Pub Date : 2026-05-01Epub Date: 2026-02-28DOI: 10.1016/j.combustflame.2026.114888
Hetong Gao, Yueming Wang, Minmin Zhou, Lunbo Duan
The interaction of static magnetic fields with diffusion flames was examined to distinguish the roles of Kelvin and Lorentz forces under higher conducting conditions. A slot burner with K2CO3 seeding was used to vary charge density, potassium atoms were measured by TDLAS, and reaction-kinetics modeling provided species and conductivity at the flame front. The experiments show that Kelvin force produces symmetric deformation—reduced height and lateral widening—while the magnetic term of the Lorentz force yields asymmetric deflection along the field-orthogonal axis. Potassium seeding elevates electron concentration and conductivity, and analysis of current pathways indicates that cation convection current dominates over induction current in driving deflection. The study relates dimensionless measures of magnetic forces to the observed symmetric and asymmetric responses, thereby identifying operating ranges in which Lorentz effects become detectable under static fields. These relationships offer a compact, quantitative basis to compare conditions and anticipate morphology changes in magnetically influenced diffusion flames.
{"title":"A comparison study between Lorentz force and Kelvin force of heavily seeded diffusion flames","authors":"Hetong Gao, Yueming Wang, Minmin Zhou, Lunbo Duan","doi":"10.1016/j.combustflame.2026.114888","DOIUrl":"10.1016/j.combustflame.2026.114888","url":null,"abstract":"<div><div>The interaction of static magnetic fields with diffusion flames was examined to distinguish the roles of Kelvin and Lorentz forces under higher conducting conditions. A slot burner with K<sub>2</sub>CO<sub>3</sub> seeding was used to vary charge density, potassium atoms were measured by TDLAS, and reaction-kinetics modeling provided species and conductivity at the flame front. The experiments show that Kelvin force produces symmetric deformation—reduced height and lateral widening—while the magnetic term of the Lorentz force yields asymmetric deflection along the field-orthogonal axis. Potassium seeding elevates electron concentration and conductivity, and analysis of current pathways indicates that cation convection current dominates over induction current in driving deflection. The study relates dimensionless measures of magnetic forces to the observed symmetric and asymmetric responses, thereby identifying operating ranges in which Lorentz effects become detectable under static fields. These relationships offer a compact, quantitative basis to compare conditions and anticipate morphology changes in magnetically influenced diffusion flames.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114888"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386935","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 : 2026-05-01Epub Date: 2026-02-24DOI: 10.1016/j.combustflame.2026.114887
Antonio Masucci , Alessandro Porcarelli , Tiziano Ghisu , Ivan Langella
Large Eddy Simulations (LES) coupled with the Eulerian Stochastic Fields (ESF) approach are used in this study to investigate the effects of tangential strain on NO emissions. The simulation framework is applied to a lean, hydrogen-air premixed flame stabilised by a conical bluff-body burner developed at the Norwegian University of Science and Technology (NTNU). Simulations are conducted at three different inlet conditions. The inlet mass flow rates of premixed fuel and oxidiser are increased to systematically vary the tangential strain rate and analyse its effect on the flame dynamics and NO formation. The results are validated against experimental measurements, showing good agreement for velocity statistics and flame structure. A detailed analysis reveals that, for the present test case, the tangential strain rate is the dominant contributor to flame stretch, while curvature effects are negligible. Increasing tangential strain enhances flame reactivity up to a critical threshold, beyond which the consumption speed decreases. Results show that increasing the mean tangential strain rate by 24% can lead to an almost 43% reduction in NO emissions per kW. These findings highlight the potential of strain-based control strategies for emission reduction in hydrogen combustion systems and demonstrate the suitability of the ESF method in modelling highly strained, turbulent premixed flames.
Novelty and significance statement
This study provides the first demonstration of how tangential strain rate can be systematically exploited to reduce NO emissions in a practical turbulent premixed hydrogen flame configuration. While previous works have largely focused on laminar counterflow or simplified configurations, this research extends the analysis to a three-dimensional bluff-body stabilised flame, capturing realistic turbulence–chemistry interactions. By employing Large Eddy Simulation coupled with the Eulerian Stochastic Fields (LES–ESF) method, the work achieves a detailed representation of differential diffusion effects and flame–strain coupling without relying on empirical closure assumptions. The findings establish that tangential strain is the dominant contributor to flame stretch, with curvature playing a negligible role, and reveal a critical threshold beyond which increased strain reduces flame consumption speed and NO production. A moderate increase of roughly 24% in mean tangential strain rate was found to yield an almost 43% decrease in NO emissions per unit power. Considering the high tangential strain levels characterising the experimental flame, the results presented here not only demonstrate the robustness of the ESF framework in capturing the trends typical of highly strained hydrogen flames, but also open pathways for strain-based emission control strategies, offering practical relevance for the design of next-generation low-emission hydrogen combustion systems.
{"title":"Investigation of tangential strain rate impact on NO emissions in turbulent premixed hydrogen flames using the Eulerian Stochastic Fields approach","authors":"Antonio Masucci , Alessandro Porcarelli , Tiziano Ghisu , Ivan Langella","doi":"10.1016/j.combustflame.2026.114887","DOIUrl":"10.1016/j.combustflame.2026.114887","url":null,"abstract":"<div><div>Large Eddy Simulations (LES) coupled with the Eulerian Stochastic Fields (ESF) approach are used in this study to investigate the effects of tangential strain on NO emissions. The simulation framework is applied to a lean, hydrogen-air premixed flame stabilised by a conical bluff-body burner developed at the Norwegian University of Science and Technology (NTNU). Simulations are conducted at three different inlet conditions. The inlet mass flow rates of premixed fuel and oxidiser are increased to systematically vary the tangential strain rate and analyse its effect on the flame dynamics and NO formation. The results are validated against experimental measurements, showing good agreement for velocity statistics and flame structure. A detailed analysis reveals that, for the present test case, the tangential strain rate is the dominant contributor to flame stretch, while curvature effects are negligible. Increasing tangential strain enhances flame reactivity up to a critical threshold, beyond which the consumption speed decreases. Results show that increasing the mean tangential strain rate by 24% can lead to an almost 43% reduction in NO emissions per kW. These findings highlight the potential of strain-based control strategies for emission reduction in hydrogen combustion systems and demonstrate the suitability of the ESF method in modelling highly strained, turbulent premixed flames.</div><div><strong>Novelty and significance statement</strong></div><div>This study provides the first demonstration of how tangential strain rate can be systematically exploited to reduce NO emissions in a practical turbulent premixed hydrogen flame configuration. While previous works have largely focused on laminar counterflow or simplified configurations, this research extends the analysis to a three-dimensional bluff-body stabilised flame, capturing realistic turbulence–chemistry interactions. By employing Large Eddy Simulation coupled with the Eulerian Stochastic Fields (LES–ESF) method, the work achieves a detailed representation of differential diffusion effects and flame–strain coupling without relying on empirical closure assumptions. The findings establish that tangential strain is the dominant contributor to flame stretch, with curvature playing a negligible role, and reveal a critical threshold beyond which increased strain reduces flame consumption speed and NO production. A moderate increase of roughly 24% in mean tangential strain rate was found to yield an almost 43% decrease in NO emissions per unit power. Considering the high tangential strain levels characterising the experimental flame, the results presented here not only demonstrate the robustness of the ESF framework in capturing the trends typical of highly strained hydrogen flames, but also open pathways for strain-based emission control strategies, offering practical relevance for the design of next-generation low-emission hydrogen combustion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114887"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386590","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 : 2026-05-01Epub Date: 2026-02-19DOI: 10.1016/j.combustflame.2026.114867
Francisco C. Martins, José L.M. Rocha, José C.F. Pereira
<div><div>This study analyses the dynamics of streaks in laminar boundary layer flames by direct numerical simulation, under three crossflow perturbation states: unperturbed, perturbed by freestream turbulence <span><math><mrow><mo>(</mo><mn>0</mn><mo>.</mo><mn>03</mn><mtext>%</mtext><mo>≤</mo><mi>T</mi><mi>I</mi><mo>≤</mo><mn>1</mn><mtext>%</mtext><mo>)</mo></mrow></math></span>, and perturbed by a steady sinusoidal mimicking manufactured streaks. Simulations reveal that streak behaviour is highly dependent on the perturbation state. Unperturbed crossflows result in delayed streak onset and produce smaller meandering streaks that remain unsteady. Heat flux to the surface below the flame remains uniform in these conditions, due to the small streak amplitude. Freestream turbulence induces earlier onset, increases streak wavenumber, and results in larger flame surface perturbation amplitudes. Streak growth rates are consistent with quadratic scaling typical of Rayleigh–Taylor instability for <span><math><mrow><mi>T</mi><mi>I</mi><mo>≥</mo><mn>0</mn><mo>.</mo><mn>6</mn><mtext>%</mtext></mrow></math></span>, but, for lower <span><math><mrow><mi>T</mi><mi>I</mi></mrow></math></span>, the instability amplitude remains in the regime where growth is governed by Linear Stability Theory scaling. Steady sinusoidal perturbations can be used to control the number of streaks generated, which align with crossflow velocity valleys. For low wavenumber sinusoidal perturbations <span><math><mrow><mo>(</mo><mi>k</mi><mo><</mo><mn>4</mn><mo>)</mo></mrow></math></span>, larger quasi-steady streaks are overlapped by smaller unsteady meandering streaks. Larger sinusoidal perturbation wavenumbers <span><math><mrow><mo>(</mo><mi>k</mi><mo>≥</mo><mn>4</mn><mo>)</mo></mrow></math></span> induce large steady streaks that separate into finger-like structures, inside which fuel packets are carried downstream and combustion continues. This has a strong influence on estimated heat flux to the bottom surface, which is initially stronger below troughs, due to the lower flame standoff distance, but the contrary is true once the finger-like structures develop.</div><div><strong>Novelty and significance statement</strong></div><div>Boundary layer flames are a largely unexplored setup of reactive flows, especially in the laminar regime. This study features the first simulations of laminar boundary layer flames, addressing the role of crossflow perturbation state on streak development and growth, which is a major gap in the literature left by previous experimental studies. Results confirm the presence of Rayleigh–Taylor instabilities, and show that the perturbation introduced determines perturbation growth and wavenumber, and greatly influences heat flux to nearby surfaces.</div><div>The fundamental physical insights revealed provide key improvements in the understanding of fuel consumption and heating of nearby surfaces. Practical applications that rely on this include wildfire pro
{"title":"The effect of crossflow perturbations on streaks in laminar boundary layer flames","authors":"Francisco C. Martins, José L.M. Rocha, José C.F. Pereira","doi":"10.1016/j.combustflame.2026.114867","DOIUrl":"10.1016/j.combustflame.2026.114867","url":null,"abstract":"<div><div>This study analyses the dynamics of streaks in laminar boundary layer flames by direct numerical simulation, under three crossflow perturbation states: unperturbed, perturbed by freestream turbulence <span><math><mrow><mo>(</mo><mn>0</mn><mo>.</mo><mn>03</mn><mtext>%</mtext><mo>≤</mo><mi>T</mi><mi>I</mi><mo>≤</mo><mn>1</mn><mtext>%</mtext><mo>)</mo></mrow></math></span>, and perturbed by a steady sinusoidal mimicking manufactured streaks. Simulations reveal that streak behaviour is highly dependent on the perturbation state. Unperturbed crossflows result in delayed streak onset and produce smaller meandering streaks that remain unsteady. Heat flux to the surface below the flame remains uniform in these conditions, due to the small streak amplitude. Freestream turbulence induces earlier onset, increases streak wavenumber, and results in larger flame surface perturbation amplitudes. Streak growth rates are consistent with quadratic scaling typical of Rayleigh–Taylor instability for <span><math><mrow><mi>T</mi><mi>I</mi><mo>≥</mo><mn>0</mn><mo>.</mo><mn>6</mn><mtext>%</mtext></mrow></math></span>, but, for lower <span><math><mrow><mi>T</mi><mi>I</mi></mrow></math></span>, the instability amplitude remains in the regime where growth is governed by Linear Stability Theory scaling. Steady sinusoidal perturbations can be used to control the number of streaks generated, which align with crossflow velocity valleys. For low wavenumber sinusoidal perturbations <span><math><mrow><mo>(</mo><mi>k</mi><mo><</mo><mn>4</mn><mo>)</mo></mrow></math></span>, larger quasi-steady streaks are overlapped by smaller unsteady meandering streaks. Larger sinusoidal perturbation wavenumbers <span><math><mrow><mo>(</mo><mi>k</mi><mo>≥</mo><mn>4</mn><mo>)</mo></mrow></math></span> induce large steady streaks that separate into finger-like structures, inside which fuel packets are carried downstream and combustion continues. This has a strong influence on estimated heat flux to the bottom surface, which is initially stronger below troughs, due to the lower flame standoff distance, but the contrary is true once the finger-like structures develop.</div><div><strong>Novelty and significance statement</strong></div><div>Boundary layer flames are a largely unexplored setup of reactive flows, especially in the laminar regime. This study features the first simulations of laminar boundary layer flames, addressing the role of crossflow perturbation state on streak development and growth, which is a major gap in the literature left by previous experimental studies. Results confirm the presence of Rayleigh–Taylor instabilities, and show that the perturbation introduced determines perturbation growth and wavenumber, and greatly influences heat flux to nearby surfaces.</div><div>The fundamental physical insights revealed provide key improvements in the understanding of fuel consumption and heating of nearby surfaces. Practical applications that rely on this include wildfire pro","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114867"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386876","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 : 2026-05-01Epub Date: 2026-03-05DOI: 10.1016/j.combustflame.2026.114913
Lei Zhou , Haoran Xi , Lijia Zhong , Wanhui Zhao , Haiqiao Wei
Previous studies employed the high-reactivity fuels to ignite the ammonia via a dual fuel injection strategy for compression ignition (CI) engines. However, there are still bottleneck problems. Therefore, the objective of this letter is to demonstrate a promising alternative method to achieve pre-chamber turbulent jet flame inducing liquid ammonia spray flame (PC-LASF). The effect of mixture reactivity in PC and injection timing on the ignition and propagation of liquid ammonia spray flame is investigated in a constant-volume chamber. The results have proven the feasibility of PC-LASF method and a stable ammonia spray flame with a two-stage combustion phenomenon is successfully achieved. The increase of hydrogen amount in pre-chamber will enhance the jet intensity. Two ignition modes, including the high-temperature jet flame and thermal atmosphere, are performed by precisely controlling the ammonia injection timing or ignition timing.
{"title":"Liquid ammonia spray flame with pre-chamber turbulent jet ignition","authors":"Lei Zhou , Haoran Xi , Lijia Zhong , Wanhui Zhao , Haiqiao Wei","doi":"10.1016/j.combustflame.2026.114913","DOIUrl":"10.1016/j.combustflame.2026.114913","url":null,"abstract":"<div><div>Previous studies employed the high-reactivity fuels to ignite the ammonia via a dual fuel injection strategy for compression ignition (CI) engines. However, there are still bottleneck problems. Therefore, the objective of this letter is to demonstrate a promising alternative method to achieve pre-chamber turbulent jet flame inducing liquid ammonia spray flame (PC-LASF). The effect of mixture reactivity in PC and injection timing on the ignition and propagation of liquid ammonia spray flame is investigated in a constant-volume chamber. The results have proven the feasibility of PC-LASF method and a stable ammonia spray flame with a two-stage combustion phenomenon is successfully achieved. The increase of hydrogen amount in pre-chamber will enhance the jet intensity. Two ignition modes, including the high-temperature jet flame and thermal atmosphere, are performed by precisely controlling the ammonia injection timing or ignition timing.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114913"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386887","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}
Laser-controllable micro-propulsion is an emerging micro-propulsion technology capable of rapidly igniting propellant upon laser irradiation and extinguishing it quickly once the laser is removed. It offers advantages such as on/off controllability and adjustable burning rates. Gel propellants, which combine the benefits of both liquid and solid propellants, represent a novel class of propellants. Their application in laser-controllable combustion broadens the scope of their use. However, the flame structure, combustion flow field, and controllable combustion mechanisms of gel propellants under low-pressure environments remain poorly understood. In this study, an ADN-based laser-controlled gel propellant was prepared using the freeze-thaw method, and its combustion boundaries and burning rate variations under low pressure were investigated. The effects of pressure and laser power density on the flame structure of the propellant were further analyzed, elucidating the mechanisms behind controllable combustion. Under a fixed pressure of 0.1 MPa and laser power densities of 0.17 W•mm⁻², 0.34 W•mm⁻², and a range from 0.51 W•mm⁻² to 1.54 W•mm⁻², the gel propellant exhibited three distinct states: non-ignition, self-sustained combustion, and controllable combustion. When the laser power density was fixed at 0.51 W•mm-2 and the pressure was reduced from atmospheric (0.1 MPa) to 0.04 MPa, the propellant maintained good controllable combustion performance, with an increase in the gas jet velocity generated by combustion. The analysis suggested that under conditions of low pressure and high laser power density, the increased thickness of the dark zone in the gas phase region caused the flame to move away from the burning surface. Simultaneously, the enhanced gas jet velocity reduced the heat flux conducted back to the burning surface from the gas-phase flame. This decrease in heat flux diminished the accumulation of chemical reaction heat and ultimately enabled controllable combustion of the propellant. This study provides valuable data and theoretical insights into the laser-controlled combustion mechanisms of gel propellants.
Novelty and significance statement
ADN-based gel propellant is a novel green propellant capable of solid-liquid phase transition. This study reveals for the first time the combustion wave structure of an ADN-based laser-controlled gel propellant. By establishing a quantitative burning rate model under different pressures and laser power densities, combined with combustion flow field analysis, it clarifies that the thickness of the gas-phase zone is the critical factor enabling the transition to non-self-sustaining combustion. This research provides crucial theoretical insights for the active control of combustion waves and offers a new paradigm for designing intelligent, throttleable propulsion systems.
{"title":"Flame structure variation and controllable combustion mechanism of ADN-based laser-controlled gel propellant under low-pressure environment","authors":"Jingyuan Zhang , Jiabin Yang , Buren Duan , Xueying Guo , Hongyu Chen , Yuhan Zhang , Wangxiang Fang , Ziyi Mao , Ruiqi Shen , Lizhi Wu","doi":"10.1016/j.combustflame.2026.114921","DOIUrl":"10.1016/j.combustflame.2026.114921","url":null,"abstract":"<div><div>Laser-controllable micro-propulsion is an emerging micro-propulsion technology capable of rapidly igniting propellant upon laser irradiation and extinguishing it quickly once the laser is removed. It offers advantages such as on/off controllability and adjustable burning rates. Gel propellants, which combine the benefits of both liquid and solid propellants, represent a novel class of propellants. Their application in laser-controllable combustion broadens the scope of their use. However, the flame structure, combustion flow field, and controllable combustion mechanisms of gel propellants under low-pressure environments remain poorly understood. In this study, an ADN-based laser-controlled gel propellant was prepared using the freeze-thaw method, and its combustion boundaries and burning rate variations under low pressure were investigated. The effects of pressure and laser power density on the flame structure of the propellant were further analyzed, elucidating the mechanisms behind controllable combustion. Under a fixed pressure of 0.1 MPa and laser power densities of 0.17 W•mm⁻², 0.34 W•mm⁻², and a range from 0.51 W•mm⁻² to 1.54 W•mm⁻², the gel propellant exhibited three distinct states: non-ignition, self-sustained combustion, and controllable combustion. When the laser power density was fixed at 0.51 W•mm<sup>-2</sup> and the pressure was reduced from atmospheric (0.1 MPa) to 0.04 MPa, the propellant maintained good controllable combustion performance, with an increase in the gas jet velocity generated by combustion. The analysis suggested that under conditions of low pressure and high laser power density, the increased thickness of the dark zone in the gas phase region caused the flame to move away from the burning surface. Simultaneously, the enhanced gas jet velocity reduced the heat flux conducted back to the burning surface from the gas-phase flame. This decrease in heat flux diminished the accumulation of chemical reaction heat and ultimately enabled controllable combustion of the propellant. This study provides valuable data and theoretical insights into the laser-controlled combustion mechanisms of gel propellants.</div></div><div><h3>Novelty and significance statement</h3><div>ADN-based gel propellant is a novel green propellant capable of solid-liquid phase transition. This study reveals for the first time the combustion wave structure of an ADN-based laser-controlled gel propellant. By establishing a quantitative burning rate model under different pressures and laser power densities, combined with combustion flow field analysis, it clarifies that the thickness of the gas-phase zone is the critical factor enabling the transition to non-self-sustaining combustion. This research provides crucial theoretical insights for the active control of combustion waves and offers a new paradigm for designing intelligent, throttleable propulsion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114921"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387005","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 : 2026-05-01Epub Date: 2026-02-25DOI: 10.1016/j.combustflame.2026.114883
Leilei Xu , Carl-Otto Olsson Sjögren , Yuchen Zhou , Fang Chen , Zubayr O. Hassan , Abdulrahman S. Alsuhaibani , Bandar H. Solami , Aqil Jamal , Osamah Siddiqui , William L. Roberts , Xue-Song Bai , Ayman M. Elbaz
An innovative coaxial dual-swirl combustor was developed to address the challenges of combustion instability and NO emissions inherent to ammonia combustion. The combustor employs an inner swirler supplying a premixed ammonia/air stream and an outer swirler generating a premixed methane/air flame that stabilizes the inner ammonia flame. Combined large-eddy simulations (LES) and planar laser-induced fluorescence (PLIF) measurements were conducted to systematically examine the effects of the inner-stream equivalence ratio and outer-stream Reynolds number on NO emissions. The results demonstrate a marked reduction in NO emissions for stoichiometric to fuel-rich ammonia/air flames, while lean flames near the blowout limit exhibit strong sensitivity of NO emissions to the outer-stream Reynolds number. LES and PLIF analyses reveal that flame–flame interactions in the shear layer between the two flames govern this behavior. Depending on the inner equivalence ratio, merged single reaction zone, distinct twin reaction zones or triple-flame structures form, altering radical concentrations and NO formation pathways. The central recirculation zone (CRZ), originating from vortex breakdown, also plays a key role in stabilizing the flames and oxidizing residual fuel. Hot gases from the outer flame recirculate into the inner ammonia stream, promoting complete combustion similar to the Rich–Quench–Lean (RQL) concept. Overall, NO emissions are primarily governed by the intensified flame–flame interactions. At higher outer-stream Reynolds numbers, lean flames () exhibit enhanced NO formation via the HNO pathway, driven by local flame extinction, partial mixing of methane and ammonia through extinction holes, and subsequent downstream oxidation. Near-stoichiometric flames show reduced NO emissions due to dilution and radical pool modification, without evidence of local extinction. In contrast, fuel-rich flames () exhibit effective de-NO reduction with only moderate sensitivity to the Reynolds number, owing to the robust triple-flame structure. This study provides critical insights into flame–flame interactions and NO formation in ammonia/methane dual-swirl flames, offering a pathway to more stable, low-emission ammonia combustion technologies and advancing the practical deployment of ammonia as a carbon-free fuel.
{"title":"Turbulent mixing and flame stability in a dual-swirler ammonia/methane co-flame burner: Reynolds number effects on NOx emissions","authors":"Leilei Xu , Carl-Otto Olsson Sjögren , Yuchen Zhou , Fang Chen , Zubayr O. Hassan , Abdulrahman S. Alsuhaibani , Bandar H. Solami , Aqil Jamal , Osamah Siddiqui , William L. Roberts , Xue-Song Bai , Ayman M. Elbaz","doi":"10.1016/j.combustflame.2026.114883","DOIUrl":"10.1016/j.combustflame.2026.114883","url":null,"abstract":"<div><div>An innovative coaxial dual-swirl combustor was developed to address the challenges of combustion instability and NO<span><math><msub><mrow></mrow><mrow><mi>x</mi></mrow></msub></math></span> emissions inherent to ammonia combustion. The combustor employs an inner swirler supplying a premixed ammonia/air stream and an outer swirler generating a premixed methane/air flame that stabilizes the inner ammonia flame. Combined large-eddy simulations (LES) and planar laser-induced fluorescence (PLIF) measurements were conducted to systematically examine the effects of the inner-stream equivalence ratio and outer-stream Reynolds number on NO emissions. The results demonstrate a marked reduction in NO emissions for stoichiometric to fuel-rich ammonia/air flames, while lean flames near the blowout limit exhibit strong sensitivity of NO emissions to the outer-stream Reynolds number. LES and PLIF analyses reveal that flame–flame interactions in the shear layer between the two flames govern this behavior. Depending on the inner equivalence ratio, merged single reaction zone, distinct twin reaction zones or triple-flame structures form, altering radical concentrations and NO formation pathways. The central recirculation zone (CRZ), originating from vortex breakdown, also plays a key role in stabilizing the flames and oxidizing residual fuel. Hot gases from the outer flame recirculate into the inner ammonia stream, promoting complete combustion similar to the Rich–Quench–Lean (RQL) concept. Overall, NO emissions are primarily governed by the intensified flame–flame interactions. At higher outer-stream Reynolds numbers, lean flames (<span><math><mrow><msub><mrow><mi>Φ</mi></mrow><mrow><msub><mrow><mtext>NH</mtext></mrow><mrow><mn>3</mn></mrow></msub></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>4</mn></mrow></math></span>) exhibit enhanced NO formation via the HNO pathway, driven by local flame extinction, partial mixing of methane and ammonia through extinction holes, and subsequent downstream oxidation. Near-stoichiometric flames show reduced NO emissions due to dilution and radical pool modification, without evidence of local extinction. In contrast, fuel-rich flames (<span><math><mrow><msub><mrow><mi>Φ</mi></mrow><mrow><msub><mrow><mtext>NH</mtext></mrow><mrow><mn>3</mn></mrow></msub></mrow></msub><mo>=</mo><mn>1</mn><mo>.</mo><mn>4</mn></mrow></math></span>) exhibit effective de-NO<span><math><msub><mrow></mrow><mrow><mi>x</mi></mrow></msub></math></span> reduction with only moderate sensitivity to the Reynolds number, owing to the robust triple-flame structure. This study provides critical insights into flame–flame interactions and NO<span><math><msub><mrow></mrow><mrow><mi>x</mi></mrow></msub></math></span> formation in ammonia/methane dual-swirl flames, offering a pathway to more stable, low-emission ammonia combustion technologies and advancing the practical deployment of ammonia as a carbon-free fuel.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114883"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386851","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 : 2026-05-01Epub Date: 2026-03-01DOI: 10.1016/j.combustflame.2026.114895
Youri Prokesch, Rory Underwood, Gregory Young
A small-scale, optically accessible crossflow burner was used to investigate the effects of thermodynamic properties of inert diluent/oxidizer mixtures on solid fuel combustion. Experiments were conducted utilizing three oxidizer mixtures, each comprising O₂ with an inert diluent (60 % by mole) (He, N₂, and Ar). Polymethyl methacrylate (PMMA) was considered in two geometrical configurations, flush and rearward facing step, with two flow conditions for each case based on either constant Reynolds number or constant port velocity (Vp). Optical access facilitated the use of OH* chemiluminescence, OH planar laser induced fluorescence (PLIF), and rainbow schlieren to visualize the flow field. In the flush configuration, under constant Vp, the He case demonstrated a laminar reaction zone with unsteadiness increasing according to molecular weight of the mixtures. In the step configuration, a shear layer stabilized reaction zone was observed for all cases except the lowest velocity He mixture, which adhered closer to a diffusion dominated mixing process. Regression rates were obtained and correlated with thermal diffusivities and adiabatic flame temperatures of the diluent mixtures with He producing the highest regression and N2 the lowest. Between geometrical configurations, N2 and Ar exhibited no notable difference in regression rate, whereas He mixtures experienced a decrease in the step case due to increased reaction zone standoff from diffusion dominated transport. The results suggest that thermodynamic properties were the dominating influence for regression rates compared to secondary flow field factors such as turbulence.
{"title":"Study of solid fuel diffusion flames in a crossflow burner","authors":"Youri Prokesch, Rory Underwood, Gregory Young","doi":"10.1016/j.combustflame.2026.114895","DOIUrl":"10.1016/j.combustflame.2026.114895","url":null,"abstract":"<div><div>A small-scale, optically accessible crossflow burner was used to investigate the effects of thermodynamic properties of inert diluent/oxidizer mixtures on solid fuel combustion. Experiments were conducted utilizing three oxidizer mixtures, each comprising O₂ with an inert diluent (60 % by mole) (He, N₂, and Ar). Polymethyl methacrylate (PMMA) was considered in two geometrical configurations, flush and rearward facing step, with two flow conditions for each case based on either constant Reynolds number or constant port velocity (V<sub>p</sub>). Optical access facilitated the use of OH* chemiluminescence, OH planar laser induced fluorescence (PLIF), and rainbow schlieren to visualize the flow field. In the flush configuration, under constant V<sub>p</sub>, the He case demonstrated a laminar reaction zone with unsteadiness increasing according to molecular weight of the mixtures. In the step configuration, a shear layer stabilized reaction zone was observed for all cases except the lowest velocity He mixture, which adhered closer to a diffusion dominated mixing process. Regression rates were obtained and correlated with thermal diffusivities and adiabatic flame temperatures of the diluent mixtures with He producing the highest regression and N<sub>2</sub> the lowest. Between geometrical configurations, N<sub>2</sub> and Ar exhibited no notable difference in regression rate, whereas He mixtures experienced a decrease in the step case due to increased reaction zone standoff from diffusion dominated transport. The results suggest that thermodynamic properties were the dominating influence for regression rates compared to secondary flow field factors such as turbulence<strong>.</strong></div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114895"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386879","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 : 2026-05-01Epub Date: 2026-03-02DOI: 10.1016/j.combustflame.2026.114896
Tianbao Ma , Jiangtao Lian , Tianwei Yang , Jian Li
The propagation mechanism of gaseous detonation in a rough channel with regularly spaced obstacles is statistically investigated by quantitatively examining changes in cellular patterns and cell sizes as a function of obstacle geometry. A comprehensive map of detonation propagation modes is presented by analyzing the effects of obstacle geometry and cell size. It has been found that obstacle spacing affects the detonation-propagation mode by shifting the position at which the Mach reflection occurs. Near the limit, periodically appearing transverse detonations, synchronized with the obstacle spacing, are found to sustain detonation propagation from failure. A relation between the measured cell sizes of the quasi-detonation and the velocity is proposed and validated using Ng’s cell-size prediction model. In addition, to account for differences in tube-section shape, roughness, obstacle spacing, and cell size, a model for predicting detonation velocity in a rough tube is proposed by modifying the Fay model. The applicability and accuracy of the modified model under quasi-detonation are verified by comparing with experimental results and those from the literature.
{"title":"Statistical study on cell size variation of gaseous detonation in a two-dimensional obstructed channel","authors":"Tianbao Ma , Jiangtao Lian , Tianwei Yang , Jian Li","doi":"10.1016/j.combustflame.2026.114896","DOIUrl":"10.1016/j.combustflame.2026.114896","url":null,"abstract":"<div><div>The propagation mechanism of gaseous detonation in a rough channel with regularly spaced obstacles is statistically investigated by quantitatively examining changes in cellular patterns and cell sizes as a function of obstacle geometry. A comprehensive map of detonation propagation modes is presented by analyzing the effects of obstacle geometry and cell size. It has been found that obstacle spacing affects the detonation-propagation mode by shifting the position at which the Mach reflection occurs. Near the limit, periodically appearing transverse detonations, synchronized with the obstacle spacing, are found to sustain detonation propagation from failure. A relation between the measured cell sizes of the quasi-detonation and the velocity is proposed and validated using Ng’s cell-size prediction model. In addition, to account for differences in tube-section shape, roughness, obstacle spacing, and cell size, a model for predicting detonation velocity in a rough tube is proposed by modifying the Fay model. The applicability and accuracy of the modified model under quasi-detonation are verified by comparing with experimental results and those from the literature.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114896"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387007","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 : 2026-05-01Epub Date: 2026-03-04DOI: 10.1016/j.combustflame.2026.114862
Gangchui Zhang , Jiangong Zhao , Wen Ao , Zhuopu Wang , Peijin Liu
This study first investigated the combustion behavior of aluminum particles in solid propellants under acoustic oscillations in a custom high-pressure combustor, and subsequently developed a combustion model based on the experimental results. Combustion tests of aluminized propellants were conducted under representative conditions, including a time-averaged pressure of 1 MPa, temperature of approximately 2600 K, and a combustion gas environment typical of aluminized propellant. The experiments were performed across a range of acoustic frequencies (100–1000 Hz) and pressure oscillation amplitudes (200–1200 Pa), aiming to investigate the response of aluminum particle combustion to controlled oscillatory environments. Using a 3000 FPS high-speed camera with spatial resolution of 3.4 μm/pixel and normalized flame intensity processing, heat release rate (HRR) fluctuations were quantified. Key findings reveal: The fluctuations in heat release rate (HRR) demonstrated pronounced nonlinear characteristics. The fluctuation amplitude reached its maximum value (11.9%) at 100 Hz while decaying significantly to 1.1% at 1000 Hz. Simultaneously, HRR fluctuations exhibited high sensitivity to pressure variations—peaking at 800 Pa and decaying to 10.8% when pressure increased to 1200 Pa. This phenomenon confirmed the nonlinear coupling relationship between combustion instability and both excitation frequency and pressure. An unsteady combustion model incorporating an empirical acoustic response function was developed and validated against experimental data. The model accurately predicts oscillatory combustion behavior, providing a theoretical basis for mitigating combustion instabilities in solid rocket motors.
{"title":"Experimental and modeling study on aluminum combustion under oscillatory conditions","authors":"Gangchui Zhang , Jiangong Zhao , Wen Ao , Zhuopu Wang , Peijin Liu","doi":"10.1016/j.combustflame.2026.114862","DOIUrl":"10.1016/j.combustflame.2026.114862","url":null,"abstract":"<div><div>This study first investigated the combustion behavior of aluminum particles in solid propellants under acoustic oscillations in a custom high-pressure combustor, and subsequently developed a combustion model based on the experimental results. Combustion tests of aluminized propellants were conducted under representative conditions, including a time-averaged pressure of 1 MPa, temperature of approximately 2600 K, and a combustion gas environment typical of aluminized propellant. The experiments were performed across a range of acoustic frequencies (100–1000 Hz) and pressure oscillation amplitudes (200–1200 Pa), aiming to investigate the response of aluminum particle combustion to controlled oscillatory environments. Using a 3000 FPS high-speed camera with spatial resolution of 3.4 μm/pixel and normalized flame intensity processing, heat release rate (HRR) fluctuations were quantified. Key findings reveal: The fluctuations in heat release rate (HRR) demonstrated pronounced nonlinear characteristics. The fluctuation amplitude reached its maximum value (11.9%) at 100 Hz while decaying significantly to 1.1% at 1000 Hz. Simultaneously, HRR fluctuations exhibited high sensitivity to pressure variations—peaking at 800 Pa and decaying to 10.8% when pressure increased to 1200 Pa. This phenomenon confirmed the nonlinear coupling relationship between combustion instability and both excitation frequency and pressure. An unsteady combustion model incorporating an empirical acoustic response function was developed and validated against experimental data. The model accurately predicts oscillatory combustion behavior, providing a theoretical basis for mitigating combustion instabilities in solid rocket motors.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114862"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387008","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 : 2026-05-01Epub Date: 2026-02-18DOI: 10.1016/j.combustflame.2026.114881
Wenchao Zhu , Taipeng Mao , Zechuan Cui , Xinyang Tian , Jiabei Cao , Jiangping Tian , Xiangyu Meng , Mingshu Bi
The proposal of carbon neutrality targets has accelerated the deployment of C0–C1 low- and zero-carbon fuels such as ammonia (NH3), hydrogen (H2), methane (CH4), and methanol (CH3OH) in energy conversion and power systems. Multi-component fuel blending is widely employed to tailor reactivity and improve emission performance. In this work, laminar burning velocities (LBVs) of NH3/H2/air, NH3/H2/CH4/air, and NH3/H2/CH3OH/air blends were measured in a constant-volume combustion chamber at 473 K and 2–8 atm. Based on a previously developed NH3/CH4/H2/CO kinetic mechanism, three key CN cross reactions were incorporated and the rate constants of fifteen CH and HN reactions were updated. This yielded a comprehensive C0–C1 kinetic mechanism that comprises 53 species and 354 reactions and accurately reproduces the measured LBVs. To further assess broader applicability, this mechanism was evaluated against C0–C1 single and multi-component fuel datasets, including 2035 LBV data points (298–750 K, 1–15 atm, equivalence ratios ϕ = 0.4–5.0), 1618 ignition delay time data points (817–2517 K, 1–50 atm, ϕ = 0.1–2.0), and 6172 species data points measured in jet-stirred reactors (500–1400 K, 1–100 atm, ϕ = 0.1–4.35). Five performance metrics with normalized weights were applied for quantitative evaluation. The results indicated that this mechanism significantly improves overall predictive accuracy relative to previous mechanisms and also shows the closest agreement with experimental data among six recently published representative mechanisms.
{"title":"A combined experimental and comprehensive kinetic modeling study of laminar burning velocities for C0–C1 multi-component fuel blends","authors":"Wenchao Zhu , Taipeng Mao , Zechuan Cui , Xinyang Tian , Jiabei Cao , Jiangping Tian , Xiangyu Meng , Mingshu Bi","doi":"10.1016/j.combustflame.2026.114881","DOIUrl":"10.1016/j.combustflame.2026.114881","url":null,"abstract":"<div><div>The proposal of carbon neutrality targets has accelerated the deployment of C<sub>0</sub>–C<sub>1</sub> low- and zero-carbon fuels such as ammonia (NH<sub>3</sub>), hydrogen (H<sub>2</sub>), methane (CH<sub>4</sub>), and methanol (CH<sub>3</sub>OH) in energy conversion and power systems. Multi-component fuel blending is widely employed to tailor reactivity and improve emission performance. In this work, laminar burning velocities (LBVs) of NH<sub>3</sub>/H<sub>2</sub>/air, NH<sub>3</sub>/H<sub>2</sub>/CH<sub>4</sub>/air, and NH<sub>3</sub>/H<sub>2</sub>/CH<sub>3</sub>OH/air blends were measured in a constant-volume combustion chamber at 473 K and 2–8 atm. Based on a previously developed NH<sub>3</sub>/CH<sub>4</sub>/H<sub>2</sub>/CO kinetic mechanism, three key C<img>N cross reactions were incorporated and the rate constants of fifteen C<img>H and H<img>N reactions were updated. This yielded a comprehensive C<sub>0</sub>–C<sub>1</sub> kinetic mechanism that comprises 53 species and 354 reactions and accurately reproduces the measured LBVs. To further assess broader applicability, this mechanism was evaluated against C<sub>0</sub>–C<sub>1</sub> single and multi-component fuel datasets, including 2035 LBV data points (298–750 K, 1–15 atm, equivalence ratios <em>ϕ</em> = 0.4–5.0), 1618 ignition delay time data points (817–2517 K, 1–50 atm, <em>ϕ</em> = 0.1–2.0), and 6172 species data points measured in jet-stirred reactors (500–1400 K, 1–100 atm, <em>ϕ</em> = 0.1–4.35). Five performance metrics with normalized weights were applied for quantitative evaluation. The results indicated that this mechanism significantly improves overall predictive accuracy relative to previous mechanisms and also shows the closest agreement with experimental data among six recently published representative mechanisms.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"287 ","pages":"Article 114881"},"PeriodicalIF":6.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386588","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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