This study aims to obtain an idealized burning rate constant for polymers without internal bubble effects through a systematic investigation of the combustion behavior of spherical polymethyl methacrylate (PMMA) samples under controlled conditions. The initial void fraction, defined as the relative volumetric expansion resulting from internal bubble formation within the test specimen, was one of the key parameters in this work and was varied within the range of 10 % to 100 %. Burning tests were performed at various sub-atmospheric levels (< 101 kPa). At 100 kPa, buoyancy-induced flows led to asymmetric flame structures and localized overheating of the polymer, triggering active bubble dynamics. As a result, the specific influence of initial void fraction on the burning behavior was difficult to distinguish. By reducing the ambient pressure while maintaining the flame temperature, buoyancy effects were effectively suppressed, allowing for more stable and symmetric flame development. This condition enabled a clearer examination of the relationship between initial void fraction and the burning rate constant. At 20 kPa, for instance, a distinctive linear correlation between the burning rate constant and the initial void fraction was clearly observed, which was masked under relatively higher ambient pressures. Using the extrapolation technique, a reference burning rate constant of 0.43 mm2/s was obtained under conditions free of initial void effects. This value is considered an idealized burning rate constant without any void and deformation effects. Indeed, this value is less than half of the values shown in the previous literature (∼1–1.5 mm2/s), implying that the effect of volume expansion of the polymer specimen during the burning, accelerated by the internal bubble, is significant. Having an idealized burning rate constant is essential for systematically discussing the internal bubble effects on burning behavior, and this work has a meaningful innovative impact on the deep understanding of polymer combustion.
{"title":"Effect of internal void on the burning rate constant of PMMA","authors":"Yue Zhang, Goki Kawai, Masayuki Yamabayashi, Daiki Matsugi, Yuji Nakamura","doi":"10.1016/j.combustflame.2025.114704","DOIUrl":"10.1016/j.combustflame.2025.114704","url":null,"abstract":"<div><div>This study aims to obtain an idealized burning rate constant for polymers without internal bubble effects through a systematic investigation of the combustion behavior of spherical polymethyl methacrylate (PMMA) samples under controlled conditions. The initial void fraction, defined as the relative volumetric expansion resulting from internal bubble formation within the test specimen, was one of the key parameters in this work and was varied within the range of 10 % to 100 %. Burning tests were performed at various sub-atmospheric levels (< 101 kPa). At 100 kPa, buoyancy-induced flows led to asymmetric flame structures and localized overheating of the polymer, triggering active bubble dynamics. As a result, the specific influence of initial void fraction on the burning behavior was difficult to distinguish. By reducing the ambient pressure while maintaining the flame temperature, buoyancy effects were effectively suppressed, allowing for more stable and symmetric flame development. This condition enabled a clearer examination of the relationship between initial void fraction and the burning rate constant. At 20 kPa, for instance, a distinctive linear correlation between the burning rate constant and the initial void fraction was clearly observed, which was masked under relatively higher ambient pressures. Using the extrapolation technique, a reference burning rate constant of 0.43 mm<sup>2</sup>/s was obtained under conditions free of initial void effects. This value is considered an idealized burning rate constant without any void and deformation effects. Indeed, this value is less than half of the values shown in the previous literature (∼1–1.5 mm<sup>2</sup>/s), implying that the effect of volume expansion of the polymer specimen during the burning, accelerated by the internal bubble, is significant. Having an idealized burning rate constant is essential for systematically discussing the internal bubble effects on burning behavior, and this work has a meaningful innovative impact on the deep understanding of polymer combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114704"},"PeriodicalIF":6.2,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789263","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 : 2025-12-16DOI: 10.1016/j.combustflame.2025.114709
Xuhai Pan , Guanshen Yan , Langqing Lu , Min Hua , Yong Cao
The influences of porous material parameter and the placement position on the spontaneous combustion suppression and flame quenching are investigated during the high-pressure hydrogen leakage. The pressure dynamic, photoelectric signal, and flame propagation are analyzed to reveal the spontaneous combustion suppression mechanism of porous metal material. Experimental results show that the porous material achieves effective flame blockage through synergistic physical and chemical mechanisms, establishing an exemplary case of flame inhibition inside the pipe. The porous material with smaller pore sizes leads to the stronger initial shock wave intensity. Increasing the length of the porous medium can significantly enhance flame suppression effectiveness. The reduced pore size significantly enhances hydrogen self-ignition suppression capability. Flame propagation process categorize these phenomena into three distinct types. When porous material is installed within the pipeline, it significantly alters the flow field characteristics of the orifice flame. The under-expanded jet structure transitions from a single Mach disk in straight pipes to a double Mach disk configuration. The flame quenching phenomenon arises from the inhibitory effect of porous material on the flame within the tube. Under specific operating conditions, porous copper can paradoxically enhance flame propagation, significantly increasing flame velocity and intensity.
{"title":"Flame quenching and spontaneous combustion suppression during high pressure hydrogen leakage by metal porous medium","authors":"Xuhai Pan , Guanshen Yan , Langqing Lu , Min Hua , Yong Cao","doi":"10.1016/j.combustflame.2025.114709","DOIUrl":"10.1016/j.combustflame.2025.114709","url":null,"abstract":"<div><div>The influences of porous material parameter and the placement position on the spontaneous combustion suppression and flame quenching are investigated during the high-pressure hydrogen leakage. The pressure dynamic, photoelectric signal, and flame propagation are analyzed to reveal the spontaneous combustion suppression mechanism of porous metal material. Experimental results show that the porous material achieves effective flame blockage through synergistic physical and chemical mechanisms, establishing an exemplary case of flame inhibition inside the pipe. The porous material with smaller pore sizes leads to the stronger initial shock wave intensity. Increasing the length of the porous medium can significantly enhance flame suppression effectiveness. The reduced pore size significantly enhances hydrogen self-ignition suppression capability. Flame propagation process categorize these phenomena into three distinct types. When porous material is installed within the pipeline, it significantly alters the flow field characteristics of the orifice flame. The under-expanded jet structure transitions from a single Mach disk in straight pipes to a double Mach disk configuration. The flame quenching phenomenon arises from the inhibitory effect of porous material on the flame within the tube. Under specific operating conditions, porous copper can paradoxically enhance flame propagation, significantly increasing flame velocity and intensity.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114709"},"PeriodicalIF":6.2,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789257","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 : 2025-12-16DOI: 10.1016/j.combustflame.2025.114720
Siyi Zhang , Chongpeng Chen , Wang Han , Jingxuan Li , Chao Li , Changlu Zhao , Lijun Yang , Yue Jiang
This work demonstrates that one-dimensional (1D) fluorinated carbon nanotubes (FCNTs) exhibit superior efficacy as a fluorocarbon additive for enhancing aluminum (Al) combustion, outperforming conventional 3D polytetrafluoroethylene (PTFE) and 2D graphene fluoride (GF). Through a combined approach of experimental diagnostics and reactive molecular dynamics (RMD) simulations, this work systematically evaluated the effects of three fluorocarbons on the energetic performance of Al. The unique 1D nanostructure of FCNTs leverages distinct advantages in regulating the combustion process via promoting intimate interfacial contact in the Al/FCNTs composite. Thermal behavior results show that FCNTs exhibit a higher onset decomposition temperature than GF and PTFE, demonstrating enhanced thermal stability. The Al/FCNTs composite can efficiently suppress pre-ignition coalescence and exhibited the shortest ignition delay time among all formulations. RMD simulations revealed that FCNTs facilitate Al fluorination, thus achieving the rapidest and greatest energy release. A clear correlation between the dimensionality of fluorocarbon and its efficacy in promoting ignition and energy release is established, following the trend: FCNTs (1D) > GF (2D) > PTFE (3D). Analysis of the condensed combustion products (CCPs) showed that the agglomeration-inhibition effect decreases in the order GF > FCNTs > PTFE. These findings highlight the significant potential of low-dimensional fluorocarbons, with 1D FCNTs offering a distinct advantage for next-generation Al-based energetic composites.
{"title":"Leveraging the dimensionality effect of fluorinated carbon nanotubes to promote aluminum combustion","authors":"Siyi Zhang , Chongpeng Chen , Wang Han , Jingxuan Li , Chao Li , Changlu Zhao , Lijun Yang , Yue Jiang","doi":"10.1016/j.combustflame.2025.114720","DOIUrl":"10.1016/j.combustflame.2025.114720","url":null,"abstract":"<div><div>This work demonstrates that one-dimensional (1D) fluorinated carbon nanotubes (FCNTs) exhibit superior efficacy as a fluorocarbon additive for enhancing aluminum (Al) combustion, outperforming conventional 3D polytetrafluoroethylene (PTFE) and 2D graphene fluoride (GF). Through a combined approach of experimental diagnostics and reactive molecular dynamics (RMD) simulations, this work systematically evaluated the effects of three fluorocarbons on the energetic performance of Al. The unique 1D nanostructure of FCNTs leverages distinct advantages in regulating the combustion process via promoting intimate interfacial contact in the Al/FCNTs composite. Thermal behavior results show that FCNTs exhibit a higher onset decomposition temperature than GF and PTFE, demonstrating enhanced thermal stability. The Al/FCNTs composite can efficiently suppress pre-ignition coalescence and exhibited the shortest ignition delay time among all formulations. RMD simulations revealed that FCNTs facilitate Al fluorination, thus achieving the rapidest and greatest energy release. A clear correlation between the dimensionality of fluorocarbon and its efficacy in promoting ignition and energy release is established, following the trend: FCNTs (1D) > GF (2D) > PTFE (3D). Analysis of the condensed combustion products (CCPs) showed that the agglomeration-inhibition effect decreases in the order GF > FCNTs > PTFE. These findings highlight the significant potential of low-dimensional fluorocarbons, with 1D FCNTs offering a distinct advantage for next-generation Al-based energetic composites.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114720"},"PeriodicalIF":6.2,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789253","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 : 2025-12-15DOI: 10.1016/j.combustflame.2025.114717
Jian Zheng , Haiou Wang , Evatt R. Hawkes , Kun Luo , Jianren Fan
<div><div>In the present work, direct numerical simulations (DNS) are employed to investigate the effects of body force on the flame and turbulence characteristics in turbulent premixed hydrogen/air flames. The influence of both thermodiffusive (TD) and Rayleigh–Taylor (RT) instabilities is examined for laminar and turbulent premixed flames at various Karlovitz numbers. Under laminar or weak turbulence conditions, the RT instability plays a significant role, causing noticeable differences in flame morphology between the cases without and with body force. The turbulent flame speed is larger in the cases with body force compared to the corresponding cases without body force, which is mainly attributed to the increased flame wrinkling, while the local reactivity remains unchanged. As the Karlovitz number of the flame increases, the role of turbulent mixing in the transport of species and heat becomes more important, leading to a reduction in the differences between the cases without and with body force. Notably, when the Karlovitz number of the flame reaches 500, the flame morphology and turbulent flame speed between the cases without and with body force are nearly identical. The statistics of turbulence were investigated. It was found that the Reynolds stress in the cases with body force can be either greater or smaller than in the corresponding cases without body force, depending on the Karlovitz number. The budget of Reynolds stress transport equation was examined. It was revealed that the velocity–pressure gradient term is the main source of the Reynolds normal stress in the streamwise direction, which is primarily determined by the mean pressure gradient <span><math><mover><mrow><mi>∂</mi><mi>p</mi><mo>/</mo><mi>∂</mi><mi>x</mi></mrow><mo>¯</mo></mover></math></span>. The relative magnitudes of the negative <span><math><mover><mrow><mi>∂</mi><mi>p</mi><mo>/</mo><mi>∂</mi><mi>x</mi></mrow><mo>¯</mo></mover></math></span> induced by the turbulent flame and the positive <span><math><mover><mrow><mi>∂</mi><mi>p</mi><mo>/</mo><mi>∂</mi><mi>x</mi></mrow><mo>¯</mo></mover></math></span> due to the body force lead to the different behaviors of Reynolds stress at various Karlovitz numbers.</div><div><strong>Novelty and significance statement</strong></div><div>In this work, DNS are employed to investigate the effects of body force on the flame and turbulence statistics in turbulent premixed hydrogen/air flames. The influence of both TD and RT instabilities is examined. It was found that RT instability plays a significant role under laminar or weak turbulence conditions, leading to a thickened flame brush and a larger turbulent flame speed compared to RT-neutral cases. In the presence of strong turbulence, turbulent mixing dominates species and heat transport, resulting in nearly identical flame characteristics between cases without and with body force. Interestingly, the Reynolds stress in the cases with body force can be either greater or smaller than
{"title":"The effects of body force on the flame and turbulence characteristics in premixed hydrogen/air flames at various Karlovitz numbers","authors":"Jian Zheng , Haiou Wang , Evatt R. Hawkes , Kun Luo , Jianren Fan","doi":"10.1016/j.combustflame.2025.114717","DOIUrl":"10.1016/j.combustflame.2025.114717","url":null,"abstract":"<div><div>In the present work, direct numerical simulations (DNS) are employed to investigate the effects of body force on the flame and turbulence characteristics in turbulent premixed hydrogen/air flames. The influence of both thermodiffusive (TD) and Rayleigh–Taylor (RT) instabilities is examined for laminar and turbulent premixed flames at various Karlovitz numbers. Under laminar or weak turbulence conditions, the RT instability plays a significant role, causing noticeable differences in flame morphology between the cases without and with body force. The turbulent flame speed is larger in the cases with body force compared to the corresponding cases without body force, which is mainly attributed to the increased flame wrinkling, while the local reactivity remains unchanged. As the Karlovitz number of the flame increases, the role of turbulent mixing in the transport of species and heat becomes more important, leading to a reduction in the differences between the cases without and with body force. Notably, when the Karlovitz number of the flame reaches 500, the flame morphology and turbulent flame speed between the cases without and with body force are nearly identical. The statistics of turbulence were investigated. It was found that the Reynolds stress in the cases with body force can be either greater or smaller than in the corresponding cases without body force, depending on the Karlovitz number. The budget of Reynolds stress transport equation was examined. It was revealed that the velocity–pressure gradient term is the main source of the Reynolds normal stress in the streamwise direction, which is primarily determined by the mean pressure gradient <span><math><mover><mrow><mi>∂</mi><mi>p</mi><mo>/</mo><mi>∂</mi><mi>x</mi></mrow><mo>¯</mo></mover></math></span>. The relative magnitudes of the negative <span><math><mover><mrow><mi>∂</mi><mi>p</mi><mo>/</mo><mi>∂</mi><mi>x</mi></mrow><mo>¯</mo></mover></math></span> induced by the turbulent flame and the positive <span><math><mover><mrow><mi>∂</mi><mi>p</mi><mo>/</mo><mi>∂</mi><mi>x</mi></mrow><mo>¯</mo></mover></math></span> due to the body force lead to the different behaviors of Reynolds stress at various Karlovitz numbers.</div><div><strong>Novelty and significance statement</strong></div><div>In this work, DNS are employed to investigate the effects of body force on the flame and turbulence statistics in turbulent premixed hydrogen/air flames. The influence of both TD and RT instabilities is examined. It was found that RT instability plays a significant role under laminar or weak turbulence conditions, leading to a thickened flame brush and a larger turbulent flame speed compared to RT-neutral cases. In the presence of strong turbulence, turbulent mixing dominates species and heat transport, resulting in nearly identical flame characteristics between cases without and with body force. Interestingly, the Reynolds stress in the cases with body force can be either greater or smaller than ","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114717"},"PeriodicalIF":6.2,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145750134","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 : 2025-12-15DOI: 10.1016/j.combustflame.2025.114685
Nikita Bystrov, Alexander Emelianov, Alexander Eremin, Pavel Yatsenko
A two–part study on the oxidation of basic furan compounds – furan and tetrahydrofuran – is presented. The first part focuses on investigating the oxidation kinetics of furan mixtures with molecular oxygen and nitrous oxide under highly diluted conditions in argon at temperatures of 1700–3450 K and pressures of 1.9–3 bar. Time–resolved quantitative measurements of atomic oxygen O(3P) formation and consumption were performed for the first time using a high–vacuum shock tube combined with atomic resonance absorption spectrometry. These measurements revealed primary oxidation pathways of furan that are challenging to detect. The new experimental data were compared with numerical results obtained using state–of–the–art kinetic models of furan combustion. Through comparative analysis, the kinetics of the interaction of furan and its fragments with atomic and molecular oxygen in the presence of NOx were investigated. The pathways and specific features of the formation of incomplete oxidation products of furan, including toxic compounds, were traced. Key reaction routes were identified, and a set of reactions and sub–mechanisms important for the further development of kinetic models for furan–based fuel combustion were outlined.
{"title":"Study of kinetics of high–temperature oxidation of basic furan compounds under high–dilute conditions – part I: Furan","authors":"Nikita Bystrov, Alexander Emelianov, Alexander Eremin, Pavel Yatsenko","doi":"10.1016/j.combustflame.2025.114685","DOIUrl":"10.1016/j.combustflame.2025.114685","url":null,"abstract":"<div><div>A two–part study on the oxidation of basic furan compounds – furan and tetrahydrofuran – is presented. The first part focuses on investigating the oxidation kinetics of furan mixtures with molecular oxygen and nitrous oxide under highly diluted conditions in argon at temperatures of 1700–3450 K and pressures of 1.9–3 bar. Time–resolved quantitative measurements of atomic oxygen O(<sup>3</sup>P) formation and consumption were performed for the first time using a high–vacuum shock tube combined with atomic resonance absorption spectrometry. These measurements revealed primary oxidation pathways of furan that are challenging to detect. The new experimental data were compared with numerical results obtained using state–of–the–art kinetic models of furan combustion. Through comparative analysis, the kinetics of the interaction of furan and its fragments with atomic and molecular oxygen in the presence of NO<sub>x</sub> were investigated. The pathways and specific features of the formation of incomplete oxidation products of furan, including toxic compounds, were traced. Key reaction routes were identified, and a set of reactions and sub–mechanisms important for the further development of kinetic models for furan–based fuel combustion were outlined.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114685"},"PeriodicalIF":6.2,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145750128","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 : 2025-12-15DOI: 10.1016/j.combustflame.2025.114686
Nikita Bystrov, Alexander Emelianov, Alexander Eremin, Pavel Yatsenko
The second part of this work examines the oxidation of tetrahydrofuran (THF) in O2/N2O mixtures, performed under highly diluted conditions in argon to ensure consistency with the furan experiments. Measurements were carried out over the same temperature (1700–3450 K) and pressure (1.9–3 bar) ranges. Temporally resolved profiles of atomic oxygen O(3P) were recorded using shock–wave heating combined with atomic resonance absorption spectrometry. The experimental data were evaluated against numerical simulations based on actual kinetic models for THF combustion. Modeling enabled a detailed analysis of the interaction of THF and its decomposition fragments with molecular and atomic oxygen, as well as oxygen–containing species such as CO, NO, and N2O. Pathways leading to the formation of major products, including toxic aldehydes and hydrogen cyanide, were identified, and the key reactions governing THF oxidation were determined. As a result, several essential combustion sub–mechanisms were outlined, whose accurate representation is critical for the further refinement of kinetic models for THF–based fuel combustion.
{"title":"Study of kinetics of high–temperature oxidation of basic furan compounds under high–dilute conditions – part II: Tetrahydrofuran","authors":"Nikita Bystrov, Alexander Emelianov, Alexander Eremin, Pavel Yatsenko","doi":"10.1016/j.combustflame.2025.114686","DOIUrl":"10.1016/j.combustflame.2025.114686","url":null,"abstract":"<div><div>The second part of this work examines the oxidation of tetrahydrofuran (THF) in O<sub>2</sub>/N<sub>2</sub>O mixtures, performed under highly diluted conditions in argon to ensure consistency with the furan experiments. Measurements were carried out over the same temperature (1700–3450 K) and pressure (1.9–3 bar) ranges. Temporally resolved profiles of atomic oxygen O(<sup>3</sup>P) were recorded using shock–wave heating combined with atomic resonance absorption spectrometry. The experimental data were evaluated against numerical simulations based on actual kinetic models for THF combustion. Modeling enabled a detailed analysis of the interaction of THF and its decomposition fragments with molecular and atomic oxygen, as well as oxygen–containing species such as CO, NO, and N<sub>2</sub>O. Pathways leading to the formation of major products, including toxic aldehydes and hydrogen cyanide, were identified, and the key reactions governing THF oxidation were determined. As a result, several essential combustion sub–mechanisms were outlined, whose accurate representation is critical for the further refinement of kinetic models for THF–based fuel combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114686"},"PeriodicalIF":6.2,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145750130","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 : 2025-12-15DOI: 10.1016/j.combustflame.2025.114690
Sergey Minaev , Vladimir Gubernov , Evgeniy Sereshchenko
Theoretical analysis performed within the reaction sheet model and numerical simulations undertaken within the model with spatially distributed chemical reactions showed the possibility of the flame existence near the source of combustible mixture with a constant concentration of the deficient reagent. The theory predicts that such flames can exist near the source only in a certain region of combustible mixture velocities which are much lower than the laminar flame velocity. Heat and reagents are transported to the reaction zone by diffusion processes that dominate convective transfer. These properties allow flames with dominant diffusion transfer to be classified in the same phenomena as the flame ball. The results of asymptotic analysis are shown to be in qualitative agreement with the numerical simulations.
{"title":"Premixed flames with dominant diffusion processes stabilized near the source of combustible mixture with the deficient reagent constant concentration","authors":"Sergey Minaev , Vladimir Gubernov , Evgeniy Sereshchenko","doi":"10.1016/j.combustflame.2025.114690","DOIUrl":"10.1016/j.combustflame.2025.114690","url":null,"abstract":"<div><div>Theoretical analysis performed within the reaction sheet model and numerical simulations undertaken within the model with spatially distributed chemical reactions showed the possibility of the flame existence near the source of combustible mixture with a constant concentration of the deficient reagent. The theory predicts that such flames can exist near the source only in a certain region of combustible mixture velocities which are much lower than the laminar flame velocity. Heat and reagents are transported to the reaction zone by diffusion processes that dominate convective transfer. These properties allow flames with dominant diffusion transfer to be classified in the same phenomena as the flame ball. The results of asymptotic analysis are shown to be in qualitative agreement with the numerical simulations.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114690"},"PeriodicalIF":6.2,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145750129","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 : 2025-12-12DOI: 10.1016/j.combustflame.2025.114707
J. Mich, J.V. Hennings de Lara, T. Hazenberg, H. Nicolai, C. Hasse
<div><div>Aluminum can serve as a carbon-free energy carrier suitable for transport and storage, releasing energy as heat and hydrogen during combustion in steam. This requires a detailed understanding of the macro- and microscopic flame structures that govern aluminum particle combustion and oxide nanoparticle formation and transport While advancements have been made in the fields of sophisticated boundary layer resolved single particle simulations and large scale flame simulations using simplified particle models, the coupling between the scales remains insufficiently understood. In this work, a combined simulation approach is presented for macroscopic flame propagation in aluminum–steam suspensions, with the Lagrangian particle model including an improved mechanistic two-diffusion-layer formulation of the structure and transport in the micro-flames which envelope each individually burning aluminum particle. In contrast to previous approaches, the model relaxes the unity Lewis assumption. This leads to an more accurate expression for the flame standoff ratio, informed by the mixture-averaged diffusion model. Validation relies on heuristic combustion time correlations and experimental data for the standoff ratio for particles between <span><math><mi>20</mi></math></span> <span><math><mspace></mspace></math></span> <span><math><mi>μm</mi></math></span> and <span><math><mi>500</mi></math></span> <span><math><mspace></mspace></math></span> <span><math><mi>μm</mi></math></span> diameter in steam, diluted with up to <span><math><mi>50</mi></math></span> <span><math><mspace></mspace></math></span> <span><math><mi>%</mi></math></span> mole nitrogen or hydrogen. The flame simulations provide first estimates for the reaction front propagation speed in monodisperse (<span><math><mi>20</mi></math></span> <span><math><mspace></mspace></math></span> <span><math><mi>μm</mi></math></span> particle diameter) aluminum steam-suspensions for equivalence ratios between <span><math><mi>0.5</mi></math></span> and <span><math><mi>1.3</mi></math></span>. The simulation results show the link between the micro-flames around individual particles and macroscopic flame propagation along the particle suspension. By shifting the macroscopic conditions from lean to rich, qualitatively different flame structures are achieved, altering both single particle evolutions and macroscopic flame profiles in a coupled manner. These insights demonstrate the need to include and combine the processes from different scales in numerical simulations, especially in complex macroscopic configurations</div><div><strong>Novelty and significance statement</strong> The novelty of this work is the combined and coupled simulation of the micro-diffusion flame structure and macroscopic reaction front propagation in suspensions of aluminum particles in steam. The major methodological advancement which facilitates this simulation approach is the derivation of a new two-diffusion-layer formulation to repr
{"title":"Coupling of the micro and macro flame structures in aluminum–steam suspensions based on an Euler-Lagrangian modeling approach","authors":"J. Mich, J.V. Hennings de Lara, T. Hazenberg, H. Nicolai, C. Hasse","doi":"10.1016/j.combustflame.2025.114707","DOIUrl":"10.1016/j.combustflame.2025.114707","url":null,"abstract":"<div><div>Aluminum can serve as a carbon-free energy carrier suitable for transport and storage, releasing energy as heat and hydrogen during combustion in steam. This requires a detailed understanding of the macro- and microscopic flame structures that govern aluminum particle combustion and oxide nanoparticle formation and transport While advancements have been made in the fields of sophisticated boundary layer resolved single particle simulations and large scale flame simulations using simplified particle models, the coupling between the scales remains insufficiently understood. In this work, a combined simulation approach is presented for macroscopic flame propagation in aluminum–steam suspensions, with the Lagrangian particle model including an improved mechanistic two-diffusion-layer formulation of the structure and transport in the micro-flames which envelope each individually burning aluminum particle. In contrast to previous approaches, the model relaxes the unity Lewis assumption. This leads to an more accurate expression for the flame standoff ratio, informed by the mixture-averaged diffusion model. Validation relies on heuristic combustion time correlations and experimental data for the standoff ratio for particles between <span><math><mi>20</mi></math></span> <span><math><mspace></mspace></math></span> <span><math><mi>μm</mi></math></span> and <span><math><mi>500</mi></math></span> <span><math><mspace></mspace></math></span> <span><math><mi>μm</mi></math></span> diameter in steam, diluted with up to <span><math><mi>50</mi></math></span> <span><math><mspace></mspace></math></span> <span><math><mi>%</mi></math></span> mole nitrogen or hydrogen. The flame simulations provide first estimates for the reaction front propagation speed in monodisperse (<span><math><mi>20</mi></math></span> <span><math><mspace></mspace></math></span> <span><math><mi>μm</mi></math></span> particle diameter) aluminum steam-suspensions for equivalence ratios between <span><math><mi>0.5</mi></math></span> and <span><math><mi>1.3</mi></math></span>. The simulation results show the link between the micro-flames around individual particles and macroscopic flame propagation along the particle suspension. By shifting the macroscopic conditions from lean to rich, qualitatively different flame structures are achieved, altering both single particle evolutions and macroscopic flame profiles in a coupled manner. These insights demonstrate the need to include and combine the processes from different scales in numerical simulations, especially in complex macroscopic configurations</div><div><strong>Novelty and significance statement</strong> The novelty of this work is the combined and coupled simulation of the micro-diffusion flame structure and macroscopic reaction front propagation in suspensions of aluminum particles in steam. The major methodological advancement which facilitates this simulation approach is the derivation of a new two-diffusion-layer formulation to repr","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114707"},"PeriodicalIF":6.2,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145747746","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 : 2025-12-12DOI: 10.1016/j.combustflame.2025.114706
Christopher W. Dennis , Batikan Koroglu , Mao-Xi Zhang , Keith D. Morrison , Alan K. Burnham , Chiara Saggese , John G. Reynolds , Jason S. Moore , Keith R. Coffee , Nathaniel B. Zuckerman , Justin Urso , Subith S. Vasu , Alexander E. Gash
<div><div>This work presents the first application of isotopically labeled LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide) to investigate thermal decomposition pathways. Specially synthesized LLM-105 isotopologues were utilized to isolate the influence of labeled <sup>15</sup>NO<sub>2</sub> nitro groups on the formation of lightgas products. Simultaneous differential scanning calorimetry, thermo-gravimetric, and mass spectrometry measurements were employed to track the evolution of product gases, enabling the direct comparison of isotopically shifted species with unlabeled LLM-105. Key findings show that C<sub>2</sub>N<sub>2</sub> production is mainly dependent on nitrogen sources from either the amine groups or the pyrazine ring (i.e., not the nitro groups). The formation of NO, N<sub>2</sub>, and N<sub>2</sub>O all involves the nitro groups to some extent. NO (nitric oxide) was found to be the predominant gas species directly formed from the nitro group of LLM-105. In contrast, mixed nitrogen isotopologues of N<sub>2</sub> and N<sub>2</sub>O (i.e., <sup>14</sup>N<sup>15</sup>N and <sup>15</sup>NNO) formed more readily in comparison to their pure counterparts (i.e., <sup>15</sup>N<sub>2</sub> and <sup>15</sup>N<sub>2</sub>O). This indicates the amine and/or pyrazine groups of LLM-105, in addition to the nitro group, are involved in the decomposition pathways forming N<sub>2</sub> and N<sub>2</sub>O. In addition, our investigation led to the discovery of two previously unreported decomposition products (CHO and HNCO), which were confirmed through hydrogen labelling utilizing deuterium isotopes. These results provide detailed speciation trends of gaseous products during LLM-105 decomposition, offering new insights into reaction pathways. Experimental data reported here will support the development of a detailed chemical kinetics model for LLM-105, essential for the safe handling of high explosives.</div></div><div><h3>Novelty and significance statement</h3><div>Revealing the thermal decomposition pathways of energetic molecules such as LLM-105 is a significant challenge, primarily because these molecules contain various functional groups that participate in complex chemical reactions. While previous research has identified most of the decomposition products of LLM-105, there remains a gap in the mechanistic understanding of its breakdown pathways. In this study, we utilized three distinct isotopologues of LLM-105 for the first time, allowing us to directly trace the contributions of specific functional groups to the formation of decomposition products. This approach enabled us to assign the generation of each product species (e.g., NO, N<sub>2</sub>, N<sub>2</sub>O, NO<sub>2</sub>, and C<sub>2</sub>N<sub>2</sub>) to individual functional groups (e.g., −NO<sub>2</sub>, −NH<sub>2</sub>, and pyrazine N). Furthermore, our investigation led to the discovery of two previously unreported decomposition products, CHO and HNCO, which expand the known deco
{"title":"An isotopic labeling investigation into the influence of the nitro group on LLM-105 thermal decomposition","authors":"Christopher W. Dennis , Batikan Koroglu , Mao-Xi Zhang , Keith D. Morrison , Alan K. Burnham , Chiara Saggese , John G. Reynolds , Jason S. Moore , Keith R. Coffee , Nathaniel B. Zuckerman , Justin Urso , Subith S. Vasu , Alexander E. Gash","doi":"10.1016/j.combustflame.2025.114706","DOIUrl":"10.1016/j.combustflame.2025.114706","url":null,"abstract":"<div><div>This work presents the first application of isotopically labeled LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide) to investigate thermal decomposition pathways. Specially synthesized LLM-105 isotopologues were utilized to isolate the influence of labeled <sup>15</sup>NO<sub>2</sub> nitro groups on the formation of lightgas products. Simultaneous differential scanning calorimetry, thermo-gravimetric, and mass spectrometry measurements were employed to track the evolution of product gases, enabling the direct comparison of isotopically shifted species with unlabeled LLM-105. Key findings show that C<sub>2</sub>N<sub>2</sub> production is mainly dependent on nitrogen sources from either the amine groups or the pyrazine ring (i.e., not the nitro groups). The formation of NO, N<sub>2</sub>, and N<sub>2</sub>O all involves the nitro groups to some extent. NO (nitric oxide) was found to be the predominant gas species directly formed from the nitro group of LLM-105. In contrast, mixed nitrogen isotopologues of N<sub>2</sub> and N<sub>2</sub>O (i.e., <sup>14</sup>N<sup>15</sup>N and <sup>15</sup>NNO) formed more readily in comparison to their pure counterparts (i.e., <sup>15</sup>N<sub>2</sub> and <sup>15</sup>N<sub>2</sub>O). This indicates the amine and/or pyrazine groups of LLM-105, in addition to the nitro group, are involved in the decomposition pathways forming N<sub>2</sub> and N<sub>2</sub>O. In addition, our investigation led to the discovery of two previously unreported decomposition products (CHO and HNCO), which were confirmed through hydrogen labelling utilizing deuterium isotopes. These results provide detailed speciation trends of gaseous products during LLM-105 decomposition, offering new insights into reaction pathways. Experimental data reported here will support the development of a detailed chemical kinetics model for LLM-105, essential for the safe handling of high explosives.</div></div><div><h3>Novelty and significance statement</h3><div>Revealing the thermal decomposition pathways of energetic molecules such as LLM-105 is a significant challenge, primarily because these molecules contain various functional groups that participate in complex chemical reactions. While previous research has identified most of the decomposition products of LLM-105, there remains a gap in the mechanistic understanding of its breakdown pathways. In this study, we utilized three distinct isotopologues of LLM-105 for the first time, allowing us to directly trace the contributions of specific functional groups to the formation of decomposition products. This approach enabled us to assign the generation of each product species (e.g., NO, N<sub>2</sub>, N<sub>2</sub>O, NO<sub>2</sub>, and C<sub>2</sub>N<sub>2</sub>) to individual functional groups (e.g., −NO<sub>2</sub>, −NH<sub>2</sub>, and pyrazine N). Furthermore, our investigation led to the discovery of two previously unreported decomposition products, CHO and HNCO, which expand the known deco","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114706"},"PeriodicalIF":6.2,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145748744","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 : 2025-12-11DOI: 10.1016/j.combustflame.2025.114689
Yanqi Liu , Shengji Li , Shiyi Chen , Hehui Yao , Xuefeng Huang , Zaizheng Li , Xiru Xu , Jiangwei Song
<div><div>Boron carbide (B<sub>4</sub>C) has been considered as a promising fuel in solid fuel ramjets (SFRJ) to replace pure boron fuel of low combustion efficiency owing to the hinder of B<sub>2</sub>O<sub>3</sub> layer, for promoting the future application in rocket-based combined-cycle engine (RBCC). However, the combustion and oxidation behavior of B<sub>4</sub>C at high pressures kept veiled. This work designed and built a laser-induced ignition and combustion diagnosis experimental apparatus with high pressure (7 MPa) atmosphere for individual isolated microparticles, and investigated the combustion characteristics of single B<sub>4</sub>C microparticles in 1–7 MPa O<sub>2</sub> and revealed high pressure effect on the combustion and reaction mechanism. The results demonstrated that the combustion of B<sub>4</sub>C generally underwent three stages: first-stage combustion (Stage I), transient weak flame/extinction (Stage II), and second-stage combustion (Stage III). The ambient pressure plays a crucial role in the B<sub>4</sub>C combustion via affecting the boiling point of B<sub>2</sub>O<sub>3</sub>. At higher pressures (≥ 0.75 MPa), the boiling point of B<sub>2</sub>O<sub>3</sub> is higher than the decomposition temperature of B<sub>4</sub>C, and thus the direct oxidation and decomposition reactions of B<sub>4</sub>C, and the oxidation reactions of decomposed B and C atoms simultaneously dominate the entire combustion process. On the contrary, in lower pressure (< 0.75 MPa), the evaporation of B<sub>2</sub>O<sub>3</sub> is prior to the decomposition of B<sub>4</sub>C, the direct oxidation reaction of B<sub>4</sub>C mainly contributes the combustion. The intermediate products and combustion residues were collected by quick quenching via controlling the laser heating time and characterized by multiple techniques. The characterization confirmed that the escape of massive gaseous products generated in Stage I formed a porous structure, providing effective channels for the subsequent diffusion of O, B and C atoms. The total combustion time showed a linear decrease with increasing the ambient pressure (<em>τ</em>=-3.24<em>p</em>+27.7). As the pressure elevated, the combustion time was shortened by 79 % (23 ms at 1 MPa to 4.9 ms at 7 MPa), the emission band spectral intensity of BO<sub>2</sub> at 547 nm was increased by 30 times, the peak combustion temperature was increased by 40 % (3154 K at 1 MPa to 4423 K at 7 MPa). The increasing pressure effectively promoted the complete combustion and energy release of B<sub>4</sub>C, and accelerated the gas-phase combustion mode transition in advance. Finally, the combustion reaction mechanism of B<sub>4</sub>C microparticles in high pressure O<sub>2</sub> was proposed and deeply discussed. This study provides an insight into understanding the combustion behavior and mechanism of B<sub>4</sub>C microparticles under high-pressure conditions for boron-based fuel application in SFRJ and RBCC.</div></div>
{"title":"High pressure effect on combustion characteristics and reaction mechanism of single boron carbide microparticles","authors":"Yanqi Liu , Shengji Li , Shiyi Chen , Hehui Yao , Xuefeng Huang , Zaizheng Li , Xiru Xu , Jiangwei Song","doi":"10.1016/j.combustflame.2025.114689","DOIUrl":"10.1016/j.combustflame.2025.114689","url":null,"abstract":"<div><div>Boron carbide (B<sub>4</sub>C) has been considered as a promising fuel in solid fuel ramjets (SFRJ) to replace pure boron fuel of low combustion efficiency owing to the hinder of B<sub>2</sub>O<sub>3</sub> layer, for promoting the future application in rocket-based combined-cycle engine (RBCC). However, the combustion and oxidation behavior of B<sub>4</sub>C at high pressures kept veiled. This work designed and built a laser-induced ignition and combustion diagnosis experimental apparatus with high pressure (7 MPa) atmosphere for individual isolated microparticles, and investigated the combustion characteristics of single B<sub>4</sub>C microparticles in 1–7 MPa O<sub>2</sub> and revealed high pressure effect on the combustion and reaction mechanism. The results demonstrated that the combustion of B<sub>4</sub>C generally underwent three stages: first-stage combustion (Stage I), transient weak flame/extinction (Stage II), and second-stage combustion (Stage III). The ambient pressure plays a crucial role in the B<sub>4</sub>C combustion via affecting the boiling point of B<sub>2</sub>O<sub>3</sub>. At higher pressures (≥ 0.75 MPa), the boiling point of B<sub>2</sub>O<sub>3</sub> is higher than the decomposition temperature of B<sub>4</sub>C, and thus the direct oxidation and decomposition reactions of B<sub>4</sub>C, and the oxidation reactions of decomposed B and C atoms simultaneously dominate the entire combustion process. On the contrary, in lower pressure (< 0.75 MPa), the evaporation of B<sub>2</sub>O<sub>3</sub> is prior to the decomposition of B<sub>4</sub>C, the direct oxidation reaction of B<sub>4</sub>C mainly contributes the combustion. The intermediate products and combustion residues were collected by quick quenching via controlling the laser heating time and characterized by multiple techniques. The characterization confirmed that the escape of massive gaseous products generated in Stage I formed a porous structure, providing effective channels for the subsequent diffusion of O, B and C atoms. The total combustion time showed a linear decrease with increasing the ambient pressure (<em>τ</em>=-3.24<em>p</em>+27.7). As the pressure elevated, the combustion time was shortened by 79 % (23 ms at 1 MPa to 4.9 ms at 7 MPa), the emission band spectral intensity of BO<sub>2</sub> at 547 nm was increased by 30 times, the peak combustion temperature was increased by 40 % (3154 K at 1 MPa to 4423 K at 7 MPa). The increasing pressure effectively promoted the complete combustion and energy release of B<sub>4</sub>C, and accelerated the gas-phase combustion mode transition in advance. Finally, the combustion reaction mechanism of B<sub>4</sub>C microparticles in high pressure O<sub>2</sub> was proposed and deeply discussed. This study provides an insight into understanding the combustion behavior and mechanism of B<sub>4</sub>C microparticles under high-pressure conditions for boron-based fuel application in SFRJ and RBCC.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114689"},"PeriodicalIF":6.2,"publicationDate":"2025-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145748748","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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