Characteristics of ammonia premixture combustion ignited by a gasoline ignition chamber

Abstract

Ammonia is a kind of clean and renewable fuel with great potential for engine applications. Since ammonia has low reaction characteristics, the addition of auxiliary fuels or special ignition techniques are required to enhance its combustion performance. In this study, a kind of ammonia combustion enhancement method was investigated, and the combustion process of ammonia, which was ignited by an ignition chamber with gasoline injection, was analyzed by visualization experiments. The experiments showed that using gasoline as ignition chamber fuel substantially reduced the ignition delay and the duration of ammonia combustion was reduced by 46.4% compared to the spark ignition mode. However, at the gasoline energy percentages of 1.0%, 1.5%, 2.0% and 2.5%, the ammonia combustion duration and peak pressure were proportional to gasoline energy. The combustion duration and high peak pressure could be balanced at the percentage of 1.5%. On the other hand, the geometrical effect of the outlet between the ignition chamber and the main chamber was also discussed. In comparison to the outlet diameters of 6.0 mm and 4.5 mm conditions, the jet flow development speed was faster under the 3.0 mm condition and it has the shortest combustion duration of 39.2 ms. Moreover, the fundamental experimental results indicated that the ignition chamber with gasoline had great potential in dealing with the equivalence ratio of 0.8, 1.0 and 1.1, which were detrimental to the combustion process of ammonia. Due to poor ignition at 1.0% gasoline energy percentage condition during lean combustion, resulting in poor performance of peak pressure and combustion duration, the 1.5% one was regarded to be more suitable within wide range of engine operations. Therefore, the results are expected to provide theoretical foundation for organizing and controlling the combustion of ammonia fueled engines.