Abstract
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 the spray and combustion were applied. Combustion in a stratified DISI engine was found to have combustion characteristics of both lean premixed and diffusion controlled flame. The stratified mixture characteristics corresponding injection timing condition was verified as a dominant factor of these flame characteristics. For the early injection timing, non luminous blue flame and low combustion efficiency were observed due to the lean homogeneous mixture formation. On the other hand, 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. On the other hand, nitrogen oxides (NOx) emissions were decreased and indicated mean effective pressure (IMEP) was increased as the injection timing was retarded. Combustion phasing resulted by the injection timing was verified as the reason in this observation.
