Proceedings of the Combustion Institute最新文献

{"title":"Side-wall quenching of thermodiffusively unstable hydrogen flames with conjugate heat transfer","authors":"Benjamin Traut, Felix Rong, Max Schneider, Christian Hasse, Hendrik Nicolai","doi":"10.1016/j.proci.2026.106090","DOIUrl":"10.1016/j.proci.2026.106090","url":null,"abstract":"<div><div>Lean hydrogen/air flames enable low <figure><img></figure> emissions but are susceptible to thermodiffusive (TD) instabilities (TDIs), which strongly increase flame propagation and enhance flame wrinkling. In practical combustors, such flames frequently interact with solid walls, where flame–wall interaction (FWI) governs quenching and heat losses and therefore determines the wall heat flux (WHF). For two-dimensional head-on quenching, TDIs were shown to induce pronounced spatiotemporal WHF fluctuations and to elevate its mean level. Yet, how TDIs interact with the wall thermal response remains largely unexplored. To address this gap, laminar side-wall quenching is investigated using high-fidelity simulations with conjugate heat transfer (CHT) for different wall materials, complemented by cold and preheated isothermal reference cases. Across all cases, impingement of TDI structures on the wall generates strong spatiotemporal WHF fluctuations. The near-wall behavior, however, is governed by the competition between two mechanisms that elevate WHFs through reactivity enhancement: the intrinsic TD response, which promotes local mixture variations, and wall-induced preheating, which raises the fresh-gas temperature near the wall. For insulating CHT walls, weak upstream heat conduction limits preheating, so the WHF remains largely governed by the TD response and approaches the cold isothermal limit. With increasing wall conductivity, upstream heat conduction progressively strengthens near-wall preheating, increases reactivity, and attenuates the TD response, shifting the behavior toward the preheated isothermal limit. Accordingly, the hierarchy of mean WHFs (preheated isothermal <span><math><mo>></mo></math></span> conductive CHT <span><math><mo>></mo></math></span> cold isothermal <span><math><mo>></mo></math></span> insulating CHT) shows that wall thermal boundary conditions govern the near-wall flame dynamics. Although WHF fluctuations remain strong, solid thermal inertia suppresses pronounced transient surface-temperature variations in the CHT simulations. The impact of TDIs on FWI is therefore governed mainly by the mean gas–solid heat transfer and the resulting wall thermal response, rather than by transient thermal loading.</div><div><em>Novelty and significance statement:</em> This work presents the first investigation of flame–wall interaction (FWI) in thermodiffusively (TD) unstable lean hydrogen/air flames with fully coupled heat exchange between the gas and solid phase using conjugate heat transfer (CHT). It shows that near-wall quenching is governed by two competing mechanisms that enhance reactivity and wall heat fluxes (WHFs): intrinsic TD-driven effects and wall-induced thermal preheating. Realistic wall materials fall into an intermediate regime between the cold-wall and preheated isothermal-wall limits, where near-wall flame behavior shifts from being governed by the intrinsic TD response to increasingly controlled ","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106090"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567187","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ejected flame outflow from a compartment opening: PIV measurements and analysis","authors":"Wei Gao, Zijian Yan, Jiao Lei, Yan Jiao, Naian Liu","doi":"10.1016/j.proci.2026.105993","DOIUrl":"10.1016/j.proci.2026.105993","url":null,"abstract":"<div><div>In compartment fires, flame ejections through openings transfer heat to adjacent structures via radiation and convection. Despite progress in understanding the dynamics of ejected flames, convective heat transfer remains poorly quantified due to the scarcity of detailed flow-field measurements and theoretical models describing their outflow behavior. The present study, for the first time, employs particle image velocimetry (PIV) to quantify the outflow dynamics of ejected flames. Experiments were conducted over a range of internal heat release rates (HRRs) and opening dimensions, yielding two-dimensional velocity fields. Results show that increasing HRR enhances time-averaged flame velocity (<em>ū</em>) and vorticity. Spatial profiles of <em>ū</em> and velocity fluctuations (<em>u'</em>) rapidly evolve into self-similar forms in the downstream region. Horizontally, <em>ū</em> profiles collapse onto a Gaussian profile when normalized by its peak (<em>ū<sub>m</sub></em>) and half-width (<em>b<sub>u</sub></em>). Normalized by the convective heat flux, <em>ū<sub>m</sub></em> follows a power-law relationship with height (<em>z</em>). For <em>u'</em>, horizontal profiles evolve from a unimodal to an M-shaped distribution downstream, while vertical profiles decrease monotonically with <em>z</em> and asymptotically approach 0.32<em>ū<sub>m</sub></em>. Second-order turbulence statistics reveal that horizontal velocity fluctuations are primarily shear-driven, whereas vertical fluctuations originate directly from buoyancy. A comparison of turbulent kinetic energy and shear production shows that a portion of the energy generated in the shear layer is transported downstream, sustaining turbulence in the far field. Increasing HRR amplifies both the production and transport of turbulent energy. A predictive model for flame geometry is developed, incorporating three-dimensional flow effects induced by variations in opening geometry, and validated against experimental measurements. These findings establish a foundation for quantifying convective heat transfer in ejected flames and provide benchmark data for the validation of numerical models.</div></div><div><h3>Novelty and significance statement</h3><div>This study presents the first quantitative characterization of the outflow dynamics of flames ejected from compartment openings using PIV. Experiments were conducted across a range of heat release rates and opening geometries. Results show that both the time-averaged velocity and its fluctuations rapidly evolve into self-similar profiles, enabling the development of generalized predictive correlations. A flame geometry model incorporating three-dimensional flow effects is formulated and validated against experimental data, establishing a foundation for quantifying convective heat transfer in ejected flames. The turbulence measurements reported herein serve as benchmark data to refine flame geometry models and advance numerical simulations of ejected fl","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 105993"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567520","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 numerical simulation study of spotting ignition on high–rise building external wall insulation materials after natural aging","authors":"Yanming Ding,&nbsp;Yu Zhong,&nbsp;Minghao Cai,&nbsp;Changhai Li,&nbsp;Juan Zhang","doi":"10.1016/j.proci.2026.106071","DOIUrl":"10.1016/j.proci.2026.106071","url":null,"abstract":"<div><div>Expanded polystyrene (EPS) insulation used on the external walls of high-rise buildings becomes more susceptible to spotting ignition after natural aging. In the present study, EPS samples were naturally aged for 3, 12 and 24 months. To quantify aging penetration, specimens were sectioned at 1 mm intervals and characterized by depth-resolved thermophysical properties and pyrolysis kinetics. Ignition experiments were performed using stainless-steel spheres heated to 800–1000 °C, yielding ignition delay time and temperature-dependent ignition probabilities. The aging effect was distinctly non-monotonic, with the ignition delay time decreasing at 3 months, slightly increasing at 12 months, and decreasing again at 24 months. A multilayer ignition model coupling transient heat transfer, depth-resolved pyrolysis, and gas combustion was established. It accurately reproduced ignition delay time over a range of particle sizes and aging times. The results indicate that ignition is surface-controlled, as heating and pyrolysis are largely confined to the upper ∼1 mm while deeper layers exhibit a pronounced thermal lag. Compared with the solid-phase pyrolysis time and gas-phase chemical reaction time, the gas-phase mixing time dominates the ignition delay. The ignition delay of aged EPS shows a non-monotonic dependence on aging time, resulting from increased thermal inertia during the early aging stage and structural degradation during long-term aging. Moreover, a predictive correlation of ignition delay time with particle size and aging-dependent thermophysical parameters is proposed and shown to capture the observed delay trends, offering a tractable basis for ignition-risk assessment of EPS insulation subjected to long-term natural aging.</div><div>Novelty and significance statement</div><div>The natural aging experiments span up to 24 months, providing a rare long-term basis for evaluating the evolution of ignition behavior in external wall insulation materials. Unlike studies on unaged EPS, it reveals a non-monotonic dependence of ignition delay and critical ignition temperature on natural aging. A validated multilayer ignition model coupling depth-resolved pyrolysis with gas combustion captures the observed trends. Compared with the solid-phase pyrolysis time and gas-phase chemical reaction time, the gas-phase mixing time dominates the ignition delay. A predictive correlation for ignition delay time, parameterized by particle size and aging-dependent thermophysical parameters, is further proposed to enable practical ignition-risk assessment for aged EPS.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106071"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567309","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":"The effect of strain rate on heat release rate markers in lean premixed hydrogen flames","authors":"Elias Öhman,&nbsp;Eirik Æsøy,&nbsp;Håkon T. Nygård,&nbsp;James R. Dawson","doi":"10.1016/j.proci.2026.105996","DOIUrl":"10.1016/j.proci.2026.105996","url":null,"abstract":"&lt;div&gt;&lt;div&gt;We investigate lean, premixed axisymmetric hydrogen flames stabilised on a bluff-body and compare the effect of strain rate and equivalence ratio on &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; -chemiluminescence, OH-Planar Induced Fluorescence (OH-PLIF), and the dilatation rate as markers of the mean heat release rate (HRR). To compare with and complement the experimental measurements, laminar counterflow flame simulations were performed, which included an &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; sub-mechanism. The simulations show that the dilatation rate is well correlated to the heat release rate (HRR) for increasing tangential strain rate. Moreover, the ratio of the dilatation rate to the HRR was found to be independent of strain rate over the ranges of lean equivalence ratios tested, confirming it as a robust marker of the HRR. However, the ratio of &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; -chemiluminescence to HRR was found to vary non-monotonically with strain rate, with its magnitude depending on equivalence ratio. Examining key steps in the &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; sub-mechanism suggests that this effect results from preferential diffusion of hydrogen, which modifies the reaction zone and the radical concentrations. We then examine this phenomena experimentally through analysis of the mean &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; , OH-PLIF, and dilatation rate of bluff-body stabilised axisymmetric flames measured for several bulk velocities and lean equivalence ratios. Close to the bluff-body, the flame is flat and parallel to the flow and is subjected to decaying levels of tangential strain rate moving downstream. At low bulk velocities, strain-induced &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; appear near the flame anchoring region, leading to a significant overestimation compared to the dilatation profiles. Overall, the measurements show that the &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; response for different strain rates and equivalence ratios closely follow the non-monotonic behaviour observed in the counter flow flame simulations. These results highlight that &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; can introduce significant errors when used to obtain the flame length, which is important for measuring the mean flame speed, or obtaining convective time delays, which are crucial for thermoacoustic analysis.&lt;/div&gt;&lt;div&gt;&lt;em&gt;Novelty and Significance Statement&lt;/em&gt;: Through simulations and experiments, we systematically assess the effect of strain rate and equivalence ratio on three markers of heat release rate (HRR): &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; -chemiluminescence, OH-PLIF, and the dilatation rate in lean premixed hydrogen flames. Local discrepancies between these markers are shown to arise from the thermodiffusive properties of hydrogen flames in the presence of high tangential strain rate, which modifies the local flame structure. The dilatation field is found to provide a robust quantitative marker for HRR, &lt;figure&gt;&lt;img&gt;&lt;/figure&gt; becomes increasingly decorrelated with the HRR for increasing tangential strain, and OH-PLIF is challenging to interpret due to the a","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 105996"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567573","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oxidation and kinetic interaction of ammonia and methyl formate mixtures up to 100 atm","authors":"Yuanxinxin Cao,&nbsp;Bowen Mei,&nbsp;Mohammad Adil,&nbsp;Wenbin Xu,&nbsp;Yiguang Ju","doi":"10.1016/j.proci.2026.106170","DOIUrl":"10.1016/j.proci.2026.106170","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Ammonia (NH&lt;sub&gt;3&lt;/sub&gt;) is a carbon-free fuel, but its low reactivity and high NO&lt;sub&gt;x&lt;/sub&gt; formation present challenges for direct engine applications. Blending NH&lt;sub&gt;3&lt;/sub&gt; with reactive oxygenated fuels offers a promising strategy to enhance oxidation characteristics while decreasing emissions. In this work, the oxidation and kinetic coupling of NH&lt;sub&gt;3&lt;/sub&gt; and methyl formate (CH&lt;sub&gt;3&lt;/sub&gt;OCHO, MF) mixtures are studied in Princeton’s supercritical-pressure jet-stirred reactor (SP-JSR) at 20 and 100 atm between 400 and 950 K, under both fuel-lean and rich conditions. MF is found to be more reactive than NH&lt;sub&gt;3&lt;/sub&gt; at all investigated conditions. HP-Mech model for high-pressure NH&lt;sub&gt;3&lt;/sub&gt; and MF oxidation was developed and examined in this study, which consists of the most recent NH&lt;sub&gt;3&lt;/sub&gt; and MF kinetic mechanisms with updates of new reactions and rate constants from the literature as well as NH&lt;sub&gt;3&lt;/sub&gt;−MF interactions. The results show that the updated model provides better predictions of fuel oxidation onset temperature and intermediate species formation compared with other models. Kinetic analyses reveal that MF kinetically interacts with NH&lt;sub&gt;3&lt;/sub&gt; through CH&lt;sub&gt;3&lt;/sub&gt;OCHO/NH&lt;sub&gt;2&lt;/sub&gt;/NO&lt;sub&gt;x&lt;/sub&gt; couplings. OH radical production via HONO decomposition from the reaction CH&lt;sub&gt;3&lt;/sub&gt;OCHO + NO&lt;sub&gt;2&lt;/sub&gt; = HONO + CH&lt;sub&gt;2&lt;/sub&gt;OCHO/CH&lt;sub&gt;3&lt;/sub&gt;OCO enhances oxidation of NH&lt;sub&gt;3&lt;/sub&gt;, while the reaction NH&lt;sub&gt;2&lt;/sub&gt; + CH&lt;sub&gt;3&lt;/sub&gt;OCHO = NH&lt;sub&gt;3&lt;/sub&gt; + CH&lt;sub&gt;2&lt;/sub&gt;OCHO/CH&lt;sub&gt;3&lt;/sub&gt;OCO inhibits NH&lt;sub&gt;3&lt;/sub&gt; oxidation, especially under low-pressure and fuel-rich conditions. In addition, at low and intermediate temperatures, MF promotes NH&lt;sub&gt;3&lt;/sub&gt; oxidation primarily through HO&lt;sub&gt;2&lt;/sub&gt; and NO&lt;sub&gt;x&lt;/sub&gt; chemistry. HO&lt;sub&gt;2&lt;/sub&gt; radical production from HCO in MF oxidation plays an additional promoting role in ammonia oxidation by increasing H&lt;sub&gt;2&lt;/sub&gt;NO to HNO conversion and the catalytic NO/NO&lt;sub&gt;2&lt;/sub&gt;/HONO cycle. Additional coupling between CH&lt;sub&gt;2&lt;/sub&gt;O and NH&lt;sub&gt;2&lt;/sub&gt; further links blend fuel chemistry by promoting MF oxidation while inhibiting NH&lt;sub&gt;3&lt;/sub&gt; oxidation. The relative importance of these pathways depends strongly on pressure and equivalence ratio, with stronger radical propagation under high-pressure and fuel-lean conditions and greater inhibition of NH&lt;sub&gt;3&lt;/sub&gt; oxidation under lower-pressure or fuel-rich conditions.&lt;/div&gt;&lt;/div&gt;&lt;div&gt;&lt;h3&gt;Novelty significance statement&lt;/h3&gt;&lt;div&gt;This study provides the first combined experimental and kinetic modeling investigation of ammonia (NH&lt;sub&gt;3&lt;/sub&gt;)/methyl formate (CH&lt;sub&gt;3&lt;/sub&gt;OCHO, MF) oxidation at ultra-high pressures (20–100 atm) using the Princeton supercritical-pressure jet-stirred reactor (SP-JSR). A newly developed high-pressure kinetic mechanism (HP-Mech) integrates recent MF oxidation chemistry and introduces MF/NH&lt;sub&gt;2&lt;/sub&gt;/NO&lt;sub&gt;x&lt;/sub&gt; coupling pathways to capture carbon-nitrogen inter","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106170"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582319","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":"Kinetic studies of NO formation of methane at elevated pressures using a novel high-pressure well-stirred turbulent combustor","authors":"Kaii Ri,&nbsp;Bowen Mei,&nbsp;Liang Ji,&nbsp;Yuanxinxin Cao,&nbsp;Toshiro Fujimori,&nbsp;Kaoru Maruta,&nbsp;Yiguang Ju","doi":"10.1016/j.proci.2026.106255","DOIUrl":"10.1016/j.proci.2026.106255","url":null,"abstract":"<div><div>In this study, NO formation in methane combustion at elevated temperatures and pressures was measured using a newly developed High-Pressure Well-Stirred Turbulent Combustor (HP-WSTC), which enables kinetic characterization at millisecond flow residence times under the assumption of a zero-dimensional homogeneous reactor at elevated pressures. Methane combustion and NO kinetic experiments were conducted at 1 to 10 atm over equivalence ratios between 0.8 and 1.2. Major species concentrations and NO formation were measured and compared with predictions of five kinetic mechanisms. Significant differences in predictions of NO formation were found among these mechanisms, particularly at higher pressure. Reaction-path analysis revealed that CH + N₂ = NCN + H, NCN + H = HCN + N, and the recently proposed NCN + CH₃ = CH₂NH + CN are key pathways governing prompt NO formation. However, these pathways remain insufficiently constrained under the present high-pressure, prompt NO-dominant conditions. The results also show that additional contributions from third-body reactions such as NCN + H (+M) = HNCN (+M) and CH + N₂ (+M) = HNCN (+M) become increasingly important at elevated pressures. Furthermore, CH formation and the competing oxidation pathways leading to CH₂O were identified as the key processes influencing NO production. These findings demonstrate that the HP-WSTC provides a new validation platform for prompt NO chemistry under elevated pressures and short residence times, a regime that has not been thoroughly investigated.</div><div><strong>Novelty and significance statement</strong></div><div>This study investigates NO formation kinetics in methane combustion at elevated temperatures and pressures up to 10 atm using a new High-Pressure Well-Stirred Turbulent Combustor (HP-WSTC). The HP-WSTC enables kinetic measurements at high temperatures, elevated pressures, and short residence times over a wide range of equivalence ratios relevant to gas-turbine combustion, thereby extending prompt NO validation data to higher pressures at near-flame temperatures. The results identify several key reactions that remain poorly constrained at elevated pressures, including NCN + CH₃ = CH₂NH + CN, the competition between CH + N₂ = NCN + H and CH + N₂ (+M) = HNCN (+M), and the competition between NCN + H = HCN + N and NCN + H (+M) = HNCN (+M). Pathways governing CH formation and competing CH₂O-forming oxidation routes are also shown to influence prompt NO predictions. These findings clarify the pressure dependence of prompt NO chemistry and support improved predictive capabilities for NO formation in methane-fueled gas-turbine systems.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106255"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermal-radiation effects in steam-diluted hydrogen flames: From unsteady 1D propagation to a 2D expanding flame DNS","authors":"Julie Ben Zenou,&nbsp;Ronan Vicquelin","doi":"10.1016/j.proci.2026.106062","DOIUrl":"10.1016/j.proci.2026.106062","url":null,"abstract":"<div><div>Steam- or EGR-diluted hydrogen flames can involve strong radiative participation of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O, yet most available data and models rely on steady 1D or adiabatic assumptions. Previous studies have identified key mechanisms such as radiative cooling and fresh-gas preheating in simplified configurations.</div><div>The present work extends this analysis to unsteady and multidimensional flames using a high-fidelity framework combining DNS-quality reactive-flow simulations with a non-gray Monte Carlo radiation solver, coupled in a parallel multi-physics environment. The approach is first assessed in a pseudo-1D unsteady configuration, and then applied to the expansion of a cylindrical premixed flame.</div><div>In diluted mixtures, radiation induces continuous variations of both absolute and consumption flame speeds through time-dependent radiative preheating and cooling effects. As a result, the propagation cannot be uniquely associated with the nominal fresh-gas conditions during unsteady evolution. In the cylindrical configuration, radiation initially slows flame propagation through burnt-gas cooling, then accelerates it via fresh-gas preheating, and advances the onset of thermodiffusive instabilities.</div><div>Overall, the canonical radiation mechanisms identified in 1D (emission, reabsorption, and flow effects) remain active in multidimensional configurations, while additional interactions with unsteadiness, curvature, and instabilities emerge. These results highlight the importance of accounting for radiation when predicting diluted hydrogen flame dynamics and interpreting expanding-flame measurements.</div><div><em>Novelty and significance statement:</em> This work extends previous analyses of radiation–combustion interactions in steady 1D configurations to unsteady and multidimensional expanding flames. It introduces a coupled DNS–Monte Carlo framework enabling the consistent resolution of radiative emission, absorption, and flow–radiation interactions in dynamically evolving configurations.</div><div>The study shows that, in steam-diluted flames, fresh-gas preheating by radiation reabsorption and burnt-gas cooling induce a time-dependent modification of the thermochemical state ahead of the flame. Because radiative reabsorption is inherently non-local, it depends on the evolving distributions of fresh and burnt gases surrounding the flame. As a result, the propagation cannot be uniquely associated with the nominal fresh-gas conditions during unsteady evolution, challenging the definition of an intrinsic flame speed as commonly inferred from expanding-flame measurements.</div><div>In addition, the work demonstrates that radiation modifies instability onset in expanding flames and provides a detailed characterization of radiation–flow–chemistry coupling in canonical configurations relevant to flame-speed measurements.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106062"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582368","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":"Enhancing cool-flame oxidation of cyclic ethers via linear ether addition: a case study on tetrahydrofuran and diethyl ether in a jet-stirred reactor","authors":"Bakr Hoblos,&nbsp;Zeynep Serinyel,&nbsp;Guillaume Dayma,&nbsp;Philippe Dagaut","doi":"10.1016/j.proci.2026.106230","DOIUrl":"10.1016/j.proci.2026.106230","url":null,"abstract":"<div><div>Diethyl ether (DEE) and tetrahydrofuran (THF) are two promising candidates for second-generation biofuels. Although both are ethers and have the same number of carbon atoms, their molecular structures lead to markedly different reactivity. While DEE is highly reactive at very low temperatures, THF exhibits weak and delayed low-temperature reactivity under identical conditions. The present work aims to enhance THF cool-flame oxidation and to trigger it at lower temperatures by adding DEE. This novel study allows us to explore, for the first time, the interactions between a linear ether (DEE) and a cyclic ether (THF), and to investigate more deeply the low-temperature reaction pathways of the latter, rarely studied in detail in the literature. Three DEE/THF blends – differing only in DEE content – were considered, and a neat THF case served as a reference. All experiments were conducted in a jet-stirred reactor for stoichiometric mixtures between 450 and 1260 K, at a pressure of 10 bar, and a residence time of 0.7 s. Gas chromatography and Fourier transform infrared spectroscopy were used to determine the mole fraction profiles of the reactants, products, and intermediates observed during oxidation. As expected, increasing DEE proportion in the blend enhanced THF reactivity and shifted its onset to lower temperatures. A detailed kinetic mechanism was developed to reproduce the experimental results and to elucidate the underlying reaction pathways. Overall, the present mechanism predicts well the general trends of the detected species. This mechanism also reveals the significance of a quasi-latent low-temperature pathway of THF promoted by the earlier reactivity initiation induced by DEE addition: the disproportionation of its peroxy radicals adjacent to the ether group. Finally, the mechanism is further tested against previously reported data on the oxidation and ignition of DEE and THF to assess its ability to accurately represent the kinetic behavior of both ethers.</div></div><div><h3>Novelty and significance statement</h3><div>Based on current knowledge, the ether blends investigated in this work show significant potential as second-generation biofuels for compression-ignition engines. Such fuels present promising features: renewability, lower emissions, production from non-edible feedstocks, and compatibility with existing combustion systems. While the oxidation of DEE and THF has been widely studied separately, the present study presents the first characterization of the oxidation behavior of their blends, combining detailed speciation and kinetic modeling. This work also explores the interactions between linear and cyclic ethers and helps elucidate the cool-flame chemistry of cyclic ethers, and consequently that of hydrocarbons, where cyclic ethers act as key oxidation intermediates.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106230"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A semi-supervised learning technique for the region-wise simplification of chemical kinetics: Application to Hydrogen–Ammonia flames","authors":"Oscar Bucca,&nbsp;Pietro Paolo Ciottoli,&nbsp;Francesco Creta,&nbsp;Mauro Valorani,&nbsp;Riccardo Malpica Galassi","doi":"10.1016/j.proci.2026.106130","DOIUrl":"10.1016/j.proci.2026.106130","url":null,"abstract":"&lt;div&gt;&lt;div&gt;High-fidelity simulations of complex reacting flows require accurate yet computationally affordable kinetic models. Heuristic simplification methods such as those based on Computational Singular Perturbation (CSP) are used to obtain skeletal kinetic mechanisms by removing unnecessary species/reactions. However, these mechanisms are expected to be accurate only in the proximity of the operating conditions at which the training dataset was generated. This paper proposes a method that uses CSP analysis and clustering techniques together to identify chemical dynamics common to large regions in the operating space and to find a skeletal mechanism representative of that region. The developed workflow is tested to derive skeletal kinetic models for 1D strained premixed &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mtext&gt;H&lt;/mtext&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mtext&gt;NH&lt;/mtext&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; counterflow flames. Starting from a comprehensive database spanning a wide range of equivalence and blending ratios, the algorithm autonomously partitions the operational space into chemically coherent regions. For each region, a representative skeletal mechanism is then generated. These region-wise models overcome the inherent inefficiency of large comprehensive mechanisms and the extrapolation limitations of local models delivering maximum target errors below 2.5% while retaining strictly between 18 and 24 species across all regions. Furthermore, we employ the CSP analysis to confirm a-posteriori that the data-driven clustering is consistent with the fundamental behaviors of the underlying chemical manifold, such as the complex nitrogen sub-mechanisms that limit the degree of reduction in ammonia-heavy regimes. Finally, the scalability of the approach is demonstrated on a larger hydrocarbon mechanism.&lt;/div&gt;&lt;div&gt;&lt;em&gt;Novelty and significance statement:&lt;/em&gt; We address the classic trade-off in mechanism simplification between many small, strictly condition-specific skeletals and a single, computationally inefficient comprehensive mechanism. We propose a novel, simplification-algorithm-agnostic workflow that partitions the operating-conditions domain into chemistry-consistent regions and assigns one certified skeletal mechanism per region. For each operating point, we collect retained-species sets generated by the simplification algorithm at multiple reduction thresholds and encode their persistence into a single, fidelity-aware species signature. Constrained clustering of these signatures autonomously reveals the underlying kinetic manifold. This semi-supervised approach delivers offline, region-wise mechanisms that retain a compactness comparable to that of adaptive chemistry, but circumventing the computational overhead of on-the-fly reduction algorithms and complex solver couplings. Tested primarily with &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mtext&gt;H&lt;/mtext&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;ms","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106130"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582475","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Kinetics of methyl radical formation during dimethyl ether pyrolysis","authors":"Zhenhai Wang,&nbsp;Dapeng Liu,&nbsp;Aamir Farooq","doi":"10.1016/j.proci.2026.106215","DOIUrl":"10.1016/j.proci.2026.106215","url":null,"abstract":"<div><div>Dimethyl ether (DME) is a promising alternative fuel and an important intermediate in oxygenated hydrocarbon combustion. This work reports the first direct, time-resolved measurements of methyl radical evolution during DME thermal decomposition behind reflected shock waves. Experiments were conducted over 1277–1601 K and 1.03–1.44 bar in Ar bath gas using a deep-UV absorption diagnostic at 216.6 nm. High dilution in argon (999–1498 ppm DME) was employed to minimize thermal and chemical interferences, ensuring high-fidelity kinetic data. The measured CH₃ profiles were used to evaluate the predictive performance of existing kinetic models. The extracted rate coefficients of DME thermal decomposition exhibit Arrhenius behavior with an activation energy of 67.5 kcal mol⁻¹, given as (unit: s^-1): <span><math><mrow><msub><mi>k</mi><mn>1</mn></msub><mo>=</mo><mn>6.48</mn><mspace></mspace><mo>×</mo><msup><mrow><mn>10</mn></mrow><mn>13</mn></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>(</mo><mrow><mo>−</mo><mfrac><mrow><mn>33</mn><mo>,</mo><mn>992</mn><mspace></mspace><mi>K</mi></mrow><mi>T</mi></mfrac></mrow><mo>)</mo></mrow></msup></mrow></math></span></div><div>The measured rate coefficients are below the available high-pressure-limit estimates, indicating that DME decomposition remains in the fall-off regime near 1 bar. Previous studies relying on indirect product measurements (OH or H atoms) underestimate our rate by roughly 60% at 1520 K. Incorporating these updated rate coefficients into literature mechanisms substantially improves the prediction of CH₃ formation. Furthermore, analysis of late-time profiles revealed that omitting an argon third-body efficiency in existing models leads to an over-prediction of CH₃ consumption. Finally, the updated kinetics yield superior predictions of OH time histories and ignition delay times under oxidation conditions, demonstrating the broader impact of this work on refining oxygenated fuel combustion chemistry.</div><div><strong>Novelty and significance statement</strong> This study addresses a critical gap in dimethyl ether (DME) pyrolysis kinetics by providing the first direct, time-resolved measurements of methyl radical evolution via deep-UV absorption at 216.6 nm. The measured methyl radical time histories enable a rigorous assessment of literature models and resolve long-standing discrepancies among mechanisms previously reliant on indirect data. Furthermore, the experimentally derived rate coefficients for primary C–O bond fission (CH₃OCH₃ ↔ CH₃ + CH₃O) provide a new benchmark for oxygenated fuels, representing a significant advance in probing elementary bond-breaking reactions.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106215"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582479","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}