Study and Visualization of the Fuel Distribution in a Stratified Spark Ignition Engine with EGR Using Laser-Induced Fluorescence

In this study, we report experimental investigations on the air/fuel distribution in the combustion chamber of a spark ignition engine during the first stage of combustion, and prior to ignition. Several modifications were made to a single cylinder to give optical access to the combustion chamber via a glass cylinder. These modifications included the addition of electro-magnetic valves, with a strategic placement for internal exhaust gas recirculation (EGR), and a quartz glass cylinder for optical access. With the placement and timing of the electro-magnetic valves and exhaust gas recirculation rates up to 40 % mass, the engine's combustion process was greatly improved. These improvements included a reduction of fuel consumption by 8 % and a reduction in NO_x emissions of 90 %.

The flow of air/fuel mixture into the combustion chamber was visualized by Planar Laser-Induced Fluorescence (PLIF) and captured as 8-bit gray scale images. Highly resolved temporal and spatial images of the fuel distribution were obtained for different engine operating conditions. Specifically, the load and engine speed were varied. These images were then employed to develop a model for the fuel distribution obtained in the combustion chamber. This model was used to explain how the improvements to the combustion process were obtained. The effects of varying the engine load and speed on the stratification of fuel in the chamber were compared. The results of this comparison showed that similar engine performance improvements were obtainable for different loads and engine speeds.