Experimental Study On High-efficiency And Low-emissions Compression Ignition Engine Based On Injection Strategy And Fuel Design Technologies

With intensifying of urban environment pollution, the expansion of the energy consumption pressure and increasingly stringent CO2 emissions or fuel consumption regulations, the development of high efficiency and low emissions engines become an urgent matter.In order to find solutions for “trade-off” relationships among emissions formation of NOx vs. soot, HC and CO vs. CO2 in conventional combustion mode, and obtain lower fuel consumption, more and more technologies are applied to internal combustion engines, such as advanced injection system, new combustion mode, aftertreatment, high quality fuel and clean fuel technologies.In this research, a Partially Premixed Compression Ignition(PPCI) engine test bench was set up based on a four-cylinder diesel engine. Influences of fuel injection strategy and fuel design concept on the engine performance were studied. In addition, exhaust gas recirculation(EGR) technology was used. This thesis' s research consists of three aspects: Influence of double injection on the gasoline PPCI engine combustion and emission characteristics; experimental study of biodiesel/gasoline on a PPCI engine; experimental study of biodiesel/ethanol on a PPCI engine.The results of fuel injection strategy research indicated that the main injection mainly affects the engine performance, reasonably adjusting the pilot injection can further enhance the performance of the engine. The optimal interval angle between the pilot and main injection was 25 oCA; under high load, delaying the main injection timing and making some adjustments to the pilot injection can control the combustion phase well and reach high load range, also NOx emission was reduced dramatically( 1400r/min, BMEP=0.529 MPa, 47? intake temperature operation condition: the PPCI engine can get 55% indicated efficiency and 2.12g/k Wh NOx emission with the optimized fuel injection strategy.); under low load, adopting pilot injection(50oCA BTDC) + main injection(25oCA BTDC) with 42% mass fration of pilot injection quantity realized gasoline PPCI in 37? intake air condition; NOx reduction degree of 22% Quasi-EGR using CO2 addition in intake air was similar to delaying 5 ? injection, and the engine had better comprehensive performance with Quasi-EGR.10% volume fraction biodiesel can make gasoline PPCI getting rid of dependence on intake air heating; the engine can obtain the best comprehensive performance with 30% biodiesel. Under the load of 0.316 MPa BMEP, the indicated efficiency was 52%, UHC emission was 1.37 g/k Wh, CO emission was 2.23 g/k Wh, NOx emission was 3.46 g/k Wh, and soot emission was 0.3BSU with the blend fuel. The optimal fuel supply advance angle was 21oCA BTDC; Hot-EGR without cooling under low load and Quasi-EGR under moderate load can both reduce 70% NOx emission, and the fuel consumption changed little.Experimental research of alternative fuels(biodiesel/ethanol) on the PPCI engine has also been carried out. The results showed that alternative fuels PPCI engine can keep soot emission at very low level through the whole engine load without advanced injection and EGR; 50% biodiesel + 50% ethanol(volume fraction) alternative fuels had better comprehensive performance compared to the proportional limit of ethanol(60%) which can keep the engine operating normally. The engine performance could be further enhanced if EGR was introduced.Overall, both fuel injection strategy and fuel design concept can improve the PPCI engine performance in different degree. Fuel design has excellent performance in improving the PPCI engine's ignition performance under low load, Fuel injection strategy has great potential in expanding the PPCI engine's high load range. In addition, the alternative fuel PPCI engine is one of the solutions to reduce the pressure of energy and the environment.