23rd International Colloquium Tribology - January 2022 371 Tribological Assessment of Marine Distillate Fuels under a variant HFRR Method Theodora Tyrovola Laboratory of Fuels and Lubricants, Chemical Engineering Department, National Technical University of Athens. Corresponding author: theodoratirovola@gmail.com Fanourios Zannikos Laboratory of Fuels and Lubricants, Chemical Engineering Department, National Technical University of Athens. 1. Introduction: Negative Environmental Effect of Maritime Industry Maritime transport consists an integral part of global economy, as it accounts for around 80% of worldwide trade. Per mass of cargo and per distance travelled, ships are the most energy efficient means of transportation. In recent years thought, the consumption of large amounts of fossil fuels has turned shipping industry into an emerging source of greenhouse gas emissions and a growing source of air pollution. In the context of the massive effort to reduce hazardous pollutants from maritime transport and improve air quality, the environmental regulations adopted by the International Maritime Organization (IMO) on 1 January 2020 in Annex VI of MARPOL73/ 78 convention (Marine Pollution), pose stricter limitations on sulphur oxide (SOx) emissions from ships. The IMO2020 rule limits the sulphur content of the fuel used on board ships either operating outside designated emission control areas (ECAs) to 0.50% m/ m or within ECAs to 0.10% m/ m -. IMO aims to mandate cleaner-burning fuels at sea by 2020 and to curb greenhouse gas e1missions (GHG) from ships by 2050. With the ever-changing technology in shipping industry, the fuel that is used to run marine engines is also changing rapidly. Stakeholders now focus on inherently low or zero sulphur marine gasoils (MGO) and predominantly to marine distillates (DM), in order to achieve compliance with the Sulphur Cap 2020. 2. Low-Sulphur Marine Gasoils 2.1 Tribological Properties of Marine Distillates Marine distillates carry five per cent more energy per unit volume than high sulphur fuel oil and require no major up-front investment nor costly modification or retrofitting of the vessel. Distillates are considered the most viable solution to date; however, they are accompanied by a huge range of side effects related to their storage, combustion, ignition and lubricity. Marine engines are basically compression ignited twoand four-stroke diesel engines. The operation of the vessel’s fuel injection system (pumps, injectors, etc.) depends directly on the lubricating capacity of the fuel. Marine distillates undergo a refining process (desulphurisation), where apart from sulphur and nitrogen compounds, a significant proportion of oxygenated and polyaromatic (polar) compounds, are removed. Loss of the polar compounds is considered to be responsible for the limited tribological abilities of low sulphur marine gasoils. The new desulphurized fuels are interwoven with a high decline in the engine’s lubricating properties, leading to excessive wear and scarring on the engine’s components. 2.2 High Frequency Reciprocating Rig (HFRR) Test The lubricating capacity of marine distillates is determined by the High Frequency Reciprocating Rig (HFRR) test according to ISO 12156-1 and ASTM D6079 international standards. The parameters of HFRR test method simulate marginal lubrication and welding wear conditions. Lubricating capacity is determined by measuring the wear scar diameter, expressed in micrometers (μm). For all seven types of distillate marine fuels, according to ISO 8217: 2017 fuel standard, the maximum limit of wear scar diameter (WSD) is 520 μm [1] . HFRR test consists the global standard for the lubricity assessment of automotive diesel fuel, providing high-precision results. It was established when ultra-low sulphur diesel (ULSD) fuels became the common type of diesel, used in automotive diesel engines in the mid-2000s. Lubricity is of paramount importance when operating in low-sulphur marine gasoils, nevertheless is not yet sufficiently understood in the marine sector. After the implementation of the IMO2020 sulphur regulation, more and more insufficient knowledge and inaccuracies related to lubricity, came to light. 3. Measurement and Evaluation of Wear 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 372 23rd International Colloquium Tribology - January 2022 Tribological Assessment of Marine Distillate Fuels under a variant HFRR Method 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. Properties of both fuels are similar. The sulphur content in DM 1 is 900 ppm and in DM 2 is 850 ppm. Case 1: Following the test conditions of HFRR method as determined in ISO 12156-1. An upper spherical specimen (test ball) with 6 mm diameter is subject to reciprocating motion, with frequency of 50Hz and oscillation width of 1mm, 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 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: Altering only the load imposed on the spherical specimen and keeping all the rest parameters unchanged. The permissible load that HFRR PCS Instruments device (mechanical unit) can bear is 1000g. Wear diameter is measured per 100 grams added, starting from the base load (200g). Case 3: Altering both the imposed load and the type of the upper specimen (test ball). 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. Wear diameter is measured per 100 grams added, starting from the base load (200g). Table 1: Wear Scar Diameter with variable load. Table 2: Wear Scar Diameter with variable load and variable test ball. Diagram 1: Wear Scar Diameter vs Imposed Load (*mod: modified test ball type) Under no modification both fuels have excellent tribological properties. 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 R & r of the method, there is a slight but significant limitation in fuel’s lubricity. Τhe replacement of standard specimens with mοre sensitive and vulnerable to reciprocating motion, reveals an increased wear on their surfaces, which eventually leads to excessive friction. Τhe most significant increase in wear scar diameter occurs when both 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. When increasing the load, wear in DM 2 is remarkably substantial than the corresponding one in DM 1 . This finding indicates that as sulphur content diminishes it induces lack of lubricity and consists a prominent factor for the malfunction of fuel’s injection system. 4. Conclusion: The Next Step in Lubrication Assessment 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 23rd International Colloquium Tribology - January 2022 373 Tribological Assessment of Marine Distillate Fuels under a variant HFRR Method 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 avoid future breakdowns [3] . 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. References [1] Petroleum Products-Fuels (Class F)-Specifications of Marine Fuels, International Standard ISO/ FDIS 8217: 2017. [2] Diesel Fuel-Assessment of Lubricity using the high-frequency reciprocating rig (HFRR)-ISO/ DIS 12156-1: 2018. [3] Nikanjam M. and Rutherford J.,“Improving the Precision of the HFRR Lubricity Test”, SAE 16- 10-06.