Large eddy simulation (LES) of a CH₄/H₂ diffusion jet flame in hot coflow (JHC) is undertaken to find distinct behaviors of moderate or intense low oxygen dilution (MILD) combustion (MILDC), high temperature combustion (HTC), and traditional combustion (TC). These three JHC flames are realized by using different coflow temperatures and oxygen mass fractions: (1) 1300 K and 9% for MILDC; (2) 1300 K and 30% for HTC; (3) 600 K and 30% for TC. The modeling of LES combining the eddy dissipation concept (EDC) with a global four-step reaction mechanism is validated by the JHC measurements of Dally et al. (Proc. Combust. Inst.2002, 29, 1147–1154). The instantaneous and time-averaged velocities, temperatures, and species concentrations such as carbon monoxide (CO) are presented and compared for the three cases. It is demonstrated that the JHC flames of MILDC and HTC both develop from autoignition nearly immediately downstream of the nozzle exit, while the lift-off JHC flame of TC evolves from an induced-ignition with a significant delay. Manifestly, combustion reactions proceed gently in the MILDC case and highly aggressively in the TC case. In both MILDC and HTC cases, stable combustion ensues in the very near field. While most heat releases around the stoichiometric location and transfers away slowly, combustion species, for example, CO, diffuse more rapidly across the jet flow. The JHC flame for TC behaves completely differently. With a wobbling flame base, large-scale flame oscillations enhance crosswise turbulent mixing and heat transfer. Consequently, high temperatures and high CO concentrations concurrently emerge across the central region in the mid field. Besides, local extinction and reignition appear to occur frequently in the TC and do not happen in the HTC and MILDC.

中文翻译：

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在热氧化器气流中，传统的，高温的，中度或强烈的低氧稀释燃烧过程在CH ₄ / H ₂喷射火焰中的大涡模拟有什么区别？

进行了热同流（JHC）中CH ₄ / H ₂扩散射流火焰的大涡模拟（LES），以发现中等或强烈的低氧稀释（MILD）燃烧（MILDC），高温燃烧（HTC），和传统燃烧（TC）。这三种JHC火焰是通过使用不同的同流温度和氧气质量分数来实现的：（1）1300 K，MILDC为9％；（2）1300 K，HTC为30％；（3）600 K，TC为30％。通过Dally等人的JHC测量验证了结合涡流消散概念（EDC）和全局四步反应机理的LES模型。（PROC。燃烧。研究所。2002年，29，1147–1154）。给出了三种情况下的瞬时和时间平均速度，温度和物种浓度，例如一氧化碳（CO）并进行了比较。结果表明，MILDC和HTC的JHC火焰几乎都是在喷嘴出口的紧邻下游处由自燃产生的，而TC的提离JHC火焰则是由诱导点燃而产生的，并具有明显的延迟。显然，在MILDC情况下燃烧反应缓慢进行，而在TC情况下燃烧反应非常剧烈。在MILDC和HTC情况下，都在近场中实现稳定燃烧。尽管大多数热量在化学计量位置附近释放并缓慢转移，但燃烧物质（例如，CO）在喷射流中的扩散速度更快。TC的JHC火焰的行为完全不同。火焰底震颤，大范围的火焰振荡增强了横向湍流混合和热传递。因此，中场中部地区同时出现高温和高CO浓度。此外，局部灭绝和重生在TC中似乎频繁发生，而在HTC和MILDC中则不常见。