| A more comprehensive understanding of the in-cylinder air/fuel mixing and combustion processes in port and direct fuel injected spark-ignition engines was obtained using quantitative, laser-based fuel distribution and combustion measurements. Various measurement techniques, optical engines, and related hardware/diagnostic systems were developed in support of this research.; A port fuel injected engine was operated under CSSRE operating conditions and characterized using quantitative, laser-induced fluorescence and cylinder pressure analysis. Various ignition timings, charge motion control device positions, and fuel preparations were examined. Significant differences in quantitative fuel distributions were observed during the intake stroke for the various operating conditions, including differences in fuel droplet and vapor distribution. However, by the end of the compression stroke, it was difficult to discern between the quantitative fuel distributions for the various operating conditions, suggesting that all achieved approximately the same level of homogeneity. These results were supported by the cylinder pressure analysis which illustrated that the standard deviation in NMEP was explained completely by the effect of combustion phasing.; A direct fuel injected engine was operated under homogeneous and stratified operating conditions and characterized using quantitative, laser-induced fluorescence, flame emission imaging, and piston top soot printing. For homogenous charge, the air/fuel mixture became increasingly homogeneous during the compression stroke. However, it was evident that the mixture did not achieve complete homogeneity, and a slight stratification persisted. For stratified charge, the mixture became increasingly homogeneous in small scale, yet remained stratified in large scale, during the remaining part of the compression stroke. The effectiveness of the of the wall-guided direct fuel injected process was demonstrated; the fuel spray evaporated as it impinged on the advancing piston bowl, and the resultant dispersing vapor phase exited the bowl guided toward the spark plug. Additionally, for stratified charge operation, the laser induced fluorescence, flame emission imaging, and piston top soot printing measurements identified several potential sources of unburned hydrocarbon and soot emissions. These included over-mixing and incomplete combustion in the end gas regions, out-gassing of the piston top land crevice volume, a spark plug out-gassing phenomena, and a piston bowl roll-up phenomena. |
