基于喷油策略和阿特金森循环的汽油压燃发动机高负荷性能优化研究

Optimization of Gasoline Compression Ignition Engine Performance at High Loads with Advanced Injection Strategy and Atkinson Cycle

基于单缸机开展了多次喷射和阿特金森循环对汽油压燃(gasoline compression ignition,GCI)发动机性能影响的试验研究,试验分别研究了单次喷射、两次喷射及两次喷射结合阿特金森循环对GCI中高负荷性能的影响。结果表明,单次喷射中喷油压力、喷油时刻和喷油量对GCI燃烧有显著的影响,提高喷射压力可提高发动机的平均指示压力,降低循环波动,但喷油压力过高会导致燃烧对喷油时刻变化异常敏感,使燃烧难以正常进行;喷油量增加可提高发动机的平均指示压力,但过高的喷油量会导致不完全燃烧的燃油量增加,热效率下降。在两次喷射中,主喷时刻对燃烧起着决定性的影响。主喷时刻提前,发动机动力性有所提升,但压升率也随之增加;主喷时刻推迟,发动机动力性相应降低,同时循环波动增加。增加预喷量有利于发动机性能的提升,但预喷量过大会导致燃烧可控性降低。阿特金森循环能明显提升GCI热效率,其主要原因是减少了压缩行程的压缩负功,同时燃烧并未恶化,膨胀做功并未降低。

Based on a single cylinder engine,the effects of injection parameter,multiple injection and the Atkinson cycle on the performance of gasoline compression injection(GCI)engine at high loads were studied.The results show that with the single injection strategy,the injection pressure,injection timing and injection mass have significant effects on GCI combustion.Increasing injection pressure can increase the indicated mean effective pressure(IMEP)of the engine and reduce cycle-to-cycle variation,but too high injection pressure causes the combustion to be extremely sensitive to the change of the injection timing,which makes it difficult to organize normal combustion.The increase of fuel injection can increase IMEP,but excessive fuel injection mass will lead to the increase of incomplete combustion and the decrease of thermal efficiency.With the split injection strategy,the main injection timing plays a decisive role in combustion.Advancing the main injection timing improves the engine performance and increases the pressure rise rate simultaneously.And as the main injection timing is delayed,the engine performance is deteriorated,and the cycle-to-cycle variation becomes great.Increasing pilot injection ratio is beneficial to the improvement of engine performance,but excessive pilot injection ratio leads to less combustion controllability.The Atkinson cycle can obviously improve the thermal efficiency of GCI engine.The main reason is that it reduces negative work during the compression stroke,while maintaining positive work during the expansion stroke.