Numerical Prediction of Stratified Charge Distribution in a Gasoline Direct-Injection Engine - Parametric Studies

Numerical analysis of the flow field and fuel spray in a gasoline direct-injection (GDI) engine is performed by a modified version of the KIVA code. A simple valve treatment technique is employed to handle multiple moving valves without difficulties in generation of a body-fitted grid. The swirl motion of a hollow-cone spray is simulated by injecting droplets with initial angular momentum around the nozzle periphery. The model for spray-wall impingement is based on single droplet experiments with the droplet behaviors after impingement determined by experimental correlations. Different behaviors of an impinging droplet depend on the wall temperature and the critical temperature of fuel with the fuel film taken into account.

The test engine is a 4-stroke 4-valve gasoline engine with a pent-roof head and vertical ports to form a reverse tumble flow during the intake stroke. A hollow-cone spray by a high-pressure swirl injector is employed to enhance mixture preparation and mixing. A piston bowl is implemented to trap the mixture around the sparkplug and to enhance evaporation by retarding impingement of the spray. Parametric study is performed for two different chamber geometries with respect to the speed/load, the fuel injection timing, the spray cone angle and the incidence angle of the fuel injector. Results show that poor mixture distribution can be improved by adjusting some of these parameters.