Influence of Crankcase Oil Properties on Low-Speed Pre-Ignition Encountered in a Highly-Boosted Gasoline Direct Injection Engine

This paper reports an experimental investigation on the influence of the crankcase oil properties on the engine combustion in the low-speed pre-ignition (LSPI) zone. The investigation was conducted on a highly boosted 1.5L TGDI engine operated at the low-speed-end maximum torque, at which LSPI events were observed most frequently. Six different engine oils were tested, covering SAE 0W-20, 0W-30, 0W-40, 5W-20, 5W-30 and 5W-40. In order to evaluate the evaporative characteristics of the crankcase oil, for each of the selected engine oils, the tests were conducted at two different coolant temperatures, 90°C and 105°C. Because SAE 5W-30 was the base oil for the engine under study, for this particular oil, the investigation was extended to the impact of different levels of the mixture enrichment. Followings were found: 1) LSPI events were observed when the engine was operated with a stoichiometric mixture for all the oils tested. 2) No clear indication on which SAE oil tested had a stronger influence on LSPI than other oils, either promoting or inhibiting LSPI, because the influences on LSPI of the related oil properties might not be as strong as that of the high gasoline content in the oils, which reached about 6% in the tests. 3) Behavior of LSPI was random in all the tests and a particular LSPI pattern observed in a test was difficult to be reproduced under the same condition. This suggests that LSPI may be triggered at a complicated condition with contributions from many variable parameters. It may be meaningful to characterize the behavior of LSPI with a statistical approach.