Modeling the Effect of Split Injections on DISI Engine Performance

A spray model for pressure-swirl atomizers that is based on a linearized instability analysis of liquid sheets has been combined with an ignition and combustion model for stratified charge spark ignition engines. The ignition model has been advanced, such that the presence of dual spark plugs can now be accounted for.

Independent validation of the spray model is achieved by investigating a pressure-swirl injector inside a pressure bomb containing air at ambient temperature. In a second step, the complete model is used to estimate the performance of a small marine DISI Two-Stroke engine operating in stratified charge mode. Simulation results and experimental data are compared for several different injection timings and the agreement is generally good such that there is confidence in the predictive quality of the combustion model.

Finally the model is applied in a conceptual study to investigate possible benefits of split injections. The simulation results suggest that both fuel economy and NO_x-emissions can be improved when a two-pulse injection is used such that the late injected, stratified fuel ensures stable ignition at the spark plug whereas the early injected, diluted fuel reduces the maximum combustion temperature and controls NO_x-formation.