Proceedings of the Combustion Institute最新文献

{"title":"Ozone-initiated low-temperature oxidation of 1,3-dioxane","authors":"Caroline Smith Lewin,&nbsp;Huanhuan Wang,&nbsp;Jiabiao Zou,&nbsp;Alvina Mendy,&nbsp;Olivier Herbinet,&nbsp;Jérémy Bourgalais,&nbsp;Frédérique Battin-Leclerc","doi":"10.1016/j.proci.2026.106385","DOIUrl":"10.1016/j.proci.2026.106385","url":null,"abstract":"<div><div>This study explores the influence of ozone addition on the low-temperature oxidation of 1,3-dioxane, a recently proposed cyclic oxymethylene ether biofuel. Experiments were conducted in a jet-stirred reactor operated slightly above atmospheric pressure over 375–850 K. A new detailed kinetic model was developed, incorporating theoretically calculated rate constants for hydrogen abstraction reactions by atomic oxygen (O), the primary decomposition product of O₃. Experimental results reveal that introducing 1000 ppm of O₃ significantly accelerates fuel reactivity, initiating 1,3-dioxane consumption near 450 K, whereas oxidation without O₃ begins around 550 K. Between 600–700 K, the pronounced negative temperature coefficient (NTC) behavior observed under O₃-free conditions is notably diminished when O₃ is present. Simulations using the new kinetic model successfully reproduce these experimental trends, including fuel conversion and formation of major products. Kinetic analyses demonstrate that O₃-derived O atoms enhance early-stage chain initiation and alter dominant reaction pathways, providing mechanistic insight into O₃-assisted low-temperature oxidation chemistry of oxygenated fuels.</div></div><div><h3>Novelty and significance statement</h3><div>This study is the first to experimentally and computationally investigate the ozone-initiated low-temperature oxidation of 1,3-dioxane. It introduces a new detailed kinetic mechanism that incorporates ab initio–derived rate constants for hydrogen abstraction by O atoms, the primary reactive species generated from ozone decomposition. The study uniquely demonstrates how ozone addition accelerates dioxygenated cyclic ether consumption, lowers the onset temperature of oxidation by ∼100 K, and suppresses negative temperature coefficient (NTC) behavior, providing unprecedented mechanistic insights into O₃-assisted oxidation of oxygenated biofuels.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106385"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149153694","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 ReaxFF molecular dynamics approach to modeling hardwood hemicellulose pyrolysis","authors":"Shuaihong Liu,&nbsp;Xinru Han,&nbsp;Song Lu,&nbsp;Xiaoyu Ju,&nbsp;Hanfeng Jin","doi":"10.1016/j.proci.2026.106372","DOIUrl":"10.1016/j.proci.2026.106372","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Hemicellulose pyrolysis plays a crucial role in biomass combustion and thermochemical conversion processes. But its kinetic models reported in literature heavily rely on experimental data due to its complex molecular structure. These models thus cannot be widely applied under different combustion conditions. In this study, we proposed a novel \"lumped-simplified\" modeling approach based on ReaxFF molecular dynamics (MD) simulations to well predict the pyrolysis behavior of hardwood hemicellulose. Firstly, we identified the critical intermediates in the reaction system using carbon flux analysis. Then, we quantitatively correlated the concentrations of these critical intermediates, which were later used to formulate the stoichiometric coefficients in the lumped-simplified reaction expression of hemicellulose decomposition. At last, we adopted a double-Gaussian distributed activation energy model (DG-DAEM) to identify two subprocesses with different activation-energy distributions. Two pseudo-components, HCE1 and HCE2, were introduced to describe the early primary decomposition stage and the deep-conversion stage, respectively. Our lumped-simplified model can well reproduce the weight-loss behavior, bimodal DTG characteristics, main product distribution, and typical gaseous product release rate of hardwood hemicellulose pyrolysis across a wide range of heating rates (5 – 100 K/min). The deviations of DTG peak-temperature predictions are below 16 K, and deviations for char, gas, volatiles, and water yields are 1.58%, 1.75%, 2.43%, and 5.51%, respectively. In conclusion, the modeling approach proposed in this study significantly simplifies the development of a kinetic model for complex solid combustibles, which contributes to the advancement of numerical simulations of combustion processes in solid combustibles.&lt;/div&gt;&lt;/div&gt;&lt;div&gt;&lt;h3&gt;Novelty and significance statement&lt;/h3&gt;&lt;div&gt;Accurate modeling of hemicellulose pyrolysis benefits the prediction of wildfire spread and industrial biomass utilization. Traditional models require extensive experimental data and rigorous parameter optimization across broad combustion conditions. In this study, we proposed a novel \"lumped-simplified\" modeling approach based on ReaxFF MD. Utilizing its rich molecular-level information, we identified critical combustion intermediates by carbon flux analysis, and determined the reaction stoichiometric coefficients by intermediate correlation analysis. This approach simplifies the model development, reduces the experimental data dependence, and enables the prediction of complicated solid fuel combustion across wide conditions. Such a simplified model is specially designed for CFD applications, which contains necessary chemical information but saves computational resources in numerical simulation. It may help to answer those crucial questions in fire science and industrial engineering, such as the fire ignition in wooden architecture, the fire spread in wildfire or wildla","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106372"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149153704","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 ammonia on hydrogen oxidation near the second explosion limit in a turbulent flow reactor","authors":"Gabriel J. Gotama,&nbsp;Felipe Augusto Ferreira Gomes,&nbsp;Alex Sherwood,&nbsp;Yi Yang,&nbsp;Liang Yu,&nbsp;Xingcai Lu","doi":"10.1016/j.proci.2026.106529","DOIUrl":"10.1016/j.proci.2026.106529","url":null,"abstract":"<div><div>The contrasting combustion properties of ammonia (NH₃) and hydrogen (H₂) offer potential to promote NH₃ oxidation with H₂ and to moderate H₂ reactivity with NH₃. This paper examines the latter in a turbulent flow reactor using mixtures containing 0–20% NH₃ and 0–155 ppm nitric oxide (NO) in H₂ at ϕ = 0.033–0.044. Time-resolved concentrations of H₂, NH₃, NO, NO₂, and N₂O were measured at 926–976 K and at 1.1 bar and 4 bar, corresponding to H₂ oxidation near the second explosion limit where increasing pressure reduces hydrogen oxidation reactivity. At 1.1 bar, NH₃ addition strongly inhibits H₂ oxidation. However, at 4 bar, a small NH₃ addition (H₂:NH₃ = 95:5) promotes H₂ oxidation, which is unexpected given NH₃ is less reactive than H₂. A chemical kinetic model is developed to simulate the experiment. Analysis using the model indicates that at 4 bar, NH₃ promotes H₂ oxidation by generating NO via NH₃ oxidation; NO then converts the less reactive HO₂ to OH through the chain NO + HO₂ → NO₂ + OH and H + NO₂ → NO + OH. In contrast, when NO is present in the reactants, added NH₃ introduces additional OH sinks, which diminishes NO’s promotional effect on H₂ oxidation and reduces the stiffness of the H₂/NO oxidation system at 1.1 bar.</div></div><div><h3>Novelty and significance statement</h3><div>This study reports the first time-resolved species concentrations of H₂/NH₃ and H₂/NH₃/NO oxidations in a turbulent flow reactor. The measurements show that while NH₃ generally slows down H₂ oxidation, conditions exist in which NH₃ addition could promote H₂ oxidation. Such promotion has not been previously observed but potentially affects the use of H₂/NH₃ fuels in practical combustion. By extending the investigation to NO-containing mixtures, it was found that the introduction of NH₃ moderates the steep promotion of NO on H₂ oxidation. This work revealed novel chemistry in H₂/NH₃ and H₂/NH₃/NO combustion and provided new targets to improve ammonia combustion models.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106529"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149153705","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":"Formation of aromatics in a 2,5-dimethylfuran-isooctane laminar premixed flame","authors":"Kanika Sood,&nbsp;Sylvie Gosselin,&nbsp;Shunsuke Suzuki,&nbsp;Alessandro Faccinetto,&nbsp;Pascale Desgroux,&nbsp;Laurent Gasnot,&nbsp;Luc-Sy Tran","doi":"10.1016/j.proci.2026.106570","DOIUrl":"10.1016/j.proci.2026.106570","url":null,"abstract":"<div><div>2,5-Dimethylfuran (DMF) has emerged as a promising cellulose-derived biofuel additive and octane booster for gasoline engines. Although prior studies have discussed its combustion chemistry, experimental data quantifying polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs) in flames remain limited. In the present work, a premixed low sooting atmospheric flame of DMF blended with isooctane (a gasoline surrogate component) and methane is investigated. The presence of soot particles smaller than 7 nm was confirmed by using a nano-SMPS (Scanning Mobility Particle Sizer). &gt;60 species, including 22 aromatic compounds, were quantified using gas chromatography. Using the preconcentration step upstream of the gas chromatography (GC) setup, PAHs and OPAHs, even at concentrations as low as ∼1 ppb were quantified. This constitutes, to the best of our knowledge, the first experimental dataset providing quantitative measurements of both PAHs and OPAHs in a DMF-isooctane-methane flame. Benzene and phenol were found to be the most abundant aromatics, with mole fractions in the order of 100–300 ppm, whereas three-ring PAHs such as phenanthrene were detected at much lower levels (∼20 ppb). Notably, dibenzofuran was observed at concentrations comparable to acenaphthylene (∼300 ppb) and approximately three times higher than its structural analog fluorene. A comparison with an anisole (a lignin-derived biofuel) flame indicated that DMF produces aromatics, particularly OPAHs, at levels approximately 3–20 times lower under similar conditions. Finally, simulations based on existing kinetic models were unable to satisfactorily reproduce the measured PAH/OPAH profiles, highlighting the need for improved chemical mechanisms capable of accurately describing aromatic formation in DMF-containing fuel blends.</div></div><div><h3>Novelty and significance statement</h3><div>This study presents, to the best of our knowledge, the first detailed quantification of aromatics, including polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs), formed in a 2,5-dimethylfuran (DMF)-isooctane-methane flame in a regime where soot becomes measurable. Such data, not previously reported for DMF or for cellulosic-derived oxygenated fuels more broadly, provides a valuable basis for validating and refining kinetic models while highlighting their current limitations in predicting PAH and OPAH formation. Under the investigated conditions, DMF produces approximately 3–20 times lower concentrations of PAHs and OPAHs than anisole, a lignin-derived biofuel. This difference may be attributed to the greater ease of phenoxy radical formation during anisole combustion. Additionally, OPAHs appear to form closer to the burner surface, whereas PAHs develop further downstream. These findings can offer a foundation for improving predictive combustion models for advanced biofuels.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106570"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149153707","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":"High pressure and temperature H2 laminar flame speeds: bridging experiments and kinetic models","authors":"Seif Zitouni,&nbsp;Patrick J. Singal,&nbsp;Nicolas Villenave,&nbsp;Olfa Mechergui,&nbsp;Joachim Beeckmann,&nbsp;Fabien Halter,&nbsp;Michael P. Burke,&nbsp;Guillaume Dayma","doi":"10.1016/j.proci.2026.106035","DOIUrl":"10.1016/j.proci.2026.106035","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Laminar flame speeds of hydrogen–air mixtures were measured under isochoric conditions using a spherical constant-volume chamber, providing reference data for model validation under conditions relevant to advanced combustion systems. Measurements were performed for equivalence ratios &lt;em&gt;φ&lt;/em&gt; = 1.4–5 and initial pressures between 0.5–2 bar, corresponding to unburned gas pressures and temperatures up to 8.8 bar and 460 K. Three state-of-the-art kinetic mechanisms, namely Konnov, CRECK, and ThInK, were assessed, with and without inclusion of recently proposed chemically termolecular reactions (H + O&lt;sub&gt;2&lt;/sub&gt; + R; R = H, O, OH). Additionally, reduced-pressure-based linear mixture rules (LMR-R) were implemented for key pressure-dependent reactions to better capture mixture dependence of complex-forming reactions, and to incorporate &lt;em&gt;ab initio&lt;/em&gt; determined temperature-dependent third-body efficiencies. At pressures below 3 bar, all mechanisms reproduce the measured laminar flame speeds within experimental uncertainty. However, at higher pressures and fuel-rich conditions, models including chemically termolecular reactions tend to underestimate laminar flame speeds due to enhanced radical termination, while their exclusion leads to systematic large overprediction. Incorporation of LMR-R with recent &lt;em&gt;ab initio&lt;/em&gt; data mitigates these deviations, improving agreement by balancing termination and chain-branching kinetics. Sensitivity analyses reveal that H + O&lt;sub&gt;2&lt;/sub&gt; ⇄ O + OH and competing HO&lt;sub&gt;2&lt;/sub&gt; formation pathways dominate under these conditions, while HO&lt;sub&gt;2&lt;/sub&gt; + H pathways and H recombination also have a significant influence on flame speed. Collider-resolved sensitivity analysis further shows that bath-gas effects are concentrated primarily in the HO&lt;sub&gt;2&lt;/sub&gt;-forming channel from H + O&lt;sub&gt;2&lt;/sub&gt; recombination, with H&lt;sub&gt;2&lt;/sub&gt;O emerging as the most influential collider, whereas collider dependence is much weaker for H + OH + M ⇄ H&lt;sub&gt;2&lt;/sub&gt;O + M and 2 OH + M ⇄ H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; + M. The results demonstrate that accurate simulation of hydrogen flames at elevated pressures and rich equivalence ratios requires not only chemically termolecular reactions, but also temperature-, pressure-, and collider-dependent treatment of pressure-dependent kinetics.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This study reports new isochoric laminar flame speed measurements of hydrogen–air mixtures under fuel-rich, high-pressure conditions up to 8.8 bar and 460 K, where experimental data remain scarce. The experiments are combined with detailed kinetic modeling to evaluate three state-of-the-art hydrogen combustion mechanisms, with and without chemically termolecular reactions, and to implement a reduced-pressure-based linear mixture rule (LMR-R) for key pressure-dependent reactions using recent &lt;em&gt;ab initio&lt;/em&gt; evaluations. The analysis isolates the competing roles of radical ter","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106035"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567186","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":"Unravelling the pyrolysis chemistry of a HEFA-SPK under normal-to-high pressures: Insights into effects of fuel molecular branching degree","authors":"Qiying Zhang,&nbsp;Qilong Fang,&nbsp;Baojia Tong,&nbsp;Jun Fang,&nbsp;Wei Li,&nbsp;Yuyang Li","doi":"10.1016/j.proci.2026.106270","DOIUrl":"10.1016/j.proci.2026.106270","url":null,"abstract":"&lt;div&gt;&lt;div&gt;In this work, the pyrolysis characteristics of a HEFA-SPK fuel were experimentally investigated in a flow reactor under normal-to-high pressures. The fuel composition was analyzed using GC × GC&lt;img&gt;HMS, and the degree of molecular branching was evaluated via nuclear magnetic resonance (NMR) spectroscopy. Based on these analyses, two surrogate fuels (SF-1: 10% n-tetradecane, 75% 2-methyltridecane, and 15% n‑butyl cyclohexane; SF-2: 14% n-tetradecane, 55% 2-methyltridecane, 23% 2,2,4,6,6-pentamethylheptane, and 8% n‑butyl cyclohexane) and their corresponding kinetic models were proposed and validated against experimental pyrolysis data. The results indicate that SF-2 incorporating branching degree exhibits significantly improved predictive accuracy for pyrolysis species compared to SF-1 without considering branching effects, particularly for methane, ethane and ethylene. Highly branched alkanes with a higher ratio of primary carbon significantly promote the formation of methane and ethane through unimolecular decomposition. Lightly branched alkanes and n-alkanes are major contributors to ethylene and propylene formation through &lt;em&gt;β&lt;/em&gt;-scission of alkyl/alkenyl radicals. This finding highlights the importance of constraining molecular branching degree when formulating surrogate fuels for sustainable aviation fuels. Kinetic analyses were performed to investigate the pressure-dependent mechanism of HEFA-SPK pyrolysis. The unimolecular decomposition pathways of 2,2,4,6,6-pentamethylheptane promotes the decomposition of 2-methyltridecane at normal pressure, but inhibits it under elevated pressures. In addition, the formation pathways of benzene and its pressure dependence were examined. The reaction C&lt;sub&gt;4&lt;/sub&gt;H&lt;sub&gt;6&lt;/sub&gt; + C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt; = C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;6&lt;/sub&gt; + H&lt;sub&gt;2&lt;/sub&gt; + H was identified as the dominant pathway for benzene formation, and its contribution is enhanced at elevated pressures. Finally, a comparison with RP-3 kerosene was conducted to demonstrate significant differences in the formation of ethylene, propylene, and benzene, reflecting the influence of molecular composition on pyrolysis chemistry.&lt;/div&gt;&lt;/div&gt;&lt;div&gt;&lt;h3&gt;Novelty and significance statement&lt;/h3&gt;&lt;div&gt;Sustainable aviation fuels (SAFs), influenced by synthesis processes, are primarily composed of alkanes with varying carbon numbers and degrees of branching. Conventional surrogate fuel construction often relies on matching physicochemical properties; however, the similar physicochemical characteristics of alkane isomers make it difficult to effectively constrain the combustion behavior of SAFs through property matching alone. In this work, detailed fuel composition and molecular structure information obtained from multiple analytical techniques are used to explicitly incorporate molecular branching into surrogate formulation. In addition, a comprehensive high pressure pyrolysis dataset for HEFA-SPK is established and used to assess the impact o","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106270"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582327","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":"Insights into the micro-explosion of burning iron particle under ammonia co-firing conditions","authors":"Jingruo Chen,&nbsp;Kun Li,&nbsp;Jun Chen,&nbsp;Shuheng Zheng,&nbsp;Yutao Zheng,&nbsp;Ning Liu,&nbsp;XiaoCheng Mi,&nbsp;Shijie Xu,&nbsp;Weiwei Cai","doi":"10.1016/j.proci.2026.106209","DOIUrl":"10.1016/j.proci.2026.106209","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Iron powder is a promising zero-carbon energy carrier. For large-scale industrial application, an hydrocarbon flame co-combustion strategy is typically adopted owing to the challenging stabilization of iron powder combustion. However, this approach still entails carbon emissions. To enable a fully zero-carbon iron powder cycle, ammonia/iron co-combustion has been proposed. A markedly elevated iron particle micro-explosion probability has been observed in ammonia/iron co-combustion. In our previous work, it was hypothesized that iron nitride formed from the reaction of iron with ammonia or its combustion products is the most likely cause of the significantly higher micro-explosion probability. To elucidate the underlying mechanism, the ball-milled Fe:Fe&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 particles are synthesized by planetary ball milling in this work. The substantially higher micro-explosion probability of ball-milled particles relative to pure iron particles indicates a strong influence of iron nitride on micro-explosion. Tube furnace experiments further shows an inert interaction between ammonia and micron-sized iron powder, suggesting that the iron powders used for combustion are unlikely nitrided by ammonia at approximately 650 K. An iron particle micro-explosion dynamics model is established utilizing diffusion-limited reaction theory and linear perturbation analysis. This heuristic model demonstrates that the reactions of nitrogen-centered radicals with iron particles are most likely the dominant pathway for iron nitride formation. The transition in the controlled regime of iron particle micro-explosion with increasing initial bubble size is first revealed by the developed micro-explosion model. Overall, these insights into micro-explosion not only provide a critical foundation for evaluating ammonia/iron co-combustion but also offer valuable methodologies and findings applicable to broader metal and solid fuel combustion.&lt;/div&gt;&lt;div&gt;&lt;em&gt;Novelty and significance statement:&lt;/em&gt; Ammonia/iron co-combustion is a viable pathway for realizing a fully zero-carbon iron powder cycle. A significantly higher micro-explosion probability of iron particles has been observed in this co-combustion process. However, the underlying micro-explosion mechanism remains unclear. In this work, for the first time, the direct experimental results is provided that iron nitride induces the micro-explosion of iron particles in ammonia/iron co-combustion. Furthermore, a micro-explosion dynamics model is first established to demonstrate that iron nitride is most likely formed from the reaction of nitrogen-centered radicals with the iron particle. Based on the proposed heuristic model, the transition in the controlled regime of iron particle micro-explosions is investigated. Overall, the investigation into the most characteristic micro-explosion process of the co-combustion method offers the iron combustion community crit","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106209"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582415","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":"AlO evolution and dynamics around aluminum droplets burning in water-vapor-rich environments","authors":"Weitian Wang,&nbsp;Zhiyong Wu,&nbsp;Zihao Song,&nbsp;Xing Chao,&nbsp;Marcus Aldén,&nbsp;Zhongshan Li","doi":"10.1016/j.proci.2026.106171","DOIUrl":"10.1016/j.proci.2026.106171","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Aluminum combustion in steam offers a promising route for recyclable, zero-carbon cogeneration of heat and hydrogen. However, the development and validation of mechanisms and models for micron-sized Al droplet combustion is limited by the scarcity of quantitative, high spatiotemporal resolution experimental data. We combine high-speed microscopy with laser absorption imaging tomography to quantitatively investigate the spatiotemporal evolution of the key intermediate species, aluminum monoxide (AlO), during the combustion of Al droplets of different radii in both &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;O&lt;/mi&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;-containing and &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;O&lt;/mi&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;-free water-vapor-rich environments. After correcting for the non-resonant laser extinction interference caused by the condensed-phase products, the resolved characteristic AlO absorption images reveal that AlO molar concentration is negligible near the droplet surface, peaks within the condensed layer, and extends beyond it. The &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;O&lt;/mi&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;-containing environments yield faster Al consumption rates and roughly triple the peak AlO concentration (up to 2.2% for larger droplets), with the peak located further from the condensed layer. Two dynamic features are identified: droplet coalescence between the parent Al and the product alumina droplets associated with asymmetric combustion, alongside radius and AlO oscillation for large droplets in symmetric combustion mode. During the coalescence, the alumina droplet heats the Al droplet, increasing the AlO level by a factor of approximately 1.5, but no violent phase change or localized AlO-producing reaction is observed. The high-frequency AlO oscillation, decoupled from the droplet oscillation, may indicate the presence of nonlinear kinetic mechanisms. The spatiotemporal evolution of AlO under different conditions provide experimental reference for developing and validating Al combustion mechanisms and models, while the transient dynamics reveal instabilities that inspire new insights into Al droplet combustion.&lt;/div&gt;&lt;div&gt;&lt;em&gt;Novelty and significance statement:&lt;/em&gt; Through an innovative high-speed microscopic laser absorption imaging tomography technique, this work reports, for the first time, the evolution and dynamics of aluminum monoxide (AlO)—a key intermediate of aluminum combustion—around varying micron-sized Al droplets burning in different water-vapor-rich environments. These quantitative, spatiotemporally resolved AlO molar concentration data provide references for developing mechanisms and models, and guide metal combustion system design. Examination of AlO level dynamics during droplet coalescence helps to understand the enhancement of combustion efficiency driven by droplet interactions. Furthermore, the observed high-frequency AlO oscillation, decoupled from the drop","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106171"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582417","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":"Examination of nonlinearity of chemical source terms for turbulent combustion closure","authors":"Haifeng Wang","doi":"10.1016/j.proci.2026.106125","DOIUrl":"10.1016/j.proci.2026.106125","url":null,"abstract":"<div><div>The grand challenge of turbulent combustion closure stems from the strong nonlinearity of chemical reaction source terms in a turbulence environment. A comprehensive understanding of the nonlinearity property of chemical source terms is crucial to the development of model closure. This work aims to improve such understanding by systematically examining the dependence of the averaged chemical source terms on the fluctuations of the independent variables—temperature and species mass fractions. In particular, the focus is placed on the effect of neglecting fluctuations in the independent variables partially or entirely, which is a common modeling strategy used in turbulent combustion closure found in the laminar chemistry model or conditional moment closure. The experimental data from the Sandia piloted jet flames are used as samples for a numerical examination. It is found that the temperature fluctuation has a much smaller effect than the fluctuations in the species mass fractions on the averaged chemical source terms. This is contrary to intuition since temperature appears in an exponential function while species mass fractions are in a quadratic term in the Arrhenius function. Interrogation is conducted to gain an explanation of the counterintuitive observation as well as deep insights into the nonlinear dependency of averaged chemical source terms on the fluctuations of temperature and species mass fractions.</div><div><em>Novelty and significance statement:</em> This work presents the first systematic investigation of how fluctuations in temperature and species mass fractions influence the averaged chemical source terms in turbulent combustion. Using experimental data from the Sandia piloted jet flames and conceptual models to isolate individual effects, the study reveals that temperature fluctuations have a surprisingly small effect compared with species fluctuations. This counterintuitive finding challenges the conventional interpretation of the Arrhenius law and provides new insights into the fundamental origin of turbulence–chemistry interactions and the closure problem in turbulent combustion modeling.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106125"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582367","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":"On the coupling between swirl-swirl interaction and NO formation in NH3/CH4 co-combustion flames","authors":"Ayman M Elbaz,&nbsp;Zubayr O Hassan,&nbsp;William L Robert","doi":"10.1016/j.proci.2026.106202","DOIUrl":"10.1016/j.proci.2026.106202","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Ammonia combustion, although carbon-free, suffers from low reactivity and high NO emissions. This study investigates flame stability, emissions, and structure in NH₃/CH₄ flames stabilized in a double-swirl burner, emphasizing the role of swirl–swirl interaction under stratified mixture equivalence ratios. NH₃/air was supplied through the inner swirler (Φᵢₙ), while lean CH₄/air was supplied through the outer swirler (Φₒᵤₜ). Tests covered far-rich to far-lean inner flames (Φᵢₙ = 1.4 – 0.4) under varying outer swirl intensities. Flame stability and NO emissions were mapped, while OH–NO PLIF and flow-field measurements elucidated how variations in outer swirl intensity and equivalence ratio influence flame structure and chemically regulate the inner NH₃/air flame, thereby controlling stability and emissions. Increasing the outer-swirl strength (S&lt;sub&gt;g&lt;/sub&gt;ₒᵤₜ) enlarged the recirculation zone and extended the lean blowout limit. NO emissions were lowest at rich Φᵢₙ, peaked near Φᵢₙ ≈ 0.8, and decreased again under far-lean conditions. Reducing S&lt;sub&gt;g&lt;/sub&gt;ₒᵤₜ altered this trend by suppressing NO across a wider range of rich flames, shifting the peak toward leaner mixtures, and increasing NO under far-lean operation, while overall NO decreased with increasing Φₒᵤₜ. OH–NO-PLIF imaging showed that at low S&lt;sub&gt;g&lt;/sub&gt;ₒᵤₜ the inner NH₃/air flame benefited from the outer CH₄/air flame in stabilizing far-rich and far-lean conditions, but its oxidation and NO formation remained largely unchanged. At high S&lt;sub&gt;g&lt;/sub&gt;ₒᵤₜ, strong recirculation diluted NO at intermediate and lean Φᵢₙ, while enhancing NO formation at rich Φᵢₙ through downstream oxidation of cracked NH₃. This effect was further amplified when the outer mixture was leaned, providing leaner recirculated gases toward the inner stream. These results demonstrate the critical role of swirl–swirl interaction in regulating NH₃ flame stabilization and NO formation and suggest that a high outer swirl equivalence ratio combined with variable-swirl operation can extend the stable flame regime while maintaining low NO emissions.&lt;/div&gt;&lt;/div&gt;&lt;div&gt;&lt;h3&gt;Novelty and significance statement&lt;/h3&gt;&lt;div&gt;This study presents the first systematic investigation of swirl–swirl interaction in NH₃/CH₄ double-swirl co-combustion and its role in controlling flame stabilization and NO formation. By independently varying outer-swirl intensity over a wide range of NH₃/air equivalence ratios, the work isolates the aerodynamic–chemical coupling between recirculation strength, inter-stream mixing, and nitrogen chemistry. Combined OH–NO PLIF and PIV diagnostics provide detailed characterization of flame structures and NO formation pathways governed by swirl-controlled transport of radicals and oxidizers. The results highlight the potential of swirl control as a parameter for tuning flame stability and NO formation, providing mechanistic insight and design guidance for low-NO, fuel-flexible combustors operating with ammonia","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106202"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582521","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}