A model for turbulent flame ignition and propagation in spark ignition engines

Abstract

A model describing flame ignition in a premixed turbulent flow is coupled to a flamelet model for turbulent combustion to describe flame ignition and propagation in a spark ignition piston engine. During the first instants of ignition, a laminar ignition model (called LI) solves the one-dimensional, spherical Navier-Stokes equations for a given chemical scheme to predict the radius of the first laminar flame kernel. In a second phase, this kernel grows because of laminar effects but is also stretched by turbulent eddies. Later, a criterion based on the comparison of the laminar stretch (due to the laminar flame kernel growth) and of the turbulent stretch (generated by turbulent eddies) is used to initiate the computation of a fully turbulent combustion. During this turbulent propagation, an extended version of the Coherent Flame Model (CFM) is used. This model includes a novel expression for turbulent flame stretch based on direct simulation results. The total model (LI-CFM) has been implemented in an improved version of KIVA including a k -e compressible model and a robust treatment for wall turbulence. The results are compared with experimental data (Schlieren visualizations, LDA measurements and pressure measurements) obtained on a fully instrumented laboratory engine. The LI-CFM model correctly predicts flame ignition and growth for a set of typical engine cases with no parameter adjustments. Computed effects of changes in spark timing, total pressure or equivalence ratio agree well with experimental results.