Development of a three-zone combustion model for stratified-charge spark-ignition engine

Abstract

A thermodynamic model for calculat-ing the operating process in the cylinder of a spark-ignition engine with internal mixture formation and stratified air-fuel charge based on the volume balance me- thod was developed. The model takes into account the change in the working fluid volume during the piston movement in the cylinder.The equation of volume balance of internal mixture formation processes during direct fuel injection into the engine cylinder was compiled. The equation takes into account the adiabatic change in the volume of the stratified air-fuel charge, consisting of fuel-air mixture volume and air volume. the heat balance equa-tion, the change in the fuel-air mixture volume during gasoline evaporation in the fuel stream and the surface of the fuel film due to external heat transfer was determined.Basic equations of combustion-expan-sion processes of the stratified air-fuel charge were derived, taking into account three zones corresponding to combus-tion products, fuel-air mixture and air vo lumes. The equation takes into account the change in the working fluid volume due to heat transfer and heat exchange between the zones and the walls of the above-piston volume. Dependences for determining the temperature in the three considered zones and pressure in the cy linder were obtained.Graphs of changes in the volumes of the combustion products, fuel-air mix-ture and air zones with the change of the above-piston volume in partial load modes (n =3,000 rpm) were plotted. With increasing load bmep =0.144 MPa to bmep =0.322 MPa, at the moment of fuel ignition, the volume of the fuel-air mix-ture increases 70 % to 92 % of the above-piston volume. At the same time, the air volume decreases 30 % to 8 %.Analysis of theoretical and experimen-tal indicator diagrams showed that dis-crepancies in the maximum combustion pressure do not exceed 5 %.