Effects of fuel injection strategies on the diesel engine cold-start characteristics and environmental adaptation at extreme cold conditions

The cold-start performances of internal combustion power equipment at extreme cold conditions in plateau is one of the essential issues affecting environmental adaptation and restricting its further development. The aim of this study was to explore the diesel engine cold-start characteristics and environmental adaptation of different fuel injection strategies at different ambient temperature in plateau, a direct injection high-pressure common rail diesel engine was taken as the research object, and a low-temperature environment test chamber and a cold-start test bench were built on the altitude of 2 000 m. Then, the diesel engine cold-start performances and environmental adaptation experiment of 3 injection strategies and different fuel injection advance angles at extreme cold conditions (the lowest ambient temperature is -45 ℃) in plateau were carried out. It was showed that compared with the single injection (SI) strategy, the double injection (DI) and triple injection (TI) strategies could effectively improve the speed stability and reliability of the diesel engine cold-start in extreme conditions. The fuel injection strategies were sorted as TI < DI < SI according to timing of the combustion mean ignition delay, while the mean maximum combustion pressure was ranked in the opposite direction. Under cold-start conditions without the assistance of glow plug, there was a longest combustion ignition delay for SI strategy and the ignition delay was 4.5 ℃A after top dead center. The ignition delay of TI strategy was advanced by 5.6 ℃A compared to SI strategy, and enhanced the proportion of pre-mixed combustion. And then the cold-start combustion of the diesel engine with TI strategy was promoted faster, more uniform and more stable. Increasing the fuel injection advance angle appropriately can develop combustion of cold-start, and the optimal fuel injection advance angle in this study is 30℃A BTDC. The peak of HC emission generated by diesel combustion based on the SI strategy was the largest, the peak of HC emission generated by diesel combustion with DI strategy was in the middle, and the peak of HC emission generated by diesel combustion with TI strategy was the smallest. Compared with SI strategy, the peak of HC emissions generated by diesel combustion with TI strategy was decreased by 58.6% and 64.8% at 20℃ and -5 ℃, respectively. The engine was started up unsuccessfully at temperatures of -25 ℃ and below for SI strategy and -45℃ for DI strategy. The TI strategy could make engine cold-start done successfully in one time in a wide temperature range environment of -45～20 ℃, improve cold-start success rate and cold-start average acceleration and shorten the cold-start duration. Under the cold-start conditions of consistent temperature, the diesel engine cold-start time of SI strategy is the longest, the diesel cold-start time of DI strategy is in the middle, and the diesel engine cold start time of TI strategy is the shortest. TI strategy greatly improves the cold-start performances and environmental adaptation of the diesel engine under extreme cold conditions in plateau. The research findings can provide a reference for improving the cold-start performance and environmental adaptation of internal combustion power equipment in multi-region and a wide ambient temperature range.