Study Of Start Control Strategy For High Pressure Common Rail Diesel Engine

The contradiction between increasing market demand of vehicles and energy and environment compels internal combustion engine researchers to constantly find engine technologies related to high efficiency and low emissions. High pressure common rail diesel engine has been a new alternative for passenger car’s power supply due to its perfect characteristic of economy, power, and emissions. As one of important working-conditions of diesel engines, the optimization of performance of starting working-condition shows great meaning to realize the energy conservation and environment protection of vehicles.In this research, DK4 A high pressure common rail diesel engine was tested and the starting process was set to be test condition to realize the final objective of enhancing the starting performance and emission performance. In this project, the control strategy of starting of diesel engine was made and the starting test controlling system was built to optimize the controlling parameters.First of all, the criterion and transition route of starting working-condition was set basing on the independently developed electronic control unit to realize the precise control of starting working-condition. The calculation strategy of fuel consumption of starting consisting of starting base fuel consumption, starting acceleration fuel consumption and the modified fuel consumption of cold start was designed. The control strategy of multiple injection was designed as well to optimize the performance of starting control.Secondly, the influence of fundamental control parameters of starting working-condition(i.e. the injection beginning speed and the switching-to-idle speed in starting) on starting performance was analyzed through test and then 200 r/min(the injection beginning speed)and 750 r/min(the switching-to-idle speed) were chosen as fundamental parameters of starting control. Simultaneously, the influence of rail pressure, starting acceleration fuel consumption and injection timing on starting performance under the condition of single injection was researched, with the result showing that a optimal value existed in each factor,which led to the shortest starting time and the lowest mean opaque smoke during start, any value higher or lower than which would lead to the deterioration of starting performance. The optimal point was 40MPa(rail pressure), 3.5mg(starting acceleration fuel consumption) and-4°CA(ATDC)( injection timing) in warm start.Thirdly, the four factors(rail pressure, main injection timing, pilot-injection ratio and pre-injection timing) and four levels orthogonal test was designed with the constant starting fuel consumption. The test results showed that, the law of influence of rail pressure and main injection timing on starting performance derived in the orthogonal test was the same as thatderived in the full test. To pilot-injection ratio and pilot-injection timing, there was a critical value each which led to the shortest starting time and the lowest mean opaque smoke during start. The factors influencing starting performance were main injection timing, rail pressure,pre-injection ratio and pre-injection timing, in the sequence of the level of influence.Finally, the optimal control parameters of warm start were obtained, which were 3.5mg(starting acceleration fuel consumption), 40MPa(rail pressure),-4°CA(ATDC)( injection timing), 20%(pilot-injection ratio) and-2°CA(ATDC)(pilot-injection timing). Comparing with single injection, the starting time was shortened by 13.0% and the mean opaque smoke during start was decreased by 51.3%.