Combustion and Flame最新文献

{"title":"Flame-induced pressure gradients in turbulent premixed natural gas-air and hydrogen-air jet flames","authors":"Luuk A. Altenburg,&nbsp;Sikke A. Klein,&nbsp;Mark J. Tummers","doi":"10.1016/j.combustflame.2025.114314","DOIUrl":"10.1016/j.combustflame.2025.114314","url":null,"abstract":"<div><div>This study focuses on flame-induced pressure gradients in turbulent premixed jet flames and its potential role in the occurrence of flame flashback. A new procedure is proposed to determine these pressure gradients experimentally from the Favre-averaged momentum equations. The procedure involves a novel experimental method to determine Favre-averaged quantities from particle image velocimetry data. The resulting pressure distributions are compared for two fuel-air mixtures with identical unstretched laminar flame speed (a stoichiometric natural gas-air mixture and a lean (<span><math><mrow><mi>ϕ</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>49</mn></mrow></math></span>) hydrogen-air mixture) for stable and near-flashback conditions. In all four cases the flame-induced pressure gradients are closely related to the intermittent behavior of the flame. Furthermore, the pressure gradients for the stable and near-flashback flames show only small differences indicating that the mean pressure distribution is not a suitable indicator for the occurrence of flame flashback. Detailed analysis shows a mild, but systematic shift in the orientation of the instantaneous flame fronts, which tend to align more perpendicular to the flow for the flames closer to flashback. This change in orientation results in local deceleration of the flow, thus increasing the probability of flashback.</div><div><strong>Novelty and significance</strong></div><div>This work presents original results of experiments in premixed hydrogen-air and natural gas-air turbulent jet flames. A new methodology is introduced to calculate Favre-averaged quantities and the pressure field in a flame from a combination of PIV and Mie scattering measurements. The focus of the experiments and follow up analyses is on the flame characteristics near flashback, since flame flashback is one of the phenomena that hampers the transition from the use of natural gas to hydrogen in, for example, gas turbines.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114314"},"PeriodicalIF":5.8,"publicationDate":"2025-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144631375","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":"Analytical study of a flame propagation front in a solid phase driven by chain-branching reactions at large Zel’dovich numbers: Steady states, stability and influence of the radicals Lewis number","authors":"Mario Napieralski ,&nbsp;Cesar Huete ,&nbsp;Mario Sanchez-Sanz ,&nbsp;Vadim N. Kurdyumov","doi":"10.1016/j.combustflame.2025.114331","DOIUrl":"10.1016/j.combustflame.2025.114331","url":null,"abstract":"<div><div>The combustion wave propagation in the condensed phase is investigated analytically in the large Zel’dovich number limit. The study is based on a two-step chain branching model for combustion reactions in which the flammability limit is explicitly present. As is common in gasless combustion, the diffusion of the initial fuel is assumed to be negligible. However, the effect of intermediate product diffusion on wave propagation velocity is analyzed, along with the stability of the corresponding dynamic response. With heat release as the controlling parameter, a Hopf bifurcation is encountered as the parameter decreases, leading to the emergence of an oscillatory instability. It is found that this instability ultimately leads to the extinction of the combustion wave, even under adiabatic conditions. Additionally, the effect of heat loss on flame stability and dynamics is examined.</div><div><strong>Novelty and significance statement</strong> For the first time, the analysis of combustion wave propagation in the solid phase using a two-stage chain branching combustion model is performed in analytical form. In the absence of fuel diffusion, which is natural for combustion in the condensed phase, the effect of the final diffusion of intermediate radicals is investigated. The effect of volumetric losses is also studied. The results are obtained for stationary solutions of propagation and their stability is investigated. It is shown that even in the absence of heat loss, there is a region of parameters in which the combustion wave is unstable, which leads to its extinction.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114331"},"PeriodicalIF":5.8,"publicationDate":"2025-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144614146","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":"Exploring the survival of premixed hydrogen flames below the lean flammability limit","authors":"E. Fernández-Tarrazo ,&nbsp;R. Gómez-Miguel ,&nbsp;M. Sánchez-Sanz","doi":"10.1016/j.combustflame.2025.114315","DOIUrl":"10.1016/j.combustflame.2025.114315","url":null,"abstract":"<div><div>Ultra-lean hydrogen flames, which can ignite unintentionally due to leaks near a heat or power source, pose significant safety risks. This study investigates why flames propagate at equivalence ratios below the theoretical flammability limit (<span><math><mrow><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>l</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>255</mn></mrow></math></span>), where the equilibrium temperature equals the crossover temperature. To find the answer, we use detailed chemistry to numerically study the conditions that explain recent experimental observations of flame propagation in confined channels at equivalence ratios <span><math><mrow><mi>ϕ</mi><mo>&lt;</mo><mn>0</mn><mo>.</mo><mn>2</mn></mrow></math></span>.</div><div>Our simulations consider a two-dimensional geometry of two parallel plates separated by a small distance to form a straight channel. Adiabatic and isothermal boundary conditions are considered at the walls to evaluate the effect of heat losses on the survival of the flame. The flame curvature, caused by the confinement within the narrow channel, leads to the formation of a high-temperature region near the center of the channel. This region is surrounded by unburned gas flowing close to the channel walls. The reaction is then sustained by the hydrogen that diffuses from the low-temperature region to the reactive front. This behavior is unique to fuels or fuel blends with sufficiently high mass diffusivity and does not occur when the Lewis number is near or above unity. A new scaling, that accounts for the flame curvature to define the characteristic velocity and lengths scales, is proposed to describe the flame dynamics at equivalence ratios near the flammability limit. According to our calculations, self-sustained 2D hydrogen flames may exist at equivalence ratios as low as <span><math><mrow><mi>ϕ</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>15</mn></mrow></math></span>, a threshold determined by the existence of a stationary flat flame that is unaffected by heat losses.</div><div><strong>Novelty and significance</strong></div><div>This study investigates the conditions under which steady flame propagation occurs below the lean flammability limit in channels, with a systematic analysis of the influence of boundary conditions. Notably, our findings reveal that imposing adiabatic or isothermal boundary conditions on the walls plays only a secondary role in flame survival. The propagation velocity and flame shape are shown to be largely independent of heat losses. Instead, hydrogen’s high mass diffusivity becomes the primary driver, inducing a significant flame curvature that creates a high-temperature region locally enriched by the rapid diffusion of hydrogen from the cold mixture towards the reactive front. Furthermore, this work introduces new characteristic velocity and length scales, specifically tailored for ultra-lean equivalence ratios, where planar flames cannot exist.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114315"},"PeriodicalIF":5.8,"publicationDate":"2025-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144595415","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":"Flame-wall interaction of thermodiffusively unstable hydrogen/air flames, Part II: Parametric variations of equivalence ratio, temperature, and pressure","authors":"Max Schneider,&nbsp;Hendrik Nicolai,&nbsp;Vinzenz Schuh,&nbsp;Matthias Steinhausen,&nbsp;Christian Hasse","doi":"10.1016/j.combustflame.2025.114319","DOIUrl":"10.1016/j.combustflame.2025.114319","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Fuel-lean hydrogen combustion systems hold significant potential for low pollutant emissions, but are also susceptible to intrinsic flame instabilities. While most research on these instabilities has focused on flames without wall confinement, practical combustors are typically enclosed by walls that strongly influence the combustion dynamics. In part I of this work (Schneider et al., Combust. Flame, 2025), the flame-wall interaction of intrinsically unstable hydrogen/air flames has been studied for a single operating condition through detailed numerical simulations in a two-dimensional head-on quenching configuration. This study builds upon the previous investigation by examining a wide range of gas turbine and engine-relevant operating conditions, including variations in equivalence ratio (0.4–1.0), unburnt gas temperature (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mtext&gt;298&lt;/mtext&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mtext&gt;K&lt;/mtext&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;–&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mtext&gt;700&lt;/mtext&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mtext&gt;K&lt;/mtext&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;), and pressure (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mtext&gt;1.013 25&lt;/mtext&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mtext&gt;bar&lt;/mtext&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;–&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mtext&gt;20&lt;/mtext&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mtext&gt;bar&lt;/mtext&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;). These parametric variations allow for a detailed analysis and establish a baseline for modeling the effects of varying instability intensities on the quenching process, as the intensity of thermodiffusive and hydrodynamic instabilities depends on the operating conditions. While the quenching characteristics remain largely unaffected by hydrodynamic instabilities, the presence of thermodiffusive instabilities significantly increases the mean wall-heat flux and reduces the mean quenching distance. Furthermore, the impact of thermodiffusive instabilities on the quenching process intensifies as their intensity increases, driven by an increase in pressures and a decrease in equivalence ratio and unburnt gas temperature. The corresponding relative increase in wall heat flux, compared to a one-dimensional inherently stable head-on quenching flame under identical operating conditions, strongly correlates with the enhanced local reactivity associated with the thermodiffusive instability across all operating conditions. Finally, a joint model fit is proposed to estimate the relative increase in wall heat flux due to intrinsic flame instabilities based on characteristic quantities of a corresponding stable one-dimensional freely-propagating flame.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and Significance Statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This work presents a novel parametric study of flame-wall interactions (head-on quenching) of intrinsically unstable hydrogen/air flames. It builds upon an investigation of an unstable head-on quenching hydrogen/air flame (part I (Schneider et al., Combust. Flame, 2025)) and extends it to a wide range of operation conditions, including variations in equivalence ratio, unburnt gas temperature, and pressure. Additionally, simulatio","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114319"},"PeriodicalIF":5.8,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144596387","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":"An experimental and kinetic modeling study of ethyl tert‑butyl ether. Part II: Intermediate and low temperature oxidation chemistry","authors":"Jin-Tao Chen ,&nbsp;A. Abd El-Sabor Mohamed ,&nbsp;Jiaxin Liu ,&nbsp;Shangkun Zhou ,&nbsp;Zijian Qi ,&nbsp;Hossein S. Saraee ,&nbsp;Yang Li ,&nbsp;Chong-Wen Zhou ,&nbsp;Henry J. Curran","doi":"10.1016/j.combustflame.2025.114342","DOIUrl":"10.1016/j.combustflame.2025.114342","url":null,"abstract":"<div><div>Ethyl tert‑butyl ether (ETBE) has captured significant research attention due to its potential to reduce harmful emissions and consequently it is used as an oxygenate additive in gasoline. A comprehensive low- to high-temperature chemistry sub-model for ETBE has been developed for the first time and is validated against experimental data including ignition delay times (IDTs), species profiles, and laminar flame speeds. This paper focuses on the low- to intermediate-temperature kinetics of ETBE oxidation. IDTs of ETBE mixtures are measured in both a high-pressure shock tube (HPST) and in a rapid compression machine (RCM) at pressures of 15 and 30 bar in the temperature range 615–1376 K at equivalence ratios of 0.5, 1.0, and 2.0 in ‘air’. The observed negative temperature coefficient behavior in ETBE oxidation can be explained by the competition between the reactions involving the formation of cyclic ethers and tert‑butyl vinyl ether (TBVE), and the reactions associated with the formation and consumption of carbonyl hydroperoxide species. Moreover, IDTs of 2,2-dimethylbutane (22DMB) and 2,2-dimethylpentane (22DMP) mixtures were also measured at 15 and 30 bar in the temperature range 666–1300 K at stoichiometric conditions in ‘air’ in order to compare the reactivities of these alkanes with their corresponding ethers, methyl tert‑butyl ether (MTBE) and ETBE. The oxygen lone pair in both MTBE and ETBE reduces the adjacent α C–H bond dissociation energy, making hydrogen atom abstraction at that site more facile which results in higher ether fuel reactivity at temperatures above 1000 K. At temperatures below 1000 K, the substitution of the corresponding secondary carbon atom in alkanes with an oxygen atom in ethers results in a much lower flux of fuel forming <span><math><mover><mi>Q</mi><mo>˙</mo></mover></math></span>OOH radicals via a six-membered ring transition state which is the key species leading to low-temperature chain-branching reactions. This is why the reactivities of MTBE and ETBE are almost two orders of magnitude <em>lower</em> than their alkane counterparts 22DMB and 22DMP in the negative temperature coefficient region. Conversely, dimethyl ether displays nearly two orders of magnitude <em>higher</em> reactivity compared to propane at lower temperatures, because of the much higher fuel flux of RȮ₂ radicals proceeding to chain branching pathways through a six-membered ring transition state isomerization reaction compared to propane. This comparative analysis provides fundamental insights into structure-reactivity relationships in oxygenated fuel combustion chemistry.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114342"},"PeriodicalIF":5.8,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144587545","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":"Laminar flames and chemical kinetics analysis of NH3/NO and NH3/N2O mixtures in the absence of oxygen","authors":"Biao Liu,&nbsp;Zunhua Zhang,&nbsp;Mengni Zhou,&nbsp;Gesheng Li","doi":"10.1016/j.combustflame.2025.114341","DOIUrl":"10.1016/j.combustflame.2025.114341","url":null,"abstract":"<div><div>Ammonia, as a zero-carbon fuel, has attracted significant attention. However, its combustion can lead to the emission of nitrogen oxides. While ammonia can reduce nitrogen oxides, the mechanism by which ammonia interacts with N<em>_i</em>O (<em>i</em> = 1 and 2) remains unclear. In this study, the laminar burning velocities (LBVs) of NH₃/N<em>_i</em>O/N₂ (Ar) mixtures were measured using a high-pressure constant volume combustion platform. The predictive performances of 16 ammonia chemical kinetic mechanisms were assessed by calculating the mean relative errors (MREs) against experimental data. Additionally, the chemical kinetic interactions between NH₃ and N<em>_i</em>O in the flames were analyzed. The results show that the LBVs of NH₃/NO/N₂ mixtures initially increase and then decrease as the equivalence ratio rises from 1.1 to 1.9, peaking near 1.4. Similarly, the LBVs of NH₃/N₂O/N₂ mixtures initially increase and then decrease as the equivalence ratio rises from 0.7 to 1.5, peaking around 1.05. With an increasing N<em>_i</em>O mixture ratio, the LBVs of the NH₃/N<em>_i</em>O/N₂ mixtures increase linearly. The LBVs of the NH₃/N<em>_i</em>O/N₂ mixtures increase with higher initial temperatures and decrease with higher initial pressures. Among the 16 mechanisms, those that accurately predict the LBVs of NH₃/N₂O/N₂ (Ar) mixtures may show significant MREs in predicting the LBVs of NH₃/NO/N₂ (Ar) mixtures. In NH₃/NO flames, NO directly reacts with key intermediates (ṄH₂ and <span><math><mrow><mover><mi>N</mi><mo>¨</mo></mover><mi>H</mi></mrow></math></span>) in NH₃ decomposition process. This indicates that NH₃ has strong selectivity for reactions with NO. In NH₃/N₂O flames, the Ö radical generated from the self-decomposition of N₂O, along with the reaction between N₂O and Ḣ radical to produce ȮH radical, further enhance the reactivity of NH₃ combustion system. The reduction of N₂O by NH₃ exhibits relatively low selectivity.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114341"},"PeriodicalIF":5.8,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144596386","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":"Revealing crucial role of fuel radicals in the pyrolysis chemistry of 1,2-dimethoxybenzene serving as a model system for lignin","authors":"Jigang Gao ,&nbsp;Jijun Guo ,&nbsp;Zaili Xiong ,&nbsp;Peiqi Liu ,&nbsp;Chen Huang ,&nbsp;Wenhao Yuan ,&nbsp;Long Zhao ,&nbsp;Meirong Zeng","doi":"10.1016/j.combustflame.2025.114344","DOIUrl":"10.1016/j.combustflame.2025.114344","url":null,"abstract":"<div><div>Understanding the pyrolysis mechanism of lignin, a key renewable biomass, is crucial for its effective utilization in mitigating environmental challenges. This work explored the pyrolysis mechanism of 1,2-dimethoxybenzene (DMOB), a lignin model compound, in a flow reactor at 0.04 atm and 873–1083 K. Using a synchrotron vacuum ultraviolet radiation photoionization mass spectrometer, various featured C_8<img>C₆ products, including 2-hydroxybenzaldehyde and 2-methylanisole, as well as smaller C_5<img>C₁ species, were detected. A detailed kinetic model was developed, revealing that DMOB mainly decomposes via unimolecular O<img>CH₃ bond cleavage, forming a 2-methoxyphenoxy radical, which elucidates the formation of 2-hydroxybenzaldehyde. Additionally, bimolecular reactions, such as ipso-substitution and H-abstraction, play a pivotal role in DMOB decomposition and products formation, accounting for approximately 49 % of DMOB consumption at 963 K. These reactions contribute the formation of 2-methylanisole, anisole, and guaiacol. Moreover, DMOB-related reactions significantly contribute to the formation of smaller C_5<img>C₁ products, with the unimolecular methyl elimination reaction exhibiting the highest sensitivity to the formation of methane and carbon monoxide. Finally, when comparing DMOB to two other lignin model compounds with distinct side chains, i.e., anisole and guaiacol, it was observed that the corresponding fuel radicals, formed during the pyrolysis of these three compounds, play a vital role in controlling the products distribution. In summary, this work provides valuable insights into the pyrolysis behaviors of lignin model systems, which have significant potential for elucidating the pyrolysis mechanism of lignin.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114344"},"PeriodicalIF":5.8,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144596888","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":"A detailed kinetic model for the pyrolysis and oxidation of monomethylhydrazine","authors":"Yifan Cheng ,&nbsp;Qian Mao ,&nbsp;Baolu Shi ,&nbsp;Xiao Hou","doi":"10.1016/j.combustflame.2025.114328","DOIUrl":"10.1016/j.combustflame.2025.114328","url":null,"abstract":"<div><div>Hydrazine-based fuels, especially monomethylhydrazine(MMH), are widely used as liquid rocket engine propellants for deep space exploration and attitude control because of their high-energy content, versatility, and reactivity. The combustion process of MMH strongly influences heat release and engine performance. An accurate and detailed kinetic model is of crucial importance to predict the pyrolysis and combustion behavior of MMH with oxidizers in liquid rocket engines. In this study, a new detailed MMH pyrolysis and oxidation kinetic model (including 106 species and 710 reactions) was developed by incorporating recent advances in <em>ab initio</em> calculations and experimental studies. The kinetic model was tested and validated against a comprehensive set of experimental data from MMH pyrolysis and oxidation over a wide range of operating conditions with the temperature range of 884–1418 K and the pressure from 0.32 to 5.2 atm. The proposed kinetic model displays good predictions of induction delay from pyrolysis conditions, ignition delay time from oxidation conditions, and speciation experimental profiles from both pyrolysis and oxidation. In particular, the prediction of the ignition delay time from 30 sets of MMH oxidation by O₂ experiments presents satisfactory agreement with the experimental measurements, with a maximum deviation below a factor of two. This is significantly improved compared to previous MMH models. According to the kinetic modeling, the N<img>N fission and the H-abstraction of MMH by CH₃ were found to be the most sensitive reactions for the consumption of MMH in pyrolysis conditions. Nevertheless, the fission of the N<img>N bonds in MMH and its radicals plays a significant role in MMH oxidation by O₂. Sensitivity analysis of the ignition delay time indicates that sequential H-abstraction reactions were crucial for the ignition of MMH with O₂.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114328"},"PeriodicalIF":5.8,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144595414","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":"Continuous combustion of ammonia in a bubbling fluidized bed: Experimental and simulation study","authors":"Suyang Pan ,&nbsp;Jiliang Ma ,&nbsp;Xiaoping Chen ,&nbsp;Wenming Yang","doi":"10.1016/j.combustflame.2025.114343","DOIUrl":"10.1016/j.combustflame.2025.114343","url":null,"abstract":"<div><div>Ammonia, as a carbon-free energy carrier, supports the large-scale use of renewable energy, and its combustion is a key utilization pathway. This study examines the continuous combustion of ammonia in a bubbling fluidized bed using experiments and numerical simulations. The effects of equivalence ratio, fluidization velocity, secondary air injection location, and secondary oxygen ratio were investigated. Measurements focused on temperature distribution, ammonia conversion, and NO emissions, while simulations based on a two-fluid model revealed key reaction pathways. Results show that combustion mainly occurs in the dense phase. Lower equivalence ratios increase NO emissions, while fuel-rich conditions reduce NO but lower ammonia conversion. Higher fluidization velocity shortens residence time, reducing both NO emissions and conversion. The dense phase shows a catalytic effect on ammonia decomposition, affecting reactor temperature. At 900 °C, equivalence ratio of 1, and 40 % diluted oxygen, the main pathway from NH₃ to NO is: NH₃ → NH₂ → H₂NO → HNO → NO Notably, staged combustion, though typically used for NO reduction, increases NO and N₂O emissions in fluidized beds due to higher freeboard temperatures and enhanced conversion of NH₂/NH to NO.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114343"},"PeriodicalIF":5.8,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144587564","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":"Flame-wall interaction of thermodiffusively unstable hydrogen/air flames, Part I: Characterization of governing physical phenomena","authors":"Max Schneider,&nbsp;Hendrik Nicolai,&nbsp;Vinzenz Schuh,&nbsp;Matthias Steinhausen,&nbsp;Christian Hasse","doi":"10.1016/j.combustflame.2025.114320","DOIUrl":"10.1016/j.combustflame.2025.114320","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Hydrogen combustion systems operated under fuel-lean conditions offer great potential for low emissions. However, these operating conditions are also susceptible to intrinsic flame instabilities. Even though technical combustors are enclosed by walls that significantly influence the combustion process, intrinsic flame instabilities have mostly been investigated in canonical freely-propagating flame configurations unconfined by walls. This study aims to close this gap by investigating the flame-wall interaction of thermodiffusive unstable hydrogen/air flame through detailed numerical simulations in a two-dimensional head-on quenching configuration. It presents an in-depth qualitative and quantitative analysis of the quenching process, revealing the major impact factors of the instabilities on the quenching characteristics. The thermodiffusive instabilities result in lower quenching distances and increased wall heat fluxes compared to one-dimensional head-on quenching flames under similar operation conditions. The change in quenching characteristics is shown not to be driven by kinematic effects. Instead, the increased wall heat fluxes are caused by the enhanced flame reactivity of the unstable flame approaching the wall, which results from mixture variations associated with the instabilities. Overall, the study highlights the importance of studying flame-wall interaction in more complex domains than simple one-dimensional configurations, where such instabilities are inherently suppressed. Further, it emphasizes the need to incorporate local mixture variations induced by intrinsic combustion instabilities in combustion models for flame-wall interactions. In part II of this study, the scope is expanded to gas turbine and internal combustion engine relevant conditions through a parametric study, varying the equivalence ratio, pressure, and unburnt temperature.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and Significance Statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This work presents novel simulations and in-depth analysis of flame-wall interaction (head-on quenching) of laminar thermodiffusively unstable hydrogen/air flames. Thermodiffusive instabilities are significant in technical combustion chambers enclosed by walls, such as gas turbines and internal combustion engines, particularly under lean conditions, where they raise safety concerns like flame flashback and increased thermal loads on walls. The study shows that these instabilities strongly affect flame-wall interaction, leading to smaller quenching distances and higher wall heat fluxes than in one-dimensional head-on quenching. Consequently, this work demonstrates that for flames susceptible to instabilities, such as lean hydrogen/air flames, one-dimensional head-on quenching simulations are inadequate for accurately determining wall heat fluxes and quenching distances. Additionally, this study highlights that differential diffusion effects induced by the intrinsic instabilities must be considered in combustion mod","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114320"},"PeriodicalIF":5.8,"publicationDate":"2025-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144580700","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}