ABSTRACT

Edge flames are a canonical two-dimensional flame structure appearing in lifted jet flames and in the growth and repair of flame holes in nonpremixed turbulent combustion. Computational studies of edge flames with hydrodynamic-coupling at high strains are difficult owing to difficulties defining a stationary state. A wedge-shaped counterflow configuration is here used to provide control over the position of the edge flame, and allowing access to stationary, hydrodynamically-coupled retreating flames (at low and high strains). ethylene–air edge flames are established in the resulting non-uniformly strained counterflow, with combustion modeled using a skeletal reduction of the USC Mech II. The details of the ethylene–air edge flame are discussed, and comparisons are made between stoichiometric, fuel-lean, and fuel-rich compositions. Mixture-fraction-based coordinates local to the flame front are developed and analysed for a range of edge-flame speeds and compositions. A strain-rate parameter is described that admits a speed-strain relationship that is insensitive to the mixture stoichiometry, and a model for retreating flame speeds at high strain rates is discussed.

摘要

边缘火焰是一种典型的二维火焰结构，出现在升力喷射火焰和非预混湍流燃烧中火焰孔的生长和修复中。由于难以定义静止状态，因此难以在高应变下对具有流体动力耦合的边缘火焰进行计算研究。这里使用楔形逆流配置来控制边缘火焰的位置，并允许进入静止的、流体动力耦合的后退火焰（在低应变和高应变下）。乙烯-空气边缘火焰在由此产生的非均匀应变逆流中建立，燃烧模型使用 USC Mech II 的骨架还原。讨论了乙烯-空气边缘火焰的细节，并在化学计量、贫燃料和富燃料组成之间进行了比较。针对一系列边缘火焰速度和成分，开发并分析了局部于火焰前沿的基于混合物分数的坐标。描述了一个应变速率参数，该参数允许对混合物化学计量不敏感的速度-应变关系，并讨论了在高应变速率下后退火焰速度的模型。