Pub Date : 2026-04-01Epub 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":"2026-04-01","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 : 2026-04-01Epub Date: 2026-02-09DOI: 10.1016/j.combustflame.2026.114859
Mayank Pandey, Krishnakant Agrawal, Anjan Ray
Plasma discharge produces complex species such as ions (O, N), electrons, radicals (O, OH, O), stable (NOx, O), and excited species (O, O(1D)), kinetically enhancing combustion. In this study, the contribution of plasma-produced species such as excited oxygen molecules (O) and atoms (O(1D)), and their individual impact on the explosion limits of a stoichiometric H/O mixture is studied computationally. Findings suggest that limited doping of the excited oxygen molecules (O) and atoms (O(1D)) non-linearly shifts the explosion limit boundary towards the left, indicating enhanced explosive behaviour. Sensitivity analysis close to enhanced regions in temperature and pressure space shows that doping O and O(1D) promotes elementary branching (H+O=O+OH, H+HO = 2OH) reactions and contributes to enhanced mixture reactivity.
Novelty and significance statement
The novelty of the present study lies in demonstrating, for the first time, the explosion limit of the system involving excited oxygen molecules (O) and atoms (O(1D)). Hydrogen is a promising zero-carbon fuel; hence, when utilized in high-speed propulsion systems enhanced by plasma discharge, the identified explosion limits must be accounted for from both utilization and safety perspectives. This study also highlights the elementary reaction steps that are important for predicting such enhancements.
{"title":"Role of excited oxygen molecules and atoms on the explosion limits of H2/O2 mixture","authors":"Mayank Pandey, Krishnakant Agrawal, Anjan Ray","doi":"10.1016/j.combustflame.2026.114859","DOIUrl":"10.1016/j.combustflame.2026.114859","url":null,"abstract":"<div><div>Plasma discharge produces complex species such as ions (O<span><math><msubsup><mrow></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math></span>, N<span><math><msubsup><mrow></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math></span>), electrons, radicals (O, OH, O), stable (NOx, O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>), and excited species (O<span><math><mrow><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>1</mn><mi>Δ</mi><mo>)</mo></mrow></mrow></math></span>, O(1D)), kinetically enhancing combustion. In this study, the contribution of plasma-produced species such as excited oxygen molecules (O<span><math><mrow><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>1</mn><mi>Δ</mi><mo>)</mo></mrow></mrow></math></span>) and atoms (O(1D)), and their individual impact on the explosion limits of a stoichiometric H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>/O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> mixture is studied computationally. Findings suggest that limited doping of the excited oxygen molecules (O<span><math><mrow><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>1</mn><mi>Δ</mi><mo>)</mo></mrow></mrow></math></span>) and atoms (O(1D)) non-linearly shifts the explosion limit boundary towards the left, indicating enhanced explosive behaviour. Sensitivity analysis close to enhanced regions in temperature and pressure space shows that doping O<span><math><mrow><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>1</mn><mi>Δ</mi><mo>)</mo></mrow></mrow></math></span> and O(1D) promotes elementary branching (H+O<span><math><mrow><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>1</mn><mi>Δ</mi><mo>)</mo></mrow></mrow></math></span>=O+OH, H+HO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> = 2OH) reactions and contributes to enhanced mixture reactivity.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of the present study lies in demonstrating, for the first time, the explosion limit of the <figure><img></figure> system involving excited oxygen molecules (O<span><math><mrow><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>1</mn><mi>Δ</mi><mo>)</mo></mrow></mrow></math></span>) and atoms (O(1D)). Hydrogen is a promising zero-carbon fuel; hence, when utilized in high-speed propulsion systems enhanced by plasma discharge, the identified explosion limits must be accounted for from both utilization and safety perspectives. This study also highlights the elementary reaction steps that are important for predicting such enhancements.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114859"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146184843","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 : 2026-04-01Epub Date: 2026-02-09DOI: 10.1016/j.combustflame.2026.114857
Katherine M. Hinnant , Clayton M. Geipel , Christopher J. Pfützner , Vidhan S. Malik , David J. Allen , Christopher M. Murzyn , Brian T. Bojko , Michael J. Soo , Brian T. Fisher
A tunable diode laser absorption spectroscopy (TDLAS) system was developed using a MEMS-VCSEL laser at 1300 nm to probe absorbance of the AlO transition within an aluminum powder flame to define spatially resolved temperature and column density. Laser wavenumber output was established using a reference hydrogen fluoride gas cell and a two-step minimization method to resolve wavenumbers within 0.03 cm-1. Absorbance data were calculated using a novel asymmetric least squares baseline fit. Temperature and column density were calculated from the absorbance data using an absorbance model with recently published machine-learning-based AlO-air broadening coefficients (reported in ExoMol). TDLAS data were collected at physical positions nominally 0.3 mm apart between lower and upper nozzles of a counterflow metal powder burner. TDLAS-defined temperatures were compared to flame temperature values obtained from non-spatially resolved AlO emission measurements and from calculated equilibrium values across a range of aluminum powder concentrations. TDLAS-defined data showed high scatter with high AlO absorbances within a narrow region between the lower and upper burner nozzles. TDLAS-based temperatures in this region were found to vary between 2900 and 3400 K, which compares favorably with flame temperatures established from AlO emission and calculated equilibrium calculations. Future experiments will involve maintaining a stationary laser position for TDLAS measurements to acquire bursts of replicate spectra in short periods of time, while leveraging natural flame fluctuations to obtain spatially resolved profiles for a range of powder concentrations.
{"title":"Aluminum monoxide tunable diode laser absorption spectroscopy (TDLAS) method to measure temperature in an aluminum powder flame","authors":"Katherine M. Hinnant , Clayton M. Geipel , Christopher J. Pfützner , Vidhan S. Malik , David J. Allen , Christopher M. Murzyn , Brian T. Bojko , Michael J. Soo , Brian T. Fisher","doi":"10.1016/j.combustflame.2026.114857","DOIUrl":"10.1016/j.combustflame.2026.114857","url":null,"abstract":"<div><div>A tunable diode laser absorption spectroscopy (TDLAS) system was developed using a MEMS-VCSEL laser at 1300 nm to probe absorbance of the AlO<span><math><mrow><mspace></mspace><msup><mrow><mi>A</mi></mrow><mn>2</mn></msup><msup><mrow><mstyle><mi>Π</mi></mstyle></mrow><mo>+</mo></msup><mo>−</mo><msup><mrow><mi>X</mi></mrow><mn>2</mn></msup><msup><mrow><mstyle><mi>Σ</mi></mstyle></mrow><mo>+</mo></msup></mrow></math></span> transition within an aluminum powder flame to define spatially resolved temperature and column density. Laser wavenumber output was established using a reference hydrogen fluoride gas cell and a two-step minimization method to resolve wavenumbers within 0.03 cm<sup>-1</sup>. Absorbance data were calculated using a novel asymmetric least squares baseline fit. Temperature and column density were calculated from the absorbance data using an absorbance model with recently published machine-learning-based AlO-air broadening coefficients (reported in ExoMol). TDLAS data were collected at physical positions nominally 0.3 mm apart between lower and upper nozzles of a counterflow metal powder burner. TDLAS-defined temperatures were compared to flame temperature values obtained from non-spatially resolved AlO emission measurements and from calculated equilibrium values across a range of aluminum powder concentrations. TDLAS-defined data showed high scatter with high AlO absorbances within a narrow region between the lower and upper burner nozzles. TDLAS-based temperatures in this region were found to vary between 2900 and 3400 K, which compares favorably with flame temperatures established from AlO emission and calculated equilibrium calculations. Future experiments will involve maintaining a stationary laser position for TDLAS measurements to acquire bursts of replicate spectra in short periods of time, while leveraging natural flame fluctuations to obtain spatially resolved profiles for a range of powder concentrations.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114857"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146185198","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 : 2026-04-01Epub Date: 2026-02-09DOI: 10.1016/j.combustflame.2026.114847
Sajjad Mohammadnejad, Amirhossein Azimi, Ritesh K. Maurya, Ömer L. Gülder
<div><div>The flow field, spray characteristics, flame chemiluminescence, soot volume fraction, and exhaust gas emissions were investigated in a hydrogen–Jet A-1 dual-fuel model gas turbine combustor. Measurements were performed using stereoscopic particle image velocimetry, Mie scattering, Fraunhofer diffraction-based spray droplet sizing, <span><math><msup><mrow><mi>OH</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> chemiluminescence imaging, laser-induced incandescence, and exhaust gas analysis. The nominal thermal power and fuel–air equivalence ratio were fixed at 8.83 kW and 0.64, respectively, with hydrogen contributing 0% to 45% of the power. Hydrogen was premixed with the airflow prior to combustion, and the liquid Jet A-1 was sprayed using a pressure-swirl atomizer. Hydrogen addition was found to influence the flow field by altering the size of the recirculation zones and shifting the location of the stagnation point. A strong connection was identified between the shape and behavior of the spray cloud and <span><math><msup><mrow><mi>OH</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> chemiluminescence. Without hydrogen enrichment, both the spray cloud and <span><math><msup><mrow><mi>OH</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> chemiluminescence formed a solid conical structure and featured a bimodal behavior. While hydrogen addition up to 25% transformed their structures into hollow cones, further enrichment led to the formation of a secondary combustion zone downstream. This was attributed to the preignition of the hydrogen–air mixture near the spray nozzle and the increased spray droplet size. The soot volume fraction decreased with hydrogen addition up to 25%. However, a sharp increase was observed at higher hydrogen enrichment levels, primarily due to the hydrogen–air mixture preignition. Considering the combustion emissions, 25% hydrogen enrichment appeared to be the optimal operating condition of the utilized combustor, resulting in nearly zero soot and CO emissions, as well as reductions of approximately 25% and 32% in <span><math><msub><mrow><mi>CO</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>NO</mi></mrow><mrow><mi>x</mi></mrow></msub></math></span> emissions, respectively.</div><div><strong>Novelty and significance statement</strong>: The soot volume fraction distribution and reactive flow field of a hydrogen–Jet A-1 dual-fuel model gas turbine combustor are experimentally measured for the first time. Only a few studies have examined hydrogen–Jet A-1 dual-fuel combustion in such combustors, especially where gaseous hydrogen is premixed with the airflow and liquid Jet A-1 is sprayed into the combustion chamber. The effect of hydrogen addition on the relation between spray and flame characteristics is also investigated to address the corresponding gap in the literature. Additionally, the spatial relations among flow and flame features, including the velocity
{"title":"Influence of premixed hydrogen enrichment on Jet A-1 spray combustion in a swirl-stabilized model gas turbine combustor","authors":"Sajjad Mohammadnejad, Amirhossein Azimi, Ritesh K. Maurya, Ömer L. Gülder","doi":"10.1016/j.combustflame.2026.114847","DOIUrl":"10.1016/j.combustflame.2026.114847","url":null,"abstract":"<div><div>The flow field, spray characteristics, flame chemiluminescence, soot volume fraction, and exhaust gas emissions were investigated in a hydrogen–Jet A-1 dual-fuel model gas turbine combustor. Measurements were performed using stereoscopic particle image velocimetry, Mie scattering, Fraunhofer diffraction-based spray droplet sizing, <span><math><msup><mrow><mi>OH</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> chemiluminescence imaging, laser-induced incandescence, and exhaust gas analysis. The nominal thermal power and fuel–air equivalence ratio were fixed at 8.83 kW and 0.64, respectively, with hydrogen contributing 0% to 45% of the power. Hydrogen was premixed with the airflow prior to combustion, and the liquid Jet A-1 was sprayed using a pressure-swirl atomizer. Hydrogen addition was found to influence the flow field by altering the size of the recirculation zones and shifting the location of the stagnation point. A strong connection was identified between the shape and behavior of the spray cloud and <span><math><msup><mrow><mi>OH</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> chemiluminescence. Without hydrogen enrichment, both the spray cloud and <span><math><msup><mrow><mi>OH</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> chemiluminescence formed a solid conical structure and featured a bimodal behavior. While hydrogen addition up to 25% transformed their structures into hollow cones, further enrichment led to the formation of a secondary combustion zone downstream. This was attributed to the preignition of the hydrogen–air mixture near the spray nozzle and the increased spray droplet size. The soot volume fraction decreased with hydrogen addition up to 25%. However, a sharp increase was observed at higher hydrogen enrichment levels, primarily due to the hydrogen–air mixture preignition. Considering the combustion emissions, 25% hydrogen enrichment appeared to be the optimal operating condition of the utilized combustor, resulting in nearly zero soot and CO emissions, as well as reductions of approximately 25% and 32% in <span><math><msub><mrow><mi>CO</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>NO</mi></mrow><mrow><mi>x</mi></mrow></msub></math></span> emissions, respectively.</div><div><strong>Novelty and significance statement</strong>: The soot volume fraction distribution and reactive flow field of a hydrogen–Jet A-1 dual-fuel model gas turbine combustor are experimentally measured for the first time. Only a few studies have examined hydrogen–Jet A-1 dual-fuel combustion in such combustors, especially where gaseous hydrogen is premixed with the airflow and liquid Jet A-1 is sprayed into the combustion chamber. The effect of hydrogen addition on the relation between spray and flame characteristics is also investigated to address the corresponding gap in the literature. Additionally, the spatial relations among flow and flame features, including the velocity ","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114847"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146185199","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 : 2026-04-01Epub Date: 2026-01-20DOI: 10.1016/j.combustflame.2026.114808
Ankit Sharma , Arland Zatania Lojo , Ya-Ting T. Liao , Paul V. Ferkul , Michael C. Johnston
The safety of spacecraft and crew members is a critical concern for space research and exploration missions. It is already known that fire hazards in a microgravity environment present unique challenges, primarily due to the absence of buoyancy, which significantly alters fire behavior. The NASA’s Artemis program, which aims to send humans to the Moon, introduces a new set of challenges due to the Moon partial gravity compared to the Earth. This necessitates a better understanding of fire behavior in partial gravity conditions. However, conducting experiments in true partial gravity environments is challenging, and the use of centrifuges to create artificial partial gravity introduces complications, including the Coriolis force and limitations in chamber size. Consequently, there have been limited studies on flame dynamics in partial gravity. To address these challenges, this research employs Computational Fluid Dynamics (CFD) techniques to investigate flame behavior in a partial gravity environment created by a rotating centrifuge. The numerical model is validated against NASA's previous experiments and provides information on the effects of the Coriolis force and flow recirculation in the chamber. The analysis reveals that the interaction between buoyancy, Coriolis force, and flow recirculation plays a significant role in flame behavior. The flame tilt angle observed in both the experiments and the numerical results is caused by the combined effects of these forces and their variations along the flame length. In conclusion, this research contributes to our understanding of how flames behave in partial gravity environments created by rotating centrifuges. It emphasizes the complexity of flame dynamics in such conditions and provides valuable insights for future centrifuge experiments, with the goal of improving space exploration safety and understanding flame behavior in unique partial gravity environment.
{"title":"Computational fluid dynamics analysis of flame dynamics in partial gravity environments in a rotating centrifuge","authors":"Ankit Sharma , Arland Zatania Lojo , Ya-Ting T. Liao , Paul V. Ferkul , Michael C. Johnston","doi":"10.1016/j.combustflame.2026.114808","DOIUrl":"10.1016/j.combustflame.2026.114808","url":null,"abstract":"<div><div>The safety of spacecraft and crew members is a critical concern for space research and exploration missions. It is already known that fire hazards in a microgravity environment present unique challenges, primarily due to the absence of buoyancy, which significantly alters fire behavior. The NASA’s Artemis program, which aims to send humans to the Moon, introduces a new set of challenges due to the Moon partial gravity compared to the Earth. This necessitates a better understanding of fire behavior in partial gravity conditions. However, conducting experiments in true partial gravity environments is challenging, and the use of centrifuges to create artificial partial gravity introduces complications, including the Coriolis force and limitations in chamber size. Consequently, there have been limited studies on flame dynamics in partial gravity. To address these challenges, this research employs Computational Fluid Dynamics (CFD) techniques to investigate flame behavior in a partial gravity environment created by a rotating centrifuge. The numerical model is validated against NASA's previous experiments and provides information on the effects of the Coriolis force and flow recirculation in the chamber. The analysis reveals that the interaction between buoyancy, Coriolis force, and flow recirculation plays a significant role in flame behavior. The flame tilt angle observed in both the experiments and the numerical results is caused by the combined effects of these forces and their variations along the flame length. In conclusion, this research contributes to our understanding of how flames behave in partial gravity environments created by rotating centrifuges. It emphasizes the complexity of flame dynamics in such conditions and provides valuable insights for future centrifuge experiments, with the goal of improving space exploration safety and understanding flame behavior in unique partial gravity environment.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114808"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036408","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}
Water vapor plays a critical role in thermal radiation within flames, affecting heat transfer and the temperature of the burning gases. This influence is particularly significant in steam-diluted flames, where radiation preheats fresh gases and affects both flame speed and combustion stability. Despite its importance, the literature review reveals a lack of studies on hydrogen–air–steam flames beyond 1D laminar configurations.
In this study, the Finite Angle Method (FAM) is combined with the Full Spectrum Correlated -Distribution (FSCK) method to formulate and solve the radiative transfer equation and then obtain the thermal radiation source term in the transported energy equation. The radiation and flow solvers are applied to stoichiometric atmospheric hydrogen–air flames diluted with 20% water vapor. The results are consistent with the existing literature and confirm the role of thermal radiation on such flames. Thermal radiation locally alters the turbulent flame structure, an alteration that would be even more pronounced at higher dilutions or pressures.
Novelty and significance statement
The novelty of this research lies in the use of a thermal radiation solver coupled with a fluid mechanics solver for DNS-type simulation of a hydrogen–air flame diluted with water vapor. This is crucial in the context of hydrogen combustion, which is a potential vector for decarbonization.
{"title":"Direct numerical simulation of Hydrogen–Air–Steam laminar and turbulent flames","authors":"Quentin Cerutti, Guillaume Ribert, Pascale Domingo","doi":"10.1016/j.combustflame.2026.114813","DOIUrl":"10.1016/j.combustflame.2026.114813","url":null,"abstract":"<div><div>Water vapor plays a critical role in thermal radiation within flames, affecting heat transfer and the temperature of the burning gases. This influence is particularly significant in steam-diluted flames, where radiation preheats fresh gases and affects both flame speed and combustion stability. Despite its importance, the literature review reveals a lack of studies on hydrogen–air–steam flames beyond 1D laminar configurations.</div><div>In this study, the Finite Angle Method (FAM) is combined with the Full Spectrum Correlated <span><math><mi>k</mi></math></span>-Distribution (FSCK) method to formulate and solve the radiative transfer equation and then obtain the thermal radiation source term in the transported energy equation. The radiation and flow solvers are applied to stoichiometric atmospheric hydrogen–air flames diluted with 20% water vapor. The results are consistent with the existing literature and confirm the role of thermal radiation on such flames. Thermal radiation locally alters the turbulent flame structure, an alteration that would be even more pronounced at higher dilutions or pressures.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this research lies in the use of a thermal radiation solver coupled with a fluid mechanics solver for DNS-type simulation of a hydrogen–air flame diluted with water vapor. This is crucial in the context of hydrogen combustion, which is a potential vector for decarbonization.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114813"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036469","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 : 2026-04-01Epub Date: 2026-02-05DOI: 10.1016/j.combustflame.2026.114799
Lei Yang , Erik Hagen , Yuxin Zhou, Keren Shi, Yuan Qin, Michael R. Zachariah
Aluminum nanoparticles (nAl) offer high energy density for solid fuels in air-breathing propulsion, but suffer from agglomeration and difficulty in particle lift-off. Here, we address this challenge by synthesizing copper-coated nAl (nAl@Cu) via a one-pot method and incorporating them into hydroxyl‑terminated polybutadiene (HTPB) fuel. The nAl@Cu/HTPB fuel demonstrated sustained continuous regressions up to 10 wt% particle loading in air counterflow, exhibiting higher regression rates than neat HTPB and demonstrating frequent droplet ejections. High-speed digital inline holography captures the process of particle ejections from the HTPB surface, revealing that the ejections are driven by the gas-bubble bursts from HTPB pyrolysis. In situ TEM shows that the coated Cu promotes nanocracking of the alumina shell of nAl, allowing more rapid and complete aluminum oxidation. A one-dimensional diffusion-flame analysis further demonstrates that back diffusion of CO2 and H2O results in oxidative heat release from a single nAl@Cu particle sufficient to pyrolyze a volume of HTPB approximately one hundred times the nAl@Cu particle’s volume, generating sufficient gaseous products to propel the particle off the surface and sustain combustion.
{"title":"Mechanism of how copper-coated nano-aluminum overcomes agglomeration and boosts air-breathing combustion of HTPB","authors":"Lei Yang , Erik Hagen , Yuxin Zhou, Keren Shi, Yuan Qin, Michael R. Zachariah","doi":"10.1016/j.combustflame.2026.114799","DOIUrl":"10.1016/j.combustflame.2026.114799","url":null,"abstract":"<div><div>Aluminum nanoparticles (nAl) offer high energy density for solid fuels in air-breathing propulsion, but suffer from agglomeration and difficulty in particle lift-off. Here, we address this challenge by synthesizing copper-coated nAl (nAl@Cu) via a one-pot method and incorporating them into hydroxyl‑terminated polybutadiene (HTPB) fuel. The nAl@Cu/HTPB fuel demonstrated sustained continuous regressions up to 10 wt% particle loading in air counterflow, exhibiting higher regression rates than neat HTPB and demonstrating frequent droplet ejections. High-speed digital inline holography captures the process of particle ejections from the HTPB surface, revealing that the ejections are driven by the gas-bubble bursts from HTPB pyrolysis. <em>In situ</em> TEM shows that the coated Cu promotes nanocracking of the alumina shell of nAl, allowing more rapid and complete aluminum oxidation. A one-dimensional diffusion-flame analysis further demonstrates that back diffusion of CO<sub>2</sub> and H<sub>2</sub>O results in oxidative heat release from a single nAl@Cu particle sufficient to pyrolyze a volume of HTPB approximately one hundred times the nAl@Cu particle’s volume, generating sufficient gaseous products to propel the particle off the surface and sustain combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114799"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146184673","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 : 2026-04-01Epub Date: 2026-01-27DOI: 10.1016/j.combustflame.2026.114819
Ziyin Chen , Song Zhao , Bruno Denet , Christophe Almarcha , Pierre Boivin
Flame intrinsic hydrodynamic and thermodiffusive instabilities are crucial for flame propagation in confined environments. The free propagation of lean premixed hydrogen/air flames in a Hele-Shaw burner is numerically studied using compressible three-dimensional direct numerical simulations (DNS). By setting two initial conditions: planar/circular, two solutions with asymmetric/symmetric flame shapes in the wall-normal direction are established, exhibiting different flame morphologies and speeds. The asymmetric solution is steady and irrelevant to the domain size, while the symmetric one propagates unsteadily, and a larger domain size yields a higher flame front surface and a higher speed accordingly. An analysis of flame front curvature and Lewis number effect shows that the two solutions have the same amplification factor and exhibit the same curvature features. The impact of the expansion-induced flow field ahead of the flame front is then discussed for both solutions through statistical analysis. The flame convex/concave curvature in the transverse direction yields divergence/convergence of the flow field ahead, leading to flow moving forward/backward relative to the flame. It is found that for both asymmetric and symmetric solutions, the increase in flow rate against the flame front leads to a higher elongation. However, in the case where the flow in the fresh gases is moving in the same direction as the flame, for the symmetric solution, the flame front surface in the wall-normal direction increases as the flow rate increases, whereas the elongation decreases for the asymmetric solution. Nevertheless, both the average flame front surface increment and the Lewis number effect on it can be recovered using a 2D configuration in the wall-normal direction, which is further combined with a 2D simulation from the front view to predict the 3D flame speed of the symmetric case.
Novelty and significance statement This study is the first three-dimensional study on lean premixed hydrogen/air flame freely propagating in narrow channels considering both hydrodynamic, including Darrieus–Landau (DL) and Saffman–Taylor (ST) instabilities, and thermodiffusive (TD) instabilities. It is also the first to quantitatively investigate the impact of expansion-induced local flow in the fresh gases on the flame front shape in the wall-normal direction. This research is significant as it validates the multiplicity of asymmetric/symmetric solutions through 3D simulations and explores the structure of flame fronts and the flame acceleration mechanism. It is also significant for combining 2D simulations in the normal and transverse directions to recover the global flame speed in 3D.
{"title":"A three-dimensional study on local flow of lean premixed hydrogen/air flame in a Hele-Shaw burner","authors":"Ziyin Chen , Song Zhao , Bruno Denet , Christophe Almarcha , Pierre Boivin","doi":"10.1016/j.combustflame.2026.114819","DOIUrl":"10.1016/j.combustflame.2026.114819","url":null,"abstract":"<div><div>Flame intrinsic hydrodynamic and thermodiffusive instabilities are crucial for flame propagation in confined environments. The free propagation of lean premixed hydrogen/air flames in a Hele-Shaw burner is numerically studied using compressible three-dimensional direct numerical simulations (DNS). By setting two initial conditions: planar/circular, two solutions with asymmetric/symmetric flame shapes in the wall-normal direction are established, exhibiting different flame morphologies and speeds. The asymmetric solution is steady and irrelevant to the domain size, while the symmetric one propagates unsteadily, and a larger domain size yields a higher flame front surface and a higher speed accordingly. An analysis of flame front curvature and Lewis number effect shows that the two solutions have the same amplification factor and exhibit the same curvature features. The impact of the expansion-induced flow field ahead of the flame front is then discussed for both solutions through statistical analysis. The flame convex/concave curvature in the transverse direction yields divergence/convergence of the flow field ahead, leading to flow moving forward/backward relative to the flame. It is found that for both asymmetric and symmetric solutions, the increase in flow rate against the flame front leads to a higher elongation. However, in the case where the flow in the fresh gases is moving in the same direction as the flame, for the symmetric solution, the flame front surface in the wall-normal direction increases as the flow rate increases, whereas the elongation decreases for the asymmetric solution. Nevertheless, both the average flame front surface increment and the Lewis number effect on it can be recovered using a 2D configuration in the wall-normal direction, which is further combined with a 2D simulation from the front view to predict the 3D flame speed of the symmetric case.</div><div><strong>Novelty and significance statement</strong> This study is the first three-dimensional study on lean premixed hydrogen/air flame freely propagating in narrow channels considering both hydrodynamic, including Darrieus–Landau (DL) and Saffman–Taylor (ST) instabilities, and thermodiffusive (TD) instabilities. It is also the first to quantitatively investigate the impact of expansion-induced local flow in the fresh gases on the flame front shape in the wall-normal direction. This research is significant as it validates the multiplicity of asymmetric/symmetric solutions through 3D simulations and explores the structure of flame fronts and the flame acceleration mechanism. It is also significant for combining 2D simulations in the normal and transverse directions to recover the global flame speed in 3D.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114819"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075096","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 : 2026-04-01Epub Date: 2026-01-24DOI: 10.1016/j.combustflame.2026.114815
Xin Li , Shumeng Xie , Shangpeng Li , Chaoyang Liu , Yu Pan , Huangwei Zhang
Investigation of shock-induced combustion in non-uniform mixtures is essential for advanced propulsion systems. In this work, the interaction between a shock wave and a reactive bubble containing a stratified hydrogen-oxygen mixture are numerically investigated, employing detailed chemistry and adaptive mesh refinement. By radially varying the local equivalence ratio ϕ within the bubble, this study examines how different ϕ distributions impact ignition and reaction wave propagation during shock bubble interactions. Six radial equivalence ratio distributions ϕ = 0.15/0.5/1.0→2.0 and ϕ = 2.0→0.15/0.5/1.0 (arrows indicate the change from bubble center to interface) are analysed in detail. For lean-to-rich bubbles, ignition initiates in the upstream. Double-corner vortex structures are observed when the central equivalence ratio is 0.15 or 0.5. A central equivalence ratio of 1.0 results in the coexistence of upstream detonation and downstream deflagration. For rich-to-lean bubbles, outer equivalence ratios of 0.15, 0.5, and 1.0 correspond to upstream, double, and downstream ignition modes, respectively. Large-scale vortices induced by wave interactions are prominent in bubbles with an outer equivalence ratio of 0.15. Detonation ignition in non-uniform equivalence ratio bubbles depends on the accumulation of free radicals. Non-uniform fuel/oxygen distributions affect H radical runaway dominated regions. The region with ϕ > 1.15 is governed by HO2 radical runaway. Reaction wave propagation shows anisotropy, especially the propagation velocity decreases after merging with the transmitted wave. Downstream ignition propagates more slowly than upstream ignition but achieves enhanced fuel consumption due to increased bubble compression. Additionally, interactions between reaction waves and interfaces suppress vorticity growth.
{"title":"Shock-induced ignition and reaction wave propagation in a stratified hydrogen bubble","authors":"Xin Li , Shumeng Xie , Shangpeng Li , Chaoyang Liu , Yu Pan , Huangwei Zhang","doi":"10.1016/j.combustflame.2026.114815","DOIUrl":"10.1016/j.combustflame.2026.114815","url":null,"abstract":"<div><div>Investigation of shock-induced combustion in non-uniform mixtures is essential for advanced propulsion systems. In this work, the interaction between a shock wave and a reactive bubble containing a stratified hydrogen-oxygen mixture are numerically investigated, employing detailed chemistry and adaptive mesh refinement. By radially varying the local equivalence ratio <em>ϕ</em> within the bubble, this study examines how different <em>ϕ</em> distributions impact ignition and reaction wave propagation during shock bubble interactions. Six radial equivalence ratio distributions <em>ϕ</em> = 0.15/0.5/1.0→2.0 and <em>ϕ</em> = 2.0→0.15/0.5/1.0 (arrows indicate the change from bubble center to interface) are analysed in detail. For lean-to-rich bubbles, ignition initiates in the upstream. Double-corner vortex structures are observed when the central equivalence ratio is 0.15 or 0.5. A central equivalence ratio of 1.0 results in the coexistence of upstream detonation and downstream deflagration. For rich-to-lean bubbles, outer equivalence ratios of 0.15, 0.5, and 1.0 correspond to upstream, double, and downstream ignition modes, respectively. Large-scale vortices induced by wave interactions are prominent in bubbles with an outer equivalence ratio of 0.15. Detonation ignition in non-uniform equivalence ratio bubbles depends on the accumulation of free radicals. Non-uniform fuel/oxygen distributions affect H radical runaway dominated regions. The region with <em>ϕ</em> > 1.15 is governed by HO<sub>2</sub> radical runaway. Reaction wave propagation shows anisotropy, especially the propagation velocity decreases after merging with the transmitted wave. Downstream ignition propagates more slowly than upstream ignition but achieves enhanced fuel consumption due to increased bubble compression. Additionally, interactions between reaction waves and interfaces suppress vorticity growth.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114815"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075140","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}
Mitigating nitrogen oxide (NOx) pollution remains a formidable challenge amid the continued utilization of fossil fuels and the emergence of zero-carbon ammonia energy. Unlike the selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR), which require additional additives to remove NO, this study integrates experimental measurements and kinetic simulations to investigate the direct removal of NO driven by dielectric barrier discharge (DBD). A two-zone DBD platform is designed, and experimental studies are conducted for the NO/Ar system. The experimental results demonstrate that, in the absence of additives (e.g., NH3, O2), the system achieves 98 % NO removal efficiency, and an N2/O2 selectivity greater than 90 %. Furthermore, it is found that increasing the voltage is more effective in enhancing the removal of NO than increasing the number of plasma-reaction-zones. The rate constants of electron collision reactions are calculated by Bolsig+ solver, while those for the excited-state species are derived from the semi-empirical models such as the Fridman-Macheret -model and the Schwartz-Slawsky Herzfeld (SSH) model. Ultimately, a kinetic model for the removal of NO by plasma is developed to reveal the reaction kinetics of NO removal under various conditions. Kinetic analysis show that electron collisions drive the Ar/NO to generate excited-state species (e.g., NO (ele), NO (vib), and NO+). Through plasma-related reactions, such as dissociative quenching reaction (Ar⁎ + NO = Ar + N + O) and dissociative recombination reaction (e + NO+ = N + O), N and O atoms are generated thereby converted into N2 and O2 through ground-state chemical reactions.
随着化石燃料的持续使用和零碳氨能源的出现，减少氮氧化物（NOx）污染仍然是一项艰巨的挑战。与选择性非催化还原（SNCR）和选择性催化还原（SCR）需要额外的添加剂来去除NO不同，本研究结合实验测量和动力学模拟来研究介质阻挡放电（DBD）驱动下直接去除NO的方法。设计了双区DBD平台，并对NO/Ar系统进行了实验研究。实验结果表明，在不添加添加剂（如NH3、O2）的情况下，该系统的NO去除率达到98%，N2/O2选择性大于90%。此外，我们还发现增加电压比增加等离子体反应区的数量更有效地促进了NO的去除。电子碰撞反应的速率常数由Bolsig+求解器计算，激发态种的速率常数由Fridman-Macheret α-模型和schwartz - slavsky Herzfeld （SSH）模型等半经验模型计算。最后，建立了等离子体去除NO的动力学模型，揭示了不同条件下去除NO的反应动力学。动力学分析表明，电子碰撞驱动Ar/NO生成激发态物质（如NO （ele）、NO （vib）和NO+）。通过等离子体相关反应，如解离猝灭反应（Ar + NO = Ar + N + O）和解离重组反应（e + NO+ = N + O），产生N和O原子，从而通过基态化学反应转化为N2和O2。
{"title":"Direct NO removal driven by dielectric barrier discharge: An experimental and kinetic modeling study","authors":"Menglei Zheng , Yong Bao , Xianhui Chen , Xiaoyuan Zhang","doi":"10.1016/j.combustflame.2026.114790","DOIUrl":"10.1016/j.combustflame.2026.114790","url":null,"abstract":"<div><div>Mitigating nitrogen oxide (NO<sub>x</sub>) pollution remains a formidable challenge amid the continued utilization of fossil fuels and the emergence of zero-carbon ammonia energy. Unlike the selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR), which require additional additives to remove NO, this study integrates experimental measurements and kinetic simulations to investigate the direct removal of NO driven by dielectric barrier discharge (DBD). A two-zone DBD platform is designed, and experimental studies are conducted for the NO/Ar system. The experimental results demonstrate that, in the absence of additives (e.g., NH<sub>3</sub>, O<sub>2</sub>), the system achieves 98 % NO removal efficiency, and an N<sub>2</sub>/O<sub>2</sub> selectivity greater than 90 %. Furthermore, it is found that increasing the voltage is more effective in enhancing the removal of NO than increasing the number of plasma-reaction-zones. The rate constants of electron collision reactions are calculated by Bolsig<sup>+</sup> solver, while those for the excited-state species are derived from the semi-empirical models such as the Fridman-Macheret <span><math><mi>α</mi></math></span>-model and the Schwartz-Slawsky Herzfeld (SSH) model. Ultimately, a kinetic model for the removal of NO by plasma is developed to reveal the reaction kinetics of NO removal under various conditions. Kinetic analysis show that electron collisions drive the Ar/NO to generate excited-state species (e.g., NO (ele), NO (vib), and NO<sup>+</sup>). Through plasma-related reactions, such as dissociative quenching reaction (Ar<sup>⁎</sup> + NO = Ar + N + O) and dissociative recombination reaction (e + NO<sup>+</sup> = N + O), N and O atoms are generated thereby converted into N<sub>2</sub> and O<sub>2</sub> through ground-state chemical reactions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114790"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036410","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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