Impact of Engine Age and Engine Hardware on Low-Speed Pre-Ignition 2018-01-1663
Low-speed pre-ignition (LSPI) is a well-studied phenomenon in boosted, spark ignition engines. The impact of lubricant formulation has received a lot of attention in recent years, yet the impact of engine hardware and engine wear on LSPI is still not fully understood. This paper addresses some of these questions using results from multiple installations of the GM 2.0 L LHU engine platform. In the first part of the study, the effect of engine life on LSPI activity was observed, and it was found that engines were susceptible to variations in LSPI activity during the initial LSPI tests with the activity eventually reaching a “stabilized” level. It was further observed that the LSPI activity generally continued to decline at a steady rate as the engine aged. For engines used in LSPI testing, the life of the engine is often limited as LSPI activity decays with age. This reduction in LSPI activity may correlate to the engine liner wear and it is suggested that the amount of oil transport along the engine liner, which is a function of the liner roughness amongst other factors, is a dominant mechanism for this observed reduction. This observation highlights the importance of baseline testing throughout the life of the engine which is critical for severity adjustments of oils tested at different times. The effect of hardware component replacement on LSPI activity was also investigated. It was determined that the removing, cleaning, and replacing of both pistons and rings had no effect on LSPI activity and did not require re-stabilization of the test engine.