Abstract A numerical investigation was conducted to study ignition and the initial phases of methane combustion in a two-dimensional setup consisting of a pre- (PC) and main (MC) chamber. The effect of the wall thermal boundary condition (isothermal T w = 500 K or adiabatic), initial mixture temperature ( T u = 300 and 800 K) and equivalence ratio in the main chamber ( ϕ M C = 0.5 and 1.0) was studied. A stoichiometric mixture was used in the PC and the mixtures were initially quiescent in all cases. Flame propagation in the prechamber is affected mainly by the initial temperature, while the thermal state of the wall plays a minor role. The transient jet that is generated at the exit of the orifice connecting the two chambers creates an intense flow field with vortical structures that, depending on the initial temperature, persist for a long time or dissipate quickly affecting combustion in the main chamber. Depending on the local flow and mixing conditions close to the orifice exit, the hot jet can be broken into small kernels at low Tu or forms quickly a flame torch at hot conditions, strongly affecting ignition of the MC mixture and flame propagation in the main chamber. In the lean MC cases, the intense mixing with the stoichiometric PC mixture creates local compositions that are more favorable for ignition by the hot turbulent reactive jet that subsequently exits from the PC at a temperature that is significantly lower than the adiabatic flame temperature of the corresponding mixture. Despite the short residence time, the reactive state of the mixture is affected as it flows through the nozzle. The flame structures in the MC are described in terms of the progress variable and mixture fraction and compared to flamelet-type calculations. The local flame structure differs strongly from that of the 1-D unstrained premixed flame, particularly for the low Tu cases. The flamelet-type calculations show that ignition of the most reactive mixture is enhanced by the radicals in the hot reactive jet, while scalar dissipation rate accelerates the ignition of the whole mixture. The 2-D simulations show that ignition is significantly longer than what is predicted by the flamelet calculations.

中文翻译：

---

前室点火：初始温度和主室成分影响的探索性二维 DNS 研究

摘要 进行了数值研究以研究由预 (PC) 和主 (MC) 室组成的二维设置中甲烷燃烧的点火和初始阶段。研究了壁热边界条件（等温 T w = 500 K 或绝热）、初始混合物温度（ T u = 300 和 800 K）和主室中的当量比（ ϕ MC = 0.5 和 1.0）的影响。在 PC 中使用化学计量混合物，并且在所有情况下混合物最初都是静止的。预燃室内的火焰传播主要受初始温度的影响，而壁的热状态起次要作用。在连接两个腔室的孔口出口处产生的瞬态射流产生具有涡旋结构的强烈流场，该涡旋结构取决于初始温度，长时间持续或迅速消散，影响主燃烧室的燃烧。根据靠近孔口出口的局部流动和混合条件，热射流可以在低 Tu 下破碎成小颗粒或在热条件下迅速形成火焰火炬，强烈影响 MC 混合物的点火和主室中的火焰传播. 在稀薄 MC 的情况下，与化学计量 PC 混合物的强烈混合产生局部成分，这些成分更利于被热湍流反应射流点燃，随后在显着低于相应绝热火焰温度的温度下从 PC 中排出。混合物。尽管停留时间很短，但当混合物流过喷嘴时，混合物的反应状态会受到影响。MC 中的火焰结构根据进程变量和混合分数进行描述，并与小焰型计算进行比较。局部火焰结构与一维无应变预混火焰的结构有很大不同，特别是在低 Tu 情况下。火焰型计算表明，热反应射流中的自由基增强了最具反应性的混合物的点火，而标量耗散率加速了整个混合物的点火。二维模拟表明点火时间明显长于火焰计算所预测的时间。火焰型计算表明，热反应射流中的自由基增强了最具反应性的混合物的点火，而标量耗散率加速了整个混合物的点火。二维模拟表明点火时间明显长于火焰计算所预测的时间。火焰型计算表明，热反应射流中的自由基增强了最具反应性的混合物的点火，而标量耗散率加速了整个混合物的点火。二维模拟表明点火时间明显长于火焰计算所预测的时间。