Hydrogen Lean-Combustion Studies in a Four-Stroke DI Radical-Ignition Diesel Engine with EGR

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. In the absence of other control measures, and because the re-circulated gases are cooled to intake conditions to eliminate the thermal effects of the EGR, in this study it is primarily the regulation of this recycled portion of the RI species that is used to control autoignition. This study conclusively illustrates that in response to load and speed changes, appropriate adjustments in the EGR percentages can be used alone to control the timing of the autoignition event. The simulation simultaneously solves the H₂-air chemical-kinetics occurring within the mini and main chambers as these chambers exchange heat with the environment and as they exchange momentum, mass and chemical species with each other and with the engine manifold.