Effect Of VNT And EGR On Altitude Performance Of High Pressure Common Rail Diesel Engine

Diesel engine main emissions is NOx and particles.EGR as a means of reducing NOx emissions measures, has been widely used; but EGR introduction lead to fuel economy decline and particulate emissions increased problems, and because of the engine pressure difference deficit situation under partial load, it can’t meet the requirements of driving EGR.VNT can effectively solve the low-speed torque economical efficiency, the transient reponse delay, intake and exhaust deficit, increasing EGR range, can be realized to reduce NOx emissions.TO some with VNT and EGR four cylinder high pressure common rail diesel engine as the research object,Experiment study effect of the VNT opening on air system and external characteristic; and diesel air condition is effected by VNT position under different EGR rate, analysis of the performance parameters change with VNT and EGR under different altitude. On the basis of experimental research, the establishment of a high pressure common rail diesel engine GT-Power simulation model, simulation was studied EGR rate on fuel economy, characteristics of combustion and emission characteristics, under different opening of the VNT; Carried out the following research work.(1) VNT effect of high pressure common rail diesel engine air condition by experimentIntake and Exhaust pressure decrease with VNT opening increasing,Intake and exhaust gas temperature and air-fuel ratio with the change of the VNT opening is highly correlation.when the VNT opening is greater than 30%、35%、and 30% respectively, began to appear engine differential negative situation at 1800r/min small、medium、and large operation mode. It did not appear the engine under different load pressure difference less than zero at 4000r/min; considering air-fuel ratio, pressure difference and engine test actual operation on the premise of limited factors, It determine the various conditions of the opening of the VNT range, for later research VNT and EGR on the high pressure common rail diesel engine performance influence foundation is established.(2) EGR and VNT effect of high pressure common rail diesel engine air system by simulation researching1800r/min 180N.m as well as 4000r/min 120N.m operation mode corresponds to biggest EGR rate are 24%、20% respectively. Maxium EGR rate corresponde to minimum VNT opening at 4000r/min 120N.m operation mode; Maxium EGR rate corresponde to 22% VNT opening at 1800r/min 180N.m operation mode.The higher the altitude, the lower the atmosphere pressure, the lower the intake and exhaust pressure and the air fuel ratio; when compared to the intake pressure accompanied by atmospheric pressre changes, the pressure is almost unchanged with EGR rate. The air fuel ratio corresponding to the EGR rate 10%、VNT opening 60% at 100kpa atmospheric pressure environment is same the air fuel ratio corresponding to the EGR rate 10%、VNT opening 40% at 80kpa atmospheric pressure environment.(3) EGR and VNT effect of high pressure common rail diesel engine performance by simulation researchingWhen introducing EGR at plateau environment, it can recover part of the fuel economy by reducing the VNT opening.Compared with 1800r/min, EGR rate should be reduced accordingly at 4000r/min different load.It should not use large EGR rate at 4000r/min small load. The maximum cylinder pressure and temperature and decreases with the EGR rate increasing, When EGR rate is constant, the maximum cylinder pressure and decreases with the opening of the VNT increasing. In 1800 r/min big load condition,when the EGR rate is less than 2%,2%,4% respectively, appropriately increasing EGR rate can improve relations between the trade-off NOx and particulate emissions.(4) On the basis of the experimental data which is the impact VNT opening to external characteristic, in comprehensive consideration of exhaust temperature, air-fuel ratio, with the minimum fuel consumption as the goal, based on the sweeping parameter value the opening of the VNT was optimized under the external characteristic; And compared original engine, fuel economy improved about 1.82% on average. Under partial load, on the premise of considering fuel economy and particulate emissions, with the minimum NOx emissions as the optimization goal, based on the RBF neural network and genetic algorithm the EGR rate and VNT is optimized;NOx emissions and particulate matter emissions fall 19.5% and 10.8%; The average fuel economy rise 0.85%.