Study On Fuel Injection Control Strategy And Emission Characteristics Of High Pressure Common Rail Diesel Engine

With the emission regulations has been increasingly stringent, realizing the high efficiency, energy saving, environmental protection of diesel engine has become a mainstream of the development of the internal combustion engine industry. The operation process of the diesel engine is complex and changeable. It’s torque and speed in most operating conditions vary with time. A single jet cannot acquire a reasonable compromise between the dynamic performance and emission performance. Therefore,it is necessary to choose a reasonable injection combination combined with the operating condition of the diesel engine,to realize the precise control of the fuel injection pressure,fuel injection timing and fuel injection pulse width. That can effectively improve the combustion of the mixture gas in cylinder and realize the optimization of the power performance and emission performance of diesel engine.The development of electronic controlled fuel injection system of high-pressure common rail diesel engine,the present study situation and the research results of the fuel injection control in domestic and abroad has been introduced in this article. Fuel injection demands has been analyzed from the prospective of combustion process in cylinder,control object of fuel injection and typical operating conditions by combining with the injection characteristics of fuel injection system. Several corresponding solving measures has been put forward for the design of fuel injection control strategy.Based on the demand of fuel injection,the fuel injection control strategy of high-pressure common rail diesel engine has been introduced in detail,including the build of control architecture,the division and function of control modules. In this paper,a correction method for main fuel injection quantity based on the change of speed has been put forward. Through the correction algorithm,the injection quantity has been corrected. To a certain extent,this correction method can make up for the deficiency that the air-fuel ratio decrease when the speed has a abrupt change. There is a pressure fluctuation caused by multiple injection,which effect the execution accuracy of main injection quantity. Based on this,a correction algorithm has been put forward to pre-correct the pulse width of main injection quantity,then to improve the execution accuracy of main injection quantity.The control strategy of fuel injection has been implemented by using the ASCET modeling software tools of ETAS Company and the independently developed ECU （TC1728） electronic control unit. Through the INCA calibration software and communication interface equipment,the fuel injection control parameters has been preliminary calibrated on the test bench. On this basis,the influence of the injection control parameters on the performance of the diesel engine has been studied.The test results show that:1) The starting performance of diesel engine can be improved after adding the pilot injection. The optimum quantity for engine starting and pilot₁ injection, which makes the starting time shortest,respectively are 30 milligram per cycle to 40 milligram per cycle and 2milligram per cycle to 2.5milligram per cycle.2)The pilot injection timing to NOx and smoke emission in low speed has less influence,but great in medium and high speed.3)The pilot injection timing can be adjusted properly to acquire a reasonable compromise between NOx and smoke emission when the calibration works is going on. The engine performance can be improved by setting the rail pressure reasonably. At the same time, the soot emission and exhaust temperature can be decreased,but the NOx emission will increase.