Evaluation of burning rates in the vicinity of the piston in a spark-ignition engine

Abstract

The burning rate in the vicinity of the piston is estimated from the flamlet, formulation. The flame surface density Σ is measured by laser sheet tomography for three equivalence ratio methane/air flames (1.0.9, 0.8) in a spark-ignition transparent engine. Two imaging configurations are realized: five horizontal planes at different distances from the piston (0, 1, 2, 3, and 5 mm) and a vertical one at the center of the combustion chamber. To decrease the effect of the cycle-to-cycle variation on the average flame front thickness and on the determination of the mean progress variable, several methods are tested to extract the mean flame front contour. Two flame surface density methods are compared: one based on the Bray-Moss-Libby flamelet crossing density model and the other based on the burning rate formulation by Gouldin. It appears that the last one is better adapted for the determination of Σ for weakly wrinkled flames and a good compromise to estimate the burning rate locally in vicinity of the piston. All methods are also validated by applying to freely propagating spherical flames. Model adaptation is realized to include the evolution of the flamelet scalar orientation near the piston. Finally, the burning rate is determined as a function of the distance between the wall and the mean flame contour.