Study Of Optimization Control For Idle Performance Of High Pressure Common Rail Diesel Engine

In recent years, PM2.5in each big city of China goes beyond the standard greatly andfrequently, which led the cities to be sunk in fog and haze weather. As people’s daily life andhealth are facing the threat of bad air quality, environmental problems cause high attention ofthe whole society again. At the same time, as one of the major sources of air pollution,automobile exhaust emissions are also restricted more strictly.In this background, highpressure common rail diesel engine, with excellent economy, power and emissioncharacteristics, cause high attention of researchers on internal combustion engine rapidly andbecome one of the most popular research directions. As idle condition is one of the mostimportant operation modes of diesel engine, the optimization of idle performance is of greatsignificance to energy-saving and emission-reduction.The core of the article was the idle condition of high pressure common rail diesel engine,and the aim is to achieve energy-saving and emission-reduction of diesel engines. In order tooptimize the stability, economy and emission characteristics of idle performance through thebench test, the author designed and developed the software system of electric control unit,made strategy for idle condition and optimized the control parameters.First of all, in order to meet the basic control of idle condition, and the software systemof electric control unit which took the MC9S12XS128as the core was developed based on thehardware platform, including the functions of judging the engine running state, operatingmode transition, adjusting the injection pressure flexibly, controlling injection timing andinjection quantity accurately and so on.Secondly, the idle stability is optimized through the bench test. Effect of target idle speedon stability has been analyzed and800r/min has been chosen as the target idle speed of dieselengine. The results of comparative tests about effect of injection pressure, coolant temperature,idle PID control, integral separation PID control and their control parameters on stabilityshow that higher coolant temperature, higher injection pressure, and the reasonable selectionand collocation of PID control parameters benefit the idle stability. Compared with PIDcontrol in the same situation, integral separation PID control have obvious advantages tomake the idle speed fluctuation range less than±10r/min under the different coolanttemperature.Thirdly, in order to optimize the economy and emission characteristics of idle condition,the comparative tests about effect of injection pressure, injection timing, and coolanttemperature on economy and emission characteristics of idle condition have been given andthe causes have been analyzed based on the combustion parameters. The results of comparative tests about idle economy show that the higher coolant temperature is beneficialto improve the idle economy, and the reasonable selection of fuel injection timing andinjection pressure is also beneficial to improve idle economy under the different coolanttemperature. The results of comparative tests about idle emission show that does not exist anoptimal fuel injection pressure and fuel injection timing to make the NOx, HC, CO, Sootemissions to be a minimum value at the same time, so the weight of four types of emissionsneed to be considered to determine the injection timing and injection pressure.Finally, based on comprehensive consideration of the stability, economy and emissioncharacteristics of idle condition, the optimal injection pressure MAP and injection timingMAP have been determined according to the coolant temperature.