CFD Optimization of DI Diesel Engine Performance and Emissions Using Variable Intake Valve Actuation with Boost Pressure, EGR and Multiple Injections 2002-01-0959

A computational optimization study was performed for a direct-injection diesel engine using a recently developed 1-D-KIVA3v-GA (1-Dimensional-KIVA3v-Genetic Algorithm) computer code. The code performs a full engine cycle simulation within the framework of a genetic algorithm (GA) code. Design fitness is determined using a 1-D (one-dimensional) gas dynamics code for the simulation of the gas exchange process, coupled with the KIVA3v code for three-dimensional simulations of spray, combustion and emissions formation.

The 1-D-KIVA3v-GA methodology was used to simultaneously investigate the effect of eight engine input parameters on emissions and performance for four cases, which include cases at 2500 RPM and 1000 RPM, with both simulated at high-load and low-load conditions. The input parameters explored include the start of injection (SOI) timing, injection duration, exhaust gas re-circulation (EGR), percentage of total fuel mass injected in first pulse of a split injection rate shape, dwell in between the pulse of the split injection, boost pressure, and finally the gas swirl and tumble ratios at intake valve closure. The predicted optimal results reduced the engine-out emissions along with a reduction of the specific fuel consumption compared to the baseline cases.

It was observed that the effect of the flow field (i.e., swirl and tumble ratios) at IVC on engine-out emissions was predominant only for the high-speed low-load case. Taking this in account, and with the idea of matching swirl and tumble ratios at IVC with the predicted optimal values of swirl and tumble ratios, a detailed flow analysis was performed using the VECTIS. Various intake valve lift profiles were analyzed to obtain different flow fields at IVC. Although it was not possible to achieve the exact value of swirl and tumble ratios predicted by the optimal design, the understanding generated of the effect of lift profile on fluid flow parameters provides important insight on flow field development.