Parametric Study to Optimize Gasoline Compression Ignition Operation under Medium Load-Conditions

Abstract

Gasoline compression ignition (GCI) pertains to high efficiency lean burn compression ignition with gasoline fuels, where ignition is controlled by mixture’s auto-ignition chemistry as well as local mixture strength. The presented GCI combustion strategy is based on a multi-mode combustion strategy at various operating conditions. This study presents a part of work on the development of an optimum combustion strategy at medium loading condition for commercial gasoline fuel with research octane number (RON) = 91. The single cylinder engine with a compression ratio (CR) = 16 features a centrally mounted multi-hole injector with a spark plug at a distance from the injector under shallow pent-roof combustion chamber design. The design of combustion chamber and piston was previously optimized based on CFD numerical analysis. The experimental study at medium load condition (IMEP = 6 bar) investigated the effect of fuel injection strategy, exhaust gas recirculation (EGR) and re-breathing on the targeted engine results. The study revealed that large amount of EGR is required with single injection strategy to meet the required engine out nitrogen oxide (NOx) emission target with a reasonable maximum rate of pressure rise (MRPR) and indicated specific fuel consumption (ISFC) whereas double injection strategy could potentially lower the required EGR dilution to meet the same NOx target. Computational fluid dynamics (CFD) simulations were performed and the results support the experimental finding in terms of best injection timing by providing spray wall interaction and mixture preparation for SI strategy. The ignition delay based on fuel-mass-weighted mean equivalence ratio and temperature was used to explain combustion phase and agreed well with the engine experimental findings. The re-breathing favors to reduce the NO_X emission lower to 0.2 g/kWh with lower hydrocarbon (HC) and carbon monoxide (CO) emissions compared to single and double injection strategies. While the NO_X emission target could be met based on the various strategies, HC emission is not within the emission target. This study recommends further optimization studies in the near future to meet the overall engine out emission targets.