Influence Of Two Stage Turbocharging System Coupling Injection Strategy On Diesel Engine Performance

Efficient combustion and reducing emissions have become the main problems in design and development of internal combustion engines. By increasing the intake flow,two stage turbocharging system can improve engine power and solve theoretically the problem of combustion deterioration and smoke emission increasing on transient conditions. The research equipped two stage turbocharging system for a diesel engine.Adjusting the parameters of intake flow and fuel and having a control of combustion boundary conditions, the paper studied the performance of two stage turbocharging system on steady state conditions and transient state conditions.The first part mainly studied optimization of the compressor efficiency of two stage turbocharging system. The specific research results are as follows:1)To solve the problem that high stage compressor efficiency and intake pressure were both low, built-in high stage turbine discharge valve was closed in the research.Results show: the efficiency of low stage compressor and high stage compressor can be all more than 60% on external characteristic conditions, the maximum intake pressure of two stage turbocharging system is promoted to 334 kPa, which is 50 kPa higher than the two stage turbocharging system of unclosed turbine discharge valve.2)By adding high stage turbine by-pass valve and controlling the opening, intake pressure, pressure ratio distribution and efficiency of two stage compressor can be effectively adjusted.The second part mainly studied influence of injection parameters and intake flow parameters on the steady state conditions of diesel engine. The specific research results are as follows:1) Increasing the fuel injection pressure and the advancing main injection timing can improve fuel economy and reduce smoke mission, but lead to the increase of NOx emission and the rate of pressure rise at the same time. Comprehensively considering of fuel economy, emission and the rate of pressure rise, two stage turbocharging system choose own rail pressure parameters in the original rail pressure MAP range-10 MPa to +10MPa, maintain same main injection timing at low speed, and properly advance main injection timing on high speed conditions.2) Closing the bypass valve can improve the fuel economy of the two stage turbocharging diesel engine on low speed and high load conditions. Increasing appropriate the bypass valve opening is beneficial to improve fuel economy of the two stage turbocharger on other conditions. Especially on the high speed and low load conditions, the fuel economy of the two stage turbocharging diesel engine can be improved when the bypass valve was fully opened.The third part mainly studied influence of rail pressure control strategies on the transient performance of the diesel engine under different intake flow parameters when the two stage turbocharging diesel engine run transient state conditions(constant speed of 1650 rpm and increasing load from 10% to 100% over 5s transition time).The specific research results are as follows:1) Taking strategies of "Full increasing rail pressure" under transient process can reduce smoke emission peak under bypass valve closed. When the rail pressure was greatly improved(improving 20 MPa compared with the original engine), smoke emission peak can’t be inhibit in the 10% and 20% bypass valve opening.2) To control smoke emissions on transient process, two stage turbocharging diesel engine take " Partially increasing rail pressure " strategies in the 0, 10% and20% bypass valve opening, The smoke peak reduce compared with the original engine, when the air intake is low, the effect become more obvious.3) Finally, to control smoke emissions on transient process, the research consider the different strategies of injection pressure, and respectively determine "Full increasing 20 MPa rail pressure", " Increasing 10 MPa rail pressure after 30% load " and " Increasing 10 MPa rail pressure after 40% load " for the 0, 10% and 20% bypass valve opening, and the smoke peaks compared with the original engine are decreased by 2.1%, 3.6% and 8.8%, and degree of decline are 52.5%, 55.3% and 51.7%.