Fuel-Lubricant Interactions on the Propensity for Stochastic Pre-Ignition

This work explores the impact of the interaction of lubricant and fuel properties on the propensity for stochastic pre-ignition (SPI). Findings are based on statistically significant changes in SPI tendency and magnitude, as determined by measurements of cylinder pressure. Specifically, lubricant detergents, lubricant volatility, fuel volatility, fuel chemical composition, fuel-wall impingement, and engine load were varied to study the physical and chemical effects of fuel-lubricant interactions on SPI tendency. The work illustrates that at low loads, with fuels susceptible to SPI events, lubricant detergent package effects on SPI were non-significant. However, with changes to fuel distillation, fuel-wall impingement, and most importantly engine load, lubricant detergent effects could be observed even at reduced loads This suggests that there is a thermal effect associated with the higher load operation. It was hypothesized that the thermal effect was associated with lube oil nitrogenation. To test this theory, nitromethane (CH₃NO₂) was blended at 6.5% by volume CH₃NO₂ resulted in significant sensitivity to lubricant additive package effect on SPI, even at reduced loads where no lubricant sensitivity was observed without the addition of CH₃NO₂. The combined results highlight the interplay of fuel-lubricant interaction on SPI events, but more importantly suggest that there is the potential of a chemical interaction unique to high-load engine operation that results in reactive chemical processes, such as nitration, where lubricant chemistry becomes an active pathway for SPI activity.