Combustion and Flame最新文献

{"title":"Ignition and combustion characteristics of micron-sized Al-Mg alloy particles in water vapour atmosphere","authors":"Ronggang Wei ,&nbsp;Kai Ma ,&nbsp;Yu Fu ,&nbsp;Chunbo Hu","doi":"10.1016/j.combustflame.2025.114482","DOIUrl":"10.1016/j.combustflame.2025.114482","url":null,"abstract":"<div><div>This paper addresses ignition start-up challenges and low combustion efficiency in aluminum-water reactions by proposing the use of Al-Mg alloy particles to enhance ignition and combustion through microexplosion phenomena. Experiments were conducted in a high-temperature furnace with adjustable temperature and pressure in a water vapor environment, varying magnesium content, particle size, ambient conditions to study their impact on ignition delay time (<span><math><msub><mi>t</mi><mtext>ig</mtext></msub></math></span>), microexplosion generation time (<span><math><msub><mi>t</mi><mtext>expl</mtext></msub></math></span>), combustion time (<span><math><msub><mi>t</mi><mtext>com</mtext></msub></math></span>), and ignition temperature (<span><math><msub><mi>T</mi><mtext>ig</mtext></msub></math></span>). Key findings include: <span><math><msub><mi>t</mi><mtext>ig</mtext></msub></math></span> for Al-Mg particles fluctuates between 50 ms to 200 ms, secondary particles from microexplosion reduce combustion particle size significantly, and <span><math><msub><mi>t</mi><mtext>com</mtext></msub></math></span> ranges from 3 ms to 10 ms. The study shows consistency with theoretical expectations in the pre-microexplosion stage, while post-microexplosion reveals opposing effects of ambient temperature and pressure on <span><math><msub><mi>t</mi><mtext>com</mtext></msub></math></span>. Empirical equations for Al-Mg particle ignition and combustion characteristics in a water vapor atmosphere were derived, aiding in predicting effects by adjusting variable parameters. These results support the development of an (Al-Mg)/H₂O microexplosion model and engine combustion design.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114482"},"PeriodicalIF":6.2,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107629","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":"Modelling thermodiffusive instabilities in hydrogen flames and their impact on the combustion process in a direct-injection hydrogen engine","authors":"Andrea Scalambro,&nbsp;Andrea Piano,&nbsp;Federico Millo","doi":"10.1016/j.combustflame.2025.114457","DOIUrl":"10.1016/j.combustflame.2025.114457","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Hydrogen-fueled Internal Combustion Engines (H&lt;sub&gt;2&lt;/sub&gt;-ICEs) are typically operated with lean mixtures to minimize NOx emissions and reduce the risk of abnormal combustion events. Due to hydrogen’s low Lewis number, premixed hydrogen-air flames in lean conditions exhibit strong thermodiffusive instabilities, which make the numerical simulation of the combustion process particularly challenging. Indeed, the intensity of these instabilities is significantly influenced by thermodynamic parameters – such as mixture temperature, pressure, and dilution rate – resulting in substantial variations in combustion behaviour across different operating conditions. Therefore, they have to be properly considered not only to ensure model robustness, but also to improve model accuracy over a wider range of operations. In this study, the combustion process in a Direct Injection H&lt;sub&gt;2&lt;/sub&gt;-ICE was analyzed using 3D-CFD simulations, relying on a flamelet-based combustion model. Two sets of lookup flame speed maps were defined: laminar flame speed (&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;) maps derived from standard 1D-CFD simulations in homogeneous reactor, and freely propagating flame speed (&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;) maps which account for the effects of thermodiffusive instabilities. The model that uses &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; maps required the recalibration of some combustion model parameters when changing the dilution rate to ensure consistency with experimental data. Instead, the model relying on &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; maps featured a noticeable accuracy across different air-to-fuel ratios without the need for recalibration any combustion model parameter, highlighting the key role of thermodiffusive flame instabilities on the combustion process. Based on these findings, the impact of such instabilities was evaluated throughout the entire combustion process from both global and local perspectives. The relevance of thermodiffusive instabilities was observed to increase with the air-to-fuel ratio, thereby enhancing combustion speed in leaner mixtures. Additionally, the implementation of thermodiffusive instabilities was found to affect also preferred direction of flame propagation, as stronger instabilities were identified in the leanest and low-temperature portions of the flame front.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This study addresses a critical knowledge gap regarding the role of thermodiffusive flame instabilities in accurately replicating the combustion process of a direct-injection internal combustion engine within a RANS simulation framework. Indeed, while these instabilities have been shown to significantly enhance the mixture consumption rate in quiescent environments at low to moderate pressures and temperatures, particularly in lean mixtures, their impact on the burn rate under engi","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114457"},"PeriodicalIF":6.2,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107498","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":"Studies of real-fluid supercritical simulation using the 3rd virial equation of state based on Boltzmann-weighted Full-dimensional potential","authors":"Xin Zhang,&nbsp;Junfeng Bai,&nbsp;Hao Zhao","doi":"10.1016/j.combustflame.2025.114465","DOIUrl":"10.1016/j.combustflame.2025.114465","url":null,"abstract":"<div><div>Under extreme conditions such as supercritical combustion, real-fluid effects become significant, necessitating accurate and robust simulation methodologies for high-pressure environments. In this study, we propose a real-fluid simulation method, the BWF-Virial method, which integrates the Boltzmann-weighted Full-dimensional (BWF) potential into the virial equation of state (EoS) for physical properties and combustion characteristics simulations under high to ultra-high pressures. Based on the BWF potential model, the second and third virial coefficients, along with their corresponding thermodynamic and transport properties, are rigorously derived. These methods are subsequently integrated into the Cantera software package, establishing a comprehensive real-fluid simulation platform. The BWF-Virial method attains the accuracy of the third-order virial EoS, thereby offering a precise description of real-fluid behavior for various fuels. Its effectiveness has been validated through thermodynamic and transport property calculations across various species, with relative errors of 0.1%–10%. We further investigate zero-dimensional and one-dimensional combustion characteristics of supercritical methane and n-heptane. The BWF-Virial method demonstrates strong robustness and predictive accuracy in modeling combustion phenomena across a wide range of extreme operating conditions. Compared to the LJ-Virial method, it exhibits a 5%–20% difference, aligning more closely with experimental data and reinforcing its potential for high-fidelity supercritical combustion simulations.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this research lies in the development of the BWF-Virial method for real-fluid supercritical simulations. Real-fluid effects are significantly amplified in non-ideal flows, such as supercritical fluids and plasmas. These flows are highly relevant to propulsion and energy conversion processes. Unfortunately, the real-fluid intermolecular interactions in the literature are mainly based on the Lennard-Jones potential, which reveals significant errors for physical properties and combustion simulations at high to ultra-high pressures, especially for polar and long-chain molecules. The BWF-Virial method can effectively overcome these limitations. It provides comprehensive and robust support in (i) the thermodynamic and transport property library establishment for polar and long-chain molecules, (ii) the reactive real-fluid combustion simulations, and (iii) the physical investigations of real-fluid impact on reactive flow simulations.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114465"},"PeriodicalIF":6.2,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107630","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":"Quenching and pollutant emissions in side-wall and head-on NH3/H2/N2 premixed laminar flames","authors":"Olivier Chabot,&nbsp;Bruno Savard","doi":"10.1016/j.combustflame.2025.114463","DOIUrl":"10.1016/j.combustflame.2025.114463","url":null,"abstract":"&lt;div&gt;&lt;div&gt;We present quenching distance, wall heat loss, and pollutant emission results from a series of simulations of NH&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/N&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; premixed laminar flames in side-wall and head-on quenching configurations. Conditions cover lean to rich mixtures (equivalence ratio from 0.3 to 1.2) at both atmospheric and moderate (10 atm) pressures. For each set of conditions, two-dimensional “V”-flame simulations with side-wall quenching (SWQ) and with symmetric boundary conditions are compared to isolate wall heat loss from curvature effects. Simulations of one-dimensional head-on quenched (HOQ) flames covering the same range of conditions are also included for further comparison. First, a non-monotonic relationship between quenching Peclet number and equivalence ratio is found at 10 atm for both SWQ and HOQ, attributed to a significant change in flame structure at lean conditions, with the Jiang chemical kinetics mechanism. Second, wall heat loss normalized by laminar flame power is lower for HOQ flames, compared to SWQ, at lean conditions and higher at rich conditions, which is attributed to the effect of flame curvature on heat release rate in SWQ flames. Yet, normalized wall heat loss shows a similar correlation with quenching Peclet number for both pressures and quenching configurations. Third, similar to previously reported experimental results, we find that ammonia slip increases due to wall heat loss and curvature effects, while hydrogen slip departs negligibly from that of unstretched laminar flames. The contrast with ammonia slip is striking at low equivalence ratio and is attributed to the strongly diverging flux of hydrogen near the quenching point, promoting its consumption. Fourth, both wall heat loss and negative flame curvature at the wall significantly reduce NO emissions as the rates of NO forming reaction pathways are diminished. In the SWQ cases, NO consuming pathways are comparatively less inhibited, being in part fed by NO diffusing towards the wall from non-quenched regions. Finally, both negative curvature at the wall and wall heat loss increase N&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O emissions. A non-monotonic relationship between N&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O emissions and equivalence ratio is observed at elevated pressure, as the rate of the N&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O consuming reaction &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; increases for equivalence ratios below 0.6.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;We present the first flame-resolved simulations at elevated pressure of side-wall quenching (SWQ) and head-on quenching (HOQ) in NH&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;m","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114463"},"PeriodicalIF":6.2,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107631","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":"Measurements of NO in the post-flame region of laminar premixed ammonia/methane-air flames using laser-induced fluorescence","authors":"M. Richter ,&nbsp;J. Lill ,&nbsp;R.S. Barlow ,&nbsp;A. Dreizler ,&nbsp;J.R. Dawson ,&nbsp;D. Geyer","doi":"10.1016/j.combustflame.2025.114450","DOIUrl":"10.1016/j.combustflame.2025.114450","url":null,"abstract":"<div><div>Cofiring of ammonia (NH₃) with methane (CH₄) offers a promising route to enhance the combustion characteristics of pure ammonia while partially decarbonizing methane-based energy systems. However, the presence of fuel-bound nitrogen in ammonia leads to elevated NOx emissions. Although NO measurements in NH₃-containing flames have been reported, there is a notable lack of validation datasets for NH₃/CH₄ cofiring based on non-intrusive diagnostics. In this communication, a laser-induced fluorescence (LIF) approach recently developed for post-flame NO measurements is applied to NH₃/CH₄-air flames with CH₄ contents ranging from 50 vol.-% to 80 vol.-% in the fuel mixture. The LIF signal processing includes corrections for laser absorption, signal trapping, and pulse energy fluctuations. Thermochemical differences between calibration and target flames are addressed through corrections for number density, Boltzmann fraction, spectral line overlap, and electronic quenching. The results show good agreement with recent chemical kinetic models over a broad range of conditions. Within the tested range, increasing the NH₃ content results in a notable reduction of NO emissions under fuel-rich conditions, while the opposite trend is observed under fuel-lean conditions. The observed NO trends are interpreted using normalized radical pool indicators for <figure><img></figure> and O/H/OH species.</div><div><strong>Novelty and Significance</strong></div><div>Quantitative data on NO emissions from ammonia-based fuels remain limited, especially those obtained using non-intrusive diagnostics. In this paper, we extend a previously presented laser-induced fluorescence (LIF) method to measure post-flame NO concentrations in NH₃/CH₄-air flames across a broad range of equivalence ratios and fuel compositions. The dataset covers CH₄ contents from 50 to 80 vol.%. By introducing normalized radical pool indicators for <figure><img></figure> and O/H/OH species, the work helps to interpret observed NO trends. The results provide a basis for refining chemical kinetic models with respect to NO formation.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114450"},"PeriodicalIF":6.2,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145061356","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":"C3MechLite: An integrated component library of compact kinetic mechanisms for low-carbon, carbon neutral and zero-carbon fuels","authors":"Yuki Murakami ,&nbsp;Quan-De Wang ,&nbsp;Shuaishuai Liu ,&nbsp;Yuxiang Zhu ,&nbsp;Pengzhi Wang ,&nbsp;Luna Pratali Maffei ,&nbsp;Raymond Langer ,&nbsp;Tiziano Faravelli ,&nbsp;Heinz Pitsch ,&nbsp;Stephen J Klippenstein ,&nbsp;Jeff Bergthorson ,&nbsp;Gilles Bourque ,&nbsp;Scott Wagnon ,&nbsp;Peter Kelly Senecal ,&nbsp;Henry Curran","doi":"10.1016/j.combustflame.2025.114410","DOIUrl":"10.1016/j.combustflame.2025.114410","url":null,"abstract":"<div><div>Based on our latest detailed chemical reaction mechanism, C3MechV4.0, we have developed two reduced reaction mechanisms—C3MechLite and C3MechCore—targeting C₀–C₃ chemical species including NH₃. C3MechLite (61 species), contains a number of species comparable to GRI-Mech (53 species), that can accurately predict the combustion characteristics of hydrogen, carbon monoxide, ammonia, methane, natural gas, nitrogen oxides, and their mixtures for a wide range of conditions. C3MechCore (118 species) targets a more comprehensive range of C₀–C₃ fuels, including ammonia, methanol, ethanol, and dimethyl ether. Both mechanisms demonstrate predictive accuracy comparable to C3MechV4.0 for the combustion characteristics of the target fuels. C3MechLite is designed with a component library structure, enabling further reduction in mechanism size depending on the fuel(s) of interest for 2D/3D numerical simulations. Various combinations of component libraries were validated, and the average prediction error remains within 1 % compared to C3MechLite. Furthermore, the mechanism was applied to 3D LES simulations of H₂ lifted flames and was confirmed to reproduce flame characteristics with high accuracy. C3MechLite and its component library structure enable high-fidelity and computationally efficient chemical kinetic mechanisms, paving the way for application in more complex combustion simulations.</div></div><div><h3>Novelty and significance statement</h3><div>An integrated component library of compact kinetic mechanism is created based on C3MechV4.0, a comprehensive detailed chemical kinetic mechanism. The component library allows users to flexibly control the size of a mechanism to reduce computational costs without losing prediction accuracy. A new reduced chemical kinetic mechanism, C3MechLite, has a comparable number of chemical species (61 species) compared to GRI-Mech (53 species) and is applicable to a wider range of conditions (fuel blends, temperature and pressure) than GRI-Mech, with a comparable level of prediction accuracy as the detailed mechanism. The proposed component library and C3MechLite can be utilized in various simulation types and provide more accurate information of complex combustion phenomena.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114410"},"PeriodicalIF":6.2,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145061357","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":"Synergistic effects of hydrogen enrichment and propane-butane composition on deflagration dynamics of LPG-H2 premixed flame","authors":"Zhenzhen Zhao ,&nbsp;Yuntao Liang ,&nbsp;Xiaoxing Zhong ,&nbsp;Shuanglin Song ,&nbsp;Zhenqi Liu ,&nbsp;Tengfei Chen ,&nbsp;Lei Liu ,&nbsp;Lin Wang","doi":"10.1016/j.combustflame.2025.114467","DOIUrl":"10.1016/j.combustflame.2025.114467","url":null,"abstract":"<div><div>This study systematically investigates the deflagration characteristics of liquefied petroleum gas (LPG) and hydrogen (H₂) premixed fuels, focusing on the influence of hydrogen fraction (<em>X</em>_H) and propane proportion (<em>X</em>_p) in LPG on key parameters such as maximum flame propagation velocity (<em>V</em>_max), maximum pressure (<em>P</em>_max), thermal diffusivity (<em>D</em>_T), and heat loss (<em>Q</em>). The results reveal that when <em>X</em>_H is low (<em>X</em>_H≤0.2), the <em>V</em>_max increases with the increase of the <em>X</em>_p in LPG, while the <em>P</em>_max decreases. At higher <em>X</em>_H values (<em>X</em>_H&gt;0.2), a synergistic effect between <em>X</em>_H and <em>X</em>_P significantly enhances both <em>V</em>_max and <em>P</em>_max, with the most pronounced effect observed at a high hydrogen fraction (<em>X</em>_H=0.6). Furthermore, increasing both <em>X</em>_H and <em>X</em>_P improves the thermal diffusivity of the premixed fuel while reducing <em>Q</em> to the wall, with a linear negative correlation between the two. These findings indicate that high-diffusivity combustion systems exhibit superior thermal energy utilization efficiency, thereby enhancing the overall combustion reaction efficiency. This study provides critical theoretical insights and empirical data to guide the optimization and efficient utilization of LPG-H₂ premixed fuels.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114467"},"PeriodicalIF":6.2,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145047701","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":"Synergy of turbulence and thermo-diffusive effects on the intermittent boundary-layer flashback of swirling flames","authors":"Shiming Zhang ,&nbsp;Zhen Lu ,&nbsp;Yue Yang","doi":"10.1016/j.combustflame.2025.114458","DOIUrl":"10.1016/j.combustflame.2025.114458","url":null,"abstract":"<div><div>We simulated the intermittent boundary-layer flashback (BLF) of hydrogen-enriched swirling flames using large-eddy simulation (LES) with the flame-surface-density (FSD) method. Six cases of intermittent BLF, characterized by periodic flame entry and exit of the mixing tube, are presented. The intermittent BLF characteristics varied with the hydrogen volume fraction. Small flame bulges entered and exited the mixing tube in low hydrogen-enrichment cases. The duration of intermittent BLF events and BLF depth increased as the hydrogen content increased. Meanwhile, a large flame tongue penetrating deeply upstream characterized the highest hydrogen-enrichment case. The mean BLF peak depths and standard deviations obtained through simulations aligned well with experimental data for low and moderate hydrogen-enrichment cases. However, LES-FSD underestimated the average BLF peak depth for the highest hydrogen-enrichment case. Analysis of the flow-flame interaction revealed two mechanisms underlying the intermittent BLF phenomena. The flame bulges’ oscillation near the outlet is caused by the reverse flow induced by the recirculation zone. At the same time, the deep intermittent BLF occurs due to the boundary layer separation induced by the large turbulent burning velocity, resulting from the synergy of turbulence and thermo-diffusive effects.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114458"},"PeriodicalIF":6.2,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145045217","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":"Impact of the operating conditions on the OH* distribution and its correlation with the heat release rate in hydrogen–air flames","authors":"Francesco G. Schiavone ,&nbsp;Marco Torresi ,&nbsp;Sergio M. Camporeale ,&nbsp;Davide Laera","doi":"10.1016/j.combustflame.2025.114452","DOIUrl":"10.1016/j.combustflame.2025.114452","url":null,"abstract":"<div><div>OH* chemiluminescence is widely used as heat release rate (HRR) marker in combustion experiments. Still, its suitability for hydrogen–air flames has not been extensively assessed for a wide range of operative conditions and flame archetypes. In the present work, correlations between OH* and HRR spatial distributions are first investigated in one-dimensional unstretched laminar premixed flames at variable pressure ([1; 20] atm), unburned gas temperature ([300; 900] K), and equivalence ratio ([0.3; 3.0]). At atmospheric pressure and unburned gas temperature, two main differences are observed: a characteristic shift between the OH* and HRR peak positions and, for equivalence ratios close to stoichiometry, the presence of a non-negligible concentration of OH* in the post-flame zone, where the HRR value is zero. When pressure and unburned gas temperature are increased, the peak shift is attenuated, while the OH* concentration in the burned gases is favored.</div><div>For lean (<span><math><mrow><mi>ϕ</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>35</mn></mrow></math></span>) and stoichiometric mixtures, the effects of strain and curvature contributions of flame stretch are analyzed in one-dimensional counterflow flames and two-dimensional expanding flames. Higher strain rates slightly affect the peak shift, but sensibly enhance the production of OH* in the burned gas region. Stretch strongly impacts on expanding lean flames, for which the onset of intrinsic instabilities worsens the OH*-HRR correlation, in terms both of distribution shape and intensity.</div><div>Finally, nonpremixed one-dimensional counterflow diffusion flames and a more complex two-dimensional triple flame are analyzed. In both configurations, a significant reduction of the peak shift is observed when the combustion occurs in diffusion-controlled regimes, sustaining the adequacy of OH* as HRR marker for hydrogen–air diffusion flames under various operating conditions.</div><div><strong>Novelty and significance statement</strong></div><div>This work presents a systematic investigation of the OH* distribution and its correlation with the heat release rate in several canonical premixed and nonpremixed laminar hydrogen–air flames under various operating conditions, extending the current literature on the subject.</div><div>The chemical pathways leading to the peculiar behavior observed for stoichiometric flames are investigated, and the interaction of OH* with intrinsic thermodiffusive instabilities in lean flames is analyzed, showing how the correlation with the heat release rate is worsened.</div><div>A coherent methodology to quantitatively assess heat release surrogates, which can be extended to other measurable quantities, is provided too.</div><div>This knowledge is significant as it underlines how the parametric variation of operating conditions can differently affect the correlation between the OH* and the heat release rate distributions, highlighting the limits of OH*chemilum","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114452"},"PeriodicalIF":6.2,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145047700","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":"Flamelet models with differential diffusion effects for large eddy simulations of ammonia/hydrogen/nitrogen-air partially premixed jet flames","authors":"Junjun Guo ,&nbsp;Francisco E. Hernández-Pérez ,&nbsp;Zhaohui Liu ,&nbsp;Hong G. Im","doi":"10.1016/j.combustflame.2025.114464","DOIUrl":"10.1016/j.combustflame.2025.114464","url":null,"abstract":"<div><div>Blending ammonia with hydrogen and partially cracking ammonia are promising strategies to enhance the combustion performance of ammonia. Accurate prediction of ammonia/hydrogen blend combustion behavior requires careful consideration of differential diffusion effects associated with hydrogen. In this study, differential diffusion effects are assessed considering various flamelet-based modeling approaches: the unity Lewis number flamelet/progress variable (ULF) model, variable Lewis number flamelet/progress variable (VLF) model, and species-weighted flamelet/progress variable (SWF) model. The latter one incorporates weighting between two flamelet datasets based on the unity Lewis number assumption and the mixture-averaged diffusion models. An <em>a priori</em> analysis based on direct numerical simulation (DNS) data and an <em>a posteriori</em> analysis involving large eddy simulation (LES) of turbulent partially premixed NH₃/H₂/N₂-air jet flame are conducted. The analysis confirms the presence of strong differential diffusion in turbulent partially premixed NH₃/H₂/N₂-air flames and demonstrates the feasibility of weighted flamelet models for properly capturing the differential diffusion effects in different levels of turbulence. Moreover, due to the longer chemical time of NO formation on the fuel-lean side, adding the NO mass fraction in the definition of the progress variable effectively improves NO predictions. In the LES simulations, it is found that the SWF model performs well by considering both turbulent diffusion and molecular diffusion. The predictions of the SWF model fall between those of the ULF and VLF models and align closely with the measurements on fuel-rich side, indicating the significant roles of both turbulent diffusion and molecular diffusion in these regions.</div></div><div><h3>Novelty and Significance Statement</h3><div>This study innovates by conducting comprehensive <em>a priori</em> and <em>a posteriori</em> analyses on modeling differential mass diffusion using flamelet-based models. The <em>a priori</em> analysis based on the DNS data confirms the strong differential diffusion in turbulent partially premixed NH₃/H₂/N₂-air flames, as well as the feasibility of using weighted-based flamelet models for the modeling of differential diffusion. LES simulations further reveal that differential diffusion is more pronounced on the fuel-rich side than on the fuel-lean side.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114464"},"PeriodicalIF":6.2,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145045337","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}