Matching And Experimental Study Of Variable Nozzle Turbineturbocharger And Diesel Engine

With the increasingly strict emission regulations and fuel consumption regulations,the engine is being developed in the direction of energy saving and emission reduction.Variable geometric turbocharging technology can improve the power and economy of diesel engine under some working conditions,and significantly reduce NO_X emissions combined with exhaust gas recirculation technology?EGR?,which has a good transient response to reduce the emissions of the engine under transient conditions.The viriable nozzle turbine?VNT?and EGR coupling technology is one of the technical routes for diesel engines to achieve excellent performance.Therefore,research on the matching between VNT and EGR system and diesel engine is very important for the development of diesel engine.In this paper,an orthogonal test of VNT opening,EGR valve opening,main injection parameters and pilot-injection parameters was carried out on a four-cylinder high-pressure common rail diesel engine to study the rule of its influence on the power performance,fuel economy and emission characteristics of diesel engines under steady-state conditions.With the NO_X specific emission as the control target,and the specific fuel consumption and smoke emission as the optimization targets,the VNT and EGR systems was matched with the diesel engine.The results of the study show that diesel parameters such as turbine front pressure,boost pressure,intake air volume and EGR rate are changed by the opening of the VNT and EGR valves,which affects the performance of the diesel engine.The cooperation between VNT and EGR valve opening can ensure the EGR rate in some operating conditions and increase the controllable area of NO_X emission.The pressure ratio and mass flow rate of the compressor decreased with the increase of the EGR valve opening,and the combined operation curve of the compressor and the diesel engine moves from the center high efficiency region to the low efficiency region,which can be improved by reducing the VNT valve opening.At different VNT openings,the smoke emission increased with the decrease of NO_X specific emission,and began to increased sharply when the NO_X specific emission is around 3 g/?kW?h?.The overall level of NO_X and smoke emissions decreases with the decrease of the VNT opening.The NO_X and smoke emissions can simultaneously reduced by decreasing the VNT opening when the EGR valve opening is 5%to 10%.When the opening of the VNT valve is small,the BSFC decreases first and then increases with the increase of EGR valve opening,and pump loss is more sensitive to EGR valve opening.However,when the VNT opening is large,the BSFC increases with the increase of the EGR valve,and it is greatly affected by the EGR rate.The smoke emission and specific fuel consumption of the engine can reduced by raising the injection pressure and delaying the main injection time under the condition of constant NO_X emissions.After the optimization of VNT and EGR valve opening under low speed and large load conditions,the NO_X specific emission is reduced by 45.6%.The smoke emission and BSFC are improved with the injection parameters optimization.Under the transient operating conditions,the performance of the coordinated control strategy of VNT and EGR is discussed.In order to solve the problem of smoke and NO_X emission deterioration caused by the slow rise of intake air volume in the early stage and the high intake air volume in the later stage,the coordinated control strategy of VNT and EGR was modified.When the difference between the target and actual value of the boost pressure exceeds a certain value,the closing of the VNT and EGR valve is accelerated,so that the intake air amount can quickly reach the target value.By performing a transient correction on the MAP of the intake air volume,the EGR valve is opened early to avoid excessive intake air volume causing deterioration of emissions.Finally,the test was verified in the WLTC test cycle.After optimization,the peak NO_X emissions of the diesel engine is reduced,the overall emissions is reduced by 6%,soot emission is reduced by 22.8%.The CO,THC,NMHC and CO₂ emissions is respectively reduced by 43.7%,44.7%,48.4%and 0.6%.The increase in pumping loss and the improvement in combustion result in little change in fuel consumption level,and the emission of pollutants during the acceleration process is reduced after the transient correction strategy.