A Study of Stratified Charge Combustion Characteristics in New Concept Direct Injection SI Gasoline Engine 2001-01-0734

A new stratified charge system has been developed for direct injection gasoline engines. The special feature of this system is employment of a thin fan-shaped fuel spray formed by a slit nozzle and a shell-shaped piston cavity. This system, basically classified into the wall-guided mixture preparation concept that leads air/fuel mixture to the spark plug periphery by means of spray penetration and piston cavity configuration without an extra intake air flow controlling system, obtained wide engine operating area with stratified combustion and high output performance.

This report presents the characteristics of stratified mixture formation and combustion, especially the important factor for achieving stable stratified combustion in the high-speed region, which have been clarified through analytical studies. For mixture formation analysis, spray behavior was observed by photographing the forward-scattered light from spray particles; local fuel mixture concentration in the piston cavity was measured using a fast response FID. For combustion characteristics analysis, flame propagation was measured by the ion current analysis, and frame behavior was observed by radical luminescence measurement using a high-speed multi-spectral video camera. Furthermore, in-cylinder air flow dynamics, which have a significant influence on mixture formation, were measured by the Particle-Image-Velocimetry(PIV) method using endoscope observation. These analyses have revealed that, the newly developed system achieves stable stratified combustion in the high-speed region due to optimized the piston cavity shape and fuel spray characteristics, especially suitable spray penetration with high injection pressure which provides ensuring the mixture formation to be “robust” against air flow and accelerating mixture diffusion in the cavity.