Combustion and Flame最新文献

{"title":"Agglomeration and combustion characteristics of composite solid propellants under low-temperature conditions","authors":"Wen Ao ,&nbsp;Zhan Wen ,&nbsp;Gangchui Zhang ,&nbsp;Tuanwei Xu ,&nbsp;Xianghua Chen ,&nbsp;Peijin Liu","doi":"10.1016/j.combustflame.2025.114240","DOIUrl":"10.1016/j.combustflame.2025.114240","url":null,"abstract":"<div><div>In this paper, we propose a promising research direction for propellant combustion in low-temperature environments. In the temperature range of -60 to 20 °C, we systematically examine the thermolysis properties, ignition, and combustion characteristics of propellants containing aluminum. A decrease in temperature reduces the recrystallization temperature of ammonium perchlorate and increases the ammonium perchlorate decomposition peak temperature, which is unfavorable for the exothermic reaction of the propellant solid phase. As the initial ambient temperature decreases, the propellant ignition delay time increases (up to a 127.3 % increase), burning rate decreases (up to a 24.8 % reduction), and aggregation degree of aluminum increases, resulting in an increase in the size of the condensed combustion products (up to a 45.0 % increase). Additionally, the propellant combustion efficiency decreases (up to a 20.8 % reduction). We propose physical mechanisms by which low-temperature environments alter the combustion of propellants. Reducing the propellant initial temperature leads to a decrease in the burning surface temperature, thereby reducing radiative heat feedback and lowering the burning rate. A reduced burning rate slows down the escape of aggregates from the burning surface, enhancing the likelihood of additional collisions and fusion among aggregates. This process increases agglomeration size while diminishing combustion efficiency. The results of this study enhance our understanding of the alterations in the combustion traits of propellants in low-temperature settings.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114240"},"PeriodicalIF":5.8,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144071551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ignition and combustion characteristics of micron-sized Al-Li alloy particle in high-temperature gas flow","authors":"Zhenkun Hu ,&nbsp;Shengyu Pang ,&nbsp;Yugan Liao ,&nbsp;Yong Tang ,&nbsp;Qian Mao ,&nbsp;Baolu Shi","doi":"10.1016/j.combustflame.2025.114237","DOIUrl":"10.1016/j.combustflame.2025.114237","url":null,"abstract":"<div><div>Compared to pure aluminum particles, Al-Li alloy particles exhibit shorter ignition delay times and smaller combustion product sizes, making them a superior metallic additive for solid propellants. Therefore, this study experimentally and theoretically investigated the ignition and combustion characteristics of micron-sized Al-Li alloy particle. First, the ignition delay times of 8 μm Al-Li alloy particle over a wide range of temperatures were measured using a reflected shock tube. Second, theoretical models of ignition and combustion of micron-sized Al-Li alloy particle in high-temperature gas flow were developed, by considering comprehensive processes including convective heat transfer, radiative heat transfer, heterogeneous surface reactions, phase change, oxide layer rupture, diffusion-controlled combustion and micro-explosion. The ignition delay times and critical ignition temperature predicted by the model show good agreement with the experimental results. Detailed analysis reveals that micro-explosion can occur as the saturation vapor pressure of lithium exceeds the contact pressure at the Al-Li interface during combustion. Parametric studies further indicate that elevating ambient pressure increases the contact pressure at the Al-Li interface, thereby inhibiting micro-explosion. In contrast, raising ambient temperature increases the saturation vapor pressure of lithium, thus facilitating micro-explosion. Finally, an empirical formula was derived to predict the critical ambient pressure at which micro-explosion occurs in Al-Li alloy particle with 5 % lithium content.</div></div><div><h3>Novelty and Significance Statement</h3><div>In this study, both the ignition delay times and the critical ignition temperature of Al-Li alloy particle were measured using a reflected shock tube. Subsequently, theoretical models of ignition and combustion of micron-sized Al-Li alloy particle in high-temperature gas flow were developed, encompassing convective heat transfer, radiative heat transfer, heterogeneous surface reactions, phase change, oxide layer rupture, diffusion-controlled combustion and micro-explosion. Based on the model, the heat and mass transfer mechanism of Al-Li alloy particle during ignition and combustion was revealed, and particularly elucidating the micro-explosion mechanism as well as the effects of ambient pressure and temperature on micro-explosion. Finally, an empirical formula was proposed to predict the critical ambient pressure at which micro-explosion occurs in Al-Li alloy particle.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114237"},"PeriodicalIF":5.8,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144071552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of thermal non-equilibrium on supersonic combustion with low equivalence ratio","authors":"You Wu ,&nbsp;Bing Chen ,&nbsp;Qingchun Yang ,&nbsp;Xu Xu","doi":"10.1016/j.combustflame.2025.114220","DOIUrl":"10.1016/j.combustflame.2025.114220","url":null,"abstract":"<div><div>The distribution of the vibrational energy could have significant impact on ignition and flame stabilization in the scramjet combustor. The effect of thermal non-equilibrium on the non-premixed hydrogen/air supersonic combustion with a global equivalence ratio of 0.3 in scramjet is investigated using numerical simulations based on the thermochemical non-equilibrium model and the chemical non-equilibrium model. The results show that the cold vibrational non-equilibrium of the inflow enhances the ignition but inhibits the downstream heat release, while the thermal non-equilibrium caused by the transverse jet interaction has the opposite effect. The case with the real scramjet condition (NEQ_REAL) has the earliest ignition and the lowest downstream peak heat release rate (HRR). The internal energy distribution in the shear layer determines the control temperatures of the three key initial reactions and alters the formation rates of free radicals, which affects the ignition. The downstream peak HRR is related to the internal energy distribution and the species composition which is affected by the upstream thermal non-equilibrium. The local internal energy distribution in thermal non-equilibrium cases can promote the HRR compared to the “hypothetical” equilibrium state. The change of species concentration due to thermal non-equilibrium is the main reason why peak HRR of NEQ_REAL is lower than that of thermal equilibrium case. Using different chemical-vibrational coupling models has impacts on ignition and peak HRR. When the original Park model is used, the internal energy distribution in the thermal non-equilibrium case can reduce the heat release rate compared to the “hypothetical” thermal equilibrium state. The effect of thermal non-equilibrium in supersonic expansion flow is equivalent to heat absorption effect compared to the thermal equilibrium case, which reduces the pressure and translational temperature in the nozzle. The difference of net thrust between thermal equilibrium and non-equilibrium cases exceeds 10%.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114220"},"PeriodicalIF":5.8,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144071553","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study on symmetric/asymmetric hydrogen flame shapes in the thickness of a Hele-Shaw burner","authors":"Ziyin Chen ,&nbsp;Yves Ballossier ,&nbsp;Song Zhao ,&nbsp;Bruno Denet ,&nbsp;Christophe Almarcha ,&nbsp;Pierre Boivin","doi":"10.1016/j.combustflame.2025.114208","DOIUrl":"10.1016/j.combustflame.2025.114208","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Premixed flame front shape, which drastically depends on boundary conditions, is closely related to its propagation speed. In this work, we focus on the symmetry of steady premixed hydrogen-air flames propagating in a narrow channel, like a Hele-Shaw burner. A wide range of equivalence ratios (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;35&lt;/mn&gt;&lt;mtext&gt;–&lt;/mtext&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) and channel widths (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mstyle&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mstyle&gt;&lt;mtext&gt;–&lt;/mtext&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mstyle&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mstyle&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) are analyzed by performing detailed simulations validated by experiments.&lt;/div&gt;&lt;div&gt;A multiplicity of steady flame shape is found for channel widths above a certain critical value, that is related to flame cutoff wavelength. Our numerical results successfully reproduce steady flame fronts observed in experiments. Notably, transitions from symmetric to asymmetric with equivalence ratio are reproduced. Additionally, an increase in channel width reduces the region of symmetric solutions. Furthermore, The study explores the effects of the Darrieus-Landau instability and thermodiffusive effects on flame shapes, presenting a stability diagram for symmetric/asymmetric flame configurations. Throughout the study, an increase in flame area is associated with the asymmetry level of the flame front, showing a trend that first increases and then decreases with the equivalence ratio. The global consumption rate relative to laminar flame speed decreases monotonously with increasing equivalence ratio. It is determined by the flame area increment and stabilizing (destabilizing) effects on convex flame fronts at Lewis number greater (smaller) than 1. This effect is quantified and proved independent of flame symmetry and channel width. For very lean mixtures, the differential species diffusion significantly strengthens the consumption rate. A prediction model is established to determine the flame front length given a certain equivalence ratio and channel width.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and Significance Statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This study is, to the best of our knowledge, the first attempt to recover stable premixed hydrogen-air flame shapes observed in experiments in the thickness of a Hele-Shaw burner by performing detailed simulations. The evolution of stable flame shapes has been qualitatively and quantitatively analyzed for a wide range of equivalence ratios (0.35–2.0) and channel widths (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mstyle&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mstyle&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mstyle&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/mstyle&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;). The impacts of hydrodynamic instability and thermodiffusive effects are investigated, and the correlation between flame shape and consumption rate is analyzed. A prediction model is established to det","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114208"},"PeriodicalIF":5.8,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143948695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Directed Relation Graph-Based Species Rank (DRGSR): An efficient mechanism reduction algorithm","authors":"Yiru Wang ,&nbsp;You Wu ,&nbsp;Shengqiang Lin ,&nbsp;Chung K. Law ,&nbsp;Bin Yang","doi":"10.1016/j.combustflame.2025.114226","DOIUrl":"10.1016/j.combustflame.2025.114226","url":null,"abstract":"<div><div>While kinetic mechanisms play a pivotal role in simulating complex combustion problems, their extended scale often results in prohibitive computational cost, particularly when integrated with computational fluid dynamics simulations. This paper introduces the Directed Relation Graph Species Rank (DRGSR) algorithm, an efficient mechanism reduction technique designed to retain the essential species and reaction pathways while minimizing computational demands. Specifically, it incorporates a two-step approach: the first utilizes a directed relation graph to map species interactions and transform the kinetic information into a graph structure, and the second employs the PageRank algorithm and directed interaction coefficients to rank species based on their importance within the network. The DRGSR algorithm is validated through case studies involving both large- and small-scale, high-temperature and low-temperature mechanisms, specifically focusing on the ignition delay times for ethylene (C₂H₄) and n-heptane (C₇H₁₆). The algorithm demonstrates superior performance in reducing the number of species significantly while maintaining accuracy; for ethylene, it retains only 31 species with an error under 8 %, while for n-heptane, it achieves comparable precision with fewer species compared to existing methods. The validation is extended to predicting the laminar flame speeds, and further affirms the algorithm's reliability and generalizability. A comparative analysis of the computational cost reveals that the DRGSR algorithm not only is less time-consuming, but it also simplifies the reduction process by eliminating the iterative threshold adjustments required by methods such as Directed Relation Graph (DRG), Directed Relation Graph with Error Propagation (DRGEP) and Directed Relation Graph with Error Propagation and Sensitivity Analysis (DRGEPSA). These findings indicate that the DRGSR algorithm offers a robust, efficient and reliable approach for kinetic mechanism reduction, suitable for wide ranges of engineering applications.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114226"},"PeriodicalIF":5.8,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144071536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"When ammonia addition increases the burning velocity of a fuel blend with nitromethane","authors":"Jundie Chen,&nbsp;Alexander A. Konnov","doi":"10.1016/j.combustflame.2025.114230","DOIUrl":"10.1016/j.combustflame.2025.114230","url":null,"abstract":"<div><div>Combustion properties and combustion chemistry of ammonia (NH₃) are significantly different from those of hydrocarbons and thus require further investigation. NH₃ combustion with oxidizers different from the ambient air can reveal distinct chemistry of NOx formation, which, together with low reactivity, is one of the major obstacles in the direct deployment of ammonia as a practical fuel. In the present study, ammonia was blended with nitromethane (CH₃NO₂), which was used as a nitric oxide (NO) precursor. The laminar burning velocities (LBV) of (CH₃NO₂+NH₃)+air mixtures were investigated across a wide range of NH₃ mole fractions in the fuel blends, from 0% to 80%, spanning fuel-lean to fuel-rich conditions, at an initial temperature of 338 K and 1 atm. The results show that adding NH₃ enhances the reactivity of CH₃NO₂ when the NH₃ fraction in the fuel is below 70%. A kinetic model of the authors was updated, primarily on CH₃NO₂ chemistry, and shows very good agreement with the measurements without any rate constants tuning. Detailed kinetic analyses based on the present model reveal that the reaction NH₂+NO<img>NNH+OH significantly impacts the LBV even when a small portion of NH₃ is added to the fuel blend. NH₃ addition is found to increase adiabatic flame temperature and enrich the active radicals’ pools of H, OH, and O as well. The pathways of NH₃ and NO interaction in (CH₃NO₂+NH₃)+air flames are also analyzed, enlightening NO conversion into N₂ in the presence of ammonia.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114230"},"PeriodicalIF":5.8,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143948721","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental and kinetic study on the co-oxidation of pyridine and ammonia as a model compound of coal-ammonia co-firing","authors":"Ling-Nan Wu ,&nbsp;Zi-Cheng Wei ,&nbsp;Wang Li ,&nbsp;Kai-Ru Jin ,&nbsp;Zhi-Hao Zheng ,&nbsp;Du Wang ,&nbsp;Qian-Peng Wang ,&nbsp;Yu-Tong Hou ,&nbsp;Cheng-Yin Ye ,&nbsp;Xian-Zhi Cheng ,&nbsp;Xiao-Dong Wang ,&nbsp;Teng-Long Lv ,&nbsp;Jiu-Zhong Yang ,&nbsp;Long Zhao ,&nbsp;Zhen-Yu Tian","doi":"10.1016/j.combustflame.2025.114211","DOIUrl":"10.1016/j.combustflame.2025.114211","url":null,"abstract":"<div><div>The co-oxidation of pyridine and ammonia was studied as a model compound to investigate the kinetics of coal-ammonia co-firing. Experiments were conducted in a jet-stirred reactor coupled with synchrotron vacuum ultraviolet photoionization molecular beam mass spectrometer at atmospheric pressure up to 900 K with ammonia to pyridine molar blend ratio of 1:5. Compared with previous pyridine kinetic studies, several new oxidation intermediates were detected during the co-oxidation process, including nitrous acid, methyleneaminoacetonitrile, 2-, and 4-cyanopyridine. The pyridine LTO 3.1 kinetic model, comprising 233 species and 1572 reactions, was developed and used to simulate the reaction process with reasonable predictions, which incorporates the direct interaction between pyridine and NH₂ radical (NH₂+C₅H₅N=C₅H₄N+NH₃) and updates the rate constants of C₅H₅N+OH=C₅H₄N+H₂O, NH₃+NCO=HNCO+NH₂, NH₃+NCO=HOCN+NH₂. The major nitrogen-containing products are HCN, N₂, HNCO, N₂O, pyrrole, and NO. The co-oxidation of pyridine and NH₃ shows a mutual-sensitization effect, promoting the consumption of both pyridine and ammonia. The presence of ammonia boosts pyridine consumption by providing NO and more OH radicals at lower temperatures through the NO-NO₂ looping process (NO+HO₂=NO₂+OH and NO₂+H=NO+OH). The initial reaction temperature of NH₃ is lowered by around 200 K when co-oxidized with pyridine compared with its neat oxidation, as pyridine could supply OH radicals at a lower temperature and trigger the chain-branching reactions. NO_x emissions are also generated at lower temperatures compared with neat pyridine and NH₃ oxidation conditions. N₂O production reaches 367 ppm at 900 K, which is an order of magnitude higher than NO. The results could help better understand the microscopic mechanism of coal-ammonia interactions during the co-firing process, and the design, organization, and optimization of coal-ammonia co-firing applications.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114211"},"PeriodicalIF":5.8,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143948696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Low-frequency oscillations in ammonia/hydrogen/nitrogen and methane flames approaching lean blow off","authors":"Tong Su,&nbsp;Samuel Wiseman,&nbsp;James R. Dawson,&nbsp;Nicholas A. Worth","doi":"10.1016/j.combustflame.2025.114184","DOIUrl":"10.1016/j.combustflame.2025.114184","url":null,"abstract":"<div><div>A self-sustained low-frequency oscillation in premixed bluff-body stabilised flames approaching lean blow-off (LBO) was investigated experimentally. Simultaneous high-speed PIV and OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span>-chemiluminescence images were obtained to provide time-averaged and time-resolved flame dynamics and flow fields. The LBO limits were determined for both methane and decomposed ammonia fuel blends with different ammonia volume fractions using long or short enclosures. Flames in the long enclosure were more stable due to the longer flow residence time. For NH₃/H₂/N₂ fuel blends, higher percentages of H₂ result in wider LBO limits due to the higher extinction strain rate. It was found that close to LBO both CH₄ and NH₃/H₂/N₂ flames in the long enclosure resulted in periodic oscillations, characterised by large-scale reignition and extinction. The oscillation frequency, between 0.5 to 10 Hz, was shown to vary linearly with bulk inlet velocity (10-110 m/s) with a constant Strouhal number. This periodic reignition phenomena was attributed to the accumulation of unburnt fuel in the outer recirculation zones, which is periodically recharged by unburnt fuel issuing from the injector as lean blow-off is approached, and may also extend the LBO limits in the long confinement.</div><div><strong>Novelty and Significance Statement</strong></div><div>Lean blow-off is an important phenomena in many combustion applications, and understanding this with both hydrocarbon and carbon-free fuels is important. The lean blow-off behaviours of methane and ammonia/hydrogen/nitrogen flames in two different length confinements were presented and compared. A low-frequency oscillation was observed in the longer confinement near lean blow-off under various equivalence ratios and bulk velocities. While some previous studies have briefly reported similar observations, they lack detail on frequency scaling or the underlying physical process. A linear relationship between the oscillation frequency and bulk velocity was observed for the first time. The flame structures and flow fields during one oscillation cycle were investigated, demonstrating that the oscillation was caused by periodic reignition and extinction of the lifted flames. Other important time scales, such as the reaction time, and chamber fill time were also characterised for the first time to improve our understanding of the phenomena.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114184"},"PeriodicalIF":5.8,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143936759","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrogen addition effect on the structure of the lean premixed flame stabilized on a high-temperature bluff-body","authors":"Siqi Cai,&nbsp;Jianlong Wan","doi":"10.1016/j.combustflame.2025.114229","DOIUrl":"10.1016/j.combustflame.2025.114229","url":null,"abstract":"<div><div>It has been confirmed that the High-temperature bluff-body (HTB) can significantly improve the Lean premixed flame (LPF) stabilization. To further improve the HTB stabilized LPF performance and reduce the CO₂ emission, the hydrogen-methane is employed. This study investigates the hydrogen addition effect on the LPF structure stabilized on the HTB by the means of the numerical simulation. A new non-equidistant central difference method is employed to identify the normal vector of the flame front accurately. When the percentage <em>α</em> of hydrogen in the mixed fuel increases, the flame thickness significantly decreases and its base shifts upstream. In the case of <em>α</em>=0, the flame base immerses in the Recirculation zone (RZ), and the flame base anchors at the boundary of the RZ in the case of <em>α</em>=0.15 and 0.30. The transport path and magnitude of the reactants are visualized. It is interestingly observed that the hydrogen addition can promote the transport magnitude of methane to the flame. When <em>α</em> increases, the peak values of the net reaction rates of hydrogen and methane increase, and the corresponding locations shift upstream. The three source terms of the energy equation are visualized quantitatively employing the real specific heat rather than the conventional constant equivalent specific heat. The increase in the <em>α</em> value enlarges the magnitudes of the aforementioned three source terms significantly. For the downstream flame front, it is interestingly observed that the weight of the convection term is large in the case of <em>α</em>=0 while it is small in the case of <em>α</em>=0.30. The heat release rate structure can be classified into the adiabatic zone, the excess reaction zone, and the weak reaction zone. To the best of our knowledge, such detailed analysis of the HTB stabilized LPF structure of hydrogen-enriched methane has not been reported yet. This work offers new insights into the LPF dynamics stabilized on the HTB.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114229"},"PeriodicalIF":5.8,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143931718","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study of low-to-moderate temperature oxidation of 1,2,4-trimethylbenzene/n-heptane blends","authors":"S. Hossain ,&nbsp;M. Abdulrahman ,&nbsp;P.T. Lynch ,&nbsp;EricK. Mayhew ,&nbsp;K. Brezinsky","doi":"10.1016/j.combustflame.2025.114223","DOIUrl":"10.1016/j.combustflame.2025.114223","url":null,"abstract":"<div><div>Single-pulse shock tube experiments were performed at a nominal pressure of 50 atm and a reaction time of 13 milliseconds (ms) over a temperature range of 700–1400 K to study the oxidation speciation of a 1,2,4-trimethylbenzene/n-heptane (HTMB) blend. The oxidation experiments were conducted across a range of equivalence ratios (φ = 2.0, 1.0, 0.50, and 0.25). Gas chromatography (GC) was used to quantitatively and qualitatively analyze the post-shock gases, providing speciation data on oxidation products as a function of temperature. The speciation results were simulated using the CRECK (CRECK_2003_TOT_HT_LT), LLNL, and Zeng_Xie mechanisms. All three mechanisms simulated the experimental speciation data well, with the CRECK mechanism demonstrating the best overall agreement. At lower temperatures (∼740 K) and under fuel-lean conditions (φ = 0.25), negative temperature coefficient (NTC) behavior was observed in both the reactants and the oxidation products, specifically in alkenes and aldehydes. Rate of production, sensitivity, and reaction path analyses were also conducted to investigate the reactions affecting the oxidation process. The primary reaction channel that initiates the oxidation process is H-abstraction by OH radicals, along with an additional H-abstraction reaction channel by HO₂ radicals, particularly under fuel-lean conditions. The formation of trimethylbenzyl radicals (RC₉H₁₁) from 1,2,4-trimethylbenzene decomposition inhibits the oxidation process, slowing down radical generation and, consequently, affecting the reactivity of n-heptane and the overall HTMB blend.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114223"},"PeriodicalIF":5.8,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143931720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}