Influence of Mixture Formation on Injection and Combustion Characteristics in a Compact GDI Engine

The spray characteristics are determining factors for the quality of mixture formation respectively for the combustion, when applying GDI. Their variation with load and speed is a basic criterion for the adaptability of an injection system type to an engine with known requirements. CFD models of the fluid flow dynamics, mixture formation and combustion are a determining condition for such adaptation. The paper presents the development results of a GDI four-stroke, four-valve, single cylinder engine. The pressure pulse injection system involved in this application is analyzed and presented from the fluid-dynamic behavior up to the obtained injection spray characteristics.

The mixture formation and combustion processes are simulated for different load and speed values, respectively for favorable combinations of parameters, such as the injection system configuration, the opening pressure of the applied mechanical injector and the injection duration.

Particular aspects of the combustion when using GDI, such as non-homogeneity of the mixture structure, super position of mixture formation and combustion and the influence of additional spark sources form an object of analysis. The results of numerical simulation are compared with the experimental results.