Combustion and Flame最新文献

A comprehensive parametric study on NO and N2O formation in ammonia-methane cofired premixed flames: Spatially resolved measurements and kinetic analysis 氨-甲烷共燃预混合火焰中 NO 和 N2O 形成的综合参数研究：空间分辨测量和动力学分析

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-16 DOI: 10.1016/j.combustflame.2024.113851

Qing Li , Liuhao Ma , Jiwei Zhou , Jintao Li , Fuwu Yan , Jianguo Du , Yu Wang

Understanding the mechanism of NOx formation and destruction is a prerequisite for the development of effective NOx mitigation techniques in ammonia flames. Laboratory-scale laminar ammonia (NH₃) flames are well suited for such fundamental kinetic studies as the complex interaction between chemistry and fluid flow can be largely decoupled. However, quantitative and spatially resolved NO/N₂O concentration data in canonical laminar ammonia flames are surprisingly scarce. Such data is, on the other hand, crucial for developing and validating kinetic models for NH₃ combustion. In this regard, we developed a novel NO/N₂O measurement method combining microprobe sampling and calibration-free mid-infrared laser absorption spectroscopy and realized spatially-resolved detection with high accuracy and large dynamic ratio. The fidelity of the method has been rigorously tested before being applied to perform a comprehensive parametric study on NO and N₂O formation in NH₃-CH₄ co-fired burner-stabilized premixed flames. The effects of NH₃ fuel ratio, equivalence ratio and flame temperature on NO/N₂O formation have been experimentally determined. Corresponding numerical modelling was also performed using literature-based mechanisms to provide kinetic insights into the experimental observations. It is found that existing mechanisms generally have satisfactory predictions in fuel-lean flames; however, under fuel-rich conditions, these mechanisms overpredict NO formation but underestimate its destruction, leading to significant over-prediction. Such discrepancies were further investigated through sensitivity and reaction pathway analysis. The present study not only provides extensive spatially-resolved NO/N₂O data in ammonia flames that are urgently needed for the development and validation of NH₃ combustion mechanisms, the comparison between neat CH₄ and NH₃-cofired flames also points to the fact that traditional NOx mitigation techniques that are popular in combustion of hydrocarbon fuels may not be appropriate in NH₃ flames. Perhaps most interestingly, the present experimental results show an oxygen-enriched oxidizer can in some cases reduce NO emission from NH₃ flames.

了解氮氧化物的形成和破坏机理是开发有效的氨火焰氮氧化物减排技术的先决条件。实验室规模的层状氨（NH3）火焰非常适合进行此类基础动力学研究，因为化学与流体流动之间复杂的相互作用在很大程度上可以被分离。然而，典型层状氨火焰中的定量和空间分辨 NO/N2O 浓度数据却少得令人吃惊。另一方面，这些数据对于开发和验证 NH3 燃烧动力学模型至关重要。为此，我们开发了一种新型 NO/N2O 测量方法，该方法结合了微探针采样和免校准中红外激光吸收光谱技术，实现了高精度和大动态比的空间分辨检测。在应用该方法对 NH3-CH4 共烧燃烧器稳定预混合火焰中 NO 和 N2O 的形成进行综合参数研究之前，已经对该方法的准确性进行了严格测试。实验确定了 NH3 燃料比、当量比和火焰温度对 NO/N2O 形成的影响。还利用基于文献的机制进行了相应的数值建模，以便为实验观察提供动力学见解。研究发现，现有的机理通常对燃料贫乏火焰的预测令人满意；然而，在燃料丰富的条件下，这些机理高估了 NO 的形成，却低估了其破坏，导致严重的预测过度。通过灵敏度和反应途径分析，对这种差异进行了进一步研究。本研究不仅提供了开发和验证 NH3 燃烧机制所急需的氨火焰中广泛的空间分辨 NO/N2O 数据，而且对纯 CH4 和 NH3 燃烧火焰的比较还表明，在碳氢化合物燃料燃烧中流行的传统 NOx 减缓技术可能并不适用于 NH3 火焰。也许最有趣的是，本实验结果表明富氧氧化剂在某些情况下可以减少 NH3 火焰的氮氧化物排放。

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引用次数: 0

Elucidating high-pressure chemistry in acetylene oxidation: Jet-stirred reactor experiments, pressure effects, and kinetic interpretation 阐明乙炔氧化过程中的高压化学反应：喷射搅拌反应器实验、压力效应和动力学解释

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-15 DOI: 10.1016/j.combustflame.2024.113835

Qian-Peng Wang , Jing Yang , Yu-Feng Xu , Zi-Qiang Zhu , Ling-Nan Wu , Jiu-Jie Kuang , Du Wang , Marina Braun-Unkhoff , Zhen-Yu Tian

Acetylene plays a crucial role as an intermediate in the combustion of complex hydrocarbons, such as, e.g., jet fuels. In this study, high-pressure acetylene oxidation has been investigated by a combination of kinetic and experimental methods using a jet-stirred reactor (JSR) in the range of 497–910 K at p = 24 atm. The study covered three fuel-equivalence ratios: φ = 0.5 (fuel-lean), φ = 1.0 (stoichiometric), and φ = 3.0 (fuel-rich). Mole fraction profiles of 10 species, including CO, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, CH₃OH, CH₃CHO, and C₃H₄O, were identified and quantified using gas chromatography (GC) and gas chromatography-mass spectrometry (GC–MS). A kinetic model for describing the high-pressure chemistry of acetylene oxidation is proposed, which well characterizes important experimental findings, such as the fuel oxidation reactivity and the speciation of crucial products. At high pressures (p = 24 atm), acetylene exhibits a higher fuel consumption than at lower pressures (p = 1 and 12 atm) because of the increased sensitivity of dehydrogenation reactions by OH radicals accelerating the oxidation of the fuel at low temperatures. Furthermore, fuel-specific intermediates are observed, including acetaldehyde, propanal, small alkanes, and alkenes. These species mainly result from H-abstraction reactions by OH following O₂-addition reactions from triple carbon bond moieties in acetylene. The formation of further products, such as carbon monoxide and carbon dioxide, is closely related to the consumption of these fuel-specific species. In particular, the formation of aromatics, such as e.g., benzene and toluene, are detected at trace levels in the current experiments due to the rapid formation and decomposition process occurring at high pressures. By analyzing the distinct kinetic behavior, it was found that acetylene was almost completely depleted at higher system pressure (p = 24 atm). Some intermediates are rather active and can react with O₂ and peroxides. Consequently, the high-pressure oxidation of acetylene mainly proceeds along the pathway of CC → CHCHOH → HOCHO/OCHCHO → CO → CO₂ at the high-pressure chemistry (p = 24 atm). Overall, this study provides valuable insights into the pressure-dependent combustion behavior of acetylene and its implications for optimizing jet fuel combustion processes.

乙炔在复杂碳氢化合物（如喷气燃料）的燃烧过程中作为中间体起着至关重要的作用。本研究结合动力学和实验方法，使用喷射搅拌反应器（JSR）在 497-910 K、p = 24 atm 的条件下对高压乙炔氧化进行了研究。研究涵盖了三种燃料当量比：φ = 0.5（燃料贫乏）、φ = 1.0（化学计量）和φ = 3.0（燃料丰富）。利用气相色谱法（GC）和气相色谱-质谱法（GC-MS）对 CO、CO2、CH4、C2H4、C2H6、C3H6、C3H8、CH3OH、CH3CHO 和 C3H4O 等 10 种物质的分子分数剖面进行了鉴定和定量。提出了一个描述乙炔氧化高压化学反应的动力学模型，该模型很好地描述了重要的实验发现，如燃料氧化反应性和关键产物的种类。在高压（p = 24 atm）下，乙炔的燃料消耗量高于低压（p = 1 和 12 atm）下的燃料消耗量，这是因为在低温下，加速燃料氧化的 OH 自由基提高了脱氢反应的敏感性。此外，还观察到燃料特有的中间产物，包括乙醛、丙醛、小烷烃和烯烃。这些物质主要是乙炔中的三碳键分子发生 O2-加成反应后，OH 发生 H-萃取反应产生的。一氧化碳和二氧化碳等其他产物的形成与这些燃料特有物质的消耗密切相关。特别是，在目前的实验中，由于在高压下发生的快速形成和分解过程，在痕量水平上检测到了芳烃的形成，如苯和甲苯。通过分析不同的动力学行为，发现乙炔在较高的系统压力（p = 24 atm）下几乎完全耗尽。一些中间产物相当活跃，可以与氧气和过氧化物发生反应。因此，在高压化学反应（p = 24 atm）中，乙炔的高压氧化主要沿着 CC → CHCHOH → HOCHO/OCHCHO → CO → CO2 的路径进行。总之，这项研究为了解乙炔随压力变化的燃烧行为及其对优化喷气燃料燃烧过程的影响提供了宝贵的见解。

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引用次数: 0

Simultaneous Schlieren and direct photography of detonation diffraction regimes in hydrogen mixtures 同时拍摄氢气混合物中的席里伦衍射和直接拍摄引爆衍射机制

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-15 DOI: 10.1016/j.combustflame.2024.113845

Jacob Klein, Omid Samimi-Abianeh

The diffraction behavior of gaseous detonations through an abrupt area change is investigated using hydrogen-oxygen-nitrogen mixtures at initial pressures of 0.5 and 1.0 bar. Critical conditions are noted and detailed discussion of the differing diffraction behaviors is undertaken, supported by simultaneous Schlieren and direct photography imaging as well as pressure-based velocity measurements. The experiments reveal four distinct diffraction regimes. The subcritical outcome is characterized by transmission failure with the leading shock front decoupling from the reaction zone, seen predominantly at lower oxygen concentrations. At intermediate oxygen levels, reinitiation from reflected shock waves is consistently observed. The critical regime exhibits both subcritical and supercritical outcomes, with detonation reinitiation at the diffraction dome's head leading to localized implosions for the supercritical case. Supercritical outcomes demonstrate successful detonation transmission, maintaining the shock front and reaction zone coupling. The effects of initial conditions on the probability of successful detonation transition and diffraction are highlighted. With the use of simultaneous direct photography and Schlieren imaging techniques, previously unseen details of the detonation and diffraction processes are recorded and explained.

利用初始压力为 0.5 和 1.0 巴的氢-氧-氮混合物，研究了气态爆炸通过突然的面积变化产生的衍射行为。实验注意到了临界条件，并对不同的衍射行为进行了详细讨论，同时辅以 Schlieren 和直接摄影成像以及基于压力的速度测量。实验揭示了四种不同的衍射机制。亚临界结果的特点是传输失效，主导冲击前沿与反应区脱钩，主要出现在氧气浓度较低的情况下。在中等氧气浓度下，可持续观察到反射冲击波的重新启动。临界机制表现出亚临界和超临界两种结果，在超临界情况下，衍射穹顶头部的起爆再引发导致局部内爆。超临界结果展示了成功的爆炸传播，保持了冲击前沿和反应区的耦合。初始条件对成功引爆转换和衍射概率的影响得到了强调。利用同步直接摄影和 Schlieren 成像技术，记录并解释了以前从未见过的起爆和衍射过程的细节。

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引用次数: 0

Ab initio intermolecular interactions mediate thermochemically real-fluid effects that affect system reactivity: The first application of high-order Virial EoS and first-principles multi-body potentials in trans-/super-critical autoignition modelling Ab initio 分子间相互作用介导了影响系统反应性的热化学真实流体效应：在跨/超临界自燃建模中首次应用高阶维里尔方程和第一原理多体势垒

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-14 DOI: 10.1016/j.combustflame.2024.113844

Mingrui Wang , Ruoyue Tang , Xinrui Ren , Yanqing Cui , Molly Meng-Jung Li , Shao-Yuan Leu , Carol Sze Ki Lin , Song Cheng

The properties of supercritical fluids are dictated by intermolecular interactions that involve two or more molecules. Such intermolecular interactions were described via intermolecular potentials in historical supercritical combustion modeling studies, but have been treated empirically and with no consideration of radical interactions or multi-body interactions involving more than two molecules. This approach has been adopted long ago, assuming sufficient characterization of real-fluid effects during supercritical combustion. Here, with data from ab initio multi-body intermolecular potentials, non-empirical high-order Virial Equation of State (EoS), and real-fluid thermochemical and kinetic simulations, we reveal that empirical intermolecular potentials can lead to significant errors in representing supercritical fluids under common combustion situations, which can be impressively described by ab initio intermolecular potentials. These interactions are also found to greatly influence autoignition delay times, a common measure of global reactivity, with significant contributions from radical interactions and multi-body interactions. It is therefore of necessity to incorporate ab initio intermolecular interactions in studying supercritical combustion and various dynamic systems involving supercritical fluids, which has now been enabled through the new framework developed in the present study.

超临界流体的特性由涉及两个或两个以上分子的分子间相互作用决定。在以往的超临界燃烧建模研究中，这种分子间相互作用是通过分子间势能来描述的，但一直是根据经验来处理的，没有考虑到涉及两个以上分子的自由基相互作用或多体相互作用。这种方法很早以前就被采用了，因为它假定了超临界燃烧过程中真实流体效应的充分特征。在这里，我们利用来自非经验高阶维氏状态方程（EoS）、非经验多体分子间势能以及真实流体热化学和动力学模拟的数据，揭示了经验分子间势能在表示常见燃烧情况下的超临界流体时可能会导致重大误差，而非经验分子间势能可以很好地描述超临界流体。研究还发现，这些相互作用会极大地影响自燃延迟时间，而自燃延迟时间是衡量全局反应性的常用指标，其中自由基相互作用和多体相互作用贡献巨大。因此，在研究超临界燃烧和涉及超临界流体的各种动态系统时，有必要纳入非初始分子间相互作用。

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引用次数: 0

A Bayesian approach to estimate flame spread model parameters over the cylindrical PMMA samples under various gravity conditions 用贝叶斯方法估算各种重力条件下圆柱形 PMMA 样品上的火焰蔓延模型参数

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-14 DOI: 10.1016/j.combustflame.2024.113828

Shinji Nakaya , Taro Takemata , Yuxuan Ma , Fangsi Ren , Mitsuhiro Tsue

<div><div>The flammability limit of cylindrical polymethyl-methacrylate (PMMA) samples in an opposed-flow was observed experimentally under various gravity levels at 1<span><math><mi>G</mi></math></span> or more utilizing a centrifuge. Flame spread on the sample was observed, and the limiting oxygen concentration (LOC) was measured in various opposed-flow velocities ranging from 5 to 30 cm/s. Two rotating radii of the centrifuge were tested to assess the effects of Coriolis force on the LOC. A scale analysis model, based on an energy balance equation, was evaluated for thermally thick cylindrical samples. The buoyancy-induced flow was modeled in the analytical model. Model parameters were evaluated with a Bayesian approach: The Metropolis Hasting (a Markov Chain Monte Carlo) method. The results indicated that flames were tilted by the Coriolis force when the oxygen concentration was sufficiently rich from the LOC in 4<span><math><mi>G</mi></math></span>. However, the effects were negligible under the oxygen concentration conditions near LOC. No significant difference in the LOC was also observed even when the rotating radius of the centrifuge changed. At 1<span><math><mi>G</mi></math></span> or higher, the LOC approached to a certain value asymptotically with decreasing the opposed-flow velocity. The LOC also increased with increasing the gravity level and sample diameter. The measured LOCs were used to sample model parameters using MCMC methods. Consequently, a suitable fitting curve of the model to the experimental LOC was obtained. Using the predicted model parameters, the LOC under microgravity, Moon, and Mars conditions were predicted as a function of the opposed-flow velocity. In microgravity, the LOC increased greatly with decreasing the forced flow velocity (the radiative extinction regime), and the minimum LOC (MLOC) was recognized. On Moon, the credible interval of LOC was rather large in the low-velocity region, and the MLOC was also recognized. Moreover, it was possible that the cylindrical PMMA sample exhibited the highest flammability not under microgravity but a partial gravity condition.</div><div><strong>Novelty and Significance</strong></div><div>From observing the limiting oxygen concentration of the flammability limit for cylindrical polymethyl-methacrylate (PMMA) samples in opposed-flows under various gravity conditions, we developed a model of limiting oxygen concentration (LOC) for thick cylindrical samples with the buoyancy induced flow was developed, and we estimated difficult-to-predict parameters using Bayesian statistical methods. Using this model, we can estimate the flammability limits under various gravity conditions of manned space exploration, including Moon and Mars. In addition, the present study shows that the minimum limiting oxygen concentration (MLOC) is the lowest in partial gravity. These results open a new research field for partial gravity combustions, apart from the normal gravity and microgravity and c

利用离心机在 1G 或更高的重力水平下，对圆柱形聚甲基丙烯酸甲酯（PMMA）样品在对流下的可燃性极限进行了实验观察。观察了样品上的火焰蔓延情况，并测量了在 5 至 30 厘米/秒的不同对流速度下的极限氧浓度（LOC）。测试了离心机的两个旋转半径，以评估科里奥利力对 LOC 的影响。根据能量平衡方程，对热厚圆柱形样品的比例分析模型进行了评估。在分析模型中对浮力引起的流动进行了建模。模型参数采用贝叶斯方法进行评估：Metropolis Hasting（一种马尔可夫链蒙特卡罗）方法。结果表明，当氧气浓度与 4G 中的 LOC 相比足够丰富时，火焰会因科里奥利力而倾斜。然而，在氧气浓度接近 LOC 的条件下，这种影响可以忽略不计。即使离心机的旋转半径发生变化，LOC 也没有明显差异。在 1G 或更高的重力条件下，随着对流速度的降低，LOC 逐渐接近某一值。LOC 也随着重力水平和样品直径的增加而增加。测量的 LOC 被用于使用 MCMC 方法对模型参数进行采样。因此，得到了模型与实验 LOC 的合适拟合曲线。利用预测的模型参数，预测了微重力、月球和火星条件下的 LOC 与对流速度的函数关系。在微重力条件下，随着强制流速的降低（辐射消光机制），LOC 大大增加，并确认了最小 LOC（MLOC）。在月球上，低流速区域的 LOC 可信区间相当大，也确认了 MLOC。新颖性和意义通过观察圆柱形聚甲基丙烯酸甲酯（PMMA）样品在不同重力条件下对向流动的可燃性极限氧浓度，我们建立了浮力诱导流动下厚圆柱形样品的极限氧浓度（LOC）模型，并使用贝叶斯统计方法估算了难以预测的参数。利用该模型，我们可以估算载人太空探索（包括月球和火星）各种重力条件下的可燃性极限。此外，本研究还表明，在部分重力条件下，最低极限氧浓度（MLOC）是最低的。这些结果为除正常重力和微重力之外的部分重力燃烧开辟了一个新的研究领域，有助于人们了解月球和火星载人太空探索的消防安全。

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引用次数: 0

Inhibition of the oblique detonation wave detachment in two-phase n-heptane/air mixtures 抑制正庚烷/空气两相混合物中的斜向爆轰波脱落

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-14 DOI: 10.1016/j.combustflame.2024.113843

Hongbo Guo , Yue Sun , Ruixuan Zhu , Shuo Wang , Majie Zhao , Baolu Shi , Xiao Hou

In this work, oblique detonation wave propagations in n-heptane droplet/vapor/air mixtures induced by a wedge at high altitude and Mach number are simulated by the Eulerian-Lagrangian method with a skeletal chemical mechanism. This work is a first attempt to inhibit the detachment of oblique detonation wave (ODW) and expand the operation range of thrusters based on oblique detonation combustion in partially pre-vaporized n-heptane/air mixtures. Effects of gas/liquid equivalence ratios and droplet diameters are considered, and the ODW morphology is analyzed. Standing windows, ODW characteristics and predictability of detachment inhibition are discussed. First, the detonation theoretical calculation is performed at 25–40 km operation conditions for pure gas n-heptane/air mixtures. The results show that the wedge angle range for successful ignition, i.e., standing window, increases with the increase of flight altitude and Mach number. The internal energy and kinetic energy of mixtures are affected by the wedge angle and flight Mach number, so that the maximum angle of ODW with flight conditions presents an opposite trend over or below Mach 10. The two-dimensional (2D) ODWs in our simulation scope, which are triggered by the collision of the initiation zones formed from the wedge, show a multi-wave head structure similar to normal detonation. Detachment is inhibited in partially pre-vaporized n-heptane/air mixtures, due to the non-explosive mixtures near triple-point and the post-ODW inter-phase mass and energy transfers by the latent heat absorption and vapor addition from droplet evaporation. Moreover, the predictability of pre-vaporized n-heptane on inhibiting ODW detachment is explored through the relationship of chemical and evaporation timescales. It is demonstrated that the excitation time is very small approaching the detachment condition where an abrupt ODW tends to form. Accordingly, when the ratio of droplet heat absorption time to evaporation time is relatively high, i.e., τ_h / (τ_ev)^1/2 > 0.01, the ODW detachment is more likely to be inhibited.

在这项工作中，利用欧拉-拉格朗日方法和骨架化学机制，模拟了在高海拔和高马赫数下由楔子诱发的正庚烷液滴/蒸汽/空气混合物中的斜爆轰波传播。这项工作首次尝试抑制斜爆波（ODW）的脱离，并扩大了基于部分预汽化正庚烷/空气混合物中斜爆燃烧的推进器的工作范围。考虑了气/液当量比和液滴直径的影响，并分析了 ODW 形态。讨论了驻留窗口、ODW 特性和脱离抑制的可预测性。首先，对纯气体正庚烷/空气混合物在 25-40 km 运行条件下进行了爆轰理论计算。结果表明，成功点火的楔角范围，即驻留窗口，随着飞行高度和马赫数的增加而增大。混合物的内能和动能受楔角和飞行马赫数的影响，因此 ODW 的最大角度与飞行条件呈相反趋势，超过或低于 10 马赫。在我们的模拟范围内，二维（2D）ODWs 由楔形形成的起爆区碰撞触发，显示出与正常起爆类似的多波头结构。在部分预汽化的正庚烷/空气混合物中，由于三重点附近的非爆炸性混合物以及ODW后相间的质量和能量转移（由液滴蒸发产生的潜热吸收和蒸汽添加），分离受到抑制。此外，还通过化学和蒸发时间尺度的关系，探讨了预蒸发正庚烷对抑制 ODW 脱离的可预测性。结果表明，在接近分离条件时，激发时间非常小，在此条件下往往会形成突然的 ODW。因此，当液滴吸热时间与蒸发时间之比相对较高时（即 τh / (τev)1/2 > 0.01），ODW 脱离更容易受到抑制。

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引用次数: 0

Effects of the inflow total temperature on the non-premixed rotating detonation engine performances 流入总温度对非预混旋转爆轰发动机性能的影响

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-14 DOI: 10.1016/j.combustflame.2024.113726

Zhenyi Chen , Sihang Rao , Jian Peng , Xu Xu

As a promising propulsion system, air-breathing rotating detonation engines (RDEs) are investigated with significant interest recently. However, simulations of air-breathing RDE with real flight condition are limited, and performance of RDEs with high inflow total temperature, as well as the influence of inflow total temperature on RDEs, needs further exploration. In this paper, simulations with four inflow total temperatures (300 K, 500 K, 700 K and 900 K) were conducted to analyze the propagation features of rotating detonation waves (RDWs) and operation modes in the RDE at low and high inflow total temperatures. Additionally, injection and mixing, as well as combustion characteristics and propulsion performance of the RDE were researched. It is found that with low inflow total temperature, single wave propagates in the combustor, which degenerates into shock wave at the outer wall due to insufficient mixing. When inflow total temperature is high, the RDE is in multi-wave operation mode and detonative combustion only occurs around the outer wall. With increase of inflow total temperature, mixability of reactants initially improves but then deteriorates slightly. Moreover, RDW propagation velocity and specific impulse of the RDE decrease. Though fuel utilization rate improves, detonation fraction drops dramatically and parasitic combustion fraction rises significantly, resulting from intensification of pre-combustion. Particularly, the detonation fraction is only 16.7 % and parasitic combustion fraction reaches up to 56.35 % at inflow total temperature of 900 K. Furthermore, regardless of the variation of inflow total temperature, detonative combustion is prominent in the premixed combustion mode, and the peak fraction of detonation appears at the off-stoichiometric ratio.

作为一种前景广阔的推进系统，空气喷气旋转爆轰发动机（RDE）近来受到了广泛关注。然而，实际飞行条件下的喷气式 RDE 模拟有限，高流入总温下的 RDE 性能以及流入总温对 RDE 的影响有待进一步探讨。本文对四种流入总温度（300 K、500 K、700 K 和 900 K）进行了模拟，分析了低流入总温度和高流入总温度下旋转爆轰波（RDW）的传播特征以及在 RDE 中的运行模式。此外，还研究了 RDE 的喷射和混合以及燃烧特性和推进性能。研究发现，流入总温度低时，单波在燃烧器内传播，由于混合不充分，单波在外壁退化为冲击波。当流入总温度较高时，RDE 处于多波运行模式，爆燃只发生在外壁周围。随着流入气流总温度的升高，反应物的混合性最初有所改善，但随后略有恶化。此外，RDW 传播速度和 RDE 的比冲都有所下降。虽然燃料利用率提高了，但爆燃率却急剧下降，而且由于预燃烧加剧，寄生燃烧率显著上升。特别是在流入总温度为 900 K 时，爆燃率仅为 16.7%，寄生燃烧率高达 56.35%。此外，无论流入总温度如何变化，预混合燃烧模式下的爆燃现象都很突出，爆燃峰值出现在非计量比时。

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引用次数: 0

Coupling regimes of premixed laminar flames with thermal radiation absorption in fresh gases. Application to H2O-/CO2-diluted mixtures 新鲜气体中预混合层流火焰与热辐射吸收的耦合机制。在 H2O-/CO2 稀释混合物中的应用

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-12 DOI: 10.1016/j.combustflame.2024.113830

J. Ben Zenou, R. Vicquelin

<div><div>In the context of decarbonizing industry and transportation, the combustion of hydrogen and oxycombustion of methane play a pivotal role. Hydrogen combustion can use steam (H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O) to mitigate pollutant emissions, while methane’s oxycombustion involves recirculating burnt gases (EGR or Exhaust Gas Recirculation process), particularly CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>. This paper investigates the complex role of thermal radiation in premixed laminar flames, in particular in such H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> <img>Air<img>H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O and CH<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span> <img>O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> <img>CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> mixtures. It highlights how radiation assumes a significant role in flames diluted with radiative participating gases, through both emission and reabsorption. The main objective is to achieve a comprehensive physical understanding of the coupling between thermal radiation and combustion, examining its effects on flame structure and burning velocity and how it varies with different parameters (equivalence ratio, dilution level, pressure, and domain size). The study employs detailed 1D premixed laminar flame simulations by coupling a fluid and a radiative solver. Both a grey gas approximation for preliminary understanding and realistic radiative gas properties (CK model) are considered. Coupling numbers derived from characteristic time ratios for convection, chemistry, and radiation, are presented. These metrics facilitate the classification of radiation-combustion coupling into three distinct regimes that represent distinct qualitative physical phenomena. The regimes are defined as follows: <em>WeakAbs</em>, where the effects of thermal radiation absorption are minor; <em>RadConv</em>, where thermal radiation competes with convection in the fresh and burnt gases but does not interact directly with chemistry within the flame front; and <em>RadChem</em>, where thermal radiation also competes with chemistry within the flame front. For the investigated conditions in both H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> and CH<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span> flames, thermal radiation also quantitatively alters the flame speed, with an acceleration that can be significant. Furthermore, the paper presents an iterative two-layer model to efficiently estimate the impact of thermal radiation on flames, which shows high accuracy except in the <em>RadChem</em> regime. Lastly, it introduces a predictive model that quickly determines a flame’s coupling regime using only an adiabatic simul

在工业和运输业去碳化的背景下，氢气燃烧和甲烷富氧燃烧发挥着举足轻重的作用。氢气燃烧可以利用蒸汽（H2O）来减少污染物排放，而甲烷的富氧燃烧则涉及燃烧气体的再循环（EGR 或废气再循环过程），尤其是二氧化碳。本文研究了热辐射在预混合层流火焰中的复杂作用，特别是在 H2 AirH2O 和 CH4 O2 CO2 混合物中。它强调了辐射是如何通过发射和再吸收两种方式在被辐射参与气体稀释的火焰中发挥重要作用的。研究的主要目的是全面了解热辐射与燃烧之间的物理耦合，研究其对火焰结构和燃烧速度的影响，以及如何随不同参数（当量比、稀释程度、压力和域尺寸）而变化。研究通过耦合流体和辐射求解器，采用了详细的一维预混层流火焰模拟。既考虑了用于初步理解的灰色气体近似，也考虑了现实的辐射气体特性（CK 模型）。介绍了根据对流、化学和辐射的特征时间比得出的耦合数。这些指标有助于将辐射-燃烧耦合分为代表不同定性物理现象的三种截然不同的状态。这三种状态的定义如下弱吸收（WeakAbs），热辐射吸收的影响较小；辐射对流（RadConv），热辐射与新鲜气体和燃烧气体中的对流竞争，但不直接与火焰前沿内的化学反应相互作用；辐射化学（RadChem），热辐射也与火焰前沿内的化学反应竞争。在所研究的 H2 和 CH4 火焰条件下，热辐射也会定量改变火焰速度，其加速度可能很大。此外，论文还提出了一种迭代双层模型，用于有效估算热辐射对火焰的影响，该模型除在 RadChem 体系外均显示出很高的准确性。最后，论文介绍了一种预测模型，该模型仅使用绝热模拟就能快速确定火焰的耦合机制，有助于决定在预混合稀释火焰模拟中忽略、近似或完全整合辐射。

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引用次数: 0

Real-fluid effects on laminar premixed hydrogen flames under cryogenic and high-pressure conditions 低温和高压条件下层流预混合氢火焰的实际流体效应

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-12 DOI: 10.1016/j.combustflame.2024.113837

Ziting Lv , Hanzhang Cao , Wang Han , Lijun Yang

<div><div>The combustion of hydrogen (H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>) under cryogenic and high-pressure conditions has the potential to increase the volume-based energy density of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> and combustion efficiency. Predictive modeling of cryogenic H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> premixed flames at high pressures requires a clear understanding of real-fluid effects. While substantial effort has been made to study the real-fluid effects in nonpremixed flames, comparatively fewer investigations have been performed to explore real-fluid effects on premixed flames, especially at cryogenic and high-pressure conditions. This work aims to fill a part of this gap by conducting a series of laminar premixed H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> flame simulations at cryogenic and high-pressure conditions (<span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mi>u</mi></mrow></msub><mo>=</mo><mn>50</mn></mrow></math></span>–350K and <span><math><mrow><mi>p</mi><mo>=</mo><mn>10</mn><mo>,</mo><mspace></mspace><mn>20</mn><mo>,</mo><mspace></mspace><mn>40</mn></mrow></math></span> MPa). Four cases are considered to examine the role of corrections of the equation of state (EOS), thermodynamic properties, and transport properties in predicting flame structure and properties. It is found that the real-fluid effects mainly occur in the fresh/preheat regions and that the correction of EOS plays a critical role in the prediction of flame structure and the laminar flame speed (<span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></math></span>), while the correction of transport properties is critical for predicting flame thickness. Each correction could contribute to the predictions of the mass burning rate and the flame thickness but hardly affect the flame temperature (less than 1% relative difference). A scaling law of <span><math><mrow><msubsup><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow><mrow><mi>Real</mi></mrow></msubsup><mo>/</mo><msubsup><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow><mrow><mi>Ideal</mi></mrow></msubsup><mo>=</mo><msub><mrow><mi>Z</mi></mrow><mrow><mi>u</mi></mrow></msub></mrow></math></span> (<span><math><msub><mrow><mi>Z</mi></mrow><mrow><mi>u</mi></mrow></msub></math></span> is the compressibility factor of the unburned mixture) is proposed, which can be used to readily predict <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></math></span> of real fluid from the speed evaluated by the ideal gas model. In addition, the Monte Carlo sampling method is used to perform uncertainty quantification of S<span><math><msub><mrow></mrow><mrow><mi>L</mi></mrow></msub></math></span> due to the uncertainty of the real-fluid model parameters. The results show that the critical properties of H<span><

在低温和高压条件下燃烧氢气（H2）有可能提高氢气的体积能量密度和燃烧效率。要对低温高压条件下的氢气预混合火焰进行预测建模，就必须清楚地了解实际流体效应。虽然研究非预混合火焰中实际流体效应的工作已经做了大量努力，但探索预混合火焰实际流体效应的研究相对较少，尤其是在低温和高压条件下。本研究旨在通过在低温和高压条件下（Tu=50-350 K 和 p=10,20,40 MPa）进行一系列层状预混 H2 火焰模拟，填补部分空白。研究考虑了四种情况，以检验状态方程（EOS）、热力学特性和传输特性的修正在预测火焰结构和特性方面的作用。研究发现，实际流体效应主要发生在新鲜/预热区域，EOS 修正在预测火焰结构和层流火焰速度（SL）方面起着关键作用，而传输特性修正对预测火焰厚度至关重要。每种修正都有助于预测质量燃烧速率和火焰厚度，但几乎不影响火焰温度（相对差异小于 1%）。提出了 SLReal/SLIdeal=Zu （Zu 为未燃烧混合物的压缩系数）的比例定律，可用于根据理想气体模型评估的速度轻松预测实际流体的 SL。此外，还采用蒙特卡罗采样法对由于实际流体模型参数的不确定性而导致的 SL 进行了不确定性量化。结果表明，H2 的临界特性对 SL 的不确定性有影响，但总体相对偏差小于 2%，且随着未燃烧混合物温度的升高，不确定性显著减小。新颖性和意义声明本研究通过考虑不同程度的真实流体修正，全面评估了真实流体对低温和高压条件下层状预混合 H2/O2 火焰的影响。我们强调了修正传输特性对预测火焰厚度的重要意义。我们首次提出了真实流体层流火焰速度的比例定律。这项工作为我们加深了解真实流体对低温 H2 燃烧的影响迈出了基础性的一步。

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引用次数: 0

A framework for obtaining frequency-dependent stability maps to mitigate thermoacoustic instabilities 获取频率相关稳定性图以缓解热声不稳定性的框架

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame

Pub Date : 2024-11-11 DOI: 10.1016/j.combustflame.2024.113836

Hamed F. Ganji , Viktor Kornilov , Ines Lopez Arteaga , Philip de Goey , Jeroen van Oijen

This paper utilizes Cauchy’s argument principle in the frequency domain to develop novel stability maps, providing guidelines for measures which can be taken to mitigate thermoacoustic instabilities in combustion appliances. The existing approaches mainly concentrate on identifying the onset of thermoacoustic instabilities by calculating unstable frequencies and growth rates. However, they provide limited practical guidance for modifying system characteristics, especially those dependent on frequency, to achieve flame stabilization. In the present contribution, several thermoacoustic stability criteria are introduced that leverage the Cauchy’s argument principle and direct evaluation of the dispersion relation’s argument. These criteria offer deeper insights and facilitate a systematic flame stabilization process by enabling modifications to both the (passive) acoustic subsystems and/or the (active) subsystem containing the combustion processes. This approach allows for a construction and comprehensive understanding of the stability map for a given thermoacoustic system, leading to more effective guidelines to elaborate and implement the combustion system stabilization strategies. To demonstrate the practical application of this framework, two illustrative thermoacoustic systems are discussed.

Novelty and significance statement This study introduces a novel framework for assessing thermoacoustic stability.

•
It provides a method for detecting the onset of thermoacoustic instability and offers valuable insights into critical frequency ranges. This approach facilitates the identification of necessary modifications in flame and acoustic subsystems across different frequencies to achieve system stabilization.
•
This framework allows for the selection of the most suitable stability criterion based on the available combustion system’s characteristics. For example, by knowing acoustic properties in both upstream and downstream components, either the DDS or DCS criterion can generate a comprehensive, frequency-dependent stability map for flame transfer function values. This approach eliminates the need for iterative integration, differential equations, or direct solutions to dispersion relations.

本文利用频域中的柯西论证原理绘制了新的稳定性地图，为采取措施缓解燃烧设备中的热声不稳定性提供了指导。现有方法主要集中在通过计算不稳定频率和增长率来识别热声不稳定性的开始。然而，这些方法对于改变系统特性（尤其是那些依赖于频率的特性）以实现火焰稳定所提供的实际指导非常有限。本文介绍了几种热声稳定性标准，这些标准利用了柯西论证原理和对频散关系论证的直接评估。通过对（被动）声学子系统和/或包含燃烧过程的（主动）子系统进行修改，这些标准提供了更深入的见解，并促进了系统化的火焰稳定过程。通过这种方法，可以构建并全面理解特定热声系统的稳定图，从而为制定和实施燃烧系统稳定策略提供更有效的指导。为了演示该框架的实际应用，我们讨论了两个示例热声系统。新颖性和意义声明本研究介绍了一种评估热声稳定性的新框架。-它提供了一种检测热声不稳定性开始的方法，并为临界频率范围提供了有价值的见解。这种方法有助于确定在不同频率下对火焰和声学子系统进行必要的修改，以实现系统稳定。例如，通过了解上游和下游组件的声学特性，DDS 或 DCS 准则可为火焰传递函数值生成一个全面的、与频率相关的稳定图。这种方法无需迭代积分、微分方程或直接求解扩散关系。

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引用次数: 0