The paper describes a numerical model for the early stages of combustion in Natural Gas engines using linked CFD and detailed chemical kinetics. The importance of such a combustion device stems from the characteristics of natural gas which make it an attractive near-term solution for the automotive emissions problem. The 3-D simulation, which incorporates a chemical model, turbulence model and ignition model is taken under engine-like conditions. This is achieved by coupling the numerical codes KIVA II, developed to solve the transient equations of conservation of turbulent chemically reacting mixture of ideal gases, CHEMKIN II, designed to facilitate simulations of elementary chemical reactions in flowing systems, TRANSPORT, used for the evaluation of gas-phase multicomponent transport properties, and LIOR - a linking code. The numerical tool has predictive capability for combustion behaviour under various conditions, an ability to interpret observed combustion phenomena 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 that of the effects of variation in composition of the natural gas.