An empirical characteristic scaling model for freely-propagating lean premixed hydrogen flames
An empirical characteristic scaling model for freely-propagating lean premixed hydrogen flames
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DOI：
10.1016/j.combustflame.2021.111805
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发表时间：
2021-11-05
影响因子：
4.4
通讯作者：
Aspden, A. J.
中科院分区：
文献类型：
--
作者：
Howarth, T. L.;Aspden, A. J.
由于燃料的高流动性，贫预混氢火焰是热扩散不稳定的，这导致火焰的局部加速和变薄。因此，一维稳定的未拉伸层流火焰速度和热厚度并不代表多维火焰，并且差异的程度强烈依赖于反应物条件。本文提出了一种经验模型来预测本地以及特征自由传播的火焰速度和厚度，可以从一维模拟（例如在Cantera）进行评估的值。有人发现，热扩散响应的特点是在二阶不稳定性参数（ω 2），从经典的线性稳定性分析。该不稳定性参数强烈依赖于Zel'dovich数，并在压力/温度/当量比空间中呈现非单调行为。特别地，存在ω 2达到局部峰值的表面，并且在表面的两侧发现不同的特征相关性。具体而言，热扩散响应（在考虑的ω 2范围内）在该峰表面的高压侧更强且更不可预测（更大的不确定性）。经验模型推断出从一个大的数据集的二维自由传播的火焰在广泛的反应条件。局部火焰速度和厚度的PDF用于定义自由传播的特征值作为相应的平均表面值，隐含地提供在线0上的平均局部燃烧增强因子I。局部火焰速度，然后通过JPDF与曲率和应变率，以确定一个适当的Markstein数。由此产生的模型由特征火焰速度，厚度和Markstein数的不稳定性参数Ω 2，所有这些都可以评估仅基于廉价的一维计算的表达式。(c)2021年，任作家。爱思唯尔公司出版代表燃烧研究所这是CC BY许可下的开放获取文章（http://creativecommons.org/licenses/by/4.0/）
Lean premixed hydrogen flames are thermodiffusively unstable due to the high mobility of the fuel, which leads to localised acceleration and thinning of the flame. Consequently, the one-dimensional steady unstretched laminar flame speed and thermal thickness are not representative of multi-dimensional flames, and the extent of the disparity is strongly dependent on reactant conditions. This paper presents an empirical model to predict local as well as characteristic freely-propagating values of flame speeds and thicknesses that can be evaluated from one-dimensional simulations (in Cantera for example). It was found that the thermodiffusive response was well characterised in terms of the second-order instability parameter ( omega 2 ) that arises from classical linear stability analysis. This instability parameter depends strongly on Zel'dovich number, and presents non-monotonic behaviour in pressure/temperature/equivalence-ratio space. In particular, there is a surface where omega 2 attains a local peak, and different characteristic correlations are found either side of the surface. Specifically, the thermodiffusive response (over the range of omega 2 considered) is stronger and more unpredictable (greater uncertainties) on the higher-pressure side of this peak surface. The empirical model is inferred from a large dataset of two-dimensional freely-propagating flames over a broad range of reactant conditions. PDFs of local flame speed and thickness are used to define freely-propagating characteristic values as the corresponding mean surface value, implicitly supplying a mean local burning enhancement factor I over line 0 . Local flame speeds are then correlated with curvature and strain rate through JPDFs to identify an appropriate Markstein number. The resulting model consists of expressions for characteristic flame speeds, thicknesses and Markstein numbers in terms of the instability parameter omega 2 , all of which can be evaluated based solely on inexpensive one-dimensional calculations. (c) 2021 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )