Pub Date : 2026-01-27DOI: 10.1016/j.combustflame.2026.114794
Xudong Song , Yuanyuan Jing , Runmin Wu , Linmin Zhang , Yan Gong , Zhengdong Gu , Juntao Wei , Manoj Kumar Jena , Yonghui Bai , Guangsuo Yu
The study designed and constructed an experimental platform with different nozzle angles and conducted systematic investigations by combining high-resolution UV imaging and high-speed photography. Experiments were performed by adjusting the equivalence ratio and hydrogen addition ratio to obtain key parameters such as flame lift-off height, OH* peak intensity, and core reaction zone area under different nozzle angles. The results indicate that at smaller nozzle angles (e.g., 45°), the flame base’s shear and turbulence are enhanced, which promotes complete mixing of fuel and oxygen, and exhibits higher lift-off height and more stable combustion. In contrast, larger angles (e.g., 75°, 90°) result in asymmetric flame structures, with an expanded core reaction zone but reduced lift-off height and flame stability. Furthermore, a dimensionless prediction model for lift-off height incorporating the average velocity ratio (RV) was proposed, demonstrating good fitting performance with R² > 0.85 for flame behavior across different nozzle angles. This study provides key contributions to nozzle design optimization and enhanced flame stability in low-carbon fuel combustion.
{"title":"Investigation on the effect of nozzle angle on the stability of methane-hydrogen/oxygen inverse diffusion lifted flame","authors":"Xudong Song , Yuanyuan Jing , Runmin Wu , Linmin Zhang , Yan Gong , Zhengdong Gu , Juntao Wei , Manoj Kumar Jena , Yonghui Bai , Guangsuo Yu","doi":"10.1016/j.combustflame.2026.114794","DOIUrl":"10.1016/j.combustflame.2026.114794","url":null,"abstract":"<div><div>The study designed and constructed an experimental platform with different nozzle angles and conducted systematic investigations by combining high-resolution UV imaging and high-speed photography. Experiments were performed by adjusting the equivalence ratio and hydrogen addition ratio to obtain key parameters such as flame lift-off height, OH* peak intensity, and core reaction zone area under different nozzle angles. The results indicate that at smaller nozzle angles (e.g., 45°), the flame base’s shear and turbulence are enhanced, which promotes complete mixing of fuel and oxygen, and exhibits higher lift-off height and more stable combustion. In contrast, larger angles (e.g., 75°, 90°) result in asymmetric flame structures, with an expanded core reaction zone but reduced lift-off height and flame stability. Furthermore, a dimensionless prediction model for lift-off height incorporating the average velocity ratio (R<sub>V</sub>) was proposed, demonstrating good fitting performance with R² > 0.85 for flame behavior across different nozzle angles. This study provides key contributions to nozzle design optimization and enhanced flame stability in low-carbon fuel combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114794"},"PeriodicalIF":6.2,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-27DOI: 10.1016/j.combustflame.2026.114793
Wentao Wan , Zaizheng Li , Yuanda Li , Shengji Li , Zhu Zhuo , Xuefeng Huang , Hang Zhang , Jiangrong Xu
To address the challenges of incomplete energy release and unstable combustion in boron-based slurry fuels, the incorporation of B₄C nanoparticles has emerged as a promising strategy to improve the fuel performance. This work investigated the combustion and energy release characteristics of high-solid-content (40.0 wt.%) boron-based slurry fuels with varying B₄C mass ratios. The combustion stage, droplet diameter evolution, micro-explosion intensity, two-dimensional flame temperature distribution, droplet lifetime, flame emission spectrum and morphology of residues were obtained and analyzed. Results showed that both the micro-explosion intensity and first combustion duration increased initially and then decreased with the rising of B₄C mass ratio, reaching optimal values at a B/B₄C mass ratio of 2:3. At this ratio, the fuel exhibited the highest average flame temperature (exceeding 2300 K) during the micro-explosion stage, along with more stable and sustained energy release, and the first combustion duration was prolonged by ∼30%. SEM observations revealed that B₄C addition suppressed dense shell formation by generating CO₂ during combustion, which improved the permeability and reduces pressure-induced fragmentation. Furthermore, two distinct micro-explosion pathways were identified: a frequent pathway associated with the flexible shell (The maximum temperature was around 1800 °C), and a rarer but more intense pathway caused by agglomerated impermeable shells (The maximum temperature exceeded 2500 °C). B₄C addition favored the former by reducing oxide barriers (B₂O₃) and suppressing particle agglomeration.
Novelty and significance statement
This study innovatively explores B4C nanoparticles as additives in boron-based slurry fuels to enhance combustion efficiency and stability. By optimizing the B/B4C mass ratio (2:3), it achieves superior micro-explosion intensity, prolonged combustion, and higher flame temperatures. The key innovation lies in B4C's role in suppressing dense oxide shell formation via CO2 generation, improving permeability and reducing fragmentation. Additionally, two micro-explosion pathways are identified, with B4C favoring the more frequent, flexible shell route. These findings significantly advance slurry fuel design, offering a practical strategy for stable energy release and incomplete combustion mitigation in propulsion systems.
{"title":"Effect of B4C addition on the combustion and energy release characteristics of boron-based slurry fuel droplets","authors":"Wentao Wan , Zaizheng Li , Yuanda Li , Shengji Li , Zhu Zhuo , Xuefeng Huang , Hang Zhang , Jiangrong Xu","doi":"10.1016/j.combustflame.2026.114793","DOIUrl":"10.1016/j.combustflame.2026.114793","url":null,"abstract":"<div><div>To address the challenges of incomplete energy release and unstable combustion in boron-based slurry fuels, the incorporation of B₄C nanoparticles has emerged as a promising strategy to improve the fuel performance. This work investigated the combustion and energy release characteristics of high-solid-content (40.0 wt.%) boron-based slurry fuels with varying B₄C mass ratios. The combustion stage, droplet diameter evolution, micro-explosion intensity, two-dimensional flame temperature distribution, droplet lifetime, flame emission spectrum and morphology of residues were obtained and analyzed. Results showed that both the micro-explosion intensity and first combustion duration increased initially and then decreased with the rising of B₄C mass ratio, reaching optimal values at a B/B₄C mass ratio of 2:3. At this ratio, the fuel exhibited the highest average flame temperature (exceeding 2300 K) during the micro-explosion stage, along with more stable and sustained energy release, and the first combustion duration was prolonged by ∼30%. SEM observations revealed that B₄C addition suppressed dense shell formation by generating CO₂ during combustion, which improved the permeability and reduces pressure-induced fragmentation. Furthermore, two distinct micro-explosion pathways were identified: a frequent pathway associated with the flexible shell (The maximum temperature was around 1800 °C), and a rarer but more intense pathway caused by agglomerated impermeable shells (The maximum temperature exceeded 2500 °C). B₄C addition favored the former by reducing oxide barriers (B₂O₃) and suppressing particle agglomeration.</div></div><div><h3>Novelty and significance statement</h3><div>This study innovatively explores B<sub>4</sub>C nanoparticles as additives in boron-based slurry fuels to enhance combustion efficiency and stability. By optimizing the B/B<sub>4</sub>C mass ratio (2:3), it achieves superior micro-explosion intensity, prolonged combustion, and higher flame temperatures. The key innovation lies in B<sub>4</sub>C's role in suppressing dense oxide shell formation via CO<sub>2</sub> generation, improving permeability and reducing fragmentation. Additionally, two micro-explosion pathways are identified, with B<sub>4</sub>C favoring the more frequent, flexible shell route. These findings significantly advance slurry fuel design, offering a practical strategy for stable energy release and incomplete combustion mitigation in propulsion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114793"},"PeriodicalIF":6.2,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075141","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-27DOI: 10.1016/j.combustflame.2026.114821
Kenneth Budzinski, Kolos Retfalvi, Elektra Katz Ismael, Matthew McGurn, Paul E. DesJardin
In this study, Polymethyl methacrylate slabs are burned in a pure oxygen environment and also modeled using direct numerical simulation (DNS) of the reacting Navier–Stokes equations. The DNS is validated against experiments using novel simultaneous non-intrusive temperature and velocity measurements. The experimental temperature profiles and 3D flame hulls are measured and reconstructed using two color pyrometry (TCP) from multiple high speed camera videos of different views. The stream-wise velocity fields above the slab burner are processed from the experimental images using a methodology similar to particle image velocimetry. The DNS data is processed in a similar manner using a novel virtual-TCP (VTCP) method for temperature and velocities condition on soot volume fraction. Comparison of time averaged DNS fuel regression rates, temperatures, and velocities agree reasonably well to the experiments indicating the DNS provides a faithful representation of the physics. The DNS data is then used to examine the assumptions made in Marxman’s 1960’s analysis of an ablating reacting boundary layer. The analysis reveals that Marxman’s assumed momentum profiles are not good approximations, due to the neglection of volumetric expansion from the reacting flame. Further investigation of the DNS also reveals the existence of self-similar solutions using a new set of conservative variables. A new similarity formulation is then derived by assuming that vertical and stream-wise mass flux, total enthalpy and mass fractions are functions of the normalized boundary layer height only. The chemical state solutions of the similarity problem are shown to agree reasonably to the DNS.
Novelty and significance statement
This study presents the DNS of a fuel slab burner experiment that, for the first time, allow for detailed examination of theories used in hybrid rocket propulsion. These theories originate from Marxman’s early work in the 1960s and are still widely used today. The DNS shows the limitations of Marxman’s theories and presents a new DNS guided similarity theory. In addition, this work presents a novel virtual two-color pyrometry (TCP) technique used in the DNS so direct comparisons to data may be conducted for model validation purposes. This approach avoids many of the pitfalls comparing DNS to non-intrusive TCP measurement techniques through temperature interpretation comparisons.
{"title":"Direct numerical simulation of a PMMA–GO2 slab burner: Experimental validation and extension to Marxman theory","authors":"Kenneth Budzinski, Kolos Retfalvi, Elektra Katz Ismael, Matthew McGurn, Paul E. DesJardin","doi":"10.1016/j.combustflame.2026.114821","DOIUrl":"10.1016/j.combustflame.2026.114821","url":null,"abstract":"<div><div>In this study, Polymethyl methacrylate slabs are burned in a pure oxygen environment and also modeled using direct numerical simulation (DNS) of the reacting Navier–Stokes equations. The DNS is validated against experiments using novel simultaneous non-intrusive temperature and velocity measurements. The experimental temperature profiles and 3D flame hulls are measured and reconstructed using two color pyrometry (TCP) from multiple high speed camera videos of different views. The stream-wise velocity fields above the slab burner are processed from the experimental images using a methodology similar to particle image velocimetry. The DNS data is processed in a similar manner using a novel virtual-TCP (VTCP) method for temperature and velocities condition on soot volume fraction. Comparison of time averaged DNS fuel regression rates, temperatures, and velocities agree reasonably well to the experiments indicating the DNS provides a faithful representation of the physics. The DNS data is then used to examine the assumptions made in Marxman’s 1960’s analysis of an ablating reacting boundary layer. The analysis reveals that Marxman’s assumed momentum profiles are not good approximations, due to the neglection of volumetric expansion from the reacting flame. Further investigation of the DNS also reveals the existence of self-similar solutions using a new set of conservative variables. A new similarity formulation is then derived by assuming that vertical and stream-wise mass flux, total enthalpy and mass fractions are functions of the normalized boundary layer height only. The chemical state solutions of the similarity problem are shown to agree reasonably to the DNS.</div><div><strong>Novelty and significance statement</strong></div><div>This study presents the DNS of a fuel slab burner experiment that, for the first time, allow for detailed examination of theories used in hybrid rocket propulsion. These theories originate from Marxman’s early work in the 1960s and are still widely used today. The DNS shows the limitations of Marxman’s theories and presents a new DNS guided similarity theory. In addition, this work presents a novel virtual two-color pyrometry (TCP) technique used in the DNS so direct comparisons to data may be conducted for model validation purposes. This approach avoids many of the pitfalls comparing DNS to non-intrusive TCP measurement techniques through temperature interpretation comparisons.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114821"},"PeriodicalIF":6.2,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-27DOI: 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":"2026-01-27","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 : 2026-01-24DOI: 10.1016/j.combustflame.2026.114810
Borja Pedro-Beltran , Zin Shahin , Matthias Meinke , Sohel Herff , Dominik Krug , Wolfgang Schröder
The influence of thermal and differential-preferential diffusion on the flame dynamics and acoustic emission of laminar hydrogen–air slit flames is investigated using two-dimensional direct numerical simulations (DNS) and modal decomposition techniques. Simulations span a range of equivalence ratios (–0.7) and diffusion models, including mixture-averaged diffusion with and without the Soret effect and a simplified Unity Lewis number approximation. Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) reveal that dominant hydrodynamic instabilities persist across models, particularly at richer conditions. However, the inclusion of Soret and differential-preferential diffusion modifies the spectral structure of the dominant modes, such that energy is redistributed across higher-order components and a shift in the acoustic peak frequency is induced. These effects occur across all equivalence ratios, but are most evident at intermediate values where competing instabilities increase sensitivity to diffusion-driven modal interactions. At lean conditions, diffusion drives the dominant instability, while at richer conditions it modulates the spectral features of hydrodynamic modes. Neglecting thermal and differential-preferential diffusion fails to capture this behavior, potentially leading to underestimated sound levels at key hydrodynamic frequencies. These findings highlight the importance of detailed diffusion modeling to accurately predict combustion generated noise in hydrogen systems.
Novelty and significance statement
The present study is the first to provide a detailed numerical analysis of the effects of differential-preferential and thermal diffusion on the dynamics and acoustic emissions of hydrogen–air slit flames. The novelty of this work lies in two main contributions. First, it demonstrates that diffusion model assumptions can substantially alter predicted instability growth rates and spatial organization in slit flames. Second, it establishes a clear link between these modeling-induced changes in instability behavior and measurable differences in the resulting acoustic field, essential for accurate prediction of flame dynamics and acoustic response.
{"title":"Impact of thermal and differential-preferential diffusion on the dynamics and acoustics of hydrogen–air slit flames","authors":"Borja Pedro-Beltran , Zin Shahin , Matthias Meinke , Sohel Herff , Dominik Krug , Wolfgang Schröder","doi":"10.1016/j.combustflame.2026.114810","DOIUrl":"10.1016/j.combustflame.2026.114810","url":null,"abstract":"<div><div>The influence of thermal and differential-preferential diffusion on the flame dynamics and acoustic emission of laminar hydrogen–air slit flames is investigated using two-dimensional direct numerical simulations (DNS) and modal decomposition techniques. Simulations span a range of equivalence ratios (<span><math><mrow><mi>ϕ</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>4</mn></mrow></math></span>–0.7) and diffusion models, including mixture-averaged diffusion with and without the Soret effect and a simplified Unity Lewis number approximation. Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) reveal that dominant hydrodynamic instabilities persist across models, particularly at richer conditions. However, the inclusion of Soret and differential-preferential diffusion modifies the spectral structure of the dominant modes, such that energy is redistributed across higher-order components and a shift in the acoustic peak frequency is induced. These effects occur across all equivalence ratios, but are most evident at intermediate values where competing instabilities increase sensitivity to diffusion-driven modal interactions. At lean conditions, diffusion drives the dominant instability, while at richer conditions it modulates the spectral features of hydrodynamic modes. Neglecting thermal and differential-preferential diffusion fails to capture this behavior, potentially leading to underestimated sound levels at key hydrodynamic frequencies. These findings highlight the importance of detailed diffusion modeling to accurately predict combustion generated noise in hydrogen systems.</div><div><strong>Novelty and significance statement</strong></div><div>The present study is the first to provide a detailed numerical analysis of the effects of differential-preferential and thermal diffusion on the dynamics and acoustic emissions of hydrogen–air slit flames. The novelty of this work lies in two main contributions. First, it demonstrates that diffusion model assumptions can substantially alter predicted instability growth rates and spatial organization in slit flames. Second, it establishes a clear link between these modeling-induced changes in instability behavior and measurable differences in the resulting acoustic field, essential for accurate prediction of flame dynamics and acoustic response.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114810"},"PeriodicalIF":6.2,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075144","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-24DOI: 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":"2026-01-24","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}
Pub Date : 2026-01-24DOI: 10.1016/j.combustflame.2026.114823
Decong Zhang , Kai Yang , Peibo Li , Bin An , Mingbo Sun , Taiyu Wang , Changhai Liang , Menglei Li , Jiaoru Wang , Yu Xie , Qi Liu , Zechuan Yi , Jiangbo Peng
<div><div>Aiming at the challenges of ignition and combustion stabilization under low flight Mach number in ramjet mode of hydrocarbon fueled rocket-based combined cycle (RBCC) engines, hydrogen micro-jet was used to achieve combustion stabilization and the mechanisms had been detailed analyzed in this study. The synergistic combustion characteristics of ethylene primary fuel (equivalence ratio (<span><math><mrow><mi>E</mi><mi>R</mi></mrow></math></span>) is 0.50/0.60) and hydrogen micro-jet (<span><math><mrow><mi>E</mi><mi>R</mi></mrow></math></span> is 0.025) in the combustor of a model RBCC engine under Mach 1.43 inflow were investigated by experimental and numerical methods. In the experiments, high-speed pressure, OH-PLIF, CH* and OH* chemiluminescence synchronous imaging were used to comprehensively reveal the combustion features. A GPU-accelerated Reynolds-Averaged Navier–Stokes (RANS) solver employing the ten-step ethylene/hydrogen reaction mechanism was used to further analyze the flow field. The experimental results indicate that the hydrogen micro-jet increases the combustor pressure by 7.5%, and the CH* chemiluminescence intensity by 6.7% under <span><math><mrow><mi>E</mi><mi>R</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>50</mn></mrow></math></span> condition. Meanwhile, the dominant frequency of power spectral density is reduced from 171.48 to 79.2 Hz, and the oscillation strength denoted by standard deviation is reduced by 37.3%. The large-scale combustion oscillation is effectively suppressed. In <span><math><mrow><mi>E</mi><mi>R</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>60</mn></mrow></math></span> condition, the hydrogen micro-jet successfully prevents the flameout observed with ethylene-alone combustion and maintains stable combustion with a characteristic oscillation at 483.48 Hz. Numerical simulations show that hydrogen micro-jet facilitates a transition in combustion mode from diffusion-dominated to premixed-diffusion hybrid. Hydrogen micro-jet achieves the enhancement of flame stability and combustion efficiency by expanding the area of premixed zone and increasing the peak of heat release rate by 22.67%. This work provides a theoretical basis and engineering reference for the combustion optimization of RBCC engine in the wide speed range.</div><div><strong>Novelty and significance</strong></div><div>Experimental and numerical analyses are performed to examine hydrogen micro-jet effect on flame stabilization and enhancement for hydrocarbon fuels in RBCC engine under low flight Mach number of ramjet mode. The results in this study show that hydrogen micro-jet effectively suppresses combustion oscillation, provides a localized high-temperature zones for ethylene/air combustion, and significantly improves combustion efficiency and peak of heat release rate. Hydrogen micro-jet induces transition from diffusion-dominated to premixed-diffusion hybrid mode is revealed as the crucial mechanism for combustion enhancement. The findings offer pr
针对烃类燃料火箭基联合循环（RBCC）发动机冲压模式低飞行马赫数点火和稳定燃烧的挑战，采用氢微射流实现燃烧稳定，并对其机理进行了详细分析。采用实验和数值方法研究了1.43马赫数下，乙烯一次燃料（等效比为0.50/0.60）与氢微射流（等效比为0.025）在RBCC发动机燃烧室内的协同燃烧特性。实验采用高速压力、OH- plif、CH*和OH*化学发光同步成像，全面揭示燃烧特征。采用基于十步乙烯/氢反应机理的gpu加速reynolds - average Navier-Stokes （RANS）求解器对流场进行了进一步分析。实验结果表明，在ER=0.50条件下，氢气微射流使燃烧室压力提高7.5%，CH*化学发光强度提高6.7%。同时，功率谱密度的主导频率由171.48 Hz降低到79.2 Hz，以标准差表示的振荡强度降低了37.3%。大面积燃烧振荡得到有效抑制。在ER=0.60条件下，氢气微射流成功地防止了单乙烯燃烧时的熄火现象，并以483.48 Hz的特征振荡保持了稳定的燃烧。数值模拟结果表明，氢气微射流促进了燃烧模式由扩散为主向预混扩散混合型转变。氢气微射流通过扩大预混区面积，将放热率峰值提高22.67%，实现了火焰稳定性和燃烧效率的增强。该工作为RBCC发动机在大转速范围内的燃烧优化提供了理论依据和工程参考。在冲压模式低飞行马赫数条件下，通过实验和数值分析研究了氢微射流对RBCC发动机烃类燃料火焰稳定和增强的影响。研究结果表明，氢气微射流有效抑制了燃烧振荡，为乙烯/空气燃烧提供了局部高温区，显著提高了燃烧效率和放热速率峰值。揭示了氢微射流诱导从扩散主导模式向预混合-扩散混合模式转变是增强燃烧的重要机制。研究结果对RBCC发动机在低飞行马赫数条件下实现稳定燃烧具有实际指导意义。
{"title":"Flame stabilization and enhancement mechanisms assisted by hydrogen micro-jet in ramjet mode of RBCC engine under low flight Mach number","authors":"Decong Zhang , Kai Yang , Peibo Li , Bin An , Mingbo Sun , Taiyu Wang , Changhai Liang , Menglei Li , Jiaoru Wang , Yu Xie , Qi Liu , Zechuan Yi , Jiangbo Peng","doi":"10.1016/j.combustflame.2026.114823","DOIUrl":"10.1016/j.combustflame.2026.114823","url":null,"abstract":"<div><div>Aiming at the challenges of ignition and combustion stabilization under low flight Mach number in ramjet mode of hydrocarbon fueled rocket-based combined cycle (RBCC) engines, hydrogen micro-jet was used to achieve combustion stabilization and the mechanisms had been detailed analyzed in this study. The synergistic combustion characteristics of ethylene primary fuel (equivalence ratio (<span><math><mrow><mi>E</mi><mi>R</mi></mrow></math></span>) is 0.50/0.60) and hydrogen micro-jet (<span><math><mrow><mi>E</mi><mi>R</mi></mrow></math></span> is 0.025) in the combustor of a model RBCC engine under Mach 1.43 inflow were investigated by experimental and numerical methods. In the experiments, high-speed pressure, OH-PLIF, CH* and OH* chemiluminescence synchronous imaging were used to comprehensively reveal the combustion features. A GPU-accelerated Reynolds-Averaged Navier–Stokes (RANS) solver employing the ten-step ethylene/hydrogen reaction mechanism was used to further analyze the flow field. The experimental results indicate that the hydrogen micro-jet increases the combustor pressure by 7.5%, and the CH* chemiluminescence intensity by 6.7% under <span><math><mrow><mi>E</mi><mi>R</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>50</mn></mrow></math></span> condition. Meanwhile, the dominant frequency of power spectral density is reduced from 171.48 to 79.2 Hz, and the oscillation strength denoted by standard deviation is reduced by 37.3%. The large-scale combustion oscillation is effectively suppressed. In <span><math><mrow><mi>E</mi><mi>R</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>60</mn></mrow></math></span> condition, the hydrogen micro-jet successfully prevents the flameout observed with ethylene-alone combustion and maintains stable combustion with a characteristic oscillation at 483.48 Hz. Numerical simulations show that hydrogen micro-jet facilitates a transition in combustion mode from diffusion-dominated to premixed-diffusion hybrid. Hydrogen micro-jet achieves the enhancement of flame stability and combustion efficiency by expanding the area of premixed zone and increasing the peak of heat release rate by 22.67%. This work provides a theoretical basis and engineering reference for the combustion optimization of RBCC engine in the wide speed range.</div><div><strong>Novelty and significance</strong></div><div>Experimental and numerical analyses are performed to examine hydrogen micro-jet effect on flame stabilization and enhancement for hydrocarbon fuels in RBCC engine under low flight Mach number of ramjet mode. The results in this study show that hydrogen micro-jet effectively suppresses combustion oscillation, provides a localized high-temperature zones for ethylene/air combustion, and significantly improves combustion efficiency and peak of heat release rate. Hydrogen micro-jet induces transition from diffusion-dominated to premixed-diffusion hybrid mode is revealed as the crucial mechanism for combustion enhancement. The findings offer pr","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114823"},"PeriodicalIF":6.2,"publicationDate":"2026-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036471","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":"2026-01-23","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}
<div><div>As part of the FLARE project, long-duration microgravity experiments were conducted on two additional materials—non-charring PMMA and charring NOMEX HT90-40—using the Solid Combustion Experimental Module (SCEM) onboard the ISS/Kibo module. Flammability maps were obtained under opposed-flow velocities, including quiescent conditions, extending previous studies performed with filter paper. For PMMA, both the limiting oxygen concentration (LOC) and the minimum LOC (MLOC) agreed well with predictions from a simplified two-dimensional scaling model, confirming its applicability to thermally thin, non-charring materials. In contrast, NOMEX exhibited robust three-dimensional spherical flames once the two-dimensional thermal balance broke down, even at moderate flow velocities. Under these conditions, the flame radius <em>R<sub>f</sub></em> decreased with decreasing opposed-flow velocity, and extinction occurred when <em>R<sub>f</sub></em> reached a critical value. To quantify this behavior, the preheat-zone length <em>L<sub>g</sub></em> of three-dimensional flames was modeled as a function of <em>R<sub>f</sub></em> and the Reynolds number <em>Re</em>, and incorporated into the thermal balance to derive a limiting oxygen concentration for three-dimensional flames. The resulting expression reproduced the observed relationships among <em>R<sub>f</sub>, V<sub>g</sub></em>, and <em>L<sub>g</sub></em>, and correctly predicted the extinction behavior. Applying the same formulation to filter paper and PMMA further demonstrated that the critical flame radius provides a unified criterion for the transition and extinction of three-dimensional flames across different material classes. These findings demonstrate that both the two-dimensional and three-dimensional flammability limits of charring and non-charring materials can be predicted within a unified experimental–modeling framework, and they provide essential guidance for advancing microgravity fire-safety modeling.</div><div>Novelty and significance statement: The novelty of this work lies in establishing a unified, physics-based framework for predicting flame-spread limits of both charring and non-charring thermally thin materials in microgravity. First, long-duration ISS experiments demonstrated that the limiting oxygen concentration (LOC) and minimum LOC of PMMA are accurately captured by a simplified two-dimensional model, confirming that extinction is governed by the breakdown of two-dimensional thermal balance. A second and central contribution is the quantitative characterization of three-dimensional spherical flames observed in NOMEX beyond the two-dimensional limit. By modeling the preheat-zone length <em>L<sub>g</sub></em> as a function of flame radius <em>R<sub>f</sub></em> and Reynolds number <em>Re</em> and incorporating this into the thermal balance, an explicit LOC criterion for three-dimensional flames was derived. Applying the same formulation to filter paper and PMMA showed that the
{"title":"Flame spread over charring and non-charring materials in microgravity on ISS/Kibo","authors":"Shuhei Takahashi , Yoshinari Kobayashi , Masao Kikuchi , Osamu Fujita","doi":"10.1016/j.combustflame.2026.114803","DOIUrl":"10.1016/j.combustflame.2026.114803","url":null,"abstract":"<div><div>As part of the FLARE project, long-duration microgravity experiments were conducted on two additional materials—non-charring PMMA and charring NOMEX HT90-40—using the Solid Combustion Experimental Module (SCEM) onboard the ISS/Kibo module. Flammability maps were obtained under opposed-flow velocities, including quiescent conditions, extending previous studies performed with filter paper. For PMMA, both the limiting oxygen concentration (LOC) and the minimum LOC (MLOC) agreed well with predictions from a simplified two-dimensional scaling model, confirming its applicability to thermally thin, non-charring materials. In contrast, NOMEX exhibited robust three-dimensional spherical flames once the two-dimensional thermal balance broke down, even at moderate flow velocities. Under these conditions, the flame radius <em>R<sub>f</sub></em> decreased with decreasing opposed-flow velocity, and extinction occurred when <em>R<sub>f</sub></em> reached a critical value. To quantify this behavior, the preheat-zone length <em>L<sub>g</sub></em> of three-dimensional flames was modeled as a function of <em>R<sub>f</sub></em> and the Reynolds number <em>Re</em>, and incorporated into the thermal balance to derive a limiting oxygen concentration for three-dimensional flames. The resulting expression reproduced the observed relationships among <em>R<sub>f</sub>, V<sub>g</sub></em>, and <em>L<sub>g</sub></em>, and correctly predicted the extinction behavior. Applying the same formulation to filter paper and PMMA further demonstrated that the critical flame radius provides a unified criterion for the transition and extinction of three-dimensional flames across different material classes. These findings demonstrate that both the two-dimensional and three-dimensional flammability limits of charring and non-charring materials can be predicted within a unified experimental–modeling framework, and they provide essential guidance for advancing microgravity fire-safety modeling.</div><div>Novelty and significance statement: The novelty of this work lies in establishing a unified, physics-based framework for predicting flame-spread limits of both charring and non-charring thermally thin materials in microgravity. First, long-duration ISS experiments demonstrated that the limiting oxygen concentration (LOC) and minimum LOC of PMMA are accurately captured by a simplified two-dimensional model, confirming that extinction is governed by the breakdown of two-dimensional thermal balance. A second and central contribution is the quantitative characterization of three-dimensional spherical flames observed in NOMEX beyond the two-dimensional limit. By modeling the preheat-zone length <em>L<sub>g</sub></em> as a function of flame radius <em>R<sub>f</sub></em> and Reynolds number <em>Re</em> and incorporating this into the thermal balance, an explicit LOC criterion for three-dimensional flames was derived. Applying the same formulation to filter paper and PMMA showed that the ","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114803"},"PeriodicalIF":6.2,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-21DOI: 10.1016/j.combustflame.2026.114809
Jie Tian , Huichao Jing , Yong Xiong , Lu Wang , Yongqi Wang , Qingwu Zhao , Yong Cheng
This study experimentally investigates the discharge characteristics, ignition performance, and flame development law of NH3/air mixtures with respect to different electrode geometries, namely a pin-pin electrode (Electrode A), a conventional nanosecond surface dielectric barrier discharge (nSDBD) coaxial electrode (Electrode B), and a self-designed radiant multi-zone regulated nSDBD electrode (Electrode C). The effects of work state parameters, including initial pressure (1-3 bar), excess air coefficient λ (1.0-1.4), and initial temperature (333-393 K), were also analysed. Under the reference conditions (initial pressure of 2 bar, initial temperature of 363 K, and λ = 1.0), the results show that: Electrode A achieves the shortest flame development time (15.0 ms) relying on a single-point high energy density, but the flame morphology is irregular; Electrode B exhibits the worst combustion performance due to random discharge and dispersed energy, which easily leads to the extinction of flame kernels; Electrode C, through six symmetric conductive areas, realizes the synchronous fusion of multiple flame kernels and demonstrates the optimal stability and adaptability. Under a wide range of operating conditions, Electrode C shows excellent robustness: it still maintains stable multiple flame kernels at 3 bar (while the number of flame kernels of Electrode B decreases by more than 50%), and it is time to reach the standard heat release is 11% shorter than that of Electrode B; at λ = 1.4, the number of flame kernels of Electrode C is 2–3 times that of Electrode B; when the temperature changes, the fluctuation in the time for the combustion pressure peak to reach its maximum value is less than 5% (compared to 26% for Electrode B). This study reveals the mechanism by which electrode geometry influences plasma and ammonia ignition, confirms the advantages of Electrode C, and provides theoretical and technical support for optimizing plasma ignition systems for ammonia fuel.
{"title":"Experimental study of the effect of electrode geometry on the ignition and flame development of NH3/air mixtures in nanosecond plasma discharges","authors":"Jie Tian , Huichao Jing , Yong Xiong , Lu Wang , Yongqi Wang , Qingwu Zhao , Yong Cheng","doi":"10.1016/j.combustflame.2026.114809","DOIUrl":"10.1016/j.combustflame.2026.114809","url":null,"abstract":"<div><div>This study experimentally investigates the discharge characteristics, ignition performance, and flame development law of NH<sub>3</sub>/air mixtures with respect to different electrode geometries, namely a pin-pin electrode (Electrode A), a conventional nanosecond surface dielectric barrier discharge (nSDBD) coaxial electrode (Electrode B), and a self-designed radiant multi-zone regulated nSDBD electrode (Electrode C). The effects of work state parameters, including initial pressure (1-3 bar), excess air coefficient λ (1.0-1.4), and initial temperature (333-393 K), were also analysed. Under the reference conditions (initial pressure of 2 bar, initial temperature of 363 K, and λ = 1.0), the results show that: Electrode A achieves the shortest flame development time (15.0 ms) relying on a single-point high energy density, but the flame morphology is irregular; Electrode B exhibits the worst combustion performance due to random discharge and dispersed energy, which easily leads to the extinction of flame kernels; Electrode C, through six symmetric conductive areas, realizes the synchronous fusion of multiple flame kernels and demonstrates the optimal stability and adaptability. Under a wide range of operating conditions, Electrode C shows excellent robustness: it still maintains stable multiple flame kernels at 3 bar (while the number of flame kernels of Electrode B decreases by more than 50%), and it is time to reach the standard heat release is 11% shorter than that of Electrode B; at λ = 1.4, the number of flame kernels of Electrode C is 2–3 times that of Electrode B; when the temperature changes, the fluctuation in the time for the combustion pressure peak to reach its maximum value is less than 5% (compared to 26% for Electrode B). This study reveals the mechanism by which electrode geometry influences plasma and ammonia ignition, confirms the advantages of Electrode C, and provides theoretical and technical support for optimizing plasma ignition systems for ammonia fuel.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114809"},"PeriodicalIF":6.2,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036404","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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