Studies of Mixture Preparation in a Spark Ignition Engine Using Interferometric Laser Imaging for Droplet Sizing (ILIDS)

The transport of fuel droplets into the combustion chamber of an SI engine and their subsequent evaporation has been studied, using a new optical diagnostic technique, Interferometric Laser Imaging for Droplet Sizing (ILIDS), which allows temporally and spatially resolved measurements of droplet size distributions. The measurement technique and its application to in-cylinder engine measurements are described. Measurements were made under warmed-up conditions, with open valve injection timing, in a Ricardo Hydra single cylinder engine. The results showed differences in the evolution of the droplet size distribution in cylinder with variations in load and speed. At 1200 rpm under full load, droplets arrived quickly into the cylinder, and were small, the Sauter Mean Diameter (SMD) being in the region 10-12 μm on arrival, so that mixture preparation was good. However under part load the arrival of the droplets in cylinder was significantly delayed by inlet valve backflow and the SMD of the spray was much larger, in the region of 100 μm. At WOT, increase of speed from 1200 rpm to 1800 rpm led to a higher peak SMD in the cylinder, and the peak occurred later in the cycle. These variations in the amount of fuel present as liquid droplets in the cylinder late in the cycle have implications for hydrocarbon emissions and performance on start-up and during transients.