Performance and NO
Model of a Direct Injection Stratified Charge Engine
A model has been developed to predict the performance and NOx emission of the Texaco stratified charge engine. This complete engine cycle program starts from engine geometry, valve and fuel injection timing, fuel characteristics and operating conditions and includes the following phases: valve overlap, intake, compression, combustion, expansion and exhaust.
The fuel mixing process is described by a jet mixing model and the equations are solved in a cylindrical coordinate system with a nonuniform pressure field. The jet shape changes were calculated for the jet impingement effect against a solid wall. The air motion inside the cylinder is determined by a detailed submodel to specify the field for the fuel jet.
During combustion, the fuel jet is divided into many elements and the combustion process of each element is analyzed as a mixing process between the jet and surrounding air, entrainment into a flame front and subsequent combustion.
For heat transfer the walls of the combustion chamber are divided into five regions; intake valve, exhaust valve, cylinder head, cylinder wall and piston top. Each region is assumed to have a different temperature and different gas velocity.
Nitric oxide emissions are calculated by using the extended Zel’dovich kinetic mechanism with a steady state assumption for the N concentration and equilibrium values used for H, O, O2 and OH concentrations.
The model computes combustion rates, heat transfer and NOx based on the same jet mixing processes at each stage.
Comparison of the model predictions with the available experimental data shows reasonably good agreement.