Experimental Study On Performance Optimization Of A China Stage Ⅳ Diesel Engine Combustion System Based On EGR

The China state IV emission standards had been fully implemented in January 1,2015, the implement of China state V will be put on the agenda. The influences of boost system, combustion chamber and fuel injection strategy on combustion system were investigated in order to meet the much more stringent emission regulations.The test is conducted on a two-stage turbocharger high pressure common rail heavy-duty (HD) diesel engine based on EGR, which has met the China IV emission standards under the condition of without the after-treatment device. The results of boost system optimization show that, in most operation conditions, especially in middle to low speed and high load conditions, the turbine scheme (2TCc) where flow area of turbine is smaller, can increase the expansion ratio of turbine, improve the exhaust utilization before turbine and the air-fuel ratio in the turbine optimization test of high pressure turbocharger. On this basis, the optimization matching test of low pressure compressor was carried out. Compared with other boost schemes, the joint operating point between diesel engine and the supercharger (2TC2) where the flow area of low pressure compressor is smaller, moving in the direction of high pressure ratio and equivalent flow, and effectively improve the trade-off relationships of NOx-soot and NOx-BSFC.After optimized the supercharging system, the results of combustion chamber optimized design on reentrant diameter and bowl depth show that, combustion chamber (SF4) where reentrant down lmm based on the original combustion chamber (SF1), can enhance airflow motion in cylinder, increase the mixing uniformity and the mixing rate of fuel and gas. BSFC and soot can be decreased and keep the maximum in-cylinder pressure in the reasonable range at the same time in middle to high load conditions.On the basis of the front optimization, the results of fuel injection control strategy experiment show that, with retarded injection timing, the combustion phase delay, soot emissions decrease, but BSFC increase. The soot emissions rise, however, when the injection timing delayed too much. Increasing the pressure of injection can reduce soot and BSFC simultaneously at the high speed conditions. However, soot and BSFC is increase with the increasing of the injection pressure at low speed and high load conditions. By using proper interval between main and post injection can increase fuel economy and improve emissions. At the high speed conditions, soot emission can be obviously reduced by using high injection pressure and suitable post injection.The ESC cycle test showed that NOx and soot emission are 1.799g/kW.h and 0.015g/kW.h respectively, which both under the limit value of the China Stage V emission regulations. Meanwhile, BSFC can be reach 211.6g/kW.h. The optimized combustion chamber has the ability to meet the China stage V emissions standard while reducing the requirement of exhaust after-treatment devices.