Abstract
Downsized gasoline engines, coupled with gasoline direct injection (GDI) and turbocharging have provided an effective means to meet both emissions standards and customer drivability expectations. Unfortunately, many of these downsized, boosted engines have experienced a new type of uncontrolled combustion. This combustion occurs when the engine is operating under high load and low speed conditions and has been named Low Speed Pre-Ignition (LSPI). LSPI has been shown to be very damaging to engine hardware. Although LSPI is a random occurrence, engine oils, specifically engine oil additives, have been shown to directly impact LSPI propensity. Industry tests effectively quantify the LSPI propensity of a fresh oil, however, they do not quantify the LSPI propensity of an aged oil. This is an important distinction as many of the chemical additives in engine oils change and degrade over time. In this paper, the concept of LSPI durability is introduced. LSPI durability is defined as the ability of an engine oil to minimize or eliminate LSPI, not only while the oil is fresh, but also over a relevant oil drain interval (ODI). To quantify LSPI durability, an engine test methodology was developed which evaluates LSPI on fresh oil, then ages the oil using a relevant duty cycle and finally re-evaluates the aged oil for LSPI propensity. Using this threepart testing protocol, six different oil formulations were evaluated. Results show that some formulating strategies work well for LSPI prevention only with fresh oil, while others prevent LSPI when fresh and aged. In addition, a further study is included in this paper which examines LSPI during the life of vehicle, showing significant variability in LSPI propensity and examining the possible causes.