Effects of pressure on cellular flame structure of high hydrogen content lean premixed syngas spherical flames: A DNS study
Effects of pressure on cellular flame structure of high hydrogen content lean premixed syngas spherical flames: A DNS study
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DOI：
10.1016/j.ijhydene.2016.09.181
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发表时间：
2016-12
影响因子：
7.2
通讯作者：
K. Dinesh;H. Shalaby;K. Luo;J. A. Oijen;D. Thévenin
中科院分区：
文献类型：
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作者：
K. Dinesh;H. Shalaby;K. Luo;J. A. Oijen;D. Thévenin
采用三维直接数值模拟方法研究了高氢含量合成气在1 bar、2 bar和4 bar压力下的湍流贫燃预混火焰的结构和传播。在湍流雷诺数为50、100和150时，对三种不同的初始湍流水平进行了每种压力的模拟。扩展球形火焰的DNS考虑了详细的化学动力学和优先扩散效应。采用混合平均输运模型。研究了在低到高初始湍流条件下压力对火焰结构、热释放速率和自由基组分分布的影响。结果表明，在不同的初始湍流条件下，压力对合成气球形火焰的胞状火焰结构有很大的影响。在大气压下，由于模拟中施加的初始湍流水平，火焰显示出弱的湍流结构。在湍流条件下的高压下，火焰发展出蜂窝状燃烧结构，由于湍流而叠加有火焰褶皱。它示出，高度褶皱的细胞，在球形火焰的表面上开发增加其面积，从而在升高的压力下的全球传播速度。结果表明，随着压力的增加，局部热释放速率显着增加。分析还揭示了在负曲率区域在高压下形成低放热率值的尖瓣结构，与以前的研究一致。OH自由基的质量分数和温度的联合概率密度函数显示加宽OH值在高温区在升高的压力相比，其分布在大气压。的平均物种分布的OH和HO2在层流和湍流火焰之间的温度的比较表明，压力升高有一个主要的影响，在组成空间的火焰结构。
The structure and propagation of turbulent lean premixed high hydrogen content syngas flames at pressure values of 1 bar, 2 bar and 4 bar are studied using three-dimensional direct numerical simulations. Simulations for each pressure considered were performed for three different initial turbulence levels at the turbulent Reynolds numbers of 50, 100 and 150. The DNS of expanding spherical flames has taken into account detailed chemical kinetics and preferential diffusion effects. The mixture-averaged transport model has been employed. Effects of pressure on flame structures, heat release rate and radical species distributions under low to high initial turbulent conditions are examined. The results show that elevated pressures greatly influence the cellular flame structure of syngas spherical flames under different initial turbulent conditions. At the atmospheric pressure, the flame shows weakly wrinkling structures due to the initial turbulence level imposed in the simulation. At elevated pressures under turbulence conditions, the flame develops cellular burning structures, superimposed by flame wrinkles due to turbulence. It is shown that highly wrinkled cells that develop over the surface of a spherical flame increase its area and thereby the global propagation speed at elevated pressures. Results show noticeable increases in the local heat release rate with increasing pressure. The analysis also reveals the formation of cusped structures with low heat release rate values in areas of negative curvatures at elevated pressures, in agreement with previous studies. The joint probability density functions of OH radical mass fraction and temperature show broadening OH values in the high temperature zone at elevated pressures compared to its distribution at the atmospheric pressure. Comparisons of mean species distributions of OH and HO2over temperature between laminar and turbulent flames show that pressure elevation has a major influence on the flame structure in the composition space.