In this multi-phase study, fuel and lubricant effects on stochastic preignition (SPI) were examined. First, the behavior of fuels for which SPI data had previously been collected were characterized in terms of their combustion and emissions behavior, and correlations between these characteristics and their SPI behavior were examined. Second, new SPI data was collected for a matrix of fuels that was constructed to test and confirm hypotheses that resulted from interpretation of the earlier data in the study and from data in open literature. Specifically, the extent to which the presence of heavy components in the fuel affected SPI propensity, and the extent to which flame initiation propensity affected SPI propensity, were examined. Finally, the interaction of fuels with lubricants expected to exhibit a range of SPI propensities was examined. Although this final dataset did not yield conclusive results, it suggests that additional factors such as engine condition can have a very significant effect on SPI propensity.
The main findings of the study are that lower volatility fuel components appear to affect the propensity of the fuel to create initiation events (which could be fuel-oil droplets or deposit breakoff) that can lead to SPI, and further that the ease by which a flame can be established in the bulk mixture correlates to SPI tendency when the initiation event tendency is fixed. The study also showed that neither soot-forming tendency of a fuel nor the fuel’s antiknock quality necessarily correlate to SPI tendency.
