掺氢甲烷燃烧利用对于碳中和战略具有重要意义，但目前对中高强度低氧稀释(MILD)条件下掺氢甲烷在射流混合边界层内的各种湍流燃烧临界现象和局部模式认知依然不足。本文采用高阶精度的DNS模拟，研究了MILD条件下纯甲烷以及掺氢甲烷的湍流射流混合与燃烧机理。发现在甲烷中仅掺入5%氢气就能大大缩短甲烷的着火延迟时间，随着氢气添加量的进一步增加，氢气对均质着火延迟时间的影响减弱。在MILD条件下的射流边界层中，初始着火核心发生在ξ=0.1~0.3的范围内；随后火核以缓燃波的形式向外侧贫燃区域内传播，引燃当地的自着火反应、继而并形成第二个着火核心，其位置位于ξ<0.05的区域内。与理想的均质着火相比，纯甲烷湍流着火延迟时间明显缩短，是由于早期着火提前以及随后的缓燃波传播加速。在整体燃烧过程中，由于氧气浓度稀薄，总体呈现出非预混燃烧状态，且处在富燃状态，整个燃烧过程的温度分布较均匀，无明显的高温区域。

The combustion utilization of methane-hydrogen is of great significance for carbon neutrality, however the understanding nowadays on the critical phenomena and local modes of methane-hydrogen turbulent jet-mixing flames under the mediate-high intensity low-oxygen dilution combustion (MILD) condition is still insufficient. This paper studies combustion mechanisms of pure methane and hydrogen-blended methane in turbulent jet mixing layer under MILD condition by DNS simulation. It is found that the ignition delay time of methane can be greatly reduced if only 5% hydrogen is added to methane, and the effectiveness of hydrogen addition is mitigated with further increment. In the MILD jet mixing layer, the initial ignition kernel occurs in the fuel-rich region ξ=0.1~0.3, and then the initial reaction core propagates to the outer lean region by the deflagration wave, triggering the local spontaneous ignition reaction and forming the second flame kernel that is located in the region ξ<0.05. Compared with the ideal homogeneous ignition, the pure methane ignition delay time in turbulence is significantly shortened due to the advancement of early ignition event and speed-up of the subsequent deflagration propagation wave. Due to the dilution of oxygen concentration, the MILD combustion process exhibits behaviors of non-premixed combustion with fuel-rich premixedness, more uniform temperature distribution, and the absence of high temperature region.

TK4