A numerical experiment is conducted to examine the ignition of a near-flammability-limit low-Lewis-number mixture and the evolution processes of the resulting premixed flames in a circular thermally-conductive narrow channel. A diffusive-thermal model is adopted to describe the fuel mass conservation in the gas phase and energy conservation in both the gas and the channel wall. Spalding's ‘one-dimensional idealization’ approximation is introduced to simplify all these conservation equations to a two-dimensional form over the plane parallel to the wall surface of the channel. As a result, the half channel height h constitutes the primary parameter controlling the heat exchange rate between the gas and the wall, which serves as a conductive heat loss mechanism from the perspective of the gas phase. For relatively large h, following ignition at the centre of the channel by a hot ignition kernel, the resulting flame front suffers diffusive-thermal instability and quickly breaks into a number of discrete reaction cells, which propagate forward towards the boundary of the channel. When h becomes sufficiently small, the reaction cells close upon themselves and transform to ring-shaped flamelets, herein termed flame rings, a 2-D analogue of flame balls formed in 3-D unconfined space. The effects of the half channel height h on the formation and dynamics of the flame rings are examined, together with a demonstration of a possible means to manipulate the flame ring dynamics by exploiting the 2-D character of the narrow channel configuration. It is suggested that, as a simple ground-based buoyancy-suppression strategy, the presently considered narrow channel configuration can be conveniently employed to study the properties related to the flammability limit of combustible mixtures.

进行数值实验以检查接近可燃极限的低刘易斯数混合物的点火以及由此产生的预混火焰在圆形导热窄通道中的演变过程。采用扩散热模型来描述气相中的燃料质量守恒和气体和通道壁中的能量守恒。引入 Spalding 的“一维理想化”近似以在平行于通道壁表面的平面上将所有这些守恒方程简化为二维形式。因此，半通道高度h构成控制气体与壁面热交换率的主要参数，从气相的角度作为传导热损失机制。对于相对较大的h，在通道中心被热点火核点燃后，由此产生的火焰前沿遭受扩散热不稳定性并迅速分裂成许多离散的反应单元，这些反应单元向前传播到通道的边界。当h变得足够小时，反应池自身闭合并转变为环形小火焰，本文称为火焰环，是在 3-D 无限制空间中形成的火焰球的 2-D 类似物。半通道高度h 的影响研究了火焰环的形成和动力学，并展示了通过利用窄通道配置的二维特性来操纵火焰环动力学的可能手段。建议作为一种简单的地面浮力抑制策略，目前考虑的窄通道配置可以方便地用于研究与可燃混合物的可燃性极限相关的特性。