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Fuel Effects on the Propensity to Establish Propagating Flames at SPI-Relevant Engine Conditions
Abstract:
In order to further understand the sequence of events leading to stochastic preignition in a spark-ignition engine, a methodology previously developed by the authors was used to evaluate the propensity of a wide range of fuels to establishing propagating flames under conditions representative of those at which stochastic preignition (SPI) occurs. The fuel matrix included single component hydrocarbons, binary mixtures, and real fuel blends.
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, helps elucidate 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.