. Furthermore, impurities are generated within the operation due to oil degradation, water contamination from oil coolers or steam glands leaks or ambient humidity that condensate in oil reservoirs, gear boxes and speed up the corrosion processes. Often in process machinery (air/ gas compressors) compressed gas is carrying different impurities and can itself interact with oil (with oil base or oil additives) while entering the oil system through wet seal glands of sealing systems. Aus Wissenschaft und Forschung 35 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0030 Figure 2: Corrosion, oil aging products in the oil system pipes inspected before turbine modernization Figure 3: Oil aging deposits in the inspected - return line from turbine control valve In cases, where oil system is corroded or Varnish formation is observed, there are certain cleaning methods for restoration of the pipeline cleanliness. One of them, like steam blowing is less effective and not more used for safety reasons. Other method, like chemical cleaning is not recommended for high contamination potential of new oil. Alternatives are cleaning of oil systems with dosed detergent or other solutions that increases the solubility of Varnish contamination. Compatibility with the new oil and cleaning effect must be taken into account before applying that method and considered if Varnish is the only contamination source. Besides that, consideration of flushing scenarios and its effects. In order to displace fully or partially dissolved deposits and flush them out from surfaces and components, laminar flow flush is not usually effective method. While planning the shutdown or partial overhaul, there is a key question, how to maintain the oil system Impurities are the main cause of premature wear of elements and could lead to equipment breakdown. The most vulnerable parts include bearings, hydraulic actuators and controllers of control systems, gearboxes, drive-shaft seals, pumps (especially hydraulic and jacking system pumps) oil coolers as well as oil filters and oil reservoirs. Very troublesome group of impurities are oil degradation products from oil ageing and thermal stress creating insoluble chemical compounds that are responsible for varnish and sludge formation. cles attached to the sticky layers of Varnish or sludge. Rust that usually builds up in the return lines is also not properly removed. Effective cleaning method with clear prove of its cleaning effect in every moment is hydroblasting/ hydrojetting of the oil system pipeline and components. High pressure water stream/ water jets do penetrate the corrosion, Varnish layers and loosen them from the surface. Outflowed water displace the contaminants from the pipes. Each end every pipeline (discharge&return lines, suction pipes, overflow pipes and complete oil system piping) are intensively cleaned by this process. 4 Description of Ecol technology Based on long term experience in power generation, Ecol is offering a technology where the whole oil system is intensively cleaned/ hydroblasted with high pressure water jets and subsequently flushed with high flow rates (turbulent oil flushing). This technology is as an excellent alternative to other (often insufficient and obsolete) methods. Below described cleaning and flushing technology is most likely the most effective method of preparing new oil systems and restoring operated oil systems regardless of their size and complexity for future reliable operation. Presented technology consist of three phases: I. hydrodynamic cleaning using water at very high pressure (up to 150 MPa); II. flushing of the oil system with oil at high (turbulent) flow rates and with full-flow absolute filtration III. post-assembly by-pass oil filtration prior to turbine/ compressor start-up. The core of this technology is cleaning of all inner surfaces of oil system with high pressure water jets utilizing suitable nozzles (appropriate for water pressure and tube’s diameters), immediate drying and application of protective turbine oil spray to dried surfaces followed by flushing with continuously filtered oil at sufficient pressure and flow rates. Phase I: Intensive cleaning of the oil system using high pressure water (pressure up to 150 MPa) - “hydroblasting” The inner surfaces of the system are intensively cleaned/ blasted with high pressure water in order to remove soft deposits (loose wear debris, sand and dust grains, products of oil ageing process, sludge, biological deposits, resins and asphalts; greases and corrosion-protec- Aus Wissenschaft und Forschung 36 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0030 The fact of having fine filters, performing periodically oil analyses or just considering application of high performance lube oils leads to the underestimation of the cleanliness of the interior of the oil system itself. The overhaul of the responsible machine together with planned oil exchange is usually the factor of future difficulties. Components of the oil system used to be disassembled, controlled, repaired or exchanged and the dust, machine debris or different chemicals (silicon, grease paste, cleaners) get into the oil system on different places. Subsequent oil flushing is done usually at the end of the overhaul/ shutdown where longer period of flushing is bringing troubles. It’s not unusual that the oil is contaminated with different kind of chemicals and foaming tendency, air release properties or deemulgation are significantly influenced. Condition of the interiors of the oil system should not be neglected but rather included in the maintenance/ overhaul planning. Periodical inspection helps to avoid timeconsuming oil flushing of the dirty oil system and enable to plan intensive cleaning of the whole system. 3 How to restore/ clean heavily corroded and Varnished turbine oil system? When corrosion and/ or Varnish in machine oil system is observed effective and proven cleaning is necessary. Oil system made from carbon steel operated with increased water content are usually corroded due to this fact but not only. Most of available standards or recommendations or just industry practices put big attention to flushing process before system start-up. In fact, the common procedure of oil flushing base on the performance of oil system pumps, that generate limited flow. In the system where corrosion, sludge or varnish as well as deposited particles are present is very difficult to flush the system effectively. The flow is not big enough to loosen all parti- Figure 4: Photo of oil cooler covered by varnish tive layers such as tectyl, naphta) as well as hard deposits (such as corrosion products - rust, welding slag on welds, varnish residues, machining residues partially attached to surface). elements of the oil system (pumps, valves and fittings, coolers, etc.) must be disassembled. Completed cleaning is followed by immediate drying of cleaned surfaces using filtered compressed air and application of protection layer of turbine oil (oil spray) preventing secondary corrosion of cleaned oil system. Oil system remains completely dry after hydrodynamic cleaning phase therefore risk of ingression of water into oil during flushing is completely eliminated. Phase II: Flushing of oil system with fully filtered oil flowing at very high flow rates (high velocity oil flush) In order to remove impurities that were detached with high pressure water, but not successfully carried out by water stream, effective oil flushing is needed. Using external, high capacity oil pump and fine filters ensures reaching high velocities of the oil. By-passing the bearings, oil pumps of the system, servo valves, allows to perform this service in advance of the final startup and shorten the overhaul time. Aus Wissenschaft und Forschung 37 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0030 Figure 6: Oil pipeline after hydroblasting (compare to Figures 2,3) Figure 8: Turbulent flushing with full-flow absolute filtration (schematic) Figure 7: Thoroughly and perfectly cleaned oil cooler bundle Figure 5: Hydroblasting process (schematic and real) The following activities are carried out in the course of the cleaning process: ■ high pressure water cleaning (operating pressure 75-150MPa) of all interiors of pipelines and other elements of the oil system: pipelines - lube, seals, lever (jacking) and hydraulic systems; coolers and reservoirs; bearing stands etc.; using suitable equipment (elastic lances and nozzles; water guns etc.); ■ immediate drying of cleaned surfaces using filtered compressed air; ■ application of anticorrosive protection on dried surfaces until flushing (spraying of inner surfaces with lubricating turbine oil); ■ protection of open flanges against dust and dirt from ambient until the flushing process takes place. Comparing to other methods this technology does not require the disassembly of the whole system. Only few Phase III: By-pass oil filtration before or during system start-up In order to remove post-assembly impurities (introduced during assembly and disassembly works done after flushing) performing of by-pass oil filtration is done. Oil system pumps are in operation and oil flows already into the bearing, seals, hydraulic components and back to the oil tank. The filtration of the oil is done shortly reaching back the required cleanliness. Aus Wissenschaft und Forschung 38 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0030 Oil systems of the turbine or compressor are flushed using special filtration and pumping units (flushing skids equipped with absolute filters β5 > 1000) ensuring turbulent flows at flow rates ranging from 8,000 to 20,000 l/ min. The units have appropriate operating parameters and are connected to the oil system using hoses, manifolds, flow distributors where bearings, servomotors and other flow restricting-elements are by-passed. Figure 9: Flushing skid connected to the oil system of large utility steam turbine with high capacity oil filters (full flow filters) Figure 11: Off-line oil re-filtration before start up (schematics) Figure 10: High velocity oil flush - bypasses/ jumpers installed on large utility steam turbine Flushing is performed using fresh turbine oil, which will remain in the system for further use (extra batch of flushing oil is eliminated). The flushing process continues until predetermined purity criteria are reached in each location of the system. During this time oil temperature and flow direction are changed in order to move out remaining impurities. Effective flushing of the turbo compressor oil system is based on the following three important criteria: I. Flow rates at all pipeline sections should be sufficient to invoke turbulence (Reynolds number for the pipeline Re > 4000). In-pipeline flow velocities are measured using ultrasound flow rate meters. II. Oil cleanliness class better than required by turbine manufacturer (e.g. most often 16/ 14/ 11 or 17/ 15/ 12 acc. to ISO 4406). The cleanliness is measured in various locations of the system (inlets to the bearings, seals, servo valves). Common cleanliness after 3-4 days of flushing is 15/ 13/ 10 and better. III. No solid particles larger than 150 microns deposited on 150 µm mesh strainers installed in strategic locations of the system (inlets to friction nodes - lubricated elements). Other than 150 microns (smaller) sizes can also be warranted if agreed. 5 Conclusion The above described technology of hydrodynamic cleaning and turbulent flushing is very effective and advanced method of restoring old oil systems as well as preparing new systems for first start-up. It allows to run the machinery out of failure in the means of lubrication and secure trouble free operation to the next shutdown and even much longer. • The technology allows to renew less or more dirty and corrodes systems (to “like new” condition) and is also suitable for new assembled oil systems. • Hydroblasting shortens future flushing process because most of impurities are got out by water. Only little amount of loosen deposits remain in the system and are later easily flushed out. • Oil analyses performed in operation are providing adequate results that aren’t influenced by old deposits, debris, particles. Detecting wear process is precise and accurate (avoidance of confusing ‘background’ impurities). • Varnish and other aging products as well as chemicals are completely removed. No risk of contamination of the new oil or changing its parameters. It’s very useful before oil exchange. • The method is entirely safe for the natural environment, since pure water is the cleaning medium and the wastewater (rest of oil and water) is easy to dispose. • Flushing after hydroblasting is very fast and efficient. Time for flushing is easy to plan and schedule. No risk of long lasting flushing comparing to other methods. • Possibility of long-term warranty of the oil system cleanliness for the customer. It guarantees improve both, economical and technical factors: ■ long-term purity of oil and system itself ■ reduced quantities of flushing oil batch in the process ■ reduced wear of lubricated parts and extended MTBR ■ increased life time of the oil and machine components ■ higher equipment availability ■ significant reduction of oil filter consumption ■ no turbine outages due to dirt in the oil system ■ reduced total operation cost This method is becoming a preferred choice of OEM and maintenance/ repair companies. Now since year 1994, over 700 different turbines’ oil systems have been serviced by Ecol according to the presented technology. The references contain (new commissioned as well as overhauled and modernized machinery): ■ turbo-generators (up to 1070MW; steam and gas turbines; including rich experience in nuclear power plants) ■ process turbo-compressors and blowers (hydrocarbons, synthesis gas, hydrogen, air, ammonia etc.) ■ boiler feed pumps with hydrokinetic couplings and gearboxes ■ large industrial diesel engines (including auxiliary power supply in nuclear power plants) ■ large gas and diesel engines ■ large hydraulic and lubricating oil systems in steelworks and rolling mills ■ central lube oil distribution systems in the plants etc. About authors Wojciech Majka, MSc Eng. (mech), MBA, STLE Member, is the President of the Board and CEO of Ecol Sp. o.o. (LLC) of Rybnik, Poland. Established in 1992 company is the leading professional service company delivering lubrication reliability solutions for industrial plants, especially for power plants, petro-chemical plants and refineries as well as for light industry such as automotive and drink&food processing. Tomas Klima, MSc Eng. (mech), is the director of International Sales Division, responsible for market and business outside Poland. Responsible for development and rich experience with Ecol services in Nuclear Power Generation. Core of Ecol’s scope of services includes lubrication management and execution (industrial oil service/ fluid management), lubricants distribution for power industry. Services include also advisory and lubrication engineering. However, the most world-wide known service of Ecol is unique technology of cleaning and flushing of oil systems (dedicated to turbo-machinery, large industrial diesel engines and power hydraulics). References [1] Majka, Wojciech; Klima, Tomas. Ecol Sp. z o.o. - own materials and internal Ecol company materials Aus Wissenschaft und Forschung 39 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0030 [6] Fitch, Jim. Noria Corporation, When to Perform a Flush? ; Machinery Lubrication 5/ 2004; www.machinerylubrication.com [7] Fitch, Jim. Noria Corporation, Flushing Strategy Rationalization; Machinery Lubrication 9/ 2004; www.machinerylubrication.com [8] Hannon, James B., ExxonMobil, How to select and service Turbine Oils; Machinery Lubrication 7/ 2001; www.machinerylubrication.com Aus Wissenschaft und Forschung 40 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0030 [2] Najfus, Jan. Comprehensive safeguard of the maintenance of the machinery room in Dukovany nuclear power plant; All for Power. Published 2/ 2010; pages 28-33. [3] ASTM D6439-05 - Standard Guide for Cleaning, Flushing, and Purification of Steam, Gas, and Hydroelectric Turbine Lubrication Systems; [4] Manuals and oil specifications of turbine manufacturers (Alstom Power; Siemens, GE, Doosan Skoda); [5] ASTM D4378-08 - Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam and Gas Turbines; ISSN 0724-3472 Aus Wissenschaft und Forschung Science and Research www.expertverlag.de Neil Conway, Carsten Giebeler, Benjamin Wiesent How to get Lab Equivalent Oil Analysis 24/ 7 Thomas Emmrich, Klaus Herrmann, Michael Guenther Pre-ignition phenomena in the tension between operating agents and thermodynamic boundary conditions Frank Reichmann A practical Approach to predict Service Life and Re-lubrication Rate of Grease in Rolling Bearings Tobias Schick, Jochen Hörer, Karl-Heinz Blum, Klaus Ellenrieder, Katharina Schmitz Sensitivity analysis of operating parameters in hydraulic systems with respect to the aging of hydraulic fluids Govind Khemchandani Development of Next Generation EV Coolant Tomas Klima, Wojciech Majka How to commission the turbine oil system that was over years out of operation? Can heavily corroded and deposited turbine oil systems be restored