Fuel Effects on the Propensity to Establish Propagating Flames at SPI-Relevant Engine Conditions 2021-01-0488

In order to further understand the sequence of events leading to stochastic preignition in a spark-ignition engine, a previously developed experimental and analysis methodology was used to evaluate the propensity of fuels to establishing propagating flames under conditions representative of those at which stochastic preignition (SPI) occur. A large fuel matrix including single component hydrocarbons, binary and tertiary mixtures, and real fuel blends was evaluated. The propensity of each fuel to establish a flame was correlated to multiple fuel properties and shown to exhibit consistent blending behaviors. No single parameter strongly predicted a fuel’s propensity to establish a flame, while multiple reactivity-based parameters exhibited moderate correlation. A two-stage model of the flame establishment process was developed to interpret and explain these results. In short, the fuel-air mixture must locally reach a chemical run-away ignition temperature and then the fuel-air mixture outside of this zone must sustain a propagating flame. This model explains why various fuel properties affect the overall flame establishment propensity of a given fuel. The data of this study, and the understanding it has generated, elucidates the role of fuels on the flame establishment process under elevated pressure and temperature conditions, and ultimately aids in the understanding of the stochastic preignition problem.