Diesel Engine Combustion Chamber Geometry Optimization Using Genetic Algorithms and Multi-Dimensional Spray and Combustion Modeling 2001-01-0547

The recently developed KIVA-GA computer code was used in the current study to optimize the combustion chamber geometry of a heavy -duty diesel truck engine and a high-speed direct-injection (HSDI) small-bore diesel engine. KIVA-GA performs engine simulations within the framework of a genetic algorithm (GA) global optimization code. Design fitness was determined using a modified version of the KIVA-3V code, which calculates the spray, combustion, and emissions formation processes. The measure of design fitness includes NO_x, unburned HC, and soot emissions, as well as fuel consumption. The simultaneous minimization of these factors was the ultimate goal.

The KIVA-GA methodology was used to optimize the engine performance using nine input variables simultaneously. Three chamber geometry related variables were used along with six other variables, which were thought to have significant interaction with the chamber geometry. The input variables include the piston bowl radius, the piston bowl depth, the piston crown height, the start of injection (SOI) timing, the percent of cooled exhaust gas recirculation (EGR), the swirl ratio (SR) at intake valve closure (IVC), the duration of injection (DOI), the fuel injection nozzle hole size, and the angle of a fuel injection plume with respect to the cylinder axis. Both engines were optimized at a medium-speed, high-load condition with a similar global equivalence ratio. The results show impressive reductions in both exhaust emissions and fuel consumption.