Hirano, S., Yamashita, M., Fujimoto, K., and Kato, K., "Investigation of Engine Oil Effect on Abnormal Combustion in Turbocharged Direct Injection - Spark Ignition Engines (Part 2)," SAE Technical Paper 2013-01-2569, 2013, doi:10.4271/2013-01-2569.
As one of spark ignition (SI) engine solutions to improve fuel economy while maintaining drivability, concept of combing turbocharging and direct injection (DI) fuel injection system with engine down-sizing has increased its application in the market. Abnormal combustion phenomena referred to as Low Speed Pre-Ignition (LSPI) has been recognized as potential restriction to improve low speed engine torque that contributes fuel economy improvement. As reported in the part 1 , the study showed that engine oil composition had significant influence on the frequency of LSPI in both preventive and contributory effects.Further investigation was conducted to evaluate engine oil formulation variables and other factors that may have influences on the LSPI, such as engine oil degradation.Engine test that consisted of 2 phases was designed in order to confirm the correlation between LSPI frequency and engine oil degradation. The LSPI frequency measurement phase and engine oil degradation operation phase were conducted alternatively without changing engine oil. It was observed that the engine oil degradation increased the LSPI frequency.Several different types of engine oils, including both experimental oils that represent possible chemical & physical properties found in the market and a few commercially available engine oil products that meet industry standards, such as API S category and ACEA specification, were also evaluated to understand the feasibility of engine oil that has LSPI prevention performance.The test results showed it is feasible to formulate the engine oil that reduces LSPI significantly while maintaining basic engine oil performances.