Optimization Of Electronically Controlled High Pressure Common Rail Fuel System On Light-duty Vehicle Diesel Engine And Emission Control

In recent years,haze pollution is more and more serious in China,automotive emissions is one of main sources.This therefore necessitates the reduction and control of key pollutants such as NO_x and soot from diesel engine exhaust emissions.Electronically controlled high pressure common rail fuel injection system can be used to realize high precision and flexible control of fuel injection timing,fuel injection quantity and injection law,and fuel spray characteristics,thereby contributing to the significantly improvement of engine combustion process.It is widely used in the industry.With high influence of diesel engine injector matching parameters and fuel injection parameters on in-cylinder mixture formations,combustion process and emission control,by analyzing the influence of injector parameters and fuel injection parameters on the combustion process the exhaust emissions from diesel engine could be reduced.In this paper,a domestic electronically controlled high pressure common rail diesel engine is employed for the investigation.The research investigation involves numerical analysis simulation and experimental analysis.AVL Fire software was used to build and mesh the combustion chamber model and also simulate the combustion processes in the numerical approach.The accuracy of the model was verified by comparing it with an indicator diagram.The combustion process in the cylinder is reflected by the change in air-fuel ratio,in-cylinder pressure and temperature fields.The effects of nozzle hole diameter and injection timing on the formation and combustion of gas mixtures in the cylinder and diesel engine emission were analyzed.The results show that,injectors with relatively small nozzle hole diameters produce favorable fuel atomization that fully mixes with air.Therefore it results in high combustion thermal efficiency and higher in-cylinder temperature and pressure,which are essential for the reduction of soot emission but also,accompanied with the increment of NO_x emissions.The increase of fuel injection timing prolongs the ignition delay period.Also the advancement of fuel injection improves the combustion in the cylinder,thereby gradually increasing the temperature and pressure inside the cylinder.This also results in the advancement of the peak value of temperature and pressure.Delayed injection reduces the temperature inside the cylinder,which aids in the reduction of NO_x emissions.With fixed total injection quantity,increasing in post-injection quantities results in slight decrease of peak in-cylinder pressure,decrease in peak in-cylinder temperature and increase in the finalexhaust temperature.During the main combustion period,the peak heat release rate decreases,however during post combustion period,peak heat release rate increases.With increasing interval angle between main and post injection,peak cylinder pressure decreases slightly,decreasing the temperature and the numerical value of peak heat release rate and delaying the timing of peak heat release rate during the post combustion period.In the experiment part,diesel injector matching test and the optimization test of partial parameters involved in fuel injection systems are completed.The influence of injection hole diameter,nozzle protrusion,rail pressure,main injection timing and parameters of post-injection on smoke,NO_x and fuel consumption rate of the test prototype are analyzed through experimental comparison.It can provide a reference for the performance optimization of the prototype.It was found that with the increase of injection hole diameter from 0.132 to 0.149 mm,NO_x emission gradually decrease,while PM,CO and HC emissions gradually increase.At the nozzle hole diameter of0.132 mm,the emissions and fuel economy of the test prototype were more eclectic.Comparing smoke and fuel consumption characteristics of the diesel engine under various nozzle extension,it was found that the nozzle protrusion of 3.03 mm is the most suitable.At higher rail pressures,smoke and fuel consumption rate were reduced.The quantity of NO_x emission were significantly reduced with delayance in main injection timing.With increase in post-injection quantities,NO_x emission decreases while fuel consumption rate increases and also CO,HC decrease initially but then increase afterwards.With increasing interval angle between main and post injection,NO_x emission decrease,CO,HC and fuel consumption rates increase.Also smoke decreases initially but then increases afterwards.Compared with single injection,NO_x and smoke experience reduction,however fuel consumption rate increases with post-injection.Trade-off between emissions and fuel consumption rate could be achieved with reasonable post-injection parameters.