Modeling Mixture Formation in a GDI Engine

Argentina, Bariloche, Mec ́anica Computacional Vol. XXIII, 2004. 22 p. G.Buscaglia, E.Dari, O.Zamonsky (Eds. ) Abstract. Mixture formation and combustion in a Gasoline Direct Injection (GDI) engine were studied. A swirl-type nozzle, with an inwardly opening pintle, was used to inject the fuel directly in a 4 stroke, 4 cylinder, 4 valves per cylinder engine. The atomization of the hollow cone fuel spray was modeled by using an hybrid approach validated at first in a quiescent chamber at ambient pressure and temperature, comparing numerical penetration and spray shapes with the experimental ones. For both stoichiometric and stratified operation mode the interaction of the liquid jet and the surrounding air was studied. The most important obstacle in the development of GDI engines is that the control of the stratified-charge combustion over the entire operating range is very difficult. Since the location of the ignition source is fixed in SI engines the mixture cloud must be controlled both temporally and spatially for a wide range of operating conditions. The development of a successful combustion system depends on the design of the fuel injection system and the matching with the in-cylinder flow field. Results show that the stratification at part load appears to be the most crucial and critical step, and if the air motion is not well coupled with the fuel spray it would lead to an increase of unburned hydrocarbon emission and consumption.