Abstract 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.

中文翻译：

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混合物分层对无应变层流火焰的影响分析

摘要 给出了正弦当量比扰动下非定常无应变层流火焰的详细一维计算。研究了火焰厚度、火焰速度、物种浓度和物种反应速率对当量比变化的响应。通过在分层火焰经历的当量比下将分层火焰的结构与等效的均质混合物火焰的结构进行比较来量化分层的影响。燃烧成较稀混合物或较浓混合物的火焰之间的差异在当量比空间中产生了消耗速度和火焰厚度的滞后，随着分层越强，这种滞后变得更加突出，特别是当火焰在燃料-当量比下向负当量比梯度传播时。贫瘠的条件。对位移速度及其分量进行了分析，扩散、反应速率和交叉耗散分量都表现出很强的滞后性，但符号不同，相互部分抵消。比较标量的相空间响应并评估不同的相移。有趣的是，这些观察结果不受反应机制选择的影响。测试了相等和混合平均扩散率假设对结果的影响，其中后者导致了两倍强的滞后效应：发现火焰后面的热量和产物的热扩散效应对层流火焰传播起着重要作用分层混合物，即使是无应变的火焰。分层火焰显示物种浓度和反应速率发生显着变化，特别是对于次要和产品物种。将正弦振荡的响应与线性混合分层的情况进行比较。即使没有可压缩应变，也证明分层效应会严重影响火焰特性，并且已证明对热物理传输特性的处理对于准确预测这种行为至关重要。