EARLY STAGES OF COMBUSTION IN INTERNAL-COMBUSTION ENGINES USING LINKED CFD AND CHEMICAL-KINETICS COMPUTATIONS AND ITS APPLICATION TO NATURAL-GAS BURNING ENGINES

The paper describes a numerical model for the early stages of combusti on in Natural Gas engines using linked CFD and detailed chemical kinet ics. The importance of such a combustion device stems from the charact eristics of natural gas which make it an attractive near-term solution for the automotive emissions problem. The 3-D simulation, which incor porates a chemical model, turbulence model and ignition model is taken under engine-like conditions. This is achieved by coupling the numeri cal codes KIVA II, developed to solve the transient equations of conse rvation of turbulent chemically reacting mixture of ideal gases, CHEMK IN II, designed to facilitate simulations of elementary chemical react ions in flowing systems, TRANSPORT, used for the evaluation of gas-pha se multicomponent transport properties, and LIOR - a linking code. The numerical tool has predictive capability for combustion behaviour und er various conditions, an ability to interpret observed combustion phe nomena and ability to guide the design of better natural gas engines. A justification of the validity of the approach is discussed in terms of the asymptotic structure of the methane-air flame. The early states of the combustion event are described in some detail and two specific studies are briefly reported, that of the effects of various ignition source types for natural gas burning domestic vehicle engines, and th at of the effects of variation in composition of the natural gas.