The role of low/high- temperature chemistry in computationally reproducing flame stabilization modes of hydrogen-fueled supersonic combustion

IF 5.8 2区工程技术 Q2 ENERGY & FUELS Combustion and Flame Pub Date : 2024-09-21 DOI:10.1016/j.combustflame.2024.113711

Kun Wu , Peng Zhang , Riccardo Malpica Galassi , Xuejun Fan

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Abstract

Numerical simulations of two typical flame stabilization modes in a cavity-assisted supersonic combustor were performed using improved delay detached eddy simulation and three hydrogen oxidation mechanisms with different levels of fidelity. The simulation results with Burke's detailed mechanism agree well with the experimental measurements in terms of flame morphology and wall pressure, in both jet-wake and cavity flame modes. The comparative study shows that, lacking necessary intermediate species, Eklund's reduced mechanism and Marinov's global mechanism incorrectly yield jet wake stabilization mode under low inflow stagnation temperature $T_{0}$ . Through computational singular perturbation analysis, a sequential radical triggering mechanism was identified for flame stabilization, wherein the reaction R1: $H + O_{2} = O + O H$ dominates in fuel jet wake forming OH and O radicals, the reaction R2: $H_{2} + O = H + O H$ controls the reaction between H₂ and O forming the OH radical pool, and then the heat release completes via R3: $H_{2} + O H = H + H_{2} O$ . However, their activation differs in the two stabilization modes. The role of transport is key in the cavity flame mode, where the colder stream inhibits auto-ignition in the jet wake, activating low-temperature chemistry, and delaying R2 in the cavity region. Thus, the presence of H₂O₂ and HO₂ species was found to be essential for accurately reproducing the flame stabilization in the cavity flame stabilization mode, whereas their effect is marginal in jet wake mode. In fact, the jet-wake flame stabilization is characterized by auto-ignition under high inflow stagnation temperatures, with the chain-branching reaction R2 activating in the fuel jet-wake, causing an explosive dynamic therein. These findings suggest the H₂O₂ and HO₂ species and associated low-temperature reactions are necessary for the accurate prediction of the flame stabilization mode under low $T_{0}$ , whereas their absence does not affect the prediction of the flame mode under high $T_{0}$ , in which case all three chemical mechanisms give reasonably good agreements in flame characteristics and engine overall performances.

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低温/高温化学在计算再现氢燃料超音速燃烧火焰稳定模式中的作用

利用改进的延迟分离涡模拟和三种不同逼真度的氢氧化机制，对空腔辅助超音速燃烧器中的两种典型火焰稳定模式进行了数值模拟。采用伯克详细机制的模拟结果与实验测量结果在火焰形态和壁压方面非常吻合，无论是在喷射醒焰模式还是空腔火焰模式。比较研究表明，由于缺乏必要的中间物种，埃克伦德的简化机制和马林诺夫的全局机制在低流入停滞温度 T0 下错误地产生了喷气唤醒稳定模式。通过计算奇异扰动分析，确定了火焰稳定的顺序自由基触发机制，其中反应 R1：H+O2=O+OH 在燃料喷射尾流中起主导作用，形成 OH 和 O 自由基；反应 R2：H2+O=H+OH 在燃料喷射尾流中起主导作用，形成 OH 和 O 自由基：H2+O=H+OH 控制 H2 和 O 之间的反应，形成 OH 自由基池，然后通过 R3：H2+OH=H+H2O 完成热量释放。然而，在两种稳定模式中，它们的活化作用是不同的。在空腔火焰模式中，传输的作用非常关键，较冷的气流会抑制喷射尾流中的自燃，激活低温化学反应，并延迟空腔区域中的 R2。因此，在空腔火焰稳定模式中，H2O2 和 HO2 物种的存在对于准确再现火焰稳定至关重要，而在喷气唤醒模式中，它们的作用微乎其微。事实上，喷射-唤醒火焰稳定的特点是在高流入停滞温度下自燃，燃料喷射-唤醒中的链式支化反应 R2 被激活，在其中引起爆炸动态。这些发现表明，要准确预测低 T0 下的火焰稳定模式，H2O2 和 HO2 物种及相关的低温反应是必要的，而缺少它们并不影响对高 T0 下火焰模式的预测，在这种情况下，所有三种化学机制在火焰特性和发动机整体性能方面都有相当好的一致性。

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来源期刊

Combustion and Flame 工程技术-工程：化工

CiteScore

9.50

自引率

20.50%

发文量

631

审稿时长

3.8 months

期刊介绍： The mission of the journal is to publish high quality work from experimental, theoretical, and computational investigations on the fundamentals of combustion phenomena and closely allied matters. While submissions in all pertinent areas are welcomed, past and recent focus of the journal has been on: Development and validation of reaction kinetics, reduction of reaction mechanisms and modeling of combustion systems, including: Conventional, alternative and surrogate fuels; Pollutants; Particulate and aerosol formation and abatement; Heterogeneous processes. Experimental, theoretical, and computational studies of laminar and turbulent combustion phenomena, including: Premixed and non-premixed flames; Ignition and extinction phenomena; Flame propagation; Flame structure; Instabilities and swirl; Flame spread; Multi-phase reactants. Advances in diagnostic and computational methods in combustion, including: Measurement and simulation of scalar and vector properties; Novel techniques; State-of-the art applications. Fundamental investigations of combustion technologies and systems, including: Internal combustion engines; Gas turbines; Small- and large-scale stationary combustion and power generation; Catalytic combustion; Combustion synthesis; Combustion under extreme conditions; New concepts.