The Influence Of Injection And Intake Parameters On The Two-stage Turbocharges Diesel Engine Under Transient Operations

Diesel engine has the advantages of high thermal efficiency,good reliability and wide power range,and is widely used in the field of automotive engine.In order to obtain efficient power output while minimizing emissions,diesel engines mostly use pressurized technology.The transient performance of turbocharged diesel engine under transient condition will be deteriorated due to the hysteresis of turbine.The adjustable two stage turbocharging technology can adjust the energy distribution between the two turbines by the high pressure turbine bypass valve,which can improve the transient performance of the diesel engine.Therefore,this paper carries on a diesel engine regulated two stage turbocharging system,selecting the typical transient of B(the constant speed with the load from 10% to 100% in 5s),study the speed effects of fuel injection and gas supply strategy on performance of two stage turbocharged diesel engine under transient operations,the main content is divided into two parts.In the first part,we study the influence of the main injection timing strategy on the transient performance under different bypass valve opening degree:(1)The transient process in advance of the injection can make the combustion phase recovery to the steady-state value of the fuel consumption rate decreased,but when the large amounts of fuel injection advance,a number of fuel burning before the top deadline will lead to the late combustion temperature is not conducive to the oxidation of soot,case the transient process of the late smoke increased rapidly;at the same time due to the local temperature is too high will cause the increase of NOX emission;delayed injection to the late oxidation smoke reduce smoke emission,but the combustion phase leads to "tolerance" to reduce the will cause deterioration of fuel economy.(2)When the bypass valve is closed,the "subsection timing" strategy can reduce the peak value of smoke and NOX emissions simultaneously.Among them,the strategy of 3(after the delay of fuel injection of 2°CA)is the best compromise,which can reduce the smoke peak value by 30%,NOX emissions reduced by 7.5%,while the fuel consumption rate of deterioration of not more than 2%.(3)When the bypass valve opening are 10% and 20%,it is not necessary to delay the fuel injection in the medium and large load angle,and the small load advance injection and the delayed injection in the medium load are the optimal "piecewise positive time" scheme.The bypass valve opening is 10%,strategy 2(30% load before the main injection timing advance 4°CA,30% load after the main injection is delay after 4°CA)is the optimal compromise,can make the smoke decreased by 66.7%,fuel consumption decreased by 7%.Bypass valve opening is 20%,strategy 1(30% load before the main injection timing advance 2° CA,30% load after the main injection is delay after 4°CA)is the best compromise(can reduce the smoke peak reached 74.7%,the rate of fuel consumption reduced by 4.4%).In the second part,in order to reduce smoke emission and improve fuel economy as the goal,to explore the application of the open and close valve strategy,and with the aid of flexible fuel injection parameters to achieve the best engine transient performance.The results are as follows:(1)With the increases of bypass valve opening,the turbo lag is increased due to the increase of the turbine equivalent flow,resulting in reduced intake,lag effect increased,the deterioration of combustion,the fuel consumption rate and smoke peak increased sharply,but the decrease of oxygen enriched gas into the region will lead to reduced NOX emission reduction.(2)The bypass valve control strategy of intake response effect is not obvious,linear valve opening strategy is better than the step valve opening strategy,including strategy 7(transient process of 3s-5s from the closed linear bypass valve opens to 10% degree)is the optimal control strategy,can the smoke decreased by 58%,NOX decreased 2.6%,fuel consumption decreased by 3.4%(with the bypass valve opening compared to 10%);step off valve strategy is superior to the linear valve closing strategy(economy and emission based on the strategy of 1),strategy 1(transient bypass valve process directly from 10% to 0% off the degree)is the optimal control strategy,can make the smoke decreased by 37.6%,NOX decreased 3.4%,fuel consumption rate of deterioration is not more than 2.5%.(3)For the bypass valve optimal control strategy considering emission and economy,-2°strategy is the optimal degree of compromise(1s step off valve strategy can make the smoke decreased by 28.7%,the lowest NOX emission peak reduced 6.5%,B50 fuel consumption rate decreased by 8.4%;the 3s-5s step strategy can make the valve opening smoke decreased by 36%,NOX emission peak decreased 7.1%,B50 operating fuel consumption rate decreased 4.3%).