An experimental and numerical investigation of turbulent flame propagation and flame structure in a turbo-charged direct injection gasoline engine

Abstract

Turbulent flame propagation in a modern, turbo-charged, direct-injection gasoline engine is investigated in detail for the whole engine operating map. Different development tools are used in a combined fashion. Based on experimental results with high and low-pressure indication, a global heat release analysis coupled with a 1D gas dynamics simulation is performed. Using the data from the 1D gas dynamics simulation as initial and boundary conditions, 3D CFD calculations are carried out. From these calculations the characteristic velocity and length scales of the turbulent flow as well as the relevant scales of premixed flame propagation, flame speed and flame thickness, respectively, are analysed for all relevant operating conditions of the engine. This leads to a classification of combustion regimes and flame structures based on the Peters–Borghi diagram. The effects of engine speed and load variations are discussed in detail based on scale analysis, especially the effect on the turbulence-premixed flame interaction. Based on these results and an analysis of the global heat release profiles, a simplified model for the burn duration is derived taking into account the turbulent flow scales obtained from a 3D CFD analysis and the thermochemical properties such as gas composition including exhaust gases, pressure and temperature. The results are compared to experimental data.