Analysis of mixture stratification effects on unstrained laminar flames
Analysis of mixture stratification effects on unstrained laminar flames
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DOI：
10.1016/j.combustflame.2020.06.009
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发表时间：
2020-09-01
影响因子：
4.4
通讯作者：
Kempf, A. M.
中科院分区：
文献类型：
--
作者：
Inanc, E.;Chakraborty, N.;Kempf, A. M.
详细的一维计算非定常无应变层流火焰受到正弦当量比扰动。研究了火焰厚度、火焰速度、组分浓度和组分反应速率对当量比变化的响应。分层的效果是量化的分层火焰的结构进行比较，相当于均匀混合物火焰的当量比，分层火焰的经验。燃烧成贫混合物或更丰富的混合物的火焰之间的差异产生滞后的消耗速度和火焰厚度的当量比空间，这变得更加突出与较强的分层，特别是当火焰传播到一个负的当量比梯度在贫燃料的条件下。分析了位移速度及其分量，扩散、反应速率和交叉耗散分量均表现出较强的滞后性，但符号不同，部分相互抵消。标量的相空间响应进行了比较，并评估了不同的相移。有趣的是，这些观察结果并不受反应机制选择的影响。相等的和混合物平均扩散率假设的结果的影响进行测试，后者造成两次更强的滞后效应：热扩散效应的热量和产品背后的火焰被发现发挥了显着的作用，层流火焰传播分层混合物，即使是无应变火焰。分层火焰的物种浓度和反应速率，特别是对次要和产品物种显着改变。正弦振荡的响应与线性混合物分层的情况进行比较。即使没有的可压缩应变，它表明，分层效应严重影响的火焰特性和热物理传输性能的治疗已被证明是关键的准确预测这种行为。(C)2020燃烧研究所由爱思唯尔公司出版All rights reserved.
Detailed one-dimensional computations of unsteady unstrained laminar flames subjected to sinusoidal equivalence ratio perturbations are presented. The responses of the flame thickness, flame speeds, species concentrations and the species reaction rates to equivalence ratio variations are investigated. The effect of stratification is quantified by comparing the structure of a stratified flame to that of an equivalent homogeneous mixture flame at an equivalence ratio that the stratified flame experiences. The difference between a flame burning into a leaner mixture or a richer mixture yields hysteresis for consumption speed and flame thickness in the equivalence ratio space, which becomes more prominent with stronger stratification, especially when the flame propagates towards a negative equivalence ratio gradient under fuel-lean conditions. The displacement speed and its components are analysed, with the diffusion, reaction rate and cross-dissipation components all showing a strong hysteresis, but with different signs, partially cancelling each other. The phase space responses of the scalars are compared and the different phase shifts are evaluated. Interestingly, these observations were not affected by the choice of the reaction mechanism. The effects of equal and mixture-average diffusivity assumptions on the results are tested, where the latter caused two times stronger hysteresis effects: the thermo-diffusive effects of heat and products behind the flame were found to play a significant role for laminar flame propagation in stratified mixtures, even for unstrained flames. The stratified flame shows significant alteration in the species concentrations and reaction rates, especially for the minor and product species. The response of the sinusoidal oscillations is compared against cases with linear mixture stratification. Even with the absence of the compressible strain, it is demonstrated that the stratification effects heavily influence the flame properties and the treatment of thermo-physical transport properties has been demonstrated to be pivotal to the accurate prediction of this behaviour. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.