Study on the combustion characteristics and reaction mechanism of high-reactive-fuels-blended ammonia

In this paper, the basic combustion characteristics of blends of ammonia and several typical hydrocarbon fuels (including n-heptane, gasoline and RP-3 kerosene) are explored. The results show that the Laminar Flame Speed (LFS) of ammonia combustion assisted by n-heptane is faster than that of the ammonia combustion assisted by gasoline. The equivalent ratio of RP-3 kerosene/ammonia co-combustion corresponding to the highest LFS is evidently higher than other two fuels, and its equivalent ratio of lean burn limit is also higher. Further analysis of chemical reaction kinetics reveals that carbon-based fuels and ammonia interact with each other primarily via the competition to obtain active free radicals, such as OH, H, and O. Besides, the strength of C-N cross-reaction is relatively low and has little influence on the overall reaction path. Comparing the three co-combustion processes, the Markstein length of RP-3 kerosene-assisted ammonia combustion is higher, which is conducive to improving the stability of flame, especially under the high equivalent ratio. With the variation of temperature, the Markstein length of the n-heptane assisted ammonia combustion changes most significantly, and the addition of iso-alkanes will weaken the sensitivity of Markstein length to temperature.