Analysis of turbulent flame propagation in equivalence ratio-stratified flow
Analysis of turbulent flame propagation in equivalence ratio-stratified flow
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DOI：
10.1016/j.proci.2016.06.140
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
E. Richardson;Jacqueline H. Chen
中科院分区：
文献类型：
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作者：
E. Richardson;Jacqueline H. Chen
等比分层燃烧是实现内燃机和燃气轮机稳定低排放运行的重要技术。本文采用直接数值模拟的方法研究了等效比分层对湍流火焰传播物理特性的影响。三维模拟湍流槽-本生灯火焰配置进行了精确的多步动力学建模甲烷-空气燃烧。我们比较了一个完全预混和三个等效比分层的情况下，平均等效比梯度与平均火焰刷对齐，切向或相反。从火焰表面积和燃烧强度两个方面对模拟结果进行了分析。然后，通过检查以火焰-正常等效比梯度为条件的位移速度的统计数据，进一步研究分层的局部效应。发现局部燃烧强度取决于分层相对于火焰锋面的方向，因此当产物中的火焰速度比反应物中的火焰速度快时，燃烧强度增强。等效比梯度和火焰锋面之间的这种对齐效应以前已经在层流火焰中观察到，这里发现它也影响湍流火焰的整体行为。火焰表面积也受到等效比分层的影响，这可能是由于与等效比波动相关的火焰速度变化导致的表面平均消耗率和传播效应的差异所造成的。
Equivalence ratio-stratified combustion is an important technology for achieving stable low-emission operation in internal combustion engines and gas turbines. This study examines how equivalence ratio stratification affects the physics of turbulent flame propagation using Direct Numerical Simulation. Three-dimensional simulations of a turbulent slot-Bunsen flame configuration are performed with accurate multi-step kinetic modelling for methane–air combustion. We compare one perfectly-premixed and three equivalence ratio-stratified cases with the mean equivalence ratio gradient aligned with, tangential to or opposed to the mean flame brush. The simulation results are analysed in terms of flame surface area and the burning intensity. The local effects of stratification are then investigated further by examining statistics of the displacement speed conditioned on the flame-normal equivalence ratio gradient. The local burning intensity is found to depend on the orientation of the stratification with respect to the flame front, so that burning intensity is enhanced when the flame speed in the products is faster than in the reactants. This effect of alignment between equivalence ratio gradients and flame fronts has been observed previously in laminar flames and it is found here that it also affects the global behaviour of turbulent flames. The flame surface area is also influenced by equivalence ratio stratification and this may be explained by differences in the surface-averaged consumption rate and differential propagation effects due to flame speed variations associated with equivalence ratio fluctuations.