Search Results

A detailed examination is made of the effects of exhaust gas recirculation (EGR) on hydrogen radical ignition in a four-stroke direct-injection (DI) diesel engine. “Radical ignition” (RI) species are first generated in secondary chambers, called mini-chambers (M-Cs), located in the cylinder head. More are generated in the main chamber. Some of these are then carried over to the next cycle. It is their pre-presence and participation in the next autoignition event that enables engine operations under ultra-lean fuel conditions at normal diesel compression ratios. The thrust of this study is to explore the prospect of using the portion of the RI species being returned via EGR to better manage autoignition timings.

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 NOx production and makes use of up to 19 species and 58 reactions.

This numerical study examines the chemical-kinetics mechanism responsible for EGR NOx reduction in standard engines. Also, it investigates the feasibility of using EGR alone in hydrogen-air and methanol-air combustion to help generate and retain the same radicals previously found to be responsible for the inducement of the autoignition (in such mixtures) in IC engines with the SONEX Combustion System (SCS) piston micro-chamber. The analysis is based on a detailed chemical kinetics mechanism (for each fuel) that includes NOx production. The mechanism for H-air-NOx combustion makes use of 19 species and 58 reactions while the methanol-air-NOx mechanism is based on the use of 49 species and 227 reactions. It was earlier postulated that the combination of thermal control and charge dilution provided by the EGR produces an alteration in the combustion mechanisms (for both the hydrogen and methanol cases) that lowers peak cycle temperatures-thus greatly reducing the production of NOx.