This paper summarizes the first phase of an experimental effort focused on developing a comprehensive understanding of the in-cylinder air/fuel mixing and combustion processes in spark-ignition engines using laser-based fuel distribution and combustion measurements. As part of this first phase, a semi-quantitative, laser-induced fluorescence, fuel distribution measurement technique was developed and demonstrated. The calibration, correction, and image analysis processes associated with the technique were shown to be comparatively simple and effective (relative to other analytical and empirical methods). The error associated with the technique was shown to be 5 - 10 % under vapor phase conditions.
This work was applied to a port fuel injected optical engine, which was designed for optical access through the piston and cylinder liner under firing conditions. The engine was operated under Coordinated Strategy for Starting with Reduced Emissions (CSSRE) operating conditions and characterized using the laser-induced fluorescence technique, as well as cylinder pressure analysis. Various ignition timings, Charge Motion Control Device (CMCD) positions, and fuel preparations were examined. Significant differences in 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 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.