Combustion and emission of a diesel engine with split injection and swirl matching

In order to explore the potential and mechanism of fuel economy improvement for split injection and intake swirl, a split injection test with and without swirl was performed on a single cylinder diesel engine. Results show that the brake specific fuel consumption(BSFC) at the strategy of 5% pilot injection fraction and 10° CA dwell time between injections has got 6.1 g/(kW·h) less than that at the single injection strategy, while the NO_x emission at the split injection strategy is increased by 200×10^-6 volume fraction compared with that the single injection strategy. In the swirl comparison test, the engine is operated at an excess air coefficient of 1.6 with pilot injection.Results show that the BSFC under the operation with a swirl ratio of 1.0 is cut down by 2.0 g/(kW·h)and NO_x emission is increased by 120×10^-6 compared with the operation without swirl.In the endoscope test, KL factor was used to evaluate soot emission. It is found that at the fixed crank angle of 16° CA ATDC, the KL factor is 1.22 for single injection strategy, 0.75 for spilt injection strategy without swirl and 0.21 for split injection with swirl. The simulation analysis results show that a small amount of split injection, a short dwell time between injections and a proper intensity of swirl can make the main injection fuel development to fully utilize, but not to be restricted by the thermo-atmosphere produced by the pilot fuel burn. As a result, fuel economy is improved and in-cylinder soot concentration is decreased.