Ammonia, as a zero-carbon fuel, is considered to be an ideal alternative fuel for a reduction of carbon dioxide emissions. Owing to low laminar flame speed and high ignition energy, the utilization of pure ammonia in powerplant system still presents severe challenges. To solve these issues, the dual fuel combustion of high reactivity fuel and ammonia is a promising solution. However, the dual fuel combustion stability of ammonia and high reactivity fuel has not been clearly understood. In present study, the misfire reasons are investigated using various optical diagnostic methods. Results demonstrate that the misfire reasons are divided into two aspects. One is that the addition of ammonia increases the temperature and pressure required for direction injection fuel auto-ignition, which makes it difficult to generate auto-ignition site, resulting in misfire. The other is that the low flame development speed and degradation of the in-cylinder temperature and pressure causes the difficulty in the further flame development, which results in misfire. A collaborative regulation approach of engine operating condition and direction injection fuel reactivity is proposed to improve combustion stability, which achieves 93% ammonia energy ratio. At 93% ammonia energy ratio, increasing direction injection pressure from 600 bar to 1000 bar decrease combustion stability. The local equivalence ratio of direction injection fuel that can ignite ammonia stably is mainly concentrated between 0.56 and 0.86 in the conditions of 93% ammonia energy ratio and 22 bar in-cylinder pressure. Compared with the in-cylinder temperature, the main factor in determining combustion stability is local equivalence ratio of direction injection fuel. The addition of ammonia prolongs the low temperature reaction and constrains the high temperature reaction of direction injection fuel. In brief, the combustion stability and ammonia energy ratio can be improved simultaneously using the collaborative regulation.

中文翻译：

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使用氨和高反应性燃料的双燃料方法燃烧稳定性的光学研究


氨作为一种零碳燃料，被认为是减少二氧化碳排放的理想替代燃料。由于层流火焰速度低、点火能量高，纯氨在电厂系统中的利用仍然面临严峻的挑战。为了解决这些问题，高反应性燃料和氨的双燃料燃烧是一种有前途的解决方案。然而，氨和高反应性燃料的双燃料燃烧稳定性尚未明确。在本研究中，使用各种光学诊断方法来调查失火原因。结果表明，失火原因分为两个方面。一是氨的添加提高了直喷燃油自燃所需的温度和压力，难以产生自燃部位，导致失火。二是火焰发展速度慢，缸内温度、压力下降，导致火焰难以进一步发展，导致失火。提出了发动机工况和直喷燃料反应性协同调节方法以提高燃烧稳定性，实现了93%的氨能比。在氨能量比为 93% 时，将定向喷射压力从 600 bar 增加到 1000 bar 会降低燃烧稳定性。在氨能比93%、缸内压力22 bar的条件下，能够稳定点燃氨的直喷燃油局部当量比主要集中在0.56~0.86之间。与缸内温度相比，决定燃烧稳定性的主要因素是直喷燃油的局部当量比。 氨的添加延长了直喷燃料的低温反应并抑制了高温反应。简而言之，通过协同调节可以同时提高燃烧稳定性和氨能量比。