Simulation conditions.

Ammonia is a green zero-carbon fuel, yet its low reactivity poses challenges, including difficult ignition and slow combustion rates. Compared to diesel or biodiesel, dimethyl ether (DME) has no C-C bonds, which means it produces almost no soot and has a high cetane number that helps it ignite easily. So, using the highly reactive DME to help ignite liquid ammonia is a good way to make it burn better. This study uses computer simulations to look at how well liquid ammonia and DME work together as fuel with different injection setups. Results indicate optimal DME ignition enhancement at injector spacing L = 6 cm, injection angle 180°, and ammonia energy share 70%, outperforming cases with spacings of 7–8 cm and angles of 150°, 120°, 90°, and 60°. At the same time, having shorter spacing during DME combustion leads to smaller areas for OH but more NH₂ formation, showing that ammonia is more effective at cooling the flame and that more ammonia is being used as fuel. Additionally, when DME is not burning, both OH and NH₂ areas grow larger at shorter spacings, showing that the fuel mixes sooner, the reaction areas get bigger, and the burning process is more complete. Regarding the bimodal NH₂ peaks, the initial peak reflects partial ammonia oxidation that is flame-entrained during DME combustion, while the secondary peak indicates the onset of autoignition, which is characterized by diminished reaction rates and reduced combustion intensity.氨是一种绿色零碳燃料，但其反应活性较低，存在点火困难、燃烧速率缓慢等难题。与柴油或生物柴油相比，二甲醚（dimethyl ether, DME）不含碳-碳键，因此几乎不会产生炭黑，且拥有较高的十六烷值，易于点火。因此，利用高反应活性的二甲醚辅助液态氨点火，是改善其燃烧性能的有效途径。本研究通过计算机模拟，探究了不同喷射配置下液态氨与二甲醚混合燃料的燃烧表现。结果显示，当喷油器间距L=6 cm、喷射夹角为180°、氨能量占比为70%时，二甲醚的点火增强效果最佳，优于间距为7~8 cm、喷射夹角为150°、120°、90°及60°的工况。同时，在二甲醚燃烧阶段，较短的喷油器间距会使得羟基（OH）的生成区域更小，但氨基（NH₂）的生成量更多，这表明液态氨在冷却火焰方面的效果更为显著，且有更多的氨作为燃料参与反应。此外，当二甲醚未参与燃烧时，较短的间距会使得羟基与氨基的生成区域均有所扩大，这意味着燃料混合速率更快，反应区域更大，燃烧过程更为充分。关于双峰型氨基（NH₂）峰值，初始峰值反映了二甲醚燃烧过程中被卷吸进入火焰的部分氨氧化过程，而次级峰值则代表了自燃的起始阶段，其特征为反应速率降低、燃烧强度减弱。