Abstract Ultra-lean burn combustion can significantly improve the fuel economy of gasoline engines. However, poor combustion stability and slow combustion need to be solved. Therefore, micro-flame ignited (MFI) hybrid combustion, a concept that ultra-lean gasoline is burned with compression auto-ignition of direct injection (DI) dimethyl ether (DME) in the cylinder, was employed. The effect of single and double DI DME strategies on the combustion characteristics and flame structures was investigated in an optical gasoline engine at lambda 2.0. The results show that the heat release process in the case of single DI DME consists of oxidation reactions of DME (stage I) and hybrid combustion of DME and gasoline (stage II). In the case of double DI DME, there is gasoline auto-ignition (stage III) after stages I and II. The ignition timing delays with decreased heat released in stage I regardless of DI strategies. Indicated mean effective pressure can be enhanced and the cyclic variation is reduced in the double DI conditions. The flame brightness increases with increased heat release rate regardless of DI DME strategies. The decay rate of turbulent flame propagation speed in double DI conditions is slower than that in single DI conditions, which improves combustion stability.

中文翻译：

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超稀条件下直喷二甲醚对光学汽油机微火焰点火（MFI）混合燃烧特性的影响

摘要 超稀薄燃烧可以显着提高汽油发动机的燃油经济性。但需要解决燃烧稳定性差、燃烧慢等问题。因此，采用了微火焰点火 (MFI) 混合燃烧，即超稀薄汽油通过气缸内直接喷射 (DI) 二甲醚 (DME) 的压缩自燃燃烧的概念。在 λ 2.0 的光学汽油发动机中研究了单和双 DI DME 策略对燃烧特性和火焰结构的影响。结果表明，在单一 DI DME 情况下的放热过程包括 DME 的氧化反应（阶段 I）和 DME 和汽油的混合燃烧（阶段 II）。在双 DI DME 的情况下，在阶段 I 和 II 之后有汽油自燃（阶段 III）。无论 DI 策略如何，点火正时都会随着第一阶段释放的热量减少而延迟。在双DI条件下可以提高指示平均有效压力并减少循环变化。无论采用何种 DI DME 策略，火焰亮度都会随着热释放率的增加而增加。双DI工况下湍流火焰传播速度的衰减率比单DI工况慢，提高了燃烧稳定性。