Effects of the injection timing on spray and combustion characteristics in a spray-guided DISI engine under lean-stratified operation

An experimental study was carried out to investigate the effects of injection timing on spray and combustion characteristics in a spray guided direct injection spark ignition (DISI) engine under lean stratified operation. In-cylinder pressure analysis, exhaust emissions measurement, and visualization of combustion and spray were applied. Combustion in a stratified DISI engine was found to have both lean premixed and mixing controlled flame characteristics. The stratified mixture characteristic for the injection timing was verified as a dominant factor of the flame characteristics. For the early injection timing, non-luminous flame and low combustion efficiency were observed due to the over-mixed mixture formation. On the contrary, luminous sooting flame was shown at the late injection timing because of under-mixed mixture formation. In addition, smoke emission and incomplete combustion products were increased at the late injection timing due to increased locally rich area of the mixture. On the other hand, nitrogen oxides (NOx) emissions were decreased while indicated mean effective pressure (IMEP) was increased as the injection timing was retarded. The retarded combustion phasing was verified as the reason in this observation.