24th International Colloquium Tribology - January 2024 209 Detection of Wear in Modern Naval Engines Theodora Tyrovola 1* , Fanourios Zannikos 2 . 1 Laboratory of Fuels and Lubricants - National Technical University, Athens, Greece (Technical Academy Esslingen eV) 2 Laboratory of Fuels and Lubricants - National Technical University, Athens, Greece (Technical Academy Esslingen eV) * Theodora Tyrovola: theodoratirovola@gmail.com 1. Introduction: Cutting Emissions from Shipping Industry. 1.1 Establishing Stricter Regulations for Emissions Cut. Maritime transport is the linchpin of the global economy, acting as the physical support for its flows of freight. It remains dominated by longitudinal interactions which are considerable, having some great advantages apart from speed, like the continuity and the capacity to handle large amounts of cargo. Nevertheless, it is a growing source of greenhouse gas (GHG) emissions and a major source of air pollution, underwater noise and oil pollution. At EU level, maritime transport represents 3 to 4% of the EU’s total CO2-emissions and in terms of equivalent tonnes of CO2, over-124 million in 2021. The initial GHG strategy of the International Maritime Organization (IMO) sets a fundamental target to reduce CO2 emissions per transport work, as an average across international shipping, by-at least 40% by 2030 and 70% by 2050. IMO implemented strict regulations in 2020 (IMO2020 Rule), forcing ships to use low sulphur fuels for public health reasons. The new rules lowered the maximum percentage of sulphur from 3.5% to 0.5% for all ships operating worldwide and the highest permissible sulphur content in fuels of ships sailing in the SECAs (Sulphur Emission Control Areas) is 0.1% m/ m. The immediate shrinking of sulphur emissions is mentioned in the sixth (IV) Annex of the Marine Pollution (MAR- POL) Convention of the International Maritime Organisation (IMO) [1]. The switch from residual fuels to low sulphur distillate ones is the most viable way for shipowners and operators to comply with the emission limitation requirements. 1.2 Notorious Emitted Pollutants. Air pollution-from ships is generated mostly by-diesel engines-that burn high-sulphur-content-fuel oil, also known as bunker oil. The complete and incomplete combustion of conventional fuels inside the naval engine along with the high temperature of the intake or scavenger air inside the cylinder, result in the formation of a complex mixture of exhaust gases and particles. Shipping emissions are constituted by primary and secondary particulate matter, mainly in the fine size fraction (PM 2.5 ) and including black carbon (BC), and in addition by sulphur dioxide (SO 2 ), nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC) and carbon dioxide (CO 2 ) [2]. Nearly 70% of these emissions occur near coastlines, posing immediate environmental and human health risks to the coastal populations. Port cities especially, with high population densities, are more susceptible to ship emissions. Global shipping emissions could grow by up to 50% by 2050, depending on future economic and energy developments. The most challenging emissions are currently sulphur oxides - SO x , and nitrogen oxides - NO x. The main fuel type used today is the low-cost, highly viscous residual or else heavy fuel oil with high sulphur content and potentially carcinogenic substances. These combustible gases, emitted into the environment in the form of smoke, can have adverse effects on the ozone layer in the troposphere, which results in the “greenhouse effect” and may contribute to the global warming phenomenon. 2. Sustainable Low Sulphur Marine Gasoils. 2.1 Properties of Low Sulphur Marine Gasoils. With a far lower carbon footprint than petroleum-based fuels, environmentally friendly marine fuels are the most sustainable solution at the moment, for lowering SOx and NOx emissions, achieving ecological justice and promoting energy saving in the maritime sector. Low Sulphur Marine Gasoil (LS-MGO) is a distillate fuel with maximum sulphur content of 0,1% m/ m. Distillate marine fuel is mostly used in ships sailing in EU ports or in the Emission Control Areas (ECAs). Distillates can be unstable since they undergo chemical changes in the short term that can cause severe operational problems, they often experience low lubricity, they might contain contaminants and finally they can be incompatible. Due to fuel’s limited lubricity, pumps can suffer from adhesive wear where pump internal parts stick accelerating wear. Existing seals may need to be changed in order to deal with the challenges of the new fluid. 2.2 Weak Tribological Properties of Marine Gasoils. A diesel fuel’s lubricity is a measure of its ability to prevent or minimize wear in the components that utilize the fuel as a lubricant. Obviously, components with the greatest dependence on the fuel for lubrication demand a higher lubricity fuel. Fuel’s lubricity is related to the chemical composition of the fuel. The sliding surfaces in fuel injection system are protected from wear by hydrodynamic and boundary lubrication mechanisms. The lubricant’s ability to keep the surfaces separated is governed by its viscosity. Sulphur is one of the compounds in the fuel that imparts lubricity characteristics. The currently established refining processes for the production of low sulphur marine gasoils, remove not only the sulphur and nitrogen compounds but also a significant proportion of oxygenated and polyaromatic (polar) compounds. Loss of the polar compounds is considered to be responsible for the limited tribological abilities of low sulphur marine gasoils, making them insufficient and eventually leading to leading to excessive wear and scarring on the engine’s components [3]. Detection of Wear in Modern Naval Engines 210 24th International Colloquium Tribology - January 2024 3. Detection of Wear. 3.1 High Frequency Reciprocating Rig (HFRR) Test Method. The lubricating capacity of marine distillates is determined by the High Frequency Reciprocating Rig (HFRR) test which constitutes a microprocessor-controlled reciprocating friction and wear test system which provides a fast, repeatable assessment of the performance of fuels and lubricants. It is considered the industry’s standard test for all diesel fuels lubricity. 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 at 1.4 kPa wear diameter (WS1.4) expressed in micrometers (μm) and constitutes the lubricating capacity of the fuel [4] . Lubricity has been recognized as a potential quality issue with low-sulphur marine fuel distillates, and therefore a specific acceptable limit for lubricity is set in the recently revised version of the ISO 8217: 2017 standard for the classification and specification of marine fuels -. The maximum specified limit is 520 µm WSD (wear scar diameter) and is determined by the HFRR method according to ISO12156- 1. This limit only applies to fuels with less than 0.1% (1000 ppm) sulphur content. 3.2 Modifications in the Original Parameters of HFRR Test Method. The implementation of IMO2020 Rule, establishes more assumptions and inaccuracies related to marine distillates’ lubricity, making it not easily perceived in the marine industry. The use of a fuel with poor lubricity may result in fuel pump seizure, but it is not the only factor that provokes a failure. Marine distillates 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. In order to increase the sensitivity and accurateness of HFRR over marine distillates, we rely both on the basic parameters of ISO 12156-1 standard and on the modifications of them. Altering the basic parameters of ISO 12156-1 is performed in order to identify the possible 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. In this scientific research both temperature and the imposed load are factors that can challenge the efficacy of marine distillates. By keeping temperature stable and changing the load there is a significant limitation in fuel’s lubricity, which in fact degrades considerably. The load factor affects several aspects of the engine’s operation and can impact its efficiency in various ways by provoking lower efficacy and increased wear on the mechanical components. When the temperature progressively rises, as certain parts of the naval equipment experience regionally higher temperatures due to adhesive wear, the wear scar diameter is remarkably rising. When both the imposed load and heat are rising, WSD increases rapidly, escaping from the imposed lubricating limit and therefore the fuel’s lubricating capacity is remarkably reduced. Determining lubricity by using more vulnerable HFRR ball specimens, excess wear is observed on their surfaces leading to diminishing of the fuel’s tribological properties. At higher temperatures and loads from those that are normally applied (200g, 60 o C), wear is measured to be significantly higher when using the original hardness specimens rather than when using more susceptible to abrasion and scuffing ones. Table 1: MWSD for Marine Diesel Fuel (S content less than 0.1%) with original Rockwell hardness. Table 2: MWSD for Marine Diesel Fuel (S content less than 0.1%) with modified Rockwell hardness. 4. Conclusion Fluctuations of temperature and load in a naval diesel engine are factors that can challenge the efficacy of marine distillates. The application of more vulnerable ball specimens proves that they suffer extreme wear on their surfaces leading to excessive friction. It is necessary and imperative to conduct targeted and thorough research so as to establish an exclusive control standard for the ship’s fuel pumps and be able to avoid future breakdowns. While worldwide maritime transport sector plays a vital role for the economic well-being it has an urgent responsibility to step up its efforts to reduce the sector’s environmental footprint. While steps have been taken already based on European and international policies, much more is needed for a fundamental shift towards a sustainable maritime transport sector that contributes to secure the future well-being and survival of our most sensitive ecosystems and coastal areas, and the well-being of citizens. References: [1] MARPOL 73/ 78. 2015. “International Convention for the Prevention of Pollution from Ships” Practical Guide 38: 1-57. [2] Balcombe, P., Brierley, J., Lewis, C., Skatvedt, L., Speirs, J., Hawkes, A., Staffel, I. (2019). How to decarbonize international shipping: Options for fuels, technologies and policies. Energy Convers. Manage. 182, 72-88.- [3] Wie D., The lubricity of Fuels II, Wear Studies using model compounds, J. of Petrol. (Pet. Processing.) 1988, Vol 4, No.1, p90. [4] Diesel Fuel - Assessment of lubricity using the high frequency reciprocating rig (HFRR), Draft International Standard ISO/ DIS 12156-1.