Structure of Flames in Premixed-Charge IC Engines

Abstract

Some recent measurements of turbulence intensity, turbulerlce length scale and flame structure in valved and ported engines operated at practical conditions are reviewed and the following conclusions are reached. In an engine, what is turbulence and what is bulk flow is relative to the process that is influenced by the flow; characteristic length and time scales can be used to make the distinction. In the absence of strong squish and/or swirl, TDC turbulence intensity is homogeneoys and isotropic to within f 30 percent, except near walls, and the turbulent flame in premixed-charges is made up of laminar flames that are wrinkled by the turbulent eddies. In many practical conditions, the small-scale tubulent eddies are also likely to interact with the structure of the laminar flame. The interactionwould be stronger for lean flames. Turbulence influences the laminar flame from the very begirining to the very end of combustion. Current zero- and multi-dimensional models of premixed-charge engine combustion do not fully represent the structure of the turbulent flame but have proved very valuable because they empirically reproduce the turbulent flame speed that is the most important of.the flame parameters.