Impagnatiello Matteo, Malé Quentin, Noiray Nicolas
CAPS Laboratory, Department of Mechanical and Process Engineering, ETH Zürich, 8092 Zurich, Switzerland.
Flow Turbul Combust. 2024;112(4):1249-1273. doi: 10.1007/s10494-024-00540-8. Epub 2024 Apr 5.
Ignition and combustion behavior in the second stage of a sequential combustor are investigated numerically at atmospheric pressure for pure fueling and for two - fuel blends in 24:1 and 49:1 mass ratios , respectively, using Large Eddy Simulation (LES). Pure fueling results in a turbulent propagating flame anchored by the hot gas recirculation zones developed near the inlet of the sequential combustion chamber. As the content increases, the combustion process changes drastically, with multiple auto-ignition kernels produced upstream of the main flame brush. Analysis of the explosive modes indicates that, for the highest amount investigated, flame stabilization in the combustion chamber is strongly supported by auto-ignition chemistry. The analysis of fuel decomposition pathways highlights that radicals advected from the first stage flame, in particular OH, induce a rapid fuel decomposition and cause the reactivity enhancement that leads to auto-ignition upstream of the sequential flame. This behavior is promoted by the relatively large mass fraction of OH radicals found in the flow reaching the second stage, which is approximately one order of magnitude greater than it would be at chemical equilibrium. The importance of the out-of-equilibrium vitiated air on the ignition behavior is proven via an additional LES that features weak auto-ignition kernel formation when equilibrium is artificially imposed. It is therefore concluded that parameters affecting the relaxation towards chemical equilibrium of the vitiated flow can have an important influence on the operability of sequential combustors fueled with varying fractions of blending.
The online version contains supplementary material available at 10.1007/s10494-024-00540-8.
在常压下，使用大涡模拟（LES）分别对纯燃料以及质量比为24:1和49:1的两种燃料混合物，对顺序燃烧器第二阶段的点火和燃烧行为进行了数值研究。纯燃料供给会产生一个湍流传播火焰，该火焰由顺序燃烧室入口附近形成的热气体再循环区域固定。随着 含量的增加，燃烧过程发生剧烈变化，在主火焰刷上游产生多个自燃核。对爆炸模式的分析表明，对于所研究的最高 量，燃烧室内的火焰稳定受到自燃化学的强烈支持。对燃料分解途径的分析突出表明，从第一阶段火焰平流而来的自由基，特别是OH，会引发快速的燃料分解，并导致反应性增强，从而在顺序火焰上游引发自燃。这种行为是由到达第二阶段的气流中发现的相对较大质量分数的OH自由基促进的，该质量分数比化学平衡时大约高一个数量级。通过额外的大涡模拟证明了非平衡贫氧空气对点火行为的重要性，该模拟在人为施加平衡时呈现出自燃核形成较弱的特征。因此得出结论，影响贫氧流化学平衡弛豫的参数可能对以不同比例混合燃料的顺序燃烧器的可操作性产生重要影响。
在线版本包含可在10.1007/s10494-024-00540-8获取的补充材料。
