An investigation on the auto-ignition of fuel-air mixture induced by release of oil-fuel droplets from cylinder-liner using multi-zone model

This study investigated effects of gas inhomogeneity induced by droplets of fuels and oils on the auto ignition timing and temperature in the direct-injection spark ignition (DISI) engine by means of detailed numerical calculation using multi zone model. Recent researchers pointed out that droplets are made of fuels and oils which mix on the cylinder liner and released from the cylinder liner [1]. During the compression stroke released droplets reach the auto ignition temperature before flame propagation induced by spark ignition. It is called Pre-ignition. In combustion chamber, there is inhomogeneity caused by temperature and mixture distribution. In this study, the effects of gas inhomogeneity produced by droplet on the auto ignition timing and temperature have been investigated using Multi-Zone model of CHEMKIN-PRO by changing initial temperature and initial equivalence ratio. Especially, the volume of first ignition zone is focused on. As for fuels, this study used n-heptane to observe the impacts which the gas inhomogeneity has on low-temperature heat release (LTHR). As for calculation conditions, 15 zones model were assumed. Based on the assumption that the volume of the droplets from cylinder-liner is not always constant, ignition delay time and ignition temperature of mixture were confirmed, changing the volume of first ignition zone. Consequently, we found that the volume of first ignition zone affects the auto-ignition of air-fuel mixture and there is possibility to lead to cause Pre-ignition.