Flame structures and combustion efficiency computed for a Mach 6 scramjet engine
Flame structures and combustion efficiency computed for a Mach 6 scramjet engine
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DOI：
10.1016/j.combustflame.2004.10.004
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发表时间：
2005-08
影响因子：
4.4
通讯作者：
T. Mitani;T. Kouchi
中科院分区：
文献类型：
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作者：
T. Mitani;T. Kouchi
我们的氢燃料超燃冲压发动机长度为2.1米，提供的净推力超过发动机阻力，并在马赫数4至8的飞行条件下表现出约10公里/秒的燃料比冲。为了加速发动机的研究，开发了一个使用非结构混合网格的三维反应式CFD程序。利用该程序对超燃冲压发动机在马赫数6条件下的燃烧进行了数值模拟。本文首先对发动机试验和CFD程序进行了概述。研究了羟基自由基随时间的发展，以了解发动机中的自燃和燃烧的上游发展。在燃料混合完成后的0.1 ms，自燃发生在燃烧室段。反应区以约500 m/s的速度向上游传播，并在自燃后1 ms到达燃烧室中的后向台阶。稳态解表明，燃烧室中单个燃料射流周围有小火焰，发动机下游有大规模扩散火焰。在燃烧室中自主地实现了声波燃烧，导致在化学计量条件下提供2250 N的最大推力。燃烧效率的变化表明，燃烧性能是在一个狭窄的区域内的长度为0.15米的燃烧室和发动机下游的燃烧速率控制由一个大的扩散火焰。计算结果不仅可以提高发动机性能，而且可以优化超燃冲压发动机的计算。
Our hydrogen-fueled scramjet engines with a length of 2.1 m delivered net thrusts exceeding the engine drags and exhibited fuel specific impulses of about 10 km/s under Mach 4 to 8 flight conditions. A three-dimensional, reactive CFD code using unstructured hybrid grids was developed to accelerate the engine studies. Combustion in the scramjet engine under the Mach 6 condition was simulated by using this code. In this paper, the engine testing and the CFD code were outlined first. Timewise progress of hydroxyl radicals was investigated to understand autoignition and upstream-wise developments of combustion in the engine. Autoignition occurred from the cowl section at 0.1 ms after fuel mixing was completed. The reaction zones propagated upstream at speeds of about 500 m/s and reached the backward-facing steps in the combustor at 1 ms after the autoignition. Steady-state solutions showed small flames around individual fuel jets in the combustor and a large-scale diffusion flame downstream in the engine. Sonic combustion was autonomously realized in the combustor, resulting in delivery of a maximum thrust of 2250 N in the stoichiometric condition. Variations of combustion efficiency indicated that combustion performance was determined in a narrow region with a length of 0.15 m in the combustor and that the combustion downstream of the engine was rate-controlled by a large diffusion flame. The results found by the CFD computations enable us to not only improve engine performances but also to optimize computations for scramjet engines.