An optical study the spray and combustion characteristics of green and renewable ammonia with diesel pilot ignition under dual direct injection

Ammonia, as a typical carbon free fuel, is considered the most promising alternative for internal combustion engines. However, the spray and combustion characteristics of ammonia are not clear, especially under diesel/ammonia dual fuel duel direct injection setting. This study investigates the spray and combustion characteristics of a diesel/ammonia under various injection angle (IA) and injection interval (Δt) using optical diagnostic techniques. The results show that changing the IA and Δt can effectively change the diesel/ammonia mixture distribution and achieve concentration stratification and reactivity stratification. At IA = 180°, the liquid- and vapor-phase spray projected areas are 0.76–0.92 and 0.64–0.86 times than those at IA = 90°, respectively. Additionally, increasing Δt promotes the diffusion and evaporation of spray, thus resulting in a larger vapor-phase spray projected area and a smaller liquid-phase spray projected area. Compared with 90° IA, 180° IA increases the relative speed and collision strength of the two jets, inhibits spontaneous diesel combustion, prolongs the ignition delay, and intensifies the combustion process. when IA = 180° and Δt = 1.0 ms, the collision spray achieves high combustion rate, a short combustion duration, and the least soot generation, which can significantly improve the combustion and emission of engines.