The Optimization Of Combustion System And Experimental Study On Dual-Fuel RCCI Combustion Engine

Reactivity Controlled Compression Ignition(RCCI) combustion strategy takes advantage of two kinds of fuel mixtures which have different reactivity. In this strategy, the low ignition reactivity fuel is injected into cylinder from inlet port to create a well-mixed charge and then the high ignition reactivity one is directly injected into the combustion-chamber to ignite the premixed fuel, thus fuel reactivity gradients are developed. In this research, the piston of a diesel engine was modified to examine the effect of combustion chamber and structural diameters to reduce in-cylinder knock and achieve low emissions and high efficiency, thus the RCCI combustion mode could be more adaptive.In this study, the single-cylinder diesel engine was modified with a gasoline injector fixed on the inlet port. To provide guidance for the follow-up experiment, a numerical simulative method was used to explore the effects of combustion chamber geometries on advanced RCCI combustion mode. The results declared that by considering indicated thermal efficiency, BSFC, max pressure rise rate, NOx and soot emissions, combustion-chamber with radius of 38 cm has the optimal performance. With the help of the same evaluation method, the optimal compression ratio is 16.The design of the geometry of combustion chamber was conducted by the guidance of the simulative results. Combustion process can be controlled by RCCI combustion mode. With the increase of gasoline ratio, the heat release of initial stage reduces and ignition delay period increases while the combustion duration drops. The optimized chamber has a higher combustion duration than the original one, but with a shorter ignition delay. The experimental results indicated that NOx and soot emissions declined simultaneously at high gasoline ratio, which is quite different from conventional diesel engines. The NOx and soot emissions of optimized chamber were fewer than those of original chamber. Different gasoline ratios have great effects on the CO and HC emissions of the two kinds combustion-chamber.In the consideration of the structural parameters(fuel spray angle and nozzle number) of original engine, which do not fit the new combustion-chamber, the author selected the optimal parameters from CFD simulation. Calculation method and evaluation system were similar with that of combustion-chamber selections. As a result, the optimum selection for RCCI gasoline/diesel dual-injection system is the combustion-chamber of 38 cm radius, fuel spray angle of 156°and nozzle number with 7.