Continuation computations were performed to generate the S-curve as well as the flammability limit. Transient simulations using detailed fuel chemistry and transport models were conducted to reproduce the oscillatory extinction process. It was found that the cool spherical diffusion flame (SDF) had a much extended extinction limit than the hot SDF. The cool SDF with double-reaction-zone structure had non-stoichiometric and partially premixed combustion features. Oscillation can induce extinction prior to the steady-state bifurcation point, especially for the cool flame which exhibited much stronger and more complex oscillations due to its inherent strong coupling with transports or solid boundary. The oscillatory extinction of hot dimethyl ether SDF was governed by a single-oscillatory mode, while the cool SDF extinction by dual oscillatory modes with two distinct frequencies. However, the dual oscillatory modes exhibited only inside the flame front; the high-frequency mode vanished outside the flame zone. The hot SDF oscillatory extinction was caused by competing coupling of HRR with flux mixing, i.e. oscillations will break the thermal balance by enhancing flux mixing and inhibiting heat production which further leads to flame extinguishment. However, the cool-SDF oscillations near the extinction were driven by the thermokinetic type heat production in the NTC region.

中文翻译：

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微重力条件下二甲醚球形扩散火焰的燃烧动力学及振荡消光机理

执行连续计算以生成 S 曲线以及可燃性极限。使用详细的燃料化学和传输模型进行瞬态模拟以重现振荡消光过程。结果表明，冷球形扩散火焰 (SDF) 的消光极限比热 SDF 大得多。具有双反应区结构的冷 SDF 具有非化学计量和部分预混燃烧特征。振荡可以在稳态分叉点之前引起消光，特别是对于冷火焰，由于其与输运或固体边界的固有强耦合而表现出更强和更复杂的振荡。热二甲醚 SDF 的振荡消光受单振荡模式控制，而凉爽的 SDF 消光通过具有两个不同频率的双振荡模式。然而，双振荡模式仅在火焰前沿内部表现出来；高频模式消失在火焰区之外。热 SDF 振荡消光是由 HRR 与助焊剂混合的竞争耦合引起的，即振荡将通过增强助焊剂混合和抑制热量产生来打破热平衡，从而进一步导致火焰熄灭。然而，接近灭绝的冷 SDF 振荡是由 NTC 区域的热动力学型产热驱动的。振荡将通过增强助焊剂混合和抑制热量产生来打破热平衡，这进一步导致火焰熄灭。然而，接近灭绝的冷 SDF 振荡是由 NTC 区域的热动力学型产热驱动的。振荡将通过增强助焊剂混合和抑制热量产生来打破热平衡，这进一步导致火焰熄灭。然而，接近灭绝的冷 SDF 振荡是由 NTC 区域的热动力学型产热驱动的。