Pub Date : 2026-01-17DOI: 10.1016/j.combustflame.2026.114804
Daoguan Ning, Dongwon Ka, Andy Huu Huynh, Yuzhe Li, Xiaolin Zheng
<div><div>Ignition and combustion dynamics of boron/hydroxyl-terminated polybutadiene (B-HTPB) composites are central to propulsion performance, yet quantitative information on ignition temperature and burn rate at engine-relevant high heating rates (<span><math><mo>∼</mo></math></span>1000<!--> <!-->K/s) remains limited. In this work, we quantify the ignition temperature and combustion dynamics of individual B-HTPB microparticles using a custom-built drop-tube-like reactor with a pre-defined vertical temperature profile, achieving high heating rates (<span><math><mo>∼</mo></math></span>250–1500<!--> <!-->K/s). The ignition temperature of B-HTPB particles decreases slightly from 1005<!--> <!-->K to 975<!--> <!-->K as the particle size increases from approximately <span><math><mrow><mn>25</mn><mspace></mspace><mi>μ</mi></mrow></math></span>m to <span><math><mrow><mn>100</mn><mspace></mspace><mi>μ</mi></mrow></math></span>m and closely matches that of pure HTPB microparticles (950<!--> <!-->K–1000<!--> <!-->K). This indicates that, under rapid heating, ignition of B-HTPB is governed by the condensed-phase decomposition of HTPB and gas-phase reactions of HTPB pyrolysis products rather than the heterogeneous boron oxidation, for which the kinetics are too slow to contribute. Time-resolved flame emission intensity and high-speed imaging reveal two distinct combustion stages for B-HTPB: an initial volatile-driven gas-phase flame followed by a phase characterized by ejection and burning of boron particles. The first stage accounts for approximately 64% of the total burn time. The burn time of B-HTPB follows an empirical scaling (<span><math><mrow><msub><mrow><mi>t</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>=</mo><mn>2</mn><mo>.</mo><mn>1</mn><msubsup><mrow><mi>d</mi></mrow><mrow><mi>p</mi></mrow><mrow><mn>0</mn><mo>.</mo><mn>63</mn></mrow></msubsup></mrow></math></span>, with <span><math><msub><mrow><mi>t</mi></mrow><mrow><mi>b</mi></mrow></msub></math></span> in ms and <span><math><msub><mrow><mi>d</mi></mrow><mrow><mi>p</mi></mrow></msub></math></span> in <span><math><mi>μ</mi></math></span>m), indicating that surface pyrolysis of HTPB likely limits overall B-HTPB combustion. Using the measured particle burn time, the regression rate of B-HTPB burning in heated air is estimated as 0.09<!--> <!-->mm/s, comparable to those measured in counterflow experiments. These results provide quantitative information on ignition temperature and staged-combustion of B-HTPB composites at realistic heating rates and offer benchmarks for validating reaction-kinetic and multi-physics models of B-HTPB composite fuels.</div><div><strong>Novelty and significance statement</strong></div><div>This work, for the first time, quantitatively determines the ignition temperature of B-HTPB composites under high heating rates representative of realistic combustion scenarios. The results help to identify the controlling mechanism of the composite particle ignition. High-speed imagi
{"title":"Ignition temperature and combustion dynamics of B-HTPB composite microparticles","authors":"Daoguan Ning, Dongwon Ka, Andy Huu Huynh, Yuzhe Li, Xiaolin Zheng","doi":"10.1016/j.combustflame.2026.114804","DOIUrl":"10.1016/j.combustflame.2026.114804","url":null,"abstract":"<div><div>Ignition and combustion dynamics of boron/hydroxyl-terminated polybutadiene (B-HTPB) composites are central to propulsion performance, yet quantitative information on ignition temperature and burn rate at engine-relevant high heating rates (<span><math><mo>∼</mo></math></span>1000<!--> <!-->K/s) remains limited. In this work, we quantify the ignition temperature and combustion dynamics of individual B-HTPB microparticles using a custom-built drop-tube-like reactor with a pre-defined vertical temperature profile, achieving high heating rates (<span><math><mo>∼</mo></math></span>250–1500<!--> <!-->K/s). The ignition temperature of B-HTPB particles decreases slightly from 1005<!--> <!-->K to 975<!--> <!-->K as the particle size increases from approximately <span><math><mrow><mn>25</mn><mspace></mspace><mi>μ</mi></mrow></math></span>m to <span><math><mrow><mn>100</mn><mspace></mspace><mi>μ</mi></mrow></math></span>m and closely matches that of pure HTPB microparticles (950<!--> <!-->K–1000<!--> <!-->K). This indicates that, under rapid heating, ignition of B-HTPB is governed by the condensed-phase decomposition of HTPB and gas-phase reactions of HTPB pyrolysis products rather than the heterogeneous boron oxidation, for which the kinetics are too slow to contribute. Time-resolved flame emission intensity and high-speed imaging reveal two distinct combustion stages for B-HTPB: an initial volatile-driven gas-phase flame followed by a phase characterized by ejection and burning of boron particles. The first stage accounts for approximately 64% of the total burn time. The burn time of B-HTPB follows an empirical scaling (<span><math><mrow><msub><mrow><mi>t</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>=</mo><mn>2</mn><mo>.</mo><mn>1</mn><msubsup><mrow><mi>d</mi></mrow><mrow><mi>p</mi></mrow><mrow><mn>0</mn><mo>.</mo><mn>63</mn></mrow></msubsup></mrow></math></span>, with <span><math><msub><mrow><mi>t</mi></mrow><mrow><mi>b</mi></mrow></msub></math></span> in ms and <span><math><msub><mrow><mi>d</mi></mrow><mrow><mi>p</mi></mrow></msub></math></span> in <span><math><mi>μ</mi></math></span>m), indicating that surface pyrolysis of HTPB likely limits overall B-HTPB combustion. Using the measured particle burn time, the regression rate of B-HTPB burning in heated air is estimated as 0.09<!--> <!-->mm/s, comparable to those measured in counterflow experiments. These results provide quantitative information on ignition temperature and staged-combustion of B-HTPB composites at realistic heating rates and offer benchmarks for validating reaction-kinetic and multi-physics models of B-HTPB composite fuels.</div><div><strong>Novelty and significance statement</strong></div><div>This work, for the first time, quantitatively determines the ignition temperature of B-HTPB composites under high heating rates representative of realistic combustion scenarios. The results help to identify the controlling mechanism of the composite particle ignition. High-speed imagi","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114804"},"PeriodicalIF":6.2,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976373","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}
Pub Date : 2026-01-17DOI: 10.1016/j.combustflame.2026.114798
Daehong Lim, Rajendra Rajak, Jia Xuan Lim, Jack J. Yoh
This study experimentally resolves the effect of metal addition on the flame dynamics in electrically controlled solid propellants (ECSP) containing titanium (Ti) and aluminum (Al) additives. Planar laser-induced fluorescence (PLIF) and laser-induced breakdown spectroscopy (LIBS), diagnostics commonly applied to gaseous flames, were extended to capture the influence of metal reactivity on flame structure and potential instability. Ti-containing propellants produced a particle-dominated combustion regime, where limited combustion involvement allowed particles to propagate downstream, amplifying flame surface perturbation, burning rate oscillations, and heat release rate fluctuations. In contrast, Al additives promoted rapid particle consumption and more uniform flame fronts, leading to reduced flame surface perturbations. These contrasting behaviors demonstrate that intrinsic metal reactivity dictates flame structure, deformation, propagation, and feed rate fluctuation. By establishing direct experimental evidence of particle-governed flame instabilities, the work advances fundamental understanding of multiphase reactive flows in metalized propellants and highlights the diagnostic pathways necessary to guide additive selection for stable combustion.
{"title":"Influence of metal addition on flame structure and potential instability in solid propellant combustion driven by electric potential","authors":"Daehong Lim, Rajendra Rajak, Jia Xuan Lim, Jack J. Yoh","doi":"10.1016/j.combustflame.2026.114798","DOIUrl":"10.1016/j.combustflame.2026.114798","url":null,"abstract":"<div><div>This study experimentally resolves the effect of metal addition on the flame dynamics in electrically controlled solid propellants (ECSP) containing titanium (Ti) and aluminum (Al) additives. Planar laser-induced fluorescence (PLIF) and laser-induced breakdown spectroscopy (LIBS), diagnostics commonly applied to gaseous flames, were extended to capture the influence of metal reactivity on flame structure and potential instability. Ti-containing propellants produced a particle-dominated combustion regime, where limited combustion involvement allowed particles to propagate downstream, amplifying flame surface perturbation, burning rate oscillations, and heat release rate fluctuations. In contrast, Al additives promoted rapid particle consumption and more uniform flame fronts, leading to reduced flame surface perturbations. These contrasting behaviors demonstrate that intrinsic metal reactivity dictates flame structure, deformation, propagation, and feed rate fluctuation. By establishing direct experimental evidence of particle-governed flame instabilities, the work advances fundamental understanding of multiphase reactive flows in metalized propellants and highlights the diagnostic pathways necessary to guide additive selection for stable combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114798"},"PeriodicalIF":6.2,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036350","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}
Pub Date : 2026-01-16DOI: 10.1016/j.combustflame.2026.114802
Samuel Dillon , Renaud Mercier , Benoit Fiorina
<div><div>One of the many modelling challenges facing combustion engineers is the simulation of reactive flows within novel combustion chambers concepts, in which multiple different flame structures can coexist. Flamelet-type approaches in reactive flow simulations remain popular due to their low CPU cost. Of the many flamelet-type approaches, multi-regime flamelet tabulations have emerged as an attractive solution for capturing partially-premixed flame structures. Two key challenges associated with multi-regime flamelet tabulation are correctly distinguishing between different combustion regimes and the coupling with Large-eddy-simulation (LES), where only large turbulent structures are resolved, and the thin flame structures are often unresolved at the mesh scale. The simulation of turbulent reactive flows using LES requires modelling to account for sub-filter turbulence and flame-turbulent interactions. Despite geometric models such as the thickened flame model (TFLES) or filtered tabulated chemistry for LES (F-TACLES) being well adapted under conditions found in aeronautical combustion chambers (flamelet regime), modelling efforts remain focused on purely premixed regimes. The F-TACLES formalism is based on a conservative filtering approach and can theoretically be applied to multi-regime flames. The aim of this paper is to implement and validate the recently developed F-TACLES multi-regime model on a turbulent multi-regime flame. A posteriori tests are performed on the 3-D turbulent coaxial HYLON (Hydrogen Low-NOx) injector developed at IMFT Toulouse. This injector has two operating conditions which are investigated in the framework of the TNF workshop, an attached diffusion flame (A) and a lifted partially-premixed flame (L). Both flames exhibit large variations in local strain rate and have differing flame stabilisation mechanisms and is therefore a good candidate for model validation. The current state of the art F-TACLES models and the newly developed model are tested on both operating conditions. The F-TACLES multi-regime model predicts correct flame stabilisation mechanisms across flames A and L and shows good agreement with reference LES data whereas both premixed and diffusion based approaches show larger discrepancies. Using an iso-mesh, the dynamic TFLES approach fails to capture the complex flame structure of the partially-premixed lifted flame since the model is deactivated in the diffusion zone and the resolution is insufficient to fully resolve the flame front.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this paper is the <em>a posteriori</em> implementation of a new multi-regime turbulent combustion model. The significance of these results is illustrated by showing that the model is capable of capturing multi-regime flame structures on coarse grids where the laminar flame front is under-resolved. These conditions are often found in industrial LES simulations and therefore the model is
{"title":"Modelling turbulent multi-regime combustion in LES with filtered tabulated chemistry","authors":"Samuel Dillon , Renaud Mercier , Benoit Fiorina","doi":"10.1016/j.combustflame.2026.114802","DOIUrl":"10.1016/j.combustflame.2026.114802","url":null,"abstract":"<div><div>One of the many modelling challenges facing combustion engineers is the simulation of reactive flows within novel combustion chambers concepts, in which multiple different flame structures can coexist. Flamelet-type approaches in reactive flow simulations remain popular due to their low CPU cost. Of the many flamelet-type approaches, multi-regime flamelet tabulations have emerged as an attractive solution for capturing partially-premixed flame structures. Two key challenges associated with multi-regime flamelet tabulation are correctly distinguishing between different combustion regimes and the coupling with Large-eddy-simulation (LES), where only large turbulent structures are resolved, and the thin flame structures are often unresolved at the mesh scale. The simulation of turbulent reactive flows using LES requires modelling to account for sub-filter turbulence and flame-turbulent interactions. Despite geometric models such as the thickened flame model (TFLES) or filtered tabulated chemistry for LES (F-TACLES) being well adapted under conditions found in aeronautical combustion chambers (flamelet regime), modelling efforts remain focused on purely premixed regimes. The F-TACLES formalism is based on a conservative filtering approach and can theoretically be applied to multi-regime flames. The aim of this paper is to implement and validate the recently developed F-TACLES multi-regime model on a turbulent multi-regime flame. A posteriori tests are performed on the 3-D turbulent coaxial HYLON (Hydrogen Low-NOx) injector developed at IMFT Toulouse. This injector has two operating conditions which are investigated in the framework of the TNF workshop, an attached diffusion flame (A) and a lifted partially-premixed flame (L). Both flames exhibit large variations in local strain rate and have differing flame stabilisation mechanisms and is therefore a good candidate for model validation. The current state of the art F-TACLES models and the newly developed model are tested on both operating conditions. The F-TACLES multi-regime model predicts correct flame stabilisation mechanisms across flames A and L and shows good agreement with reference LES data whereas both premixed and diffusion based approaches show larger discrepancies. Using an iso-mesh, the dynamic TFLES approach fails to capture the complex flame structure of the partially-premixed lifted flame since the model is deactivated in the diffusion zone and the resolution is insufficient to fully resolve the flame front.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this paper is the <em>a posteriori</em> implementation of a new multi-regime turbulent combustion model. The significance of these results is illustrated by showing that the model is capable of capturing multi-regime flame structures on coarse grids where the laminar flame front is under-resolved. These conditions are often found in industrial LES simulations and therefore the model is","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114802"},"PeriodicalIF":6.2,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976374","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}
Pub Date : 2026-01-16DOI: 10.1016/j.combustflame.2026.114788
Yinan Yang, Tsukasa Hori, Shinya Sawada, Fumiteru Akamatsu
Ammonia co-combustion with hydrocarbon fuels has emerged as a promising pathway toward carbon neutrality. However, as a nitrogen-containing fuel, ammonia combustion at high temperatures inevitably leads to the formation of both thermal and a substantial amount of fuel NOx. To distinguish the nitrogen sources within ammonia co-combustion furnaces, a three-dimensional numerical analysis employing the nitrogen element-tracking method was conducted. Combustion characteristics and nitrogen oxide emission behaviors of a 10-kW ammonia co-combustion furnace were investigated under various total air ratios (λtotal = 1.0 – 1.5) and ammonia co-firing ratios (ENH3 = 0 % – 100 %). Results indicate that under air-staged combustion, increasing the total air ratio from 1.0 to 1.2 improves combustion performance with a slight increase in fuel NO (N*O), whereas a further increase to 1.5 leads to an approximately threefold rise in N*O at the furnace outlet. Thermal NO predominantly forms downstream in the furnace and shows pronounced sensitivity above temperatures of approximately 1800 K. Regarding the ammonia co-firing ratio, increasing the ammonia content enhances N*O reduction reactions but reduces the overall reaction intensity and furnace temperature, resulting in a parabolic variation of N*O emissions, with a peak occurring at an ammonia co-firing ratio of approximately 50 %. In contrast, thermal NO emissions continually decline and become negligible at ammonia co-firing ratios above 40 %. Reaction pathway analysis reveals that N*O formation is dominated by the decomposition of HN*O intermediates driven by H and OH radicals, while direct oxidation of N* and the conversion of N*H to N*O also contribute under high ammonia co-firing ratios or elevated total air ratios. The numerical results provide valuable theoretical insights for optimizing NOx emission control strategies in ammonia co-combustion systems.
{"title":"Simulation-based study of nitrogen sources and reaction pathways for NO formation in a 10-kW ammonia co-combustion furnace","authors":"Yinan Yang, Tsukasa Hori, Shinya Sawada, Fumiteru Akamatsu","doi":"10.1016/j.combustflame.2026.114788","DOIUrl":"10.1016/j.combustflame.2026.114788","url":null,"abstract":"<div><div>Ammonia co-combustion with hydrocarbon fuels has emerged as a promising pathway toward carbon neutrality. However, as a nitrogen-containing fuel, ammonia combustion at high temperatures inevitably leads to the formation of both thermal and a substantial amount of fuel NOx. To distinguish the nitrogen sources within ammonia co-combustion furnaces, a three-dimensional numerical analysis employing the nitrogen element-tracking method was conducted. Combustion characteristics and nitrogen oxide emission behaviors of a 10-kW ammonia co-combustion furnace were investigated under various total air ratios (<em>λ</em><sub><em>total</em></sub> = 1.0 – 1.5) and ammonia co-firing ratios (<em>E</em><sub><em>NH3</em></sub> = 0 % – 100 %). Results indicate that under air-staged combustion, increasing the total air ratio from 1.0 to 1.2 improves combustion performance with a slight increase in fuel NO (N*O), whereas a further increase to 1.5 leads to an approximately threefold rise in N*O at the furnace outlet. Thermal NO predominantly forms downstream in the furnace and shows pronounced sensitivity above temperatures of approximately 1800 K. Regarding the ammonia co-firing ratio, increasing the ammonia content enhances N*O reduction reactions but reduces the overall reaction intensity and furnace temperature, resulting in a parabolic variation of N*O emissions, with a peak occurring at an ammonia co-firing ratio of approximately 50 %. In contrast, thermal NO emissions continually decline and become negligible at ammonia co-firing ratios above 40 %. Reaction pathway analysis reveals that N*O formation is dominated by the decomposition of HN*O intermediates driven by H and OH radicals, while direct oxidation of N* and the conversion of N*H to N*O also contribute under high ammonia co-firing ratios or elevated total air ratios. The numerical results provide valuable theoretical insights for optimizing NOx emission control strategies in ammonia co-combustion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114788"},"PeriodicalIF":6.2,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969329","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}
Pub Date : 2026-01-16DOI: 10.1016/j.combustflame.2025.114760
Curran Schmitt , Joshua Smith , Brian Maxwell
This current work extends a Zeldovich-type loss model for detonation waves in thin channels to account for both viscous friction and heat losses in a two-dimensional framework in order to better understand the impact of these losses on the detonation velocity, cellular structure, and ability to sustain detonation in the presence of losses. Two stoichiometric hydrogen–oxygen–argon mixtures below atmospheric pressure are considered, and the geometry under investigation is a thin, rectangular channel. This two-dimensional numerical model incorporated temperature-dependent thermodynamics, the San Diego detailed chemistry mechanism, and source terms to account for the losses due to the geometry in the third dimension, which are developed from the perspective of the entrance length problem from pipe flows. The individual contributions of the viscous and heat transfer effects to the velocity deficit were determined for mixtures both near and away from the quenching limit. It was found that away from the quenching limit, the velocity deficit is fairly insensitive to the amount of heat loss, but conversely, the onset of complete detonation failure is quite sensitive to heat loss. A nondimensional measure of the rate of energy loss was proposed, and was used to show that near failure, detonations are able to sustain losing up to 30% of the released chemical energy to the channel walls before the onset of failure.
Novelty and Significance Statement
This work introduces a novel numerical framework to investigate the effects of confinement on multidimensional hydrogen–oxygen–argon detonation wave dynamics. For likely the first time, a spatially-dependent skin-friction coefficient and Reynolds analogy-based heat loss model are integrated into a quasi-two-dimensional, transient simulation with detailed chemical kinetics and temperature-dependent thermodynamics. Source terms are used to account for three-dimensional loss mechanisms, with the primary innovation being the physics-informed treatment of skin-friction. The model is validated against experimental data through calibration of a heat loss parameter which enables the separation of frictional and heat loss contributions to the detonation velocity deficit, providing new insights into the sensitivity of detonation propagation to these losses.
{"title":"The effects of friction and heat loss on two-dimensional H2–O2–Ar detonations in thin channels","authors":"Curran Schmitt , Joshua Smith , Brian Maxwell","doi":"10.1016/j.combustflame.2025.114760","DOIUrl":"10.1016/j.combustflame.2025.114760","url":null,"abstract":"<div><div>This current work extends a Zeldovich-type loss model for detonation waves in thin channels to account for both viscous friction and heat losses in a two-dimensional framework in order to better understand the impact of these losses on the detonation velocity, cellular structure, and ability to sustain detonation in the presence of losses. Two stoichiometric hydrogen–oxygen–argon mixtures below atmospheric pressure are considered, and the geometry under investigation is a thin, rectangular channel. This two-dimensional numerical model incorporated temperature-dependent thermodynamics, the San Diego detailed chemistry mechanism, and source terms to account for the losses due to the geometry in the third dimension, which are developed from the perspective of the entrance length problem from pipe flows. The individual contributions of the viscous and heat transfer effects to the velocity deficit were determined for mixtures both near and away from the quenching limit. It was found that away from the quenching limit, the velocity deficit is fairly insensitive to the amount of heat loss, but conversely, the onset of complete detonation failure is quite sensitive to heat loss. A nondimensional measure of the rate of energy loss was proposed, and was used to show that near failure, detonations are able to sustain losing up to 30% of the released chemical energy to the channel walls before the onset of failure.</div><div><strong>Novelty and Significance Statement</strong></div><div>This work introduces a novel numerical framework to investigate the effects of confinement on multidimensional hydrogen–oxygen–argon detonation wave dynamics. For likely the first time, a spatially-dependent skin-friction coefficient and Reynolds analogy-based heat loss model are integrated into a quasi-two-dimensional, transient simulation with detailed chemical kinetics and temperature-dependent thermodynamics. Source terms are used to account for three-dimensional loss mechanisms, with the primary innovation being the physics-informed treatment of skin-friction. The model is validated against experimental data through calibration of a heat loss parameter which enables the separation of frictional and heat loss contributions to the detonation velocity deficit, providing new insights into the sensitivity of detonation propagation to these losses.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114760"},"PeriodicalIF":6.2,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976375","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}
Pub Date : 2026-01-15DOI: 10.1016/j.combustflame.2026.114791
Huajie Lyu , Peng Liu , Zhenrun Wu , Hong Wang , Zhandong Wang , Xiang Gao , Bingjie Chen
Nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) are emerging pollutants originated from fuel-nitrogen in coal and nitrogen-rich biomass. They exhibit higher toxicity, carcinogenicity and mutagenicity to humans, animals, and plants in the nature than equivalent PAHs. However, the formation chemistry of even the smallest NPAH, quinoline, is still not well understood and needs further investigation. In this work, we investigated quinoline formation chemistry based on experimental measurements and quantum chemistry calculations. Pyrolysis experiments were performed in a laminar flow reactor with pyridine and acetylene as reactants at temperature range of 700–1100 K. Products were analyzed by in-situ time-of-flight molecular beam mass spectrometry using synchrotron vacuum ultraviolet radiation as photon ionization source. 33 chemical species were detected and measured, and 9 NPAHs, e.g., indole, quinoline, bi-pyridine, were identified by photon ionization energy curves and species ionization energies. Guided by the species distribution, quinoline formation pathways-two steps of acetylene addition to pyridine and cyclization-were proposed and investigated using high-level quantum chemistry calculations. The calculated yields, rate coefficients and kinetic modeling results examined the pathway competition and individual contribution to quinoline formation. The unraveled formation chemistry of quinoline may help explain how fuel-nitrogen is converted into quinoline and other NPAHs during biomass gasification, fast pyrolysis, and gas-phase combustion.
{"title":"Formation chemistry of quinoline, the smallest nitrogen-containing polycyclic aromatic hydrocarbon","authors":"Huajie Lyu , Peng Liu , Zhenrun Wu , Hong Wang , Zhandong Wang , Xiang Gao , Bingjie Chen","doi":"10.1016/j.combustflame.2026.114791","DOIUrl":"10.1016/j.combustflame.2026.114791","url":null,"abstract":"<div><div>Nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) are emerging pollutants originated from fuel-nitrogen in coal and nitrogen-rich biomass. They exhibit higher toxicity, carcinogenicity and mutagenicity to humans, animals, and plants in the nature than equivalent PAHs. However, the formation chemistry of even the smallest NPAH, quinoline, is still not well understood and needs further investigation. In this work, we investigated quinoline formation chemistry based on experimental measurements and quantum chemistry calculations. Pyrolysis experiments were performed in a laminar flow reactor with pyridine and acetylene as reactants at temperature range of 700–1100 K. Products were analyzed by <em>in-situ</em> time-of-flight molecular beam mass spectrometry using synchrotron vacuum ultraviolet radiation as photon ionization source. 33 chemical species were detected and measured, and 9 NPAHs, e.g., indole, quinoline, bi-pyridine, were identified by photon ionization energy curves and species ionization energies. Guided by the species distribution, quinoline formation pathways-two steps of acetylene addition to pyridine and cyclization-were proposed and investigated using high-level quantum chemistry calculations. The calculated yields, rate coefficients and kinetic modeling results examined the pathway competition and individual contribution to quinoline formation. The unraveled formation chemistry of quinoline may help explain how fuel-nitrogen is converted into quinoline and other NPAHs during biomass gasification, fast pyrolysis, and gas-phase combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114791"},"PeriodicalIF":6.2,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969327","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}
Pub Date : 2026-01-15DOI: 10.1016/j.combustflame.2026.114786
Vadim N. Kurdyumov, Carmen Jiménez, Daniel Fernández-Galisteo
A new mode of flame propagation from a wall with an imposed temperature in a mixture below the flammability limit is described theoretically and numerically. We consider a simple chemistry model in which the reaction rate vanishes at a temperature below some critical cut-off temperature. Unlike the standard mode, in which the flame propagates at a constant velocity through the unburned mixture, and which is not possible under the conditions under consideration, in the new mode the flame propagates at a rate inversely proportional to the square root of time. Self-sustaining flame propagation in the new mode is possible at wall temperatures below the cut-off temperature, even in the case of a cold wall. It is shown that the value of the fuel Lewis number is determinant: the new mode of propagation exists only if . An analytical solution for this new mode is proposed, showing excellent agreement with the numerical results.
Novelty and significance statement
For the first time, a new type of solutions for the propagation of a combustion wave in a mixture below the flammability limit is obtained. For the cases under consideration, the standard well-known flame solution, when the flame propagates with constant velocity along the unburned mixture, turns out to be impossible. The propagation velocity in the new regime is inversely proportional to the square root of time. An asymptotic analytical solution is obtained and it is shown that the fuel Lewis number is the controlling parameter, and that the new propagation mode is possible only in mixtures with fuel Lewis number less than unity. Excellent agreement between numerical and analytical results is demonstrated. The results are relevant for safety in the storage and handling of lean hydrogen–air or, more generally, hydrogen-containing mixtures.
{"title":"Flame initiated by a heated wall: A new mode of propagation in mixtures below the flammability limit","authors":"Vadim N. Kurdyumov, Carmen Jiménez, Daniel Fernández-Galisteo","doi":"10.1016/j.combustflame.2026.114786","DOIUrl":"10.1016/j.combustflame.2026.114786","url":null,"abstract":"<div><div>A new mode of flame propagation from a wall with an imposed temperature in a mixture below the flammability limit is described theoretically and numerically. We consider a simple chemistry model in which the reaction rate vanishes at a temperature below some critical cut-off temperature. Unlike the standard mode, in which the flame propagates at a constant velocity through the unburned mixture, and which is not possible under the conditions under consideration, in the new mode the flame propagates at a rate inversely proportional to the square root of time. Self-sustaining flame propagation in the new mode is possible at wall temperatures below the cut-off temperature, even in the case of a cold wall. It is shown that the value of the fuel Lewis number is determinant: the new mode of propagation exists only if <span><math><mrow><mi>L</mi><mi>e</mi><mo><</mo><mn>1</mn></mrow></math></span>. An analytical solution for this new mode is proposed, showing excellent agreement with the numerical results.</div><div><strong>Novelty and significance statement</strong></div><div>For the first time, a new type of solutions for the propagation of a combustion wave in a mixture below the flammability limit is obtained. For the cases under consideration, the standard well-known flame solution, when the flame propagates with constant velocity along the unburned mixture, turns out to be impossible. The propagation velocity in the new regime is inversely proportional to the square root of time. An asymptotic analytical solution is obtained and it is shown that the fuel Lewis number is the controlling parameter, and that the new propagation mode is possible only in mixtures with fuel Lewis number less than unity. Excellent agreement between numerical and analytical results is demonstrated. The results are relevant for safety in the storage and handling of lean hydrogen–air or, more generally, hydrogen-containing mixtures.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114786"},"PeriodicalIF":6.2,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969282","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}
Pub Date : 2026-01-14DOI: 10.1016/j.combustflame.2026.114771
Benoît Péden , Pierre Boivin , Nicolas Odier
<div><div>This work presents Large-Eddy Simulations of a three-dimensional airblast-type injector using a diffuse-interface Multi-Fluid approach. A four-equation model is employed, including a consistent phase transition solver and a thermodynamic closure suitable for evaporating and reacting flows. The influence of evaporation and combustion on the spray and flow dynamics is investigated through a comparative analysis of cold, evaporative, and reactive configurations. The method is first validated against reference results and known behavior for similar injector geometries. It is shown that the addition of evaporation significantly alters the liquid fuel distribution, particularly in the inner recirculation zone, while combustion further modifies both liquid and gaseous fuel fields due to temperature-induced evaporation and fuel consumption. The reacting case exhibits typical flame features, including hollow cone structures and localized high-temperature zones near stoichiometric mixture fractions. These phenomena align well with expected flame behavior under airblast conditions. Phase transition and combustion also have a notable impact on the velocity field, with increased expansion and stronger recirculation induced by heat release. The proposed model captures these effects in a unified framework. Finally, the present multi-physics approach enables consistent and efficient simulation of multiphase, reactive sprays, providing physical insight into the coupled interaction between atomization, evaporation, and combustion. The method shows good numerical performance on the 3D injector, with a reduced computational time of 2.1 <span><math><mo>×</mo></math></span> 10<sup>-5</sup> s.mpi/node /it, which has no overcost compared to the Lagrangian reference model. The fully explicit treatment of the equation of state (NASG) ensures excellent robustness on complex geometries, while avoiding the iterative procedure required by cubic-type EoS. These numerical properties make the DIM suitable for industrial LES configurations involving evaporation and combustion, and further model development.</div><div><strong>Novelty and significance statement</strong></div><div>This work presents a unified diffuse-interface Multi-Fluid framework with a four-equation model that explicitly account for atomization, evaporation, and combustion in a dense liquid regime, for Large-Eddy Simulations of multiphase reactive flows. The present method, in contrast to traditional Lagrangian injection models, effectively resolves the linked phase transition and chemical processes, allowing for realistic and predictive simulations of complex injector flows. The paper provides additional physical insights into airblast atomizers by highlighting how evaporation and heat release fundamentally change the gas-phase dynamics and liquid distribution. This methodology provides a valuable new framework for considering dense liquid phase atomization, evaporation, and induced combustion for rele
{"title":"Large-Eddy Simulation of a 3D airblast injector using a diffuse interface four-equation model: Effects of evaporation and combustion","authors":"Benoît Péden , Pierre Boivin , Nicolas Odier","doi":"10.1016/j.combustflame.2026.114771","DOIUrl":"10.1016/j.combustflame.2026.114771","url":null,"abstract":"<div><div>This work presents Large-Eddy Simulations of a three-dimensional airblast-type injector using a diffuse-interface Multi-Fluid approach. A four-equation model is employed, including a consistent phase transition solver and a thermodynamic closure suitable for evaporating and reacting flows. The influence of evaporation and combustion on the spray and flow dynamics is investigated through a comparative analysis of cold, evaporative, and reactive configurations. The method is first validated against reference results and known behavior for similar injector geometries. It is shown that the addition of evaporation significantly alters the liquid fuel distribution, particularly in the inner recirculation zone, while combustion further modifies both liquid and gaseous fuel fields due to temperature-induced evaporation and fuel consumption. The reacting case exhibits typical flame features, including hollow cone structures and localized high-temperature zones near stoichiometric mixture fractions. These phenomena align well with expected flame behavior under airblast conditions. Phase transition and combustion also have a notable impact on the velocity field, with increased expansion and stronger recirculation induced by heat release. The proposed model captures these effects in a unified framework. Finally, the present multi-physics approach enables consistent and efficient simulation of multiphase, reactive sprays, providing physical insight into the coupled interaction between atomization, evaporation, and combustion. The method shows good numerical performance on the 3D injector, with a reduced computational time of 2.1 <span><math><mo>×</mo></math></span> 10<sup>-5</sup> s.mpi/node /it, which has no overcost compared to the Lagrangian reference model. The fully explicit treatment of the equation of state (NASG) ensures excellent robustness on complex geometries, while avoiding the iterative procedure required by cubic-type EoS. These numerical properties make the DIM suitable for industrial LES configurations involving evaporation and combustion, and further model development.</div><div><strong>Novelty and significance statement</strong></div><div>This work presents a unified diffuse-interface Multi-Fluid framework with a four-equation model that explicitly account for atomization, evaporation, and combustion in a dense liquid regime, for Large-Eddy Simulations of multiphase reactive flows. The present method, in contrast to traditional Lagrangian injection models, effectively resolves the linked phase transition and chemical processes, allowing for realistic and predictive simulations of complex injector flows. The paper provides additional physical insights into airblast atomizers by highlighting how evaporation and heat release fundamentally change the gas-phase dynamics and liquid distribution. This methodology provides a valuable new framework for considering dense liquid phase atomization, evaporation, and induced combustion for rele","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114771"},"PeriodicalIF":6.2,"publicationDate":"2026-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145973265","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}
Pub Date : 2026-01-14DOI: 10.1016/j.combustflame.2026.114776
S. Hossain , M. Abdulrahman , P.T. Lynch , Eric K. Mayhew , K. Brezinsky
3-Ethyltoluene (ET) and 3-n-propyltoluene (PT) are key aromatic constituents of Virent’s synthetic aromatic kerosene (SAK), necessitating detailed understanding of their oxidation chemistry for surrogate fuel development. This study investigates the high-pressure oxidation behavior of n-heptane/ET (HET) and n-heptane/PT (HPT) blends through single-pulse shock tube experiments conducted at 50 atm, with a residence time range of 12-14 ms, and temperatures ranging from 800–1400 K. Experiments were performed across equivalence ratios φ = 0.5, 1.0, and 2.0 to capture lean, stoichiometric, and rich combustion regimes. Post-shock gases were analyzed using gas chromatography, providing speciation data for ∼30 products, including H₂, CO, CO₂, CH₄, C₂H₄, C₃H₆, CH₂O, benzene, toluene, and methylstyrene. The CRECK_ET_Theory mechanism (incorporating literature ET submodel) and CRECK_PT_Theory mechanism (developed by integrating PT decomposition chemistry) were used for kinetic modeling with Cantera, showing good agreement with experimental trends across all φ. Both mechanisms include ab initio rate calculations for key hydrogen abstraction reactions, improving the fidelity of fuel-specific pathways. Rate-of-production and sensitivity analyses revealed distinct oxidation behaviors driven by alkyl side-chain structure. ET oxidation was dominated by OH abstraction at the α-CH₂ site, especially under lean conditions, whereas PT exhibited enhanced reactivity under rich conditions due to faster unimolecular decomposition and a lower activation barrier for H-abstraction by H atoms, particularly at the benzylic and β-CH₂ positions. Neither ET nor PT suppressed n-heptane oxidation, in contrast to the radical-scavenging effects previously observed for 1,2,4-trimethylbenzene (TMB124). This study provides the first detailed oxidation dataset for ET and PT under engine-relevant conditions and delivers validated kinetic mechanisms essential for constructing accurate multi-component surrogates for SAK. The insights into structure–reactivity relationships offer a mechanistic foundation for predictive combustion modeling of synthetic fuels in propulsion applications.
{"title":"Understanding the moderate-temperature oxidation of 3-ethyltoluene and 3-n-propyltoluene in presence of n-heptane","authors":"S. Hossain , M. Abdulrahman , P.T. Lynch , Eric K. Mayhew , K. Brezinsky","doi":"10.1016/j.combustflame.2026.114776","DOIUrl":"10.1016/j.combustflame.2026.114776","url":null,"abstract":"<div><div>3-Ethyltoluene (ET) and 3-n-propyltoluene (PT) are key aromatic constituents of Virent’s synthetic aromatic kerosene (SAK), necessitating detailed understanding of their oxidation chemistry for surrogate fuel development. This study investigates the high-pressure oxidation behavior of n-heptane/ET (HET) and n-heptane/PT (HPT) blends through single-pulse shock tube experiments conducted at 50 atm, with a residence time range of 12-14 ms, and temperatures ranging from 800–1400 K. Experiments were performed across equivalence ratios φ = 0.5, 1.0, and 2.0 to capture lean, stoichiometric, and rich combustion regimes. Post-shock gases were analyzed using gas chromatography, providing speciation data for ∼30 products, including H₂, CO, CO₂, CH₄, C₂H₄, C₃H₆, CH₂O, benzene, toluene, and methylstyrene. The CRECK_ET_Theory mechanism (incorporating literature ET submodel) and CRECK_PT_Theory mechanism (developed by integrating PT decomposition chemistry) were used for kinetic modeling with Cantera, showing good agreement with experimental trends across all φ. Both mechanisms include <em>ab initio</em> rate calculations for key hydrogen abstraction reactions, improving the fidelity of fuel-specific pathways. Rate-of-production and sensitivity analyses revealed distinct oxidation behaviors driven by alkyl side-chain structure. ET oxidation was dominated by OH abstraction at the α-CH₂ site, especially under lean conditions, whereas PT exhibited enhanced reactivity under rich conditions due to faster unimolecular decomposition and a lower activation barrier for H-abstraction by H atoms, particularly at the benzylic and β-CH₂ positions. Neither ET nor PT suppressed n-heptane oxidation, in contrast to the radical-scavenging effects previously observed for 1,2,4-trimethylbenzene (TMB124). This study provides the first detailed oxidation dataset for ET and PT under engine-relevant conditions and delivers validated kinetic mechanisms essential for constructing accurate multi-component surrogates for SAK. The insights into structure–reactivity relationships offer a mechanistic foundation for predictive combustion modeling of synthetic fuels in propulsion applications.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114776"},"PeriodicalIF":6.2,"publicationDate":"2026-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145973692","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}
Pub Date : 2026-01-13DOI: 10.1016/j.combustflame.2026.114781
Feixue Cai , Xingyu Su , Matthew J. Cleary , Zhuyin Ren , Assaad R. Masri
Among various soot modelling approaches, the sectional method is widely recognized for its capability to accurately resolve particle size distributions (PSDs). Burner-stabilized stagnation flames are commonly used as benchmarks for quantifying uncertainties and conducting sensitivity analyses of kinetic parameters. However, the high computational cost of detailed sectional models poses a major challenge in generating sufficient data for sensitivity analysis. This study introduces the fixed diffusion flux approximation to enhance the efficiency of sensitivity analysis and optimization in sectional soot models. The proposed approach achieves 3 times increase in computational efficiency for sensitivity calculations. Furthermore, the optimization of reaction rate constants led to significant improvements in PSD predictions across different flame heights, with the maximum loss reduced by more than 50%. These findings underscore the efficiency and practicality of the fixed flux approximation for sectional soot model sensitivity analysis and optimization.
{"title":"Efficient sensitivity analysis and optimization of sectional soot model in burner-stabilized stagnation flame using fixed flux approximation","authors":"Feixue Cai , Xingyu Su , Matthew J. Cleary , Zhuyin Ren , Assaad R. Masri","doi":"10.1016/j.combustflame.2026.114781","DOIUrl":"10.1016/j.combustflame.2026.114781","url":null,"abstract":"<div><div>Among various soot modelling approaches, the sectional method is widely recognized for its capability to accurately resolve particle size distributions (PSDs). Burner-stabilized stagnation flames are commonly used as benchmarks for quantifying uncertainties and conducting sensitivity analyses of kinetic parameters. However, the high computational cost of detailed sectional models poses a major challenge in generating sufficient data for sensitivity analysis. This study introduces the fixed diffusion flux approximation to enhance the efficiency of sensitivity analysis and optimization in sectional soot models. The proposed approach achieves 3 times increase in computational efficiency for sensitivity calculations. Furthermore, the optimization of reaction rate constants led to significant improvements in PSD predictions across different flame heights, with the maximum loss reduced by more than 50%. These findings underscore the efficiency and practicality of the fixed flux approximation for sectional soot model sensitivity analysis and optimization.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114781"},"PeriodicalIF":6.2,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145973266","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}
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