by the California Air Resource Board, which also now requires the maximum sulphur content of marine gas oil and marine diesel oil to be 0,1 % m/ m within 24 nautical miles of the Californian coast. According to the 78 th session of the Marine Environment Protection Committee (MEPC 78) of IMO, the Mediterranean Sea will be included in the Emission Control Area for Sulphur Oxides and Particulate Matter (Med SOx ECA) in 2025 [2]. After its entry into force, no ship entering the Mediterranean Sea can use fuel with a sulphur content exceeding 0,10 % m/ m. The recently reduced limits on sulphur in fuel oil brought about a 70 % cut in total sulphur oxide (SOx) emissions from shipping, ushering in a new era of cleaner air in ports and coastal areas, by using fewer polluting fuels. Aus Wissenschaft und Forschung 36 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 1 Introduction: Maritime Industry in The Green Era Maritime transport consists the lifeblood of global economic vitality and the conduit of world trade in a costeffective and reliable manner. Given the large capacity of the fleet, shipping industry involves important economies of scale, making it a rather economic mode of transport. Seaborne shipping is one of the most important transport activities, since it generates benefits for consumers across the world through competitive freight costs. Nevertheless, it is a growing source of greenhouse gas (GHG) emissions and a major source of air pollution. Shipping industry aims to meet the International Maritime Organization’s (IMO) initial goals to reduce carbon dioxide (CO 2 ) emissions by at least 40 % by 2030 (pursuing efforts of a 70 % reduction by 2050) and total annual GHG emissions by at least 50 % by 2050, compared to 2008 levels. On January 1st 2020, a new limit in the sulphur content of the fuels used on board ships came into force, marking it a significant milestone to improve air quality, preserve the environment and protect human health. The reduction of sulphur emissions is prescribed in the sixth (IV) Annex of the Marine Pollution (MARPOL) Convention of the International Maritime Organisation (IMO) [1]. At a global level the highest permissible sulphur content of fuels is limited to 0,5 % m/ m and in some very fragile ecosystems known as SECAs (Sulphur Emission Control Areas) is already being reduced to 0,1 % m/ m. The SECAs include the Baltic Sea area, the North Sea area, The United States, Canada and the United States Caribbean Sea area. The required maximum sulphur content of 0,10 % m/ m for marine gasoils used in ships sailing or operating in the SECAs reveals that it is practically impossible to mix residual fuel with a distillate and still meet the highest permissible sulphur content. Therefore, only marine distillates that meet the environmental requirements of the fragile SECAs will be available. The shift from residual fuels to low sulphur distillates is driven not only by the EU and IMO regulations, but also Tribological Assessment of Marine Distillate Fuels under a Variant HFRR Method Theodora Tyrovola, Fanourios Zannikos* Maritime transport has a vital role in world economy. Its efficiency depends on the effective trade, transport facilitation, low cost of customs and the integration of new technologies for sustainable operation. However, the con-temporary demands have turned shipping industry into an emerging air pollutant with significant share to the global climate change problem. The industry is growing rapidly and it needs to lower greenhouse gas emissions in order to contribute towards the valuable effort for net zero emissions by 2050. A milestone to the ambitious strategy of decarbonization is the use of low or zero sulphur fuels that will contribute to the development of viable zeroemission vessels by 2030. Netherless the introduction of low-sulphur marine gasoils in the global fuel supply chain is accompanied by a huge range of side effects related to their storage, combustion, ignition and lubricity. The objective of the study is the evaluation of the lubricity of different marine distillate fuels with the High Frequency Reciprocating Rig (HFRR) test, either by following the primary conditions defined by ISO 12156-1 standard or by modifying them. The ultimate goal is the accurate and reliable assessment of their lubricating capacity so as to identify the challenges related to it, on time. Keywords Zero Emissions, Low Sulphur, Lubricity, HFRR Abstract * Theodora Tyrovola (corresponding author) Fanourios Zannikos Laboratory of Fuels and Lubricants, Chemical Engineering Department, National Technical University of Athens The global marine fuel market is steaming towards a major upheaval, as the industry has already entered the low-sulphur era. From year 2020 and on, people around the world will be able to breathe cleaner air at last because of the implementation of the International Maritime Organization’s Sulphur Cap. Under the severe pressure of IMO for immediate SOx emissions reduction, shipping enterprises take effective measures so as to meet the emission limitation requirements of relevant international organizations, regions and countries. Ship owners and operators must comply with the imperative environmental provisions, reduce their vessels’ emitted pollutants and switch to low or zero sulphur fuels that are more environmentally friendly. The path to decarbonization is paved and it requires significant changes as how power and propulsion is generated on board. 2 Major Shipping Emitted Pollutants Over 90 % of world trade is carried across the world’s oceans by some 90.000 marine vessels. Shipping has become an essential mode of transportation between trading countries due to the globalization of trade and the rapid development of the world economy, but has leaded to adhere air pollution in ocean and coastal areas due to its emitted pollutants [3]. Like all modes of transportation that use fossil fuels, ships produce hazardous emissions that significantly contribute to global climate change and acidification. It is estimated that almost 70 % of ship air pollutant emissions in global routes are emitted within 400 km of the coast. While the emitted pollutants from landbased sources are gradually reduced, the ones attributed to shipping industry are already experiencing a significant increase. The main fuels used in international shipping are HFO (Heavy Fuel Oil) and MGO / MDO (Marine Gas Oil / Marine Diesel Oil) [4]. Domestic shipping shows a large variety of fuels with the most important being MGO/ MDO (60 %), HFO (31 %) and motor gasoline 9 %). Both the complete and incomplete combustion of conventional fuels inside a naval engine result in the formation of a complex mixture of exhaust gases and particles. Ship-source pollutants most closely linked to climate change and public health impacts, include carbon dioxide (CO 2 ), nitrogen oxides (NOx), sulphur oxides (SOx) and particulate matter, as a result of the fuel used to power them. It is assumed that maritime transport emits around 940 million tons of CO 2 annually. Shipping is the lowest carbon form of transport per tonne of goods moved, but yet is responsible for more than 2,2 % of global GHG emissions. Over the last three decades, the shipping industry has grown by an average of 5 % per year. Ships generate approximately 13 % of SOx and 15 % of NOx emissions per year at a global level. Sulphur dioxide (SO 2 ) emissions can travel long distances, are responsible for the formation of acid rain and when combined with diverse pollutants they generate fine particles. Particulate matter (PM) contributes to the overall PM 2,5 air pollution burden in the European and form “black carbon”, the second largest contributor to climate change after CO 2 . The emitted CO 2 contributes to the widespread climate change by trapping the sun’s heat. Extreme climate changes include increased average temperatures, shifting rainfall patterns, thawing permafrost, and increases in hazardous weather. Sulphur oxide emissions resulting from the burning of fuel oil are proven to be a significant source of air pollution. Sulphur is a naturally occurring element, present in all fossil fuels. Its presence in the atmosphere in the form of SOx has a cooling effect on global warming but at high concentration can cause many serious health and environmental problems. Various combinations of nitrogen and oxygen can cause lung inflammation when breathed. NOx may enter the bloodstream and with longterm exposure could lead to eventual heart and lung failures. Both NOx and SOx emissions are responsible for the acidification of soil and water, causing the disastrous acid rain [5]. The IMO predicts that without establishing and implementing immediate measures and barriers to reduce emissions from shipping, CO 2 emissions from the industry could rise to 1,48 billion metric tons by 2022, equivalent to putting 65 million new cars on the road. Given the urgency of the climate crisis, and the technological advances since 2018, shipping industry can and must move faster, with a goal of reaching zeroemissions by 2050. 3 The Lubricity of Marine Diesel Fuels Lubricity of a fluid is the indicative measure of the protection efficiency of two mating surfaces, from wear or scarring, due to the relative motion between them. Fuel lubrication is absolutely necessary to diesel engine components in order to reduce the friction between the mating surfaces. In order to avoid the undesirable phenomenon of wear, it is necessary to insert a third layer that has good lubricating capacity between two rubbing surfaces in order to reduce friction. The role of this intervening layer in many metal components of a diesel engine distribution system is played by the fuel itself. Diesel fuels like all liquid hydrocarbon fuels need to possess a modicum of lubricating ability to protect sliding surfaces in fuel pumps, injection valves and other moving parts. The recognition of this requirement is originated in the mid 1960’s, when improvements in the refining and treatment processes led to the production of Aus Wissenschaft und Forschung 37 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 diesel fuel is the boundary lubrication regime. In the hydrodynamic regime, a film of fluid prevents contact between the sliding surfaces. The sulphur content of marine diesel fuels drops significantly leading to an increase in the number of fuel pump failures regardless of manufacturer and country of origin, which in many cases have been catastrophic for the pumps. As the operation of the fuel injection pump relies on the lubricity of the fuel, the failures are attributed to the sharp reduction in the lubricity level of the new refined fuels. A fuel’s ability to keep the surfaces separated is governed by its viscosity. When two liquids have the same viscosity and one gives lower friction, wear or scuffing, then is said to have better lubricity. If one fuel does not contain enough lubricating ingredients, it is considered as a “dry fuel” for its incapacity of lubricating the metal engine components. In boundary lubrication, asperities (rough spots) on the sliding surfaces are just touching, but the lubricating means still supports most of the load. The fuel’s effectiveness as a boundary lubricant is dictated by its chemistry. Diesel fuel molecules with polar groups will adhere to the metal surfaces, while the non-polar portion of these molecules will occupy space between the surfaces. These non-polar tails effectively trap additional lubricating means to reduce the degree of contact, thereby protecting the surfaces from wear. Friction and wear are the obvious requirements when one substance is moving over another substance. In engine fuel system, the relevant components experience the friction with the fuel flow activities. The effective work is obtained from the engines only when the produced energy can overcome the friction of these moving parts. 4 Reasons for the Reduction of Marine Gasoil’s Lubricating Capacity The new 0,50 % m/ m global sulphur limit consists a milestone for marine activities, as it is expected to be one of the first important steps to enter a new green season that leads to the decarbonization of the shipping industry. The global marine fuel market is steaming towards an unprecedented upgrade, as the industry is already experiencing the low-sulphur era. The growing tendency to find biological energy sources along with the global commitment for further reduction of exhaust gas emissions, are leading to the use of alternative fuels or very low sulphur fuels in ships. Low and zero sulphur fuels are proven to have positive impact both on the marine environment and coastal health, but they are accompanied by a huge range of side effects related to their storage, combustion, ignition and lubricity. Harmful gaseous emissions are obligingly being reduced since January 2020, and refineries are constantly developing new technologies in order to mi- Aus Wissenschaft und Forschung 38 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 very pure aviation fuels [6]. Later though the converging trends of increasingly rigorous fuel treatment and of higher fuel injection pressures have focused attention on the less severely refined automotive diesel fuels. In recent years there has been a particular concern regarding the reduction of unwanted emissions from diesel engines, which in turn has led to the establishment of new specifications for automotive and marine diesel fuels. The fuel quality and potential environmental impact due to sulphur and other components are dependent on the process of production of marine bunker fuels. Whereas MGO and MDO are the result of distillation processes in oil refineries, HFO is a residual product of the oil refinery process. The imperative need for reduction of harmful gaseous emissions form shipping industry, has led to the establishment of new standards for marine fuels which are included in the recently revised ISO 8217: 2017 [7]. The International Standard EN ISO 8217 specifies the requirements of petroleum fuels for use in marine diesel engines. ISO 8217: 2017 standard specifies three different distillate grades (DMA, DMB, DMZ) and a number of residual grades (RM). The changes in the specifications of marine gasoils concern the gradual reduction in their sulphur content. The peremptory demand for use of distillate fuels with extremely low sulphur content in marine engines has led to further research and data collection that allowed the incorporation of fatty acid methyl esters (FAME) in specific marine distillate grades (DFA, DFB, DFZ). A diesel fuel’s lubricity is the measure of its ability to prevent or minimize wear that the sliding components are subjected to and is a function of the way it has been refined and blended. Components with the greatest dependence on the fuel for lubrication, demand fuels with superior lubricating capacity. In -line fuel injec-tion pumps that are lubricated by a combination of the engine’s crankcase oil and the fuel are far less sensitive to the diesel fuel’s lubricity than rotary/ distributor type fuel pumps that rely solely on the fuel for lubrication. In order to perform under acceptable ranges, different components experience various lubrication regimes, e.g., hydrodynamic (HDL), elastohydrodynamic (EDHL), boundary (BL) and Mixed (ML) lubrication. The fuel guards the metallic parts away from rapid wear by forming HDL films (function of fuel viscosity) or BL films (function of diaromatic constituents) in between the solid surfaces. The sliding surfaces in fuel injection pumps are protected from wear by hydrodynamic and boundary lubrication mechanisms. Although hydrodynamic as well as boundary lubrication occur in several components of the fuel delivery system, the lubrication regime that is affected most by the removal of the sulphur and aromatics in nimize the sulphur content of fuels in an effort to comply with the strict emission limitations. The extensive interest in diesel fuel lubricity has escalated since the early 90 s, right after the commercialization of the low sulphur fuels. Their prolonged use in diesel engines revealed remarkable drivability problems and pump failures. These problems were soon linked with excessive wear on critical components of fuel injection pumps. Fuel lubricity is in correlation with the chemical composition of the fuel. Sulphur is one of the compounds in the fuel that imparts lubricity characteristics The lubricating capacity of marine diesel fuels is directly related to the polarity of its molecules [8]. Wear is increased by poly-cyclic aromatics at low concentration but it is redacted at high concentration. Therefore, polar impurities and poly-cyclic aromatics are considered as the most valuable natural lubricity additives in diesel fuels. The currently established refining processes for the production of low (LSD) and very low sulphur diesel fuel (ULSD) offer an extended engine life with significant reduced wear but also a rapid decline in the lubricating capacity of such fuels. Over the past few years, a range of hydrogenation treatments of varying severity have become common. The most efficient and least costly refining method in order to remove sulphur from fuels is the chemical process of Hydrodesulfurization. Hydrotreating or hydrodesulfurization refers to a set of operations that remove sulphur and other impurities from petroleum products, which increase the efficiency of the fuels and reduce the production of harmful combustion by-products such as NOx and SOx. During hydrotreating, crude oil cuts are selectively reacted with hydrogen in the presence of a catalyst at relatively high temperatures and moderate pressures [9]. The process converts undesirable aromatics, olefins, nitrogen, metals, and organosulphur compounds into stabilized products. Some hydrotreated cuts may require additional processing to meet final product specifications. Hydrodesulphurisation is not a selective process it removes nitrogen (N) and oxygen (O) as well as sulphur (S). The removal of N and O from heterocompounds destroys their ability to perform as lubricity agents. Thus, low S fuels have lower levels of active N and O compounds and thus worse lubricity. According to hydrotreatment technology, the sulphur content in fuel is removed and is replaced with hydrogen, delivering as a final product a cleaner fuel with extremely improved efficiency [10]. As hydrogen reacts with specific components of the fuel it removes the polar and aromatic compounds that provide the conventional diesel fuel with sufficient lubrication capacity. The loss of these polar compounds is considered to be responsible for the reduced lubricating capacity of marine diesel fuel. It is proven that the polar fraction contains compounds that adsorb on a metal surface, thus providing a protective layer. Sulphur content is usually correlated with the lubricating capacity of MGO as it reflects the refining intensity of the fuel and therefore the levels of polar and polyaromatic compounds. In particular, the more intense the desulphurization processes, the more noticeable is the reduction in the lubricating capacity of the diesel fuel. Poor lubricity significantly affects engine performance, by provoking accelerated wear and insufficient engine power. It also shortens the lifespan of the marine engine and causes energy dissipation by friction and failure of engine parts such as fuel injectors and pumps. Diesel fuel injection pumps are lubricated primarily by the fuel itself. A sustainable fuel needs a critical threshold of polar compounds in order to have a good lubricity performance. Poor lubricity fuels can still contain measurable levels of the key agents, but just not enough. Poor quality fuels or insufficient can be responsible for problems in handling and/ or combustion. In addition, higher maintenance requirements, shorter service intervals and possibly shorter service life of various components of the marine engine equipment will be required. 5 The High Frequency Reciprocating Rig Test 5.1 The History of its Development Lubricity is among the most important factors to ensure the best quality of any diesel fuel. The everchanging alterations in fuel specifications and the tighter tolerances in modern engines, render the understanding of marine gasoil’s lubricity more important now, than ever. Fuel lubricity is the most important aspect to consider when it comes to the durability of diesel engine components. Naval engine manufactures consider marine diesel fuel lubricity as a critical parameter because certain parts of the fuel injection equipment (FIE) depend entirely on the fuel for lubrication [11]. The lubricating capacity of a diesel fuel is determined either by measuring the wear prevention characteristics using the High Frequency Reciprocating Rig (HFRR) test according to ISO 12156-1 and ASTM D 6079 test methods and/ or by applying the Scuffing Load Ball on Cylinder Lubricity Evaluator (SLBOCLE) procedure based on ASTM D 6078 test method [12]. The HFRR test was first pioneered by Imperial College London. In 1994 Rinaldo Caprotti and one of his colleagues at Exxon Chemical’s PARAMINS additive division joined with Imperial College, London and Robert Bosch GmbH to develop the technique into a highly re- Aus Wissenschaft und Forschung 39 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 dary friction measurements of engine oils, greases and other compounds. It has become the industry standard test for diesel fuel lubricity and conforms to ASTM D 6079, CEC F-06-A, ISO 12156, EN 590, JPI-5S-50 and IP 450, SH/ T0765 standards. HFRR PCS instrument’s ability to collect continuous friction measurements, the wide range of specimen materials available and the ability to customise test parameters, make it the ideal choice for the evaluation of diesel fuel’s tribological properties. The High Frequency Reciprocating Rig (HFRR) test is the predominant method on a macroscopic scale and is widely used for the engineering of fuels, lubricants and engine parts [14]. It can provide macrotribological information, since the test is performed on objects of relatively large mass and under high load. Wear is inevitable and the mass properties of the components in contact dominate the tribological performance. The parameters of the HFRR test method simulate boundary lubrication conditions. The result given is the corrected - with respect to the standard water vapor pressure Aus Wissenschaft und Forschung 40 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 producible and accurate measurement of lubricity in diesel fuels [13]. The HFRR test was developed over almost 30 years ago and has stood up to all of the changes made to fuels and engines since its development. Nevertheless, since then, diesel fuel world has been through a period of significant change. Fuel sulphur has fallen dramatically, crude sources have changed and the use of biofuels and highly paraffinic diesel has increased. The specifications governing diesel fuel quality have gradually tightened in response to all qualitative changes so as to ensure the fuel in the pumps is fit for purpose and offers adequate protection to the advanced hardware which is used in today’s naval engines. 5.2 The HFRR Apparatus The High Frequency Reciprocating Rig (HFRR) of PCS Instruments is a microprocessorcontrolled reciprocating friction and wear test system which provides a fast, repeatable assessment of the performance of fuels and lubricants. It is particularly suitable for wear testing relatively poor lubricants such as diesel fuels and for boun- Scheme 1: Scheme of HFRR device Scheme 2: HFRR device of PCS Instruments / mechanical unit at 1,4 kPa - wear diameter (WS1,4) expressed in micrometers (μm) and constitutes the lubricating capacity of the fuel. The specification for the lubricating capacity of marine distillate fuels (with a sulphur content of less than 500 ppm) is specified in ISO 8217 standard, and the maximum permissible wear scar diameter is 520μm. The HFRR apparatus is based a spherical specimen of 6mm diameter which is subject to reciprocating motion in a frequency of 50Hz and an oscillation amplitude of 1mm with the help of an electromagnetic oscillator. The spherical sample is in contact with a flat sample under the application of a weight of 200 g while the contact point is immersed in a quantity of 2 ml of the fuel under examination throughout the test. The fuel is preheated to a temperature of 60 °C and the test lasts 75 minutes. During the test, humidity and ambient room temperature are controlled and noted. The results of the measurement can be observed online by means of a computer program. This software enables the operator to follow the course of the film formation as well as the changes of the friction coefficient over the testing time. The formation of a lubricating film is indicated by the electric potential existing between the steel ball and the plate. The built up lubricating film acts as an insulator and separates the test specimen, steel ball and the plate by a thin layer. After the test the abraded area on the ball is evaluated by means of an optical microscope. The observed dimensions are converted into a defined wear scar value by a formula. The WS1,4 is the standardized measure for the lubricating capacity of the marine distillate fuel. Additionally, to the wear scar dimensions, the temperature and humidity at the beginning and the end of each testing procedure are also included into the evaluation of the WS1,4. The device has also the ability to calculate the frictional force developed between the metal samples as well as the electrical contact potential (ECP). Based on these measurements there can easily be calculated the average coefficient of friction and the percentage thickness of the boundary oil layer (oil film). The measurement of the mean wear diameter is performed in a stereoscope (Leica M165C) and at 120 x magnification. 6 Detection of Wear 6.1 In Lab Analysis Lubricity is a parameter that is still not thoroughly understandable in the Marine Sector. Since the implementation of IMO’s cut down regulations, more and more misunderstandings related to lubricity have arisen. Monitoring fuel’s lubricity couldn’t be more imperative than now. By far there has been no better method than the HFRR test to accurately determine fuels’ lubricity levels. Most everyday marine diesel owners don’t need to worry about owning or operating an HFRR test by themselves, however, it is important that they understand how to interpret a lubricity rating and why it is important to the longevity of their marine engines. In order to increase the sensitivity and accurateness of HFRR over marine distillates, we rely firstly on the basic parameters of ISO 12156-1 standard and subsequently on the modification of them. The modification of the basic parameters of ISO 12156-1 is made so as to identify the poor lubricating capabilities of low-sulphur marine gasoils and to track wear on the metallic parts of the engine’s equipment that cannot be detected by the original method. Base Fuels: 1. Distillate marine DM 1 (grade DMA): Fuel’s properties comply with EN ISO 8217: 2017. 2. Distillate marine DM 2 (grade DMA): Fuel’s properties comply with EN ISO 8217: 2017. The properties of both fuels are given in Table 1. DM 1 has a slightly greenish hue, while DM 2 has a dark blue colour. The sulphur content in DM 1 is 900 ppm and in DM 2 is 850 ppm. Aus Wissenschaft und Forschung 41 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 Scheme 3: Leica Stereoscope DM1 DM2 Properties Unit Test Method Reference Kinematic viscosity at 40oC mm2/ s ISO 3104 2,7124 3,5851 Density at 15oC kg/ m3 ISO 3675 or ISO 12185 830,8 845,5 Cetane Index _ ISO 4246 38 31 Sulphur Content mass% ISO 8754 , ISO 14596, D 4294 0,0900 0,0850 oC oC -3 oC oC -24 -16 oC oC -19 -11 Lubricity, WS1,4 at 60oC μm ISO 12156-1 408 420 Fuel Type Pour point ISO 3016 CFPP IP 309 or IP 612 Cloud point ISO 3015 Result Table 1: Basic Properties of Marine Distillate Fuels Aus Wissenschaft und Forschung 42 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 Case 1: In case one the test conditions of HFRR method are followed as they are determined in ISO 12156- 1. An upper spherical specimen (test ball) with 6 mm diameter is subject to reciprocating motion, with frequency of 50 Hz and oscillation width of 1 mm, with the help of an electromagnetic oscillator. The spherical specimen is tangent to a flat specimen under a weight of 200 g while the point of contact is immersed into 2 ml of the tested fuel. The fuel is preheated to 60 °C and the test lasts 75 minutes. • The test plate is steel ISO 683-17-100Cr6 machined from annealed rod, having a Vickers hardness “HV 30” scale number of 190 to 210 (according to ISO 6507- 1. It shall be lapped and polished to a surface finish of Ra < 0,02 μm. • The test ball is grade 28 (G28) according to ISO 3290 of steel ISO 683- 17-100Cr6. It has a Rockwell Hardness “C” scale (HRC) number of 58 to 66 according to ISO 6508-1[2]. Case 2: In case two only the load imposed on the spherical specimen is altered and all the rest parameters are kept unchanged. The metal ball is firmly fixed in the vertically positioned holder and pressed with different loads on a horizontally reinforced metal plate. The ball reciprocates with the same certain frequency and stroke length as in case one. The per- Temperature Load DM1 DM2 200 443 543 300 513 569 400 509 575 500 463 522 600 437 549 700 434 564 800 461 559 900 401 612 1000 461 677 60 Fuel Type (oC) g WSD μm Modified Rockwell Hardness Scale Table 3: Wear Scar Diameter in Case 3 Temperature Load DM1 DM2 200 408 420 300 466 466 400 487 487 500 448 448 600 441 441 700 411 458 800 494 453 900 497 497 1000 463 464 Fuel Type WSD μm Test Ball Hardness ISO 12156-1 60 (oC) g Table 2: Wear Scar Diameter in Case 2 Figure 1: The graphic histogram of the variant Load & Wear Scar Diameter. (*mod: modified test ball type) missible load that HFRR PCS Instruments device (mechanical unit) can bear is 1000 g. Wear scar diameter is measured per 100 grams added, starting from the base load (200 g) and ending to 1000 g. Case 3: In case three both the imposed load and the type of the upper specimen (test ball) are changed. • The modified test ball is grade 25 (G25). It has a Rockwell Hardness “C” scale (HRC) number of 55 to 60. The spherical specimen meets the requirements of ASTM D7688, ISO 12156-1, ASTM D6079, CEC F- 06-A, EN 590, JPI-5S-50 & IP 450. • The test plate is steel ISO 683-17-100Cr6, the same as in case one. Wear scar diameter is measured per 100 grams added, starting from the base load (200 g). 6.2 Scientific Findings Under normal conditions of ISO 12156-1 standard, DM 1 and DM 2 are marine gasoils of an excellent lubricating capacity, approved for on board use. DM 1 Marine distillate has a WS1,4 of 408 μm and DM 2 marine distillate has a WS1,4 of 420 μm. They differ in their kinematic viscosity, density and cold flow properties, while they have relative sulphur content. Under no modification both fuels have excellent tribological properties, since their wear scar diameter is far less than the permissible limit. By keeping temperature stable and changing only the imposed load there is a significant limitation in fuel’s lubricity, which in fact degrades considerably. In DM 1 fuel the effect of the increasing load on its lubricating capacity is greater than in DM 2 . The imposed load can challenge the efficacy of marine distillates. By keeping all parameters immutable - only changing the load - and always taking into account the repeatability and reproducibility of the method, there is a significant limitation in fuel’s lubricity from the load of 800 grams and above. As the load gradually increases, the lubricating capacity of the fuel decreases and eventually both distillate marine fuels are marginally converted into dry fuels. Determining lubricity by using more vulnerable HFRR specimens than the ones dictated by ISO 12156-1 standard, an increased wear on their surfaces is observed, which consequently leads to excessive friction. Lubricity of DM 2 is highly affected compared to the correspondent of DM 1 , when using a softer metal ball. Τhe most significant increase in wear scar diameter of both fuels occurs when simultaneously load and upper specimen are altered. When using the more vulnerable and less hard upper specimens, as soon as the imposed load increases, wear scar diameter is maximized in both marine gasoils. Thereafter, when the load increases, given that the more fragile specimens are used, wear in DM 2 is remarkably substantial than the corresponding one in DM 1 . Through the results of the research, it can be drawn that as sulphur content diminishes it induces lack of lubricity, increase of wear and it definitely consists a prominent factor for the malfunction of fuel’s injection system. Lubricity is a complex mechanism that has a molecular structure component. Polyaromatics and oxygen constituents are likely to be the most important natural contributors to diesel fuel lubricity and the more they are limited, the more the lubricity of the fuels decrease. Based on HFRR’s repeatability (r = 70 μm), precision, and correlation with field data it is clearly demonstrated that based on the original method conditions it doesn’t consist an accurate method for determining the lubricity of marine gasoils. The considerable change in the marine diesel fuel market, and the substantial advances in fuel injection equipment are questioning the suitability of the HFRR laboratory test. The conduction of great and thorough research is imperative nowadays, in order to establish an exclusive control standard for the ship’s fuel pumps and be able to deter engine’s future breakdowns. Τhe replacement of standard specimens with mοre sensitive and vulnerable Aus Wissenschaft und Forschung 43 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 Figure 2: Wear Scar Diameter vs Imposed Load (*mod: modified test ball type) avoid future breakdowns. The need to establish an innovative perspective on the evaluation of the lubricating capacity of such fuels is imperative, since the already existing equipment might be unsatisfactory for protecting naval fuel systems. The scientific research is ongoing in the great effort to identify the weak spots of new technologies when using very thin oils. The implementation of the optimal technology is based on whether it is a costeffective means of complying, on the infrastructure of the existing fleet and ports, on the feasibility of modifications in ship’s engines and on the complexity of crew’s training. As the world moves to a lower emissions future, the shipping industry will follow the current stream of great changes. Most of the potential low-carbon technologies are still in the early stages of development with limited commercial application, meaning the majority of new orders are still for vessels powered by fuel oil and other fossil fuels. The efficient and effective transition depends on the promising and successful collaboration of governments, energy companies and shipping firms. It will take great effort by all to ensure that the industry continues to grow in a sustainable manner. Shipping is the beating heart of global trade but its pulse is progressively getting slower. Faced with uncertainty about which fuels to use in the long term to cut greenhouse gas emissions, many shipping firms are sticking with ageing fleets and older vessels will have to start sailing slower in order to comply with the new environmental rules [17]. At the moment, only about 5 % of the world’s fleet can run on lesspolluting alternatives to fuel oil, even though more than 40 % of new ship orders will have that option. The decarbonisation of the sector and eventually its sustainability, can be achieved firstly with the improvement of energy efficiency and secondly with the corporate use of renewable fuels. 8 References [1] MARPOL 73/ 78. 2015. “International Convention for the Prevention of Pollution from Ships” Practical Guide 38: 1-57. [2] UNEP - The Mediterranean is making strides in tackling air pollution from ships, September 2022.https: / / www.unep.org/ unepmap/ news/ news/ medi terranean-making-strides-tackling-air-pollution-ships . [3] The impact of international shipping on European air quality and climate forcing / EEA Technical report No 4/ 2013. [4] Ferguson, C. R., 1986. Internal combustion engines: Applied thermosciences. New York: John Wiley & sons. [5] Eyring, V., Koehler, H. W., van Aardenne, J. and Lauer, A., 2005, “Emissions from international shipping: The last 50 years”, J. Geophys. Res., 110 (D17), D17305. [6] Danping, Wei D., H.A. Spikes, The lubricity of Diesel Fuels, Wear Vol 11, Issue 2, September 1896, Pages 217- 235. Aus Wissenschaft und Forschung 44 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036 to reciprocating motion, reveals an increased wear on their surfaces, which eventually leads to excessive friction. The continued drive for improved fuel efficiency is changing the materials that engine oils interact with. A variety of analytical methods are required to adequately explore different theories regarding marine gasoils lubricity. 7 Goals to be Achieved in the Near Future Deepsea transport is yet the most trustful and reliable means for the safe exchange and transfer of the vast majority of goods between the European Union and overseas. The shipping gaseous emissions can be effectively reduced as a result of various governments’ policy formulations and implementations [15]. Maritime decarbonization and reduction of greenhouse gas emissions from ships have become a priority case for the policymakers and the industry to be achieved, through the adoption of energy-efficient technologies, the optimization of ship operations and use of low and zerosulphur fuels. The creation of a ship emission inventory is a critical step in developing ship emission control measures and related regulations. Public institutions as the European Environment Agency (EEA) and US Environmental Protection Agency (EPA) recognize the seriousness of air pollution emission and enhance the engine development in order to meet emissions and fuel economy requirements is creating new durability challenges. As a result of the enforcement of IMO’s Sulphur Cap regulations, there are a number of operational factors that must be considered in order to ensure efficient and safe vessel operation on low sulphur distillates and whenever changeovers of fuels are made. Downsizing of engines usually means that bearings are narrower and are therefore subject to increased stresses for the same load. A great number of engine operational procedures arise and they need to be followed precisely in order to ensure that short - and long - term operation on distillate fuels does not lead to wear or malfunctioning of the fuel system and engine’s components. It is a fact that fuel quality remains a major concern for ship operators. The move to thinner oils for fuel economy is gaining momentum, with several Original Equipment Manufacturers (OEMs) developing new, even lower viscosity specifications down at dynamic viscosities of 2.6 cP or less [16]. Netherless their poor lubricating capacity may result in blocking fuel lines, damaging fuel pumps, injectors and even contribute to the loss of engine power (LOP), but it is not the only factor that provokes a failure. Great and thorough research must be done so as to identify sources of variability in the HFRR test method and to improve its precision to marine distillates, in order to [7] Petroleum products - Fuels (Class F) - Specifications of Marine Fuels, International Standard ISO/ FDIS 8217: 2017, Final Draft. [8] Brewer, T.L., Regulating international maritime Ing., verifying and enforcing regulatory compliance. J. Int. Marit. Saf. Environ. Aff. Shipp. 2021, 5, 196-207. [9] Marine Fuel Oil Advisory, December 2019, American Bureau of Shipping. [10] Hydrodesulfurization, H 2 S, hydrodesulfurization reaction resultant is a kind of typical polar molecule, Advances in Chemical Engineering, 2015. [11] Maragkogianni, A.; Papaefthimiou, S.; Zopounidis, C., Mitigating Shipping Emissions in European Ports: Social and Environmental Benefits; Springer International Publishing: Berlin, Germany, 2016. [12] Diesel Fuel - Assessment of lubricity using the high frequency reciprocating rig (HFRR), Draft International Standard ISO/ DIS 12156-1. [13] The lubricity requirement of low sulphur diesels, SAE 942015. [14] Wie D., The lubricity of Fuels II, Wear Studies using model compounds, J. of Petrol. (Pet. Processing.) 1988, Vol 4, No.1, p90. [15] https: / / www.hellenicshippingnews.com/ imo-study-shipping-emissions-rose-by-almost-10-during2012-2018-period/ IMO available online, (accessed on 25 May 2022). [16] Bosch, P., Coenen, P., Fridell, E. et al., 2009, Cost Benefit Analysis to Support the Impact Assessment accompanying the revision of Directive 1999/ 32/ EC on the Sulphur Content of certain Liquid Fuels. [17] European Commission - Reducing emission from the shipping sector https: / / climate.ec.europa.eu/ eu-action/ transport-emissions/ reducing-emissions-shipping-sector _en. Aus Wissenschaft und Forschung 45 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 2/ 2022 DOI 10.24053/ TuS-2022-0036