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This four-stroke engine study examines how micro-chamber generated radicals can facilitate the robust control of autoignition in direct-injection (D.I.) diesel engines. These internally produced radicals enable combustion under much lower than normal diesel compression ratios (CR's) and temperatures and make the chemical-kinetics control of autoignition timing a reality. In an attempt to better understand the mechanisms enabling radical based chemical control, the altered chemistry of radical ignition is studied numerically for the case of H 2 combustion. Numerical simulation is based on a detailed mechanism involving as many as 19 species and 58 reactions. This H 2 chemical-kinetics mechanism is simultaneously solved within two separate but connected open systems representing the distinctive main-chamber and micro-chamber processes (Figure 1). During the combustion cycle these two open systems continuously interact, passing energy and chemical species between one another and the atmosphere while attempting to equalize pressure differences.

Using hydrogen as a fuel, this chemical-kinetics study qualitatively examines the phenomenon of "frozen equilibrium" in Stratified Charge Radical Ignition (SCRI) engines with direct injection (DI) and exhaust gas recirculation (EGR). In such engines, this phenomenon is believed to preserve select highly reactive species formed in the side chambers (called micro-chambers) embedded inside the piston bowl so that these species can be carried-over to enhance autoignition in the next engine cycle. In turn this enhancement makes possible ignition and combustion at compression ratios that are markedly lower than those considered "standard" (for a given fuel), resulting in reduced emissions. Analysis is based on a detailed chemical-kinetics mechanism that includes NO x production and makes use of up to 19 species and 58 reactions. Along with detailed versions of the momentum and energy equations, this mechanism is simultaneously solved within the two separate but interactively connected open systems representing the individual main chamber and micro-chamber combustion processes. Part of the aim of the present study is to identify several of the engine processes and dominant chemical-kinetics sub-mechanisms responsible for the much lower compression ratios and reduced NO, emissions in SCRI-DI engines with EGR.