Relative Impact of Chemical and Physical Properties of the Oil-Fuel Droplet on Pre-Ignition and Super-Knock in Turbocharged Gasoline Engines

A conceptual approach to help understand and simulate droplet induced pre-ignition is presented. The complex phenomenon of oil-fuel droplet induced pre-ignition has been decomposed to its elementary processes. This approach helps identify the key fluid properties and engine parameters that affect the pre-ignition phenomenon, and could be used to control LSPI. Based on the conceptual model, a 3D CFD engine simulation has been developed which is able to realistically model all of the elementary processes involved in droplet induced pre-ignition. The simulation was successfully able to predict droplet induced pre-ignition at conditions where the phenomenon has been experimentally observed.

The simulation has been able to help explain the observation of pre-ignition advancement relative to injection timing as experimentally observed in a previous study [6]. The results indicate that retarded injection timing leads to shorter time for mixing and subsequently relatively higher inhomogeneity and local equivalence ratios which leads to shorter ignition delay. This implies that beyond temperature and pressure, vaporization and mixing of the components of the fluid ejected from the piston crevice also affects pre-ignition.