Combustion model for a spark-ignited lean hydrocarbon-air mixture near misfire.

Abstract

A phenomenological model for a turbulent premixed flame in homogeneous turbulence, which incorporates the conservation of the probability distribution function (pdf) of a scalar, was developed. This was used to simulate the lean burn and misfire limits of combustion within a constant volume chamber. A one-dimensional numerical approximation of the pdf equation in spherical co-ordinates was obtained using the control volume formulation. The air-fuel premixture in the chamber was divided into particles of equal mass, which in turn were distributed among control volumes considered as spherical concentric shells. Monte-Carlo methods were applied to model the diffusion of particles between and mixing of particles within the concentric spherical shells. The chemical reaction of the mixture used a first order reaction from which a set of ordinary differential equations were solved for the evolution of the temperature and species concentration of each particle. Turbulence was modelled using the rapid distortion theory. A parametric study was conducted with the present model to show its operation in the misfire region of combustion. There has also been a comparison of mean expansion speeds with the compiled experimental combustion data of Bradley (1992). A suggestion for future research with the established model involves the adoption of the k-epsilon theory for the development of turbulence-related properties. This would allow comparison to the results obtained with the present rapid distortion theory for turbulence.