CNG / Methane-Combustion Kinetics (without N2) and Frozen Equilibrium in Radical-Ignition Reduced Compression Ratio D.I. Diesel Engines Using Pistons with Micro-Chambers 2004-01-1677

This qualitative numerical study examines the effects of internally generated “radicals” on the chemical-kinetics mechanism responsible for the combustion of CNG (compressed natural gas) in a direct-injection naturally aspirated diesel engine at reduced diesel compression ratios. The initial generating site for these “radical” chemical species is a set of micro-chambers well placed within the pistons. Explored in this study are not only the effects of these radical species on main chamber combustion process but also the simultaneous effects of the main chamber combustion process on the OH radical driven partial oxidation process taking place in the micro-chamber. Discovered in this study is the fact that when these radical species are passed to the main chamber, they also facilitate “radical” generation on a slightly smaller scale in the main chamber also. Unique to the overall radical ignition process is the “frozen equilibrium” reactive state that these radical species transition into in both chambers, enabling their preservation for the next cycle. It is these “carried-over” radicals that make possible autoignition of the next cycle at reduced compression ratios. The simulation is based on a detailed chemical-kinetics mechanism with 26 species and 84 reactions. This mechanism is simultaneously solved within the main and micro chambers as they interact, exchanging their energy and chemical species with each other and with the engine manifold (via valves) while equalizing pressure differences.