Simulation Study Of The Operating Process And Performance Of The Multi-Parameter Coupled Miller Cycle Diesel Engine

With the increasing prominence of environmental issues and people’s demand for quality of life,emission regulations for engines are becoming more and more stringent,and the country has put forward the goals of “carbon peak” and “carbon neutrality”.Developing new energy vehicles is an effective way to meet emission regulations and achieve “dual carbon” goals.New energy vehicles are divided into pure electric vehicles and hybrid vehicles.Among them,hybrid vehicles are safer and have longer range than pure electric vehicles,which is a better choice at present.Hybrid power system puts forward new design optimization requirements for dedicated engines.The research on gasoline engine for hybrid passenger cars is relatively mature,while the research on diesel engine for hybrid commercial vehicles is still in its infancy.Miller cycle is an advanced and efficient engine technology that is often used in hybrid engines,and coupling Miller cycle with a variety of emission-reducing technologies can help meet increasingly stringent emissions regulations.This paper studies the performance change of diesel engine for hybrid power by coupling Miller cycle technology commonly used in hybrid power engine with EGR,postinjection and other parameters.The research object is a four-cylinder high-pressure common rail diesel engine.A onedimensional simulation model of the diesel engine is established by using GT-Power software,and the model is calibrated with experimental data to verify its accuracy.Then,by redesigning the intake valve lift curves,Miller cycle diesel engine model is established by early intake valve closing(EIVC),and the influence of Miller degree,EGR,post-injection,other parameters and multi-parameter coupling on working process and performance of diesel engine for hybrid power is studied by using this model.The simulation results show that: after adopting Miller cycle,the intake valve closes earlier,the intake flow and air-fuel ratio decreases,and the pumping loss of diesel engine decreases;with the increase of Miller degree,the effective compression ratio and intake flow of diesel engine decrease,and the ignition delay period is prolonged;the compression temperature and average incylinder pressure decrease,but due to the prolongation of ignition delay period,the amount of combustible mixture in premixed combustion stage and the peak in-cylinder temperature increases.Due to the reduction of effective compression ratio,the Miller cycle reduces the power and economy of the diesel engine;the lower temperature of combustion temperature area after Miller cycle destroys the environment of NOx generation,which reduces the NOx emission of 75% and50% load by 61.4% and 48.1% at most,but the increase of anoxic area leads to the increase of Soot emission.Miller cycle coupled with EGR can further reduce NOx emission of diesel engine,10°CA Miller degree combined with 15% EGR at 75% and 50% load can reduce NOx emission by 87.8% and 76.1%;with the increase of EGR rate,in-cylinder temperature decreases,combustion quality decreases,effective power decreases,fuel consumption increases,and Soot emission rises.Coupling post injection with Miller cycle and EGR can reduce Soot emissions,and can reduce Soot emissions by 8.8～10.1% at 75% load.Finally,the multi-objective optimization software mode FRONTIER was used to optimize the performance of the multi-parameter coupling of Miller cycle diesel engine with GT-Power joint simulation,and two optimization schemes were designed according to the economy and emission requirements: in the economy mode,with the goal of improving economy and reducing emission as much as possible,the optimized diesel fuel consumption was reduced by 0.4～0.8%,NOx emission was reduced by 16.4～23.1%,and Soot emissions are maintained at a low level;in the emission mode,with the goal of reducing emissions and limiting the deterioration of fuel consumption to no more than 10%,NOx emissions are reduced by 36.5～38.1% and Soot emissions are reduced by 62.9～71.6% after optimization.Miller cycle coupled with multi-parameters such as EGR,injection strategy,compression ratio and intake pressure has great potential to reduce emissions of diesel engines designed for hybrid applications.This paper presents a multi-parameter optimisation scheme focusing on emission reduction and fuel economy improvement,which may provide some reference for related research.