24th International Colloquium Tribology - January 2024 45 Effect of Organic Friction Modifiers on Friction and Wear of HDDEO Formulations Gareth Moody 1* , Alexei Kurchan 2 , Sydne Tison 2 1 Cargill York, UK 2 Cargill Wilmington DE, USA * E-mail gareth_moody@cargill.com 1. Introduction Heavy duty engine oils remain an important part in transportation and have different requirements to their passenger car counterparts. Whilst viscosity of the oils has significantly reduced, 10W30 and 5W30 grades remain common unlike passenger car where 0W20 oils are popular. The additive package in a HDDEO (Heavy Duty Diesel Engine Oil) is designed with drain interval and component longevity in mind with other considerations such as cleanliness (soot management) and fuel economy also being important considerations. The introduction of the new heavy duty category PC-12 which will aim to improve fuel economy 1 and reduce NO x and CO 2 2 will further test lubricant formulators and OEMs to protect hardware whilst reducing emissions with lower SAPS levels proposed. In many of the future developments of heavy duty architecture engine oil will remain a necessary component of the system and although the technical roadmap for the future of heavy duty vehicles remains uncertain it is important that the oil can work effectively with new fuels and help meet new regulatory requirements. For small to medium goods delivery vehicles electrification and full battery electric vehicle numbers are on the increase but there are several other alternatives to battery electric particularly for very large heavy duty vehicles which include (but are not limited to) biofuels, compressed natural gas, liquified natural gas hybridisation, fuel cell and hydrogen 1 internal combustion engines. This work will evaluate the use of existing and new Polymeric Friction Modifiers (PFMs) with the new friction modifiers designed specifically for heavy duty engine oils with newly developed materials having enhanced oil compatibility without compromising on performance. The concept of a hydrogen fuelled internal combustion engine will be introduced and the potential impact the difference in conditions and in particular water content will have on the oil will be discussed. 2. Results and discussion The methods used for evaluation of the engine oils were MTM and 4-ball (ASTM D4172). The MTM method used stribeck curve conditions of 36N load, 0.5 - 3.0 m/ s speed, a temperature of 80-°C and a slide roll ration of 50%. Stribeck curves were measured after several rubbing stages of 31N load and a speed of 0.03 m/ s to generate a tribofilm. The rubbing stages totalled 120 mins. Figure 1 shows the MTM results of the HDDEO with and without the addition of friction modifiers. Initially, both the GMO and the MoDTC had very little impact whereas the PFM reduced friction immediately without the need for tribofilm development (dotted lines in Figure 1). After 120 mins of rubbing, the GMO reduced friction from 0.14 to 0.10 (boundary friction peak). The MoDTC and PFM after rubbing both reduced friction below 0.04. Figure 1: MTM stribeck curves of HDDEO with and without friction modifiers SLIM analysis was also done post stribeck to assess the tribofilm formation of the oils. After 120 mins rubbing, all of the test runs showed some tribofilm growth (Figure 2). The reference oil appears to have the thickest tribofilm from the darker colouration on the MTM ball but it is known that the correlation between colour and thickness is not always straightforward and that the addition of a PFM can alter the composition of the tribofilm 3 without having a negative effect on wear. Figure 2: Mapper images of the MTM ball 46 24th International Colloquium Tribology - January 2024 Effect of Organic Friction Modifiers on Friction and Wear of HDDEO Formulations Low friction is an indicator of increased efficiency which can potentially result in increased fuel economy and therefore range of the vehicle which is highly desirable in heavy duty vehicles, however these frictional improvements must not come at the detriment of hardware longevity. Figure 3 shows the 4-ball wear scars according to ASTM D4172 of a 15W-40 HDDEO with and without friction modifiers. In this test all of the oils behaved fairly similarly with the GMO, PFM and MoDTC all having no negative effect on performance of the antiwear additives in the engine oil formulation. Figure 3: 4-ball testing of the engine oil with and without friction modifiers. The difference with respect to looking forward to PC-12 style formulations is that lower friction can be achieved by a small amount by GMO and a large amount by either MoDTC or PFM but the PFM is able to achieve this without adding to the SAPS level of the oil making it a useful tool for formulators who wish to lower SAPS and improve fuel economy without impacting on wear. Whilst fuel economy and equipment lifetime will remain the most important factors sustainability and Product Carbon Footprint (PCF) will also undoubtedly increase in importance. Here, things such as ester base oils can be used to improve biobased contents of oils, increase biodegradability and reduce PCF. Looking ahead to new technologies such as hydrogen fuelled internal combustion engines, there will be some modifications required to both engine design and lubrication with things such as water levels of up to 3 times higher than diesel fuelled cases, 4 meaning the oil must be able to function in the presence of higher levels of water than in the past. 3. Conclusions The use of GMO, MoDTC or PFM can reduce the coefficient of friction in a HDDEO Using PFM or MoDTC can reduce friction more than using GMO Using a PFM can achieve high levels of friction reduction without increasing SAPS levels in the oil The use of organic or inorganic friction modifiers allows the creation of a tribofilm but it is different from that of a reference oil. The use of friction modifiers in a HDDEO was not found to have a negative effect on wear when tested in a 4-ball. The additional water content of engine oils associated with using hydrogen as a fuel instead of diesel must be taken into account to prevent potential problems including increased wear caused by moisture delaying development of ZDDP films 5 . References [1] A. Brown, R. Fowler, - Tribology & Lubrication Technology; Park Ridge Vol.-79, Iss.-9, (Sep 2023): 28-29 [2] https: / / www.infineuminsight.com/ en-gb/ articles/ pc- 12-moving-ahead/ [3] J. Eastwood, G. Moody Tribofilm chemistry for engine oils formulated with organic polymeric friction modifiers ITC conference Sendai 2019. [4] Yamada, N. and Mohamad, M.N.A., 2010. Efficiency of hydrogen internal combustion engine combined with open steam Rankine cycle recovering water and waste heat. International Journal of Hydrogen Energy, 35(3), pp. 1430-1442. [5] A. Dorgham., A. Azam, P. Parsaeian,. et al. An Assessment of the Effect of Relative Humidity on the Decomposition of the ZDDP Antiwear Additive. Tribol Lett-69, 72 (2021).