Proceedings of the Combustion Institute最新文献_第7页

Experimental investigation and optimization of ammonia–hydrogen chemical kinetics with ignition delay times from shock tubes 激波管点火延迟时间下氨氢化学动力学的实验研究与优化

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105835

Torsten Methling , Michael Pierro , Nikolas Hulliger , Justin J. Urso , Jakob Krämer , Clemens Naumann , Markus Köhler , Subith S. Vasu

A combined experimental and numerical approach investigates the ignition delay times of ammonia–hydrogen mixtures in oxygen or synthetic air measured in shock tubes under different dilutions with argon and nitrogen. A series of novel ignition delay time measurements is presented for stoichiometric fuel–air mixtures diluted 1:10 and 1:5 in argon as well as 1:2 in nitrogen at the shock tube facility of the German Aerospace Center (DLR). The initialized gas conditions behind the reflected shock waves range between 940–2200 K and 4–16 bar. Additionally, recent ignition delay time determinations of fuel–air mixtures without subsequent dilution from the shock tube facility of the University of Central Florida (UCF) are reevaluated. Experimental data sets are analyzed with the application of multiple chemical kinetic models. The study reveals deficiencies in the modeling of fuel-oxidizer mixtures with relatively low dilution, representative for real combustion applications. To improve the chemical kinetic modeling capabilities, the reaction model DLR Concise is updated with new insights from literature. Subsequently, the updated model is optimized with the new experimental data and additional data on ignition delay times available from literature. 373 ignition delay times of ammonia and its mixture with hydrogen are targeted for the optimization. The linear transformation model is applied to optimize the most sensitive N-chemistry reactions within their uncertainties. The new experimental data from DLR confirm the observed deviations between the reevaluated experimental data from UCF and established chemical kinetic models. The updated and optimized DLR Concise models are resolve these modeling deficiencies and consistently reproduce the new and reevaluated data from both shock tube facilities. The optimized reaction model consistently reproduces the complete targeted experimental data with a broad range of initial temperature, pressure and mixture boundary conditions. Thus, the model can reliably be applied for numerical investigations of internal combustion engine ignition processes.

采用实验与数值相结合的方法，研究了激波管内不同稀释度氩气和氮气条件下氨氢混合物在氧气或合成空气中的点火延迟时间。在德国航空航天中心（DLR）的激波管装置中，对1:10和1:5氩气和1:2氮气稀释的化学计量燃料-空气混合物进行了一系列新的点火延迟时间测量。反射冲击波后初始化气体条件范围为940 ~ 2200k， 4 ~ 16bar。此外，重新评估了中佛罗里达大学（UCF）激波管设施中没有后续稀释的燃料-空气混合物的点火延迟时间。应用多种化学动力学模型对实验数据集进行了分析。该研究揭示了在模拟具有较低稀释度的燃料-氧化剂混合物时存在的不足，而这些稀释度代表了实际的燃烧应用。为了提高化学动力学的建模能力，我们对反应模型DLR简明进行了更新，吸收了文献中的新见解。随后，利用新的实验数据和文献中提供的点火延迟时间数据对更新后的模型进行了优化。以氨及其与氢的混合物的373个点火延迟时间为优化目标。应用线性变换模型对最敏感的n化学反应进行不确定度优化。DLR的新实验数据证实了UCF重新评估的实验数据与建立的化学动力学模型之间的偏差。更新和优化的DLR简明模型解决了这些建模缺陷，并一致地再现了来自两个激波管设施的新的和重新评估的数据。优化后的反应模型在较宽的初始温度、压力和混合物边界条件范围内均能较好地再现完整的目标实验数据。因此，该模型可以可靠地应用于内燃机点火过程的数值研究。

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引用次数: 0

Techno-economic analysis of deep peaking for hydrogen co-firing in a 300 MWe subcritical power plant with hydrogen production from valley electricity 300兆瓦谷电制氢亚临界电厂氢共烧深度调峰技术经济分析

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105839

Tiantian Wang , Jinwei Sun , Fuqi Yuan , Mingye Yang , Yang Zhang , Fuyuan Yang , Minggao Ouyang

As the proportion of renewable power generation increases annually, thermal power plants are supposed to operate in deep peaking with high flexibility to balance power supply and power demand as well as ensure grid security. Hydrogen co-firing in thermal power plants is one of the promising approaches to maintaining stable combustion during deep peaking periods, improving peak capacity, and reducing carbon emissions. This paper numerically investigated the thermodynamic performance of deep peaking at 30 % and 20 % heating loads for hydrogen co-firing in a 300 MWe subcritical power plant using the Aspen Plus model and conducted an economic analysis of four scenarios of boiler deep peaking and hydrogen production from valley electricity. The results show that as the hydrogen blending heat ratio increases from 0 % to 15 % with the constant total excess air ratio of 1.15 at 30 % heating load, the boiler thermal efficiency increases from 91.13 % to 92.05 %, the standard coal consumption decreases from 395 g/kWh to 331 g/kWh, and the CO₂ emission per unit of fuel heat input also drops from 132.52 g/MJ to 112.55 g/MJ. If the boiler heating load is further adjusted to 20 %, hydrogen blending and oxygen enrichment can also improve the theoretical combustion temperature and boiler efficiency, as well as save coal and reduce carbon emissions. Regarding the economic analysis, the prices of standard coal and electrolyzers are two key factors affecting the payback time. As the capacity of electrolyzers decreases from 60 MW in Scenario 2 to 20 MW in Scenario 4, the payback time drops from 10.45 years to 3.63 years. In the meantime, the hydrogen blending heat ratio also decreases from 15 % to 5 % at 20 % heating load. There exists a tradeoff between a high hydrogen blending ratio (which means more stable combustion at low heating loads) and a short payback time.

随着可再生能源发电比重的逐年增加，火电厂为实现电力供需平衡，保障电网安全，需要具有较高灵活性的深调峰运行。火电厂的氢共烧是一种很有前途的方法，可以在深峰期保持稳定燃烧，提高峰值容量，减少碳排放。本文采用Aspen Plus模型对300mwe亚临界电厂在30%和20%热负荷下的氢共烧深度调峰热力性能进行了数值研究，并对锅炉深度调峰和谷电制氢四种方案进行了经济分析。结果表明：在30%热负荷下，当混氢热率由0%提高到15%，总过剩空气比为1.15恒定时，锅炉热效率由91.13%提高到92.05%，标准煤消耗量由395 g/kWh下降到331 g/kWh，单位燃料热输入CO2排放量由132.52 g/MJ下降到112.55 g/MJ。若将锅炉热负荷进一步调整为20%，配氢富氧还能提高理论燃烧温度和锅炉效率，节约煤炭，减少碳排放。从经济性分析来看，标准煤价格和电解槽价格是影响投资回收期的两个关键因素。随着电解槽容量从场景2的60mw减少到场景4的20mw，投资回收期从10.45年下降到3.63年。同时，在热负荷为20%时，混氢热率也从15%下降到5%。在高氢混合比（这意味着在低热负荷下更稳定的燃烧）和较短的投资回收期之间存在权衡。

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引用次数: 0

A shock tube study of chaperon efficiencies for the NH3 + M → NH2 + H + M reaction during ammonia pyrolysis 氨热解过程中NH3 + M→NH2 + H + M反应伴子效率的激波管研究

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105797

Padmanabha Prasanna Simha, Taylor M. Rault, Sean Clees, Jesse W. Streicher, Christopher L. Strand, Ronald K. Hanson

Ammonia (NH₃) pyrolysis behind reflected shock waves was studied using laser absorption spectroscopy. Experimental measurements of the rate coefficient for the

forward reaction were obtained by targeting the NH radical. The mole fraction of the NH radical is uniquely sensitive to the rate coefficient of the

reaction under dilute conditions since it is slower than other NH producing reactions. The NH₃ mole fraction prior to the arrival of the shock wave was measured using a scanned-wavelength infrared laser absorption diagnostic at

10.35 μ m

. A fixed-wavelength ultraviolet laser absorption diagnostic at 336.0998 nm was used to obtain the time history of NH after the passage of the reflected shock. Chemical kinetic model rates were tuned to obtain the best fit to the experimental results. Experiments in a temperature range of 1900 K to 2300 K were conducted with ammonia diluted in argon (Ar), nitrogen (N₂) and hydrogen (H₂) at a pressure of 1 atm. Results of experiments with ammonia diluted in Ar agree with current chemical kinetic models for ammonia pyrolysis. The chaperon (third-body) efficiencies of N₂ and H₂ relative to Ar were obtained. When using a linear mixture rule, N₂ and H₂ are seen to have chaperon efficiencies of 5.2 and 4.4 relative to Ar. These are the first direct measurements of chaperon efficiencies of N₂ and H₂ relative to Ar for this reaction at high temperatures.

采用激光吸收光谱法研究了氨（NH3）在反射激波后的热解过程。通过瞄准NH自由基，得到了正向反应速率系数的实验测量值。在稀释条件下，NH自由基的摩尔分数对反应的速率系数特别敏感，因为它比其他产生NH的反应慢。采用10.35μm扫描波长红外激光吸收诊断仪测量了冲击波到达前的NH3摩尔分数。在336.0998 nm处采用固定波长紫外激光吸收诊断，获得反射激波通过后NH的时程。对化学动力学模型速率进行了调整，使其最符合实验结果。实验在1900 ~ 2300 K的温度范围内进行，在1 atm的压力下，用氨水稀释氩气（Ar）、氮气（N2）和氢气（H2）。氨在Ar中稀释的实验结果与目前氨热解的化学动力学模型一致。得到了N2和H2相对于Ar的伴侣子（第三体）效率。当使用线性混合规则时，N2和H2相对于Ar的伴侣子效率分别为5.2和4.4。这是在高温下该反应中N2和H2相对于Ar的伴侣子效率的第一次直接测量。

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引用次数: 0

Laminar and turbulent hydrogen-enriched methane flames: Interaction of thermodiffusive instabilities and local fuel demixing 层流和湍流富氢甲烷火焰：热扩散不稳定性和局部燃料脱混的相互作用

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105885

Hendrik Nicolai , Vinzenz Schuh , Antonia Bähr , Max Schneider , Felix Rong , Driss Kaddar , Mathis Bode , Christian Hasse

Blending hydrogen with methane provides a practical approach for transitioning existing energy infrastructure to hydrogen-based carriers. However, under fuel-lean conditions, increasing the hydrogen content causes flames to transition rapidly from methane-like combustion to hydrogen-dominated flames, primarily driven by thermodiffusive instabilities that significantly enhance turbulent flame speeds. This study systematically examines lean methane/hydrogen/air flames of varying complexity, from three-dimensional laminar unstable cases to turbulent jet flames at two different Reynolds numbers, with an emphasis on the impact of the distinct molecular transport properties of hydrogen and methane. The large-scale simulations reveal that these blends exhibit instabilities even under turbulent conditions, albeit to a lesser degree than pure hydrogen flames. Nonetheless, synergistic interactions between turbulence and thermodiffusive instabilities lead to notable increases in turbulent flame speed and reactivity factors (

I_{0}

) at higher Reynolds/Karlovitz numbers. Moreover, beyond the effects of overall non-unity Lewis number, the different diffusivity of hydrogen and methane (i.e., non-equal Lewis numbers) significantly influence the formation and intensity of intrinsic flame instabilities. These findings underscore the importance of thermodiffusive instabilities in methane/hydrogen combustion and highlight the need for advanced modeling approaches capable of capturing local demixing effects under turbulent flows conditions.

将氢气与甲烷混合为将现有能源基础设施转变为氢基载体提供了实用的方法。然而，在燃料稀薄的条件下，增加氢含量会导致火焰迅速从甲烷燃烧转变为氢主导的火焰，这主要是由热扩散不稳定性驱动的，它显著提高了湍流火焰的速度。本研究系统地研究了不同复杂性的贫甲烷/氢/空气火焰，从三维层流不稳定情况到两种不同雷诺数下的湍流射流火焰，重点研究了氢和甲烷不同分子传输特性的影响。大规模的模拟表明，这些混合物即使在湍流条件下也表现出不稳定性，尽管程度低于纯氢火焰。尽管如此，湍流和热扩散不稳定性之间的协同相互作用导致湍流火焰速度和反应性因子（I0）在较高的雷诺数/卡罗维茨数下显著增加。此外，除了整体非单位路易斯数的影响外，氢气和甲烷的不同扩散系数（即非等路易斯数）显著影响了本然火焰不稳定性的形成和强度。这些发现强调了甲烷/氢燃烧中热扩散不稳定性的重要性，并强调了能够捕捉湍流条件下局部脱混效应的先进建模方法的必要性。

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引用次数: 0

Modeling dense droplet spray combustion with multiple-mapping conditioning 多重映射条件下稠密液滴喷雾燃烧模拟

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105895

Jan Wilhelm Gärtner, Ka Ho Lam, Andreas Kronenburg

Accurate modeling of dense spray combustion remains a key challenge due to complex two-phase interactions, turbulence, and evaporation dynamics. This study advances the sparse stochastic particle method MMC-LES by introducing a novel droplet–droplet–particle (DDP) coupling model to improve the representation of phase interactions in dense droplet-laden flows. The performance of this approach is assessed against Carrier Phase Direct Numerical Simulations (CP-DNS) for a double shear layer configuration, extending previous work on sparse-Lagrangian methods. While the nearest-neighbor (NNB) coupling strategy accurately predicts global scalar statistics for dilute sprays, it overestimates evaporation rates in dense conditions due to inadequate representation of local fuel mass fraction variations. Conditioning the nearest neighbor selection on the mixture fraction or using double conditioning on both mixture fraction and temperature does not lead to improved results due to the lack of a model for inter-droplet interactions. The newly proposed DDP model mitigates these issues by incorporating inter-droplet effects, leading to improved agreement with CP-DNS results.

由于复杂的两相相互作用、湍流和蒸发动力学，密集喷雾燃烧的精确建模仍然是一个关键的挑战。本文提出了稀疏随机粒子方法MMC-LES，通过引入一种新的DDP （drop - drop - drop - particle）耦合模型，改进了密集液滴流动中相相互作用的表征。该方法的性能通过双剪切层配置的载波相位直接数值模拟（CP-DNS）进行了评估，扩展了之前在稀疏-拉格朗日方法上的工作。虽然最近邻（NNB）耦合策略准确地预测了稀喷雾的全局标量统计，但由于局部燃料质量分数变化的不充分表示，它高估了密集条件下的蒸发速率。由于缺乏液滴间相互作用的模型，对混合分数的最近邻选择或对混合分数和温度使用双重条件都不能改善结果。新提出的DDP模型通过纳入液滴间效应缓解了这些问题，从而提高了与CP-DNS结果的一致性。

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引用次数: 0

A virtual chemistry framework compatible with thermodynamic and kinetic standards 一个与热力学和动力学标准兼容的虚拟化学框架

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105894

Matthieu Préteseille, Tan-Phong Luu, Nasser Darabiha, Benoît Fiorina

Accurate combustion modeling is essential for decarbonization, yet simulating the combustion of fuels like sustainable aviation fuels (SAF) remains challenging due to their complex chemistry. Detailed kinetic mechanisms, often involving thousands of reactions, make industrial turbulent combustion simulations computationally prohibitive, necessitating kinetic mechanism reduction techniques. Among these, virtual chemistry offers a promising solution by creating highly-reduced schemes with virtual species and reactions, optimized to reproduce specific flame characteristics. However, its original formalism relies on tabulated stoichiometric coefficients and kinetic rates as functions of the local mixture fraction, requiring source code modifications in traditional reactive flow solvers and limiting its adoption in the combustion community.

This study revisits the virtual chemistry formalism to eliminate parameter tabulation, aiming to develop universal 4-reaction virtual mechanisms for any fuel, directly compatible with traditional software like CHEMKIN and CANTERA. The methodology, divided into two steps, optimizes thermodynamic and chemical properties. Beyond retrieving the mixture’s enthalpy and heat capacity, this new thermodynamic optimization also targets the mixture’s Gibbs energy, enabling the recovery of equilibrium states across various conditions. Consequently, these novel virtual chemical mechanisms introduce equilibrium reactions, compensating for the lost degrees of freedom due to the elimination of parameter tabulation and bridging the gap between virtual and classical chemistry. Reaction rates are then optimized to match temperature and heat release rate profiles from detailed chemistry.

The formalism’s versatility is demonstrated through the optimization of 4-reaction hydrogen and SAF virtual schemes using reference equilibrium and perfectly-stirred reactor computations on CANTERA. By adhering to standard NASA polynomial approximations for thermodynamic properties and an Arrhenius-like closure for kinetic rate constants, integrating virtual chemistry into any reactive flow solver is now straightforward.

准确的燃烧建模对于脱碳至关重要，但模拟可持续航空燃料（SAF）等燃料的燃烧仍然具有挑战性，因为它们具有复杂的化学性质。详细的动力学机制，往往涉及数千个反应，使工业湍流燃烧模拟计算望而却步，需要动力学机制还原技术。其中，虚拟化学提供了一个有前途的解决方案，通过创建具有虚拟物质和反应的高度还原方案，优化以重现特定的火焰特性。然而，它最初的形式依赖于表化的化学计量系数和动力学速率作为局部混合分数的函数，这需要在传统的反应流求解器中修改源代码，并且限制了它在燃烧界的应用。这项研究重新审视了虚拟化学的形式，消除了参数表，旨在开发适用于任何燃料的通用4反应虚拟机制，并与CHEMKIN和CANTERA等传统软件直接兼容。该方法分为两步，优化热力学和化学性质。除了获取混合物的焓和热容之外，这种新的热力学优化还针对混合物的吉布斯能量，使其能够在各种条件下恢复平衡状态。因此，这些新的虚拟化学机制引入了平衡反应，弥补了由于消除参数表而失去的自由度，并弥合了虚拟化学与经典化学之间的差距。然后优化反应速率，以匹配详细化学反应的温度和热释放速率曲线。通过在CANTERA上使用参考平衡和完全搅拌反应器计算对4反应氢和SAF虚拟方案进行优化，证明了该形式的通用性。通过遵循热力学性质的标准NASA多项式近似和动力学速率常数的arrhenius闭包，将虚拟化学集成到任何反应流求解器中现在都很简单。

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引用次数: 0

Simultaneous imaging of OH and temperature in lean premixed hydrogen/air flames: Which marker for thermodiffusive instability? 稀薄预混氢/空气火焰中OH和温度的同时成像：哪个标志着热扩散不稳定性？

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105919

J. Bae , O. Chaib , L. Weller , A. Moitro , E.F. Hunt , A.J. Aspden , S. Hochgreb

This study investigates thermodiffusive (TD) instabilities in lean premixed hydrogen/air flames using simultaneous measurements of hydroxyl radical (OH) via planar laser-induced fluorescence (PLIF) and temperature via Rayleigh scattering. Correlations between flame front curvature and scalar (OH and temperature) gradients as surrogates for reaction rate were assessed in the presence of TD instabilities. Experimental 2D data were compared with corresponding 2D slices extracted from 3D direct numerical simulations (DNS). In both DNS and experiments, flame fronts defined by local maximum scalar gradients (gradient-based) leads to spurious results owing to very low gradients in highly negative curvature regions associated with near-extinction by TD instability. These discontinuous fronts exhibited weaker curvature–gradient correlations than the curvature–HRR (heat release rate) correlation, indicating that scalar gradients along gradient-based fronts are inappropriate surrogates for HRR. To address this limitation, two continuous flame fronts were evaluated: (1) laminar-based front, defined using temperature progress variable at local maximum gradients of scalar by laminar flame calculation, and (2) mode-based front, defined using the most probable temperature (mode value of PDF) at local maximum gradients of temperature. These fronts capture low gradient regions and exhibit stronger correlations between curvature and a surrogate for the reaction rate in both DNS and experiment. DNS analysis revealed that flame fronts based on temperatures (from both laminar-based and mode-based methods) and OH (from laminar-based method) exhibit strong correlation with HRR, with laminar-based flame front for OH showing the highest correlation. However, in experiments, laminar-based flame front for OH correlates poorly with HRR due to spatial misalignment between the temperature and OH fields. Flame fronts by temperature from both laminar-based and mode-based methods are determined to be the most reliable HRR surrogates in experiments. This study highlights that analyzing curvature–gradient correlations under TD instability requires a continuous flame front capturing negative curvature and low gradient regions.

本研究通过平面激光诱导荧光（PLIF）和瑞利散射同时测量羟基自由基（OH）和温度，研究了稀薄预混氢/空气火焰中的热扩散（TD）不稳定性。在TD不稳定性存在的情况下，评估了火焰前曲率和标量（OH和温度）梯度作为反应速率的替代品之间的相关性。将实验二维数据与3D直接数值模拟（DNS）提取的相应二维切片进行对比。在DNS和实验中，由局部最大标量梯度（基于梯度）定义的火焰锋面导致了虚假的结果，这是由于在与TD不稳定性近乎消光相关的高度负曲率区域中非常低的梯度。这些不连续锋面的曲率-梯度相关性弱于曲率-热释放率相关性，表明沿梯度锋面的标量梯度不适合代替热释放率。为了解决这一限制，我们对两种连续的火焰锋面进行了评估：(1)基于层流的锋面，通过层流火焰计算在局部最大标量梯度处使用温度进程变量来定义；(2)基于模式的锋面，使用局部最大温度梯度处的最可能温度（PDF的模态值）来定义。这些锋面捕获低梯度区域，并在DNS和实验中表现出曲率与反应速率代理之间更强的相关性。DNS分析显示，基于温度（基于层流和模式方法）和OH（基于层流方法）的火焰锋面与HRR具有较强的相关性，其中基于层流的火焰锋面与OH的相关性最高。然而，在实验中，由于温度场和OH场之间的空间错位，基于层流的OH火焰锋与HRR的相关性较差。实验结果表明，基于层流法和基于模态法的温度火焰锋面是最可靠的HRR替代物。该研究强调，分析TD不稳定性下的曲率-梯度相关性需要一个连续的火焰锋面，捕获负曲率和低梯度区域。

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引用次数: 0

Role of hydrodynamic instabilities in high-frequency transverse thermoacoustic instabilities in a dual-swirl H2 burner 双旋流H2燃烧器中流体动力不稳定性在高频横向热声不稳定性中的作用

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105837

Hyebin Kang , Hugo Paniez , Thierry Schuller

<div><div>High-frequency thermoacoustic instabilities pose a significant challenge to the development of new generations of combustion systems. This study investigates the interplay between helical hydrodynamic instabilities in a dual-swirl hydrogen-air burner, featuring a spinning thermoacoustic instability coupled to the first transverse acoustic mode of the combustion chamber in the absence of injector coupling. Particle image velocimetry coupled with OH planar laser-induced fluorescence, high-speed OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> imaging, and pressure measurements are used to explore how varying the swirl level <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> imparted to the hydrogen stream influences the flow and flame dynamics during self-sustained oscillations for a fixed swirl level <span><math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mi>e</mi></mrow></msub><mo>=</mo><mn>1</mn><mo>.</mo><mn>2</mn></mrow></math></span> of the air stream. A dramatic shift in flame response is revealed. At low swirl <span><math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>2</mn></mrow></math></span>, elongated flames with low-frequency self-sustained oscillations are observed, while compact flames dominated by high-frequency transverse instabilities are triggered at higher swirl levels <span><math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>6</mn></mrow></math></span> and 1.0. In the latter case, the flow dynamics in the internal recirculation zone of the swirling flow is dominated by a transverse bulk oscillation due to acoustic displacement, while the shear layers are influenced by large-scale helical hydrodynamic structures. It is demonstrated that the amplitude of the high-frequency combustion instability depends on the synchronization between hydrodynamic <span><math><msub><mrow><mi>f</mi></mrow><mrow><mi>h</mi></mrow></msub></math></span> and acoustic <span><math><msub><mrow><mi>f</mi></mrow><mrow><mi>a</mi></mrow></msub></math></span> frequencies. When synchronization occurs (<span><math><mrow><msub><mrow><mi>f</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>≃</mo><msub><mrow><mi>f</mi></mrow><mrow><mi>h</mi></mrow></msub></mrow></math></span>), large vortical structures synchronized with the transverse acoustic wave are formed. These structures strongly dominate flame deformation compared to the direct displacement caused by the transverse spinning acoustic wave, thereby substantially enhancing the amplitude of thermoacoustic instability. Conversely, when the frequencies are misaligned (<span><math><mrow><msub><mrow><mi>f</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>≠</mo><msub><mrow><mi>f</mi></mrow><mrow><mi>h</mi></mrow></msub></mrow></math></span>), transverse oscillations are weaker but persist, indicating that the helical hydrodynamic instability primarily a

高频热声不稳定性对新一代燃烧系统的开发提出了重大挑战。本研究研究了双涡流氢-空气燃烧器中螺旋流体动力不稳定性之间的相互作用，该燃烧器在没有喷油器耦合的情况下，具有旋转热声不稳定性与燃烧室第一横声模式耦合的特点。粒子图像测速与OH平面激光诱导荧光、高速OH *成像和压力测量相结合，用于探索在固定旋流水平Se=1.2时，改变注入氢流的旋流水平Si对自持续振荡过程中流动和火焰动力学的影响。火焰反应发生了戏剧性的变化。在低旋流Si=0.2时，可以观察到低频自持续振荡的细长火焰，而在高旋流Si=0.6和1.0时，可以触发以高频横向不稳定为主的致密火焰。后一种情况下，旋流内部再循环区的流动动力学主要是由声位移引起的横向体振荡，而剪切层则受大尺度螺旋水动力结构的影响。结果表明，高频燃烧不稳定性的幅值取决于水动力fh和声学fh频率之间的同步。当同步发生时，形成与横波同步的大的涡状结构。与横向自旋声波引起的直接位移相比，这些结构强烈地支配着火焰变形，从而大大增强了热声不稳定性的振幅。相反，当频率失调（fa≠fh）时，横向振荡较弱但持续存在，表明螺旋流体动力学不稳定性主要充当热声耦合的放大器而不是启动器。

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引用次数: 0

Meta-learning innovates chemical kinetics: An efficient approach for surrogate model construction 元学习创新了化学动力学：一种构建代理模型的有效方法

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105860

Chenyue Tao, Chengcheng Liu, Yiru Wang, Bin Yang

The construction of surrogate models is an essential step in the uncertainty quantification of combustion reaction kinetics. These models create a mapping between inputs and outputs of combustion kinetics simulations, thereby replacing the time-consuming numerical simulations of reaction kinetics and significantly lowering the computational costs for uncertainty quantification. However, in applications such as experimental design that require repeated construction of surrogate models under multiple operating conditions, the associated computational burden becomes substantial and can even limit the feasibility of the entire task. It is therefore essential to investigate cost-efficient surrogate model construction methods. Drawing inspiration from image classification in computer vision, this work introduces a meta-learning-assisted approach to efficiently construct surrogate models by leveraging the intrinsic shared features among them. By learning from a limited set of training tasks, the approach facilitates rapid creating surrogate models for new conditions with fewer samples. This is particularly beneficial for reducing computational costs since the most significant expense comes from the generation of original samples. The method has been tested in ammonia-hydrogen combustion targeting ignition delay time and laminar burning velocity. Results show that the efficiency of the surrogate model construction can be improved by a factor of eight for individual new conditions, and the total computational costs across the entire condition range can be reduced to 29 % and 37 % of the original values for the two prediction targets, respectively. Notably, dual pretraining across both prediction targets further enhances model performance. The meta-learning-assisted surrogate model construction approach is applicable across a broad range of operating conditions, requiring only minimal additional pretraining costs while offering flexible precision control based on task-specific requirements.

替代模型的建立是燃烧反应动力学不确定度量化的重要步骤。这些模型在燃烧动力学模拟的输入和输出之间建立了映射，从而取代了耗时的反应动力学数值模拟，并显著降低了不确定性量化的计算成本。然而，在实验设计等需要在多种操作条件下重复构建代理模型的应用中，相关的计算负担变得巨大，甚至可能限制整个任务的可行性。因此，研究具有成本效益的代理模型构建方法是必要的。从计算机视觉中的图像分类中获得灵感，本研究引入了一种元学习辅助方法，通过利用它们之间的内在共享特征来有效地构建代理模型。通过从一组有限的训练任务中学习，该方法有助于用更少的样本快速创建新条件的代理模型。这对于降低计算成本特别有益，因为最重要的费用来自原始样本的生成。针对点火延迟时间和层流燃烧速度，对该方法进行了氨氢燃烧试验。结果表明，对于单个新条件，代理模型构建的效率可以提高8倍，并且对于两个预测目标，整个条件范围内的总计算成本可以分别降低到原始值的29%和37%。值得注意的是，跨两个预测目标的双重预训练进一步提高了模型的性能。元学习辅助代理模型构建方法适用于广泛的操作条件，只需要最小的额外预训练成本，同时提供基于特定任务要求的灵活精确控制。

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引用次数: 0

Recombination of NH2 with alkyl radicals: VRC-TST rate constants from neural network potentials NH2与烷基自由基的重组：神经网络电位的VRC-TST速率常数

IF 5.2 2区工程技术 Q2 ENERGY & FUELS

Proceedings of the Combustion Institute

Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105829

Simone Vari, Carlo Cavallotti

The recombination between CH₃ and NH₂ is an important reference reaction for describing the formation of chemical bonds between hydrocarbons and nitrogen compounds in combustion. This is for example the case when ammonia is burned together with hydrocarbon mixtures. Despite the important role played by this reaction in combustion processes, the theoretical studies on the accurate determination of its rate constant, or on the pressure dependence, are limited. At present, most existing kinetic mechanism use experimental measures performed at room temperatures, or detailed balance and the rate constants measured for the reverse process at high temperatures, thus in conditions in which the reaction rate is pressure dependent. This places some limits on the ability to accurately describe the reactivity of two key radical species: methyl and NH₂, in particular when this reaction pathway is in competition with others. The present work aims at filling this gap, providing ab-initio rate constant estimations for the recombination pathway of the reaction family C_nH_2n+1 + NH₂, with n = 1, 2, 3. Rate constants are estimated using Variable Reaction Coordinate – Transition State Theory (VRC-TST) and machine learning. VRC-TST is the golden standard for kinetic studies of barrierless reactions, which do not have a well-defined transition state. The rate constants estimated with VRC-TST approach the experimental accuracy, at the cost of a computationally demanding Monte Carlo sampling of the reactive Potential Energy Surface (PES). In this work we use Artificial Neural Network (ANN) to learn the portion of the multidimensional PES relevant to the reaction of interest as a function of the degrees of freedom describing the relative orientation of the two reacting fragments. The physics-informed ANN architecture significantly reduces the number of explicit electronic structure calculations needed by VRC-TST, thus gaining significant time savings without compromising accuracy. The calculated rate constants are in good agreement with the available experimental data and are thus expected to provide a useful reference for the kinetic modelling of the co-combustion of nitrogen compounds and hydrocarbons.

CH3与NH2的复合反应是描述碳氢化合物与氮化合物在燃烧过程中形成化学键的重要参考反应。例如，当氨和碳氢化合物混合物一起燃烧时。尽管该反应在燃烧过程中起着重要的作用，但关于准确测定其速率常数或压力依赖性的理论研究却很有限。目前，大多数现有的动力学机制都是在室温下进行的实验测量，或者在高温下对逆向过程进行详细的平衡和速率常数测量，因此在反应速率依赖于压力的条件下。这就限制了准确描述两种关键自由基甲基和NH2的反应活性，特别是当这种反应途径与其他反应途径竞争时。本工作旨在填补这一空白，为n = 1,2,3的CnH2n+1 + NH2反应族的重组途径提供ab-initio速率常数估计。速率常数估计使用可变反应坐标-过渡状态理论（VRC-TST）和机器学习。VRC-TST是无势垒反应动力学研究的黄金标准，无势垒反应没有明确的过渡态。用VRC-TST估计的速率常数接近实验精度，但代价是对反应势能面（PES）进行计算要求很高的蒙特卡罗采样。在这项工作中，我们使用人工神经网络（ANN）来学习与感兴趣的反应相关的多维PES部分，作为描述两个反应片段相对方向的自由度的函数。基于物理的人工神经网络架构大大减少了VRC-TST所需的显式电子结构计算的数量，从而在不影响准确性的情况下节省了大量时间。计算得到的速率常数与实验数据吻合较好，可望为氮化合物与烃类共燃烧的动力学建模提供有益的参考。

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引用次数: 0