Abstract
This work explores the interaction of lubricant and fuel properties on stochastic pre-ignition (SPI). Findings are based statistically significant measurements of cylinder pressure to SPI tendency and magnitude. Specifically, lubricant detergents, lubricant volatility, fuel volatility, fuel chemical composition, fuel-wall impingement, and engine load were varied to study the physical-chemistry 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 or fuel chemistry, lubricant detergent effects could be observed even at reduced loads. Interestingly the effects of intentionally nitrogenation of the fuel, through 6.5% by volume addition of nitromethane, 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 nitromethane. The combined results highlight the interplay of fuel-lubricant interaction on SPI event, 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, like nitration, that are affected by lubricant chemistry.
