Pub Date : 2025-11-19DOI: 10.1016/j.combustflame.2025.114633
Rong-Kang Zhu , Yang-Fan Cheng , Zi-Han Chen , Jian-Wei Xu , Rong Liu
As the primary carriers of detonation energy in medium, shock waves govern the spatiotemporal distribution of explosion damage effects through their collision dynamics, providing critical scientific guidance for weapon design and protective engineering. In this study, the flow field structure and propagation velocity evolution characteristics following the normal collision of spherical double shock waves were investigated using an integrated high-speed schlieren and dynamic pressure measurement system. To accurately predict the overpressure at the collision point, an entropy-modified overpressure calculation model was developed. The reliability of the model was validated through AUTODYN numerical simulation and experimental data. The results showed that although the overall collision process was consistent both for shock waves of equal and unequal strength, significant differences emerged in the flow field structures. For the normal collision of unequal-strength spherical shock waves, the stronger shock wave dominated the collision process, and the strength difference determined both the Mach stem orientation and the location of the secondary collision point. Following the collision of both shock waves with equal and unequal strength, the propagation velocity of the resultant rightward-propagating shock wave initially decreased. Upon entering the explosion central region, its velocity exhibited a characteristic of “rise-fall-rise-fall” pattern, with the duration of each phase influenced by the experimental sample parameters. The introduction of the entropy correction term significantly improved the accuracy of the overpressure calculation model. Compared with the numerical simulation and experimental results, the relative errors of the model calculation values were within ±8 % and ±7 %, respectively, showing a high overall agreement. These findings provide valuable theoretical references for studying the flow field distribution and transient pressure evolution characteristics after normal collision of spherical double shock waves.
{"title":"Flow field distribution characteristics and transient pressure evolution mechanism after normal collision of spherical double shock waves","authors":"Rong-Kang Zhu , Yang-Fan Cheng , Zi-Han Chen , Jian-Wei Xu , Rong Liu","doi":"10.1016/j.combustflame.2025.114633","DOIUrl":"10.1016/j.combustflame.2025.114633","url":null,"abstract":"<div><div>As the primary carriers of detonation energy in medium, shock waves govern the spatiotemporal distribution of explosion damage effects through their collision dynamics, providing critical scientific guidance for weapon design and protective engineering. In this study, the flow field structure and propagation velocity evolution characteristics following the normal collision of spherical double shock waves were investigated using an integrated high-speed schlieren and dynamic pressure measurement system. To accurately predict the overpressure at the collision point, an entropy-modified overpressure calculation model was developed. The reliability of the model was validated through AUTODYN numerical simulation and experimental data. The results showed that although the overall collision process was consistent both for shock waves of equal and unequal strength, significant differences emerged in the flow field structures. For the normal collision of unequal-strength spherical shock waves, the stronger shock wave dominated the collision process, and the strength difference determined both the Mach stem orientation and the location of the secondary collision point. Following the collision of both shock waves with equal and unequal strength, the propagation velocity of the resultant rightward-propagating shock wave initially decreased. Upon entering the explosion central region, its velocity exhibited a characteristic of “rise-fall-rise-fall” pattern, with the duration of each phase influenced by the experimental sample parameters. The introduction of the entropy correction term significantly improved the accuracy of the overpressure calculation model. Compared with the numerical simulation and experimental results, the relative errors of the model calculation values were within ±8 % and ±7 %, respectively, showing a high overall agreement. These findings provide valuable theoretical references for studying the flow field distribution and transient pressure evolution characteristics after normal collision of spherical double shock waves.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114633"},"PeriodicalIF":6.2,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-19DOI: 10.1016/j.combustflame.2025.114637
Yu-zhe Liao , Yu-qin Gan , Ling-feng Yang , Yao-feng Mao , Jian Wang , Jie Chen , Xing-quan Zhang , Jun Wang
Improving the energy release efficiency of aluminum powder is one of the main ways to enhance the energy output of aluminum-based energetic materials. The mainly challenge is to resolve the issue of low combustion reaction efficiency and energy output resulted from inert oxide layer (Al2O3) and the aggregation. Combination structured strategy and 3D printing technology, three structured HMX/Al/PTFE has designed and prepared to understand the structured effect on the combustion reaction behaviour and energy output. Compared to the homogeneous mixed structure (HMS-1), the three-layer gradient structure (TGS-1–1) exhibits larger flame area (1345 cm²), shorter combustion duration (0.9 s), and higher-pressure output (470.33 kPa). Due to the design of the gradient structure, the median particle size (D50) of HMX/Al/PTFE combustion products decreased from 328.89 to 7.44 μm, indicating weakened agglomeration. In addition, the particle size gradient in the three-layer structure can further regulate the combustion behaviour. In summary, this work indicates that the gradient structure improves the interfacial contact between Al and PTFE while promoting the outward splashing of burning Al particles, thereby enhancing combustion and suppressing combustion agglomeration of Al. This work provides an innovative and efficient design strategy for improving the combustion performance and energy output of Al-based energetic materials.
{"title":"Enhanced combustion reaction and energy output in Aluminum-Based Energetic Materials via Gradient Structure","authors":"Yu-zhe Liao , Yu-qin Gan , Ling-feng Yang , Yao-feng Mao , Jian Wang , Jie Chen , Xing-quan Zhang , Jun Wang","doi":"10.1016/j.combustflame.2025.114637","DOIUrl":"10.1016/j.combustflame.2025.114637","url":null,"abstract":"<div><div>Improving the energy release efficiency of aluminum powder is one of the main ways to enhance the energy output of aluminum-based energetic materials. The mainly challenge is to resolve the issue of low combustion reaction efficiency and energy output resulted from inert oxide layer (Al<sub>2</sub>O<sub>3</sub>) and the aggregation. Combination structured strategy and 3D printing technology, three structured HMX/Al/PTFE has designed and prepared to understand the structured effect on the combustion reaction behaviour and energy output. Compared to the homogeneous mixed structure (HMS-1), the three-layer gradient structure (TGS-1–1) exhibits larger flame area (1345 cm²), shorter combustion duration (0.9 s), and higher-pressure output (470.33 kPa). Due to the design of the gradient structure, the median particle size (D<sub>50</sub>) of HMX/Al/PTFE combustion products decreased from 328.89 to 7.44 μm, indicating weakened agglomeration. In addition, the particle size gradient in the three-layer structure can further regulate the combustion behaviour. In summary, this work indicates that the gradient structure improves the interfacial contact between Al and PTFE while promoting the outward splashing of burning Al particles, thereby enhancing combustion and suppressing combustion agglomeration of Al. This work provides an innovative and efficient design strategy for improving the combustion performance and energy output of Al-based energetic materials.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114637"},"PeriodicalIF":6.2,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-19DOI: 10.1016/j.combustflame.2025.114641
Wanyu Luo , Jingyi Zhu , Zhaozhong Yang , Hailong Chen , Xiaogang Li , Xiaofeng Zhang , Liangping Yi
Understanding the molecular mechanism of kerogen pyrolysis under microwave fields is crucial for enhancing the hydrocarbon conversion efficiency of oil shale. In this study, ReaxFF MD simulations were performed under coupled microwave fields to explore bond-breaking sequences and reaction pathways of Type-I kerogen under both microwave and conventional heating. Results show that microwaves significantly reduce the optimal pyrolysis temperature and enhance oil yields. The non-thermal effects of microwaves induce earlier cleavage of key bonds (e.g., Cal–S, Cal-O-Cal), confirmed by quantum chemical calculations showing significant bond elongation under electric fields, which intensifies primary pyrolysis reactions and effectively suppresses secondary cracking of valuable oil and gas molecules. Non-thermal effects also facilitate cyclization of S and N atoms, concentrating heteroatoms in aromatic fractions, aiding downstream purification of aliphatic components. Moreover, adjusting microwave field strength validated its quality-enhancing effect: moderate enhancement accelerates early formation of light oil and gas, while excessive strength intensifies radical and cross-linking reactions, slowing pyrolysis and lowering final yield.
{"title":"Unraveling the molecular mechanism and non-thermal effects of microwave pyrolysis of oil shale via ReaxFF molecular dynamics","authors":"Wanyu Luo , Jingyi Zhu , Zhaozhong Yang , Hailong Chen , Xiaogang Li , Xiaofeng Zhang , Liangping Yi","doi":"10.1016/j.combustflame.2025.114641","DOIUrl":"10.1016/j.combustflame.2025.114641","url":null,"abstract":"<div><div>Understanding the molecular mechanism of kerogen pyrolysis under microwave fields is crucial for enhancing the hydrocarbon conversion efficiency of oil shale. In this study, ReaxFF MD simulations were performed under coupled microwave fields to explore bond-breaking sequences and reaction pathways of Type-I kerogen under both microwave and conventional heating. Results show that microwaves significantly reduce the optimal pyrolysis temperature and enhance oil yields. The non-thermal effects of microwaves induce earlier cleavage of key bonds (e.g., Cal–S, Cal-O-Cal), confirmed by quantum chemical calculations showing significant bond elongation under electric fields, which intensifies primary pyrolysis reactions and effectively suppresses secondary cracking of valuable oil and gas molecules. Non-thermal effects also facilitate cyclization of S and N atoms, concentrating heteroatoms in aromatic fractions, aiding downstream purification of aliphatic components. Moreover, adjusting microwave field strength validated its quality-enhancing effect: moderate enhancement accelerates early formation of light oil and gas, while excessive strength intensifies radical and cross-linking reactions, slowing pyrolysis and lowering final yield.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114641"},"PeriodicalIF":6.2,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578294","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}
To elucidate the mechanism responsible for the markedly expanded flammable range of ethylene tetrafluoroethylene (ETFE), a fluoropolymer, under microgravity conditions—where flow fields surrounding flames are substantially slower than those on Earth—numerical simulations of counterflow diffusion flames were conducted. Difluoromethane (CH2F2) and methane (CH4) were selected as representative hydrofluorocarbon (HFC) and hydrocarbon (HC) fuels, respectively, with particular attention given to the influence of flow residence time on flame behavior. As the oxygen mole fraction () in the oxidizer increased from 0.15 to 0.30, the extinction strain rate for CH2F2rose from 18s-1 to 744s-1, whereas that for CH4increased from 58s-1 to 2694 s-1. This demonstrates that the blowoff limit of CH2F2exhibits minimal sensitivity to, unlike CH4, whose flame stability improves markedly with increasing. Comparison of zero-dimensional flames with one-dimensional diffusion flames further revealed that the CH2F2exhibits a pronounced reduction in flame temperature relative to CH4under stretched conditions. For instance, at a strain rate of 10 s⁻¹, the maximum temperature of the CH4diffusion flame reached approximately 94% of its adiabatic flame temperature, whereas that of CH2F2reached only about 88%. Chemical kinetic analysis revealed that H and OH radical formation is significantly suppressed in CH2F2flames due to dominant HF-producing pathways. Furthermore, removing key radical-producing reactions from the CH4kinetic mechanism reproduced blowoff behavior similar to that of CH2F2, confirming the critical role of chain reaction for active radical formation. These findings indicate that HFCs possess unique combustion characteristics with distinct behavior under zero-dimensional idealized conditions versus structured flame conditions where chemical kinetics and transport phenomena are strongly coupled. Despite the susceptibility to blowoff, CH2F2maintains a relatively high adiabatic flame temperature, allowing combustion to persist at low oxygen concentrations if sufficient flow residence time is provided.
{"title":"Effect of flow residence time on the flame-retardant performance of fluorine-based flame retardant: Comparison of blowoff limits of CH2F2 and CH4","authors":"Yusuke Konno, Ayuto Ota, Nozomu Hashimoto, Osamu Fujita","doi":"10.1016/j.combustflame.2025.114614","DOIUrl":"10.1016/j.combustflame.2025.114614","url":null,"abstract":"<div><div><em>To elucidate the mechanism responsible for the markedly expanded flammable range of ethylene tetrafluoroethylene (ETFE), a fluoropolymer, under microgravity conditions</em>—<em>where flow fields surrounding flames are substantially slower than those on Earth</em>—<em>numerical simulations of counterflow diffusion flames were conducted. Difluoromethane</em> (CH<sub>2</sub>F<sub>2</sub>) <em>and methane</em> (CH<sub>4</sub>) <em>were selected as representative hydrofluorocarbon (HFC) and hydrocarbon (HC) fuels, respectively, with particular attention given to the influence of flow residence time on flame behavior. As the oxygen mole fraction (</em><span><math><msub><mi>X</mi><mi>O</mi></msub></math></span><em>) in the oxidizer increased from 0.15 to 0.30, the extinction strain rate for</em> CH<sub>2</sub>F<sub>2</sub> <em>rose from 18</em> <em>s<sup>-1</sup> to 744</em> <em>s<sup>-1</sup>, whereas that for</em> CH<sub>4</sub> <em>increased from 58</em> <em>s<sup>-1</sup> to 2694 s<sup>-1</sup>. This demonstrates that the blowoff limit of</em> CH<sub>2</sub>F<sub>2</sub> <em>exhibits minimal sensitivity to</em> <span><math><msub><mi>X</mi><mi>O</mi></msub></math></span><em>, unlike</em> CH<sub>4</sub><em>, whose flame stability improves markedly with increasing</em> <span><math><msub><mi>X</mi><mi>O</mi></msub></math></span><em>. Comparison of zero-dimensional flames with one-dimensional diffusion flames further revealed that the</em> CH<sub>2</sub>F<sub>2</sub> <em>exhibits a pronounced reduction in flame temperature relative to</em> CH<sub>4</sub> <em>under stretched conditions. For instance, at a strain rate of 10 s⁻¹, the maximum temperature of the</em> CH<sub>4</sub> <em>diffusion flame reached approximately 94% of its adiabatic flame temperature, whereas that of</em> CH<sub>2</sub>F<sub>2</sub> <em>reached only about 88%. Chemical kinetic analysis revealed that H and OH radical formation is significantly suppressed in</em> CH<sub>2</sub>F<sub>2</sub> <em>flames due to dominant HF-producing pathways. Furthermore, removing key radical-producing reactions from the</em> CH<sub>4</sub> <em>kinetic mechanism reproduced blowoff behavior similar to that of</em> CH<sub>2</sub>F<sub>2</sub><em>, confirming the critical role of chain reaction for active radical formation. These findings indicate that HFCs possess unique combustion characteristics with distinct behavior under zero-dimensional idealized conditions</em> versus <em>structured flame conditions where chemical kinetics and transport phenomena are strongly coupled. Despite the susceptibility to blowoff,</em> CH<sub>2</sub>F<sub>2</sub> <em>maintains a relatively high adiabatic flame temperature, allowing combustion to persist at low oxygen concentrations if sufficient flow residence time is provided.</em></div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114614"},"PeriodicalIF":6.2,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-19DOI: 10.1016/j.combustflame.2025.114609
Weiming Xu , Tao Yang , Chang Liu , Kun Wu , Peng Zhang
Dynamic mode transitions of supersonic combustion pose challenges to traditional knowledge-based methods, especially in capturing temporal evolution. This study proposes an innovative machine learning framework that combines a Dynamic Variational Autoencoder (Dynamic-VAE) with a Hidden Markov Model-Gaussian Mixture Model (HMM-GMM), to investigate the dynamics of supersonic combustion. To generate data representing diverse dynamical states, a series of kerosene-fueled scramjet combustion experiments were performed by varying gas-liquid mass flow ratios (GLR) and atomizing gases. The CH* chemiluminescence sequent snapshots were experimentally recorded as the training and validation dataset. To preserve temporal dynamic features, the Dynamic-VAE is designed by integrating a three-dimensional convolutional neural network (3DCNN) with a traditional VAE for the dimensionality reduction of high-dimensional time-series snapshots into a low-dimensional latent space. To identify transient modes in latent space, HMM-GMM is employed to model temporal state transitions as a Markov process, explicitly characterizing multimodal flame behaviors and probabilistic mode switching. Compared to static classification methods (e.g., K-means and Wasserstein distance), the proposed framework not only rectifies their misclassifications for cavity-stabilized, jet-wake-stabilized, and transitional modes but also quantifies the state occupancy rates—a capability lacking in traditional techniques. The present results demonstrate that this framework achieves higher accuracy in mode recognition and superior performance in representing transition dynamics, offering a powerful tool for analyzing complex dynamical states in supersonic combustion systems.
{"title":"Transient identification of supersonic combustion mode by dynamic-VAE and Markov probabilistic modeling","authors":"Weiming Xu , Tao Yang , Chang Liu , Kun Wu , Peng Zhang","doi":"10.1016/j.combustflame.2025.114609","DOIUrl":"10.1016/j.combustflame.2025.114609","url":null,"abstract":"<div><div>Dynamic mode transitions of supersonic combustion pose challenges to traditional knowledge-based methods, especially in capturing temporal evolution. This study proposes an innovative machine learning framework that combines a Dynamic Variational Autoencoder (Dynamic-VAE) with a Hidden Markov Model-Gaussian Mixture Model (HMM-GMM), to investigate the dynamics of supersonic combustion. To generate data representing diverse dynamical states, a series of kerosene-fueled scramjet combustion experiments were performed by varying gas-liquid mass flow ratios (GLR) and atomizing gases. The CH* chemiluminescence sequent snapshots were experimentally recorded as the training and validation dataset. To preserve temporal dynamic features, the Dynamic-VAE is designed by integrating a three-dimensional convolutional neural network (3DCNN) with a traditional VAE for the dimensionality reduction of high-dimensional time-series snapshots into a low-dimensional latent space. To identify transient modes in latent space, HMM-GMM is employed to model temporal state transitions as a Markov process, explicitly characterizing multimodal flame behaviors and probabilistic mode switching. Compared to static classification methods (e.g., K-means and Wasserstein distance), the proposed framework not only rectifies their misclassifications for cavity-stabilized, jet-wake-stabilized, and transitional modes but also quantifies the state occupancy rates—a capability lacking in traditional techniques. The present results demonstrate that this framework achieves higher accuracy in mode recognition and superior performance in representing transition dynamics, offering a powerful tool for analyzing complex dynamical states in supersonic combustion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114609"},"PeriodicalIF":6.2,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578287","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-19DOI: 10.1016/j.combustflame.2025.114629
Zhiyuan Feng , Yunjie Liu , Yajing Xiao , Yunlong Zhang , Ruixuan Xu , Qi-Long Yan , Hongqi Nie
High burning rate pressure exponent and incomplete combustion of Al constrains the further application of the composite propellant containing CL-20. In this study, various Al@CL-20 composites constructed by spray-drying method were applied to modify the HTPB/AP/Al/CL-20 propellant through interfacial control and synergistic effect of catalysts (GOCHZ-M, M=Co2+ or Ni2+) without changing the propellant formulations. The results show that the modified propellant have a greater heat of reaction (5977 J g-1, increased by 7.3 %), a reduced ignition delay time of 477 ms, an 32.1 % increase in the burning rate at 1 MPa, and the pressure exponent decreased from 0.49 to 0.15 within 0–2 MPa (about 69.4 % reduction), the mechanism can be attributed to the catalytic decomposition of CL-20 and AP by the presence of GOCHZ-M. Moreover, the agglomeration of Al was remarkably inhibited by interfacial control and precise catalysis, the proportion of condensed phase combustion products with particle size larger than 10 μm decreased from 35.1 % to 23.4 %, while the active Al content in the products declined significantly, indicating that the combustion efficiency of the propellant was greatly improved.
{"title":"Promoting the ignition and combustion performance of Al/CL-20/AP solid propellant by synergistic effects of graphene-based catalysts and interfacial control","authors":"Zhiyuan Feng , Yunjie Liu , Yajing Xiao , Yunlong Zhang , Ruixuan Xu , Qi-Long Yan , Hongqi Nie","doi":"10.1016/j.combustflame.2025.114629","DOIUrl":"10.1016/j.combustflame.2025.114629","url":null,"abstract":"<div><div>High burning rate pressure exponent and incomplete combustion of Al constrains the further application of the composite propellant containing CL-20. In this study, various Al@CL-20 composites constructed by spray-drying method were applied to modify the HTPB/AP/Al/CL-20 propellant through interfacial control and synergistic effect of catalysts (GO<img>CHZ-M, <em>M</em>=Co<sup>2+</sup> or Ni<sup>2+</sup>) without changing the propellant formulations. The results show that the modified propellant have a greater heat of reaction (5977 J g<sup>-1</sup>, increased by 7.3 %), a reduced ignition delay time of 477 ms, an 32.1 % increase in the burning rate at 1 MPa, and the pressure exponent decreased from 0.49 to 0.15 within 0–2 MPa (about 69.4 % reduction), the mechanism can be attributed to the catalytic decomposition of CL-20 and AP by the presence of GO<img>CHZ-M. Moreover, the agglomeration of Al was remarkably inhibited by interfacial control and precise catalysis, the proportion of condensed phase combustion products with particle size larger than 10 μm decreased from 35.1 % to 23.4 %, while the active Al content in the products declined significantly, indicating that the combustion efficiency of the propellant was greatly improved.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114629"},"PeriodicalIF":6.2,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-18DOI: 10.1016/j.combustflame.2025.114634
Jun Cheng , Bo Zhang , Chih-Yung Wen
<div><div>Presence of wedge surfaces and variable-section geometries in conventional combustion chambers can modify the structure and propagation characteristics of detonation waves, furtherly influences the operational stability and propulsion efficiency of detonation engines. In this study, trapezoidal obstacles were symmetrically arranged within a shock tube to create channels incorporating convergent wedge sections with different angles (30°, 60°) and subsequent narrow straight segments with various heights (5, 10, 20 mm). Experimental and numerical investigations were conducted to analyze the propagation characteristics of stoichiometric ethylene-oxygen detonation waves in the channel. The results indicate that the detonation wave reflected by the wedge surface enters the narrow segment is overdriven, with the overdriven degree gradually decreasing during its propagation. At the 30°wedge, Mach reflection occurs, and the detonation wave becomes overdriven upon reaching the contracted throat with an overdriven degree exceeds 1.5; whereas, at the 60°wedge, regular reflection occurs, and the detonation wave reaches the throat with a lower overdriven degree of 1.3. However, the overdriven degrees finally decay to 1.1 in both cases. The channel contraction effect attributes to the induction of overdriven initiation in the throat, though it operates via distinct mechanisms as the wedge angle varies. For the 30°wedge, channel contraction shortens the travel distance of triple points on the wavefronts of the incident detonation wave and Mach reflection-induced detonation wave, increasing their collision frequency, leading to significant energy accumulation in the throat region. For the 60°wedge, channel contraction prevents triple points from entering the following narrow segment along trajectories corresponding to their original cell widths, furtherly induces structural self-adjustment to sustain propagation. These findings enhance the understanding of detonation wave propagation under complex geometrical conditions and provide valuable insights for the optimal design of combustion chamber structures in detonation engines.</div><div><strong>Novelty and significance statement</strong></div><div>This study innovatively investigates the propagation process of detonation waves in a convergent channel that simultaneously incorporates a wedge surface and a variable-section structure, thereby being more relevant to practical engineering scenarios. Furthermore, it innovatively examines the coupled influence mechanism of wedge surface reflection and wall contraction effects on the propagation characteristics of detonation waves, filling the gap in related research. A detailed comparison and analysis of the propagation processes of detonation waves entering narrow straight segments after different reflections was conducted, revealing the overdriven propagation characteristics of detonation waves during this process and their induction mechanism (frequent coll
{"title":"Dynamics of detonation propagation in a wedged variable-section channel","authors":"Jun Cheng , Bo Zhang , Chih-Yung Wen","doi":"10.1016/j.combustflame.2025.114634","DOIUrl":"10.1016/j.combustflame.2025.114634","url":null,"abstract":"<div><div>Presence of wedge surfaces and variable-section geometries in conventional combustion chambers can modify the structure and propagation characteristics of detonation waves, furtherly influences the operational stability and propulsion efficiency of detonation engines. In this study, trapezoidal obstacles were symmetrically arranged within a shock tube to create channels incorporating convergent wedge sections with different angles (30°, 60°) and subsequent narrow straight segments with various heights (5, 10, 20 mm). Experimental and numerical investigations were conducted to analyze the propagation characteristics of stoichiometric ethylene-oxygen detonation waves in the channel. The results indicate that the detonation wave reflected by the wedge surface enters the narrow segment is overdriven, with the overdriven degree gradually decreasing during its propagation. At the 30°wedge, Mach reflection occurs, and the detonation wave becomes overdriven upon reaching the contracted throat with an overdriven degree exceeds 1.5; whereas, at the 60°wedge, regular reflection occurs, and the detonation wave reaches the throat with a lower overdriven degree of 1.3. However, the overdriven degrees finally decay to 1.1 in both cases. The channel contraction effect attributes to the induction of overdriven initiation in the throat, though it operates via distinct mechanisms as the wedge angle varies. For the 30°wedge, channel contraction shortens the travel distance of triple points on the wavefronts of the incident detonation wave and Mach reflection-induced detonation wave, increasing their collision frequency, leading to significant energy accumulation in the throat region. For the 60°wedge, channel contraction prevents triple points from entering the following narrow segment along trajectories corresponding to their original cell widths, furtherly induces structural self-adjustment to sustain propagation. These findings enhance the understanding of detonation wave propagation under complex geometrical conditions and provide valuable insights for the optimal design of combustion chamber structures in detonation engines.</div><div><strong>Novelty and significance statement</strong></div><div>This study innovatively investigates the propagation process of detonation waves in a convergent channel that simultaneously incorporates a wedge surface and a variable-section structure, thereby being more relevant to practical engineering scenarios. Furthermore, it innovatively examines the coupled influence mechanism of wedge surface reflection and wall contraction effects on the propagation characteristics of detonation waves, filling the gap in related research. A detailed comparison and analysis of the propagation processes of detonation waves entering narrow straight segments after different reflections was conducted, revealing the overdriven propagation characteristics of detonation waves during this process and their induction mechanism (frequent coll","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114634"},"PeriodicalIF":6.2,"publicationDate":"2025-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145532582","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-18DOI: 10.1016/j.combustflame.2025.114624
Yu Yang , Sihang Rao , Yihao Tang , Shu Zheng , Wang Han , Lijun Yang
<div><div>The suppression of polycyclic aromatic hydrocarbon (PAH) growth, a critical precursor to soot formation, is essential for optimizing ammonia-hydrocarbon co-combustion systems to reduce emissions. While ammonia blending with hydrocarbons mitigates soot, existing kinetic models lack robust mechanisms to characterize interactions between nitrogen-containing species (HCN and HNC) and PAHs, limiting accurate predictions of PAH inhibition in practical pyrolysis or combustion environments. This study combines quantum chemistry and Rice-Ramsperger-Kassel-Marcus (RRKM) methods to calculate temperature-dependent rate constants for HNC and HCN reactions with phenyl (A1-) and naphthyl (A2-) radicals. The effects of HNC+PAH and HCN+PAH chemistry on the PAH growth in a practical C<sub>2</sub>H<sub>2</sub>/HCN/N<sub>2</sub> pyrolysis system were extensively investigated. The potential energy surface analyses revealed that the HNC addition to A1- or A2- via the C-atom was more favorable than the N-atom channel. Comparisons in the rate constants and branching ratios showed that HNC maintained a certain degree of competitiveness against C<sub>2</sub>H<sub>2</sub> for A1- and A2- in the temperature range of 300-1500 K, especially at temperatures below 1000 K. While for the pyrolysis of C<sub>2</sub>H<sub>2</sub>/HCN/N<sub>2</sub> in a jet-stirred reactor, the competitiveness of HNC against C<sub>2</sub>H<sub>2</sub> for A1- and A2- was negligible. The dominant addition channel for A1- was ranked as HCN > C<sub>2</sub>H<sub>2</sub> > HNC, contrasting with predictions based solely on rate constants or branching ratios. This highlights the limitations of branching ratio-based evaluations in determining the role of HNC + PAH chemistry in PAH growth. The HCN + PAH chemistry demonstrated a suppression effect on the formation of four- and five-rings PAHs, with the inhibitory effect intensifying as the inlet mole fraction of HCN increased. The rate of production (ROP) analysis indicated that A2- + HCN = C<sub>10</sub>H<sub>7</sub>CN + H and A1- + HCN = C<sub>6</sub>H<sub>5</sub>CN + H were the two main factors for the decrease of mole fractions of pyrene (A4) and five-rings PAH (A5), and the latter exhibited a stronger suppression effect. This work uniquely establishes HNC-PAH chemistry and real-system behaviors, underscoring HCN’s critical role in mitigating soot precursors under practical conditions.</div></div><div><h3>Novelty and significance statement</h3><div>The novelty of this research lies in the first development of HNC + PAH chemistry and the detailed analyses of HCN/HNC + PAH chemistry on the formation of PAH in the pyrolysis of C<sub>2</sub>H<sub>2</sub>/HCN/N<sub>2</sub>. The significance of HCN/HNC + PAH chemistry on the formation of PAH is determined using the rate constants in earlier research, but it has not been fully assessed in a real combustion or pyrolysis system. Through detailed analyses of the formation pathway of PAH predicted wit
{"title":"Investigation of hydrogen cyanide and hydrogen isocyanide on PAH growth in the pyrolysis of HCN/C2H2","authors":"Yu Yang , Sihang Rao , Yihao Tang , Shu Zheng , Wang Han , Lijun Yang","doi":"10.1016/j.combustflame.2025.114624","DOIUrl":"10.1016/j.combustflame.2025.114624","url":null,"abstract":"<div><div>The suppression of polycyclic aromatic hydrocarbon (PAH) growth, a critical precursor to soot formation, is essential for optimizing ammonia-hydrocarbon co-combustion systems to reduce emissions. While ammonia blending with hydrocarbons mitigates soot, existing kinetic models lack robust mechanisms to characterize interactions between nitrogen-containing species (HCN and HNC) and PAHs, limiting accurate predictions of PAH inhibition in practical pyrolysis or combustion environments. This study combines quantum chemistry and Rice-Ramsperger-Kassel-Marcus (RRKM) methods to calculate temperature-dependent rate constants for HNC and HCN reactions with phenyl (A1-) and naphthyl (A2-) radicals. The effects of HNC+PAH and HCN+PAH chemistry on the PAH growth in a practical C<sub>2</sub>H<sub>2</sub>/HCN/N<sub>2</sub> pyrolysis system were extensively investigated. The potential energy surface analyses revealed that the HNC addition to A1- or A2- via the C-atom was more favorable than the N-atom channel. Comparisons in the rate constants and branching ratios showed that HNC maintained a certain degree of competitiveness against C<sub>2</sub>H<sub>2</sub> for A1- and A2- in the temperature range of 300-1500 K, especially at temperatures below 1000 K. While for the pyrolysis of C<sub>2</sub>H<sub>2</sub>/HCN/N<sub>2</sub> in a jet-stirred reactor, the competitiveness of HNC against C<sub>2</sub>H<sub>2</sub> for A1- and A2- was negligible. The dominant addition channel for A1- was ranked as HCN > C<sub>2</sub>H<sub>2</sub> > HNC, contrasting with predictions based solely on rate constants or branching ratios. This highlights the limitations of branching ratio-based evaluations in determining the role of HNC + PAH chemistry in PAH growth. The HCN + PAH chemistry demonstrated a suppression effect on the formation of four- and five-rings PAHs, with the inhibitory effect intensifying as the inlet mole fraction of HCN increased. The rate of production (ROP) analysis indicated that A2- + HCN = C<sub>10</sub>H<sub>7</sub>CN + H and A1- + HCN = C<sub>6</sub>H<sub>5</sub>CN + H were the two main factors for the decrease of mole fractions of pyrene (A4) and five-rings PAH (A5), and the latter exhibited a stronger suppression effect. This work uniquely establishes HNC-PAH chemistry and real-system behaviors, underscoring HCN’s critical role in mitigating soot precursors under practical conditions.</div></div><div><h3>Novelty and significance statement</h3><div>The novelty of this research lies in the first development of HNC + PAH chemistry and the detailed analyses of HCN/HNC + PAH chemistry on the formation of PAH in the pyrolysis of C<sub>2</sub>H<sub>2</sub>/HCN/N<sub>2</sub>. The significance of HCN/HNC + PAH chemistry on the formation of PAH is determined using the rate constants in earlier research, but it has not been fully assessed in a real combustion or pyrolysis system. Through detailed analyses of the formation pathway of PAH predicted wit","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114624"},"PeriodicalIF":6.2,"publicationDate":"2025-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145532580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-18DOI: 10.1016/j.combustflame.2025.114606
Tongpo Yu , Guangda Luo , Mengqi Wu , Xinlang Yang , Qiang Xu , Hong Wang , Jinyang Zhang , Xiaoguo Zhou , Zhandong Wang , Feng Zhang
In this study, we investigates the pyrolysis mechanism of iso-amyl nitrate (iAN) at temperatures ranging from 400 to 900 K under low-pressure conditions, employing synchrotron vacuum ultraviolet photoionization mass spectrometry combined with quantum chemical calculations and reactive force field molecular dynamics (ReaxFF-MD) simulations. Key intermediates and products, including formaldehyde, propene, 3-methyl-butyraldehyde, NO2, and HONO, were identified through photoionization efficiency curves. The results reveal that the primary decomposition pathways involve direct ONO2 bond cleavage, producing NO2 and C5H11O• radicals, and CC bond fission, yielding butyl radicals and CH2ONO2. Subsequent/secondary reactions of these radicals lead to the formation of dominant products like formaldehyde. Theoretical calculations highlight the role of hydrogen migration pathways, although their contribution is minor compared to direct bond fission. The findings provide a comprehensive understanding of iAN pyrolysis, contributing to improved combustion models for nitrate esters.
{"title":"Unraveling the pyrolysis mechanism of iso-amyl nitrate at 400–900 K under low pressure: A combined VUV-photoionization mass spectrometry and theoretical study","authors":"Tongpo Yu , Guangda Luo , Mengqi Wu , Xinlang Yang , Qiang Xu , Hong Wang , Jinyang Zhang , Xiaoguo Zhou , Zhandong Wang , Feng Zhang","doi":"10.1016/j.combustflame.2025.114606","DOIUrl":"10.1016/j.combustflame.2025.114606","url":null,"abstract":"<div><div>In this study, we investigates the pyrolysis mechanism of iso-amyl nitrate (iAN) at temperatures ranging from 400 to 900 K under low-pressure conditions, employing synchrotron vacuum ultraviolet photoionization mass spectrometry combined with quantum chemical calculations and reactive force field molecular dynamics (ReaxFF-MD) simulations. Key intermediates and products, including formaldehyde, propene, 3-methyl-butyraldehyde, NO<sub>2</sub>, and HONO, were identified through photoionization efficiency curves. The results reveal that the primary decomposition pathways involve direct O<img>NO<sub>2</sub> bond cleavage, producing NO<sub>2</sub> and C<sub>5</sub>H<sub>11</sub>O• radicals, and C<img>C bond fission, yielding butyl radicals and CH<sub>2</sub>ONO<sub>2</sub>. Subsequent/secondary reactions of these radicals lead to the formation of dominant products like formaldehyde. Theoretical calculations highlight the role of hydrogen migration pathways, although their contribution is minor compared to direct bond fission. The findings provide a comprehensive understanding of iAN pyrolysis, contributing to improved combustion models for nitrate esters.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114606"},"PeriodicalIF":6.2,"publicationDate":"2025-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578293","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-18DOI: 10.1016/j.combustflame.2025.114628
Zeying Hu, Hecong Liu, Peng Zhang
A “jumping” combustion phenomenon of iron microwires was discovered and characterized by using an advanced optical diagnostic setup capable of 10k fps shadowgraph imaging and synchronized two-color thermometry. We systematically examined the iron microwires with a fixed length (6 mm) but varying cross-sectional areas (3000–23400 µm2). The results reveal that all the tested cases exhibit an almost-periodic “jumping” combustion propagation, which can be divided into four distinct phases: tip combustion—continuous heat release from the molten droplet melts the downstream microwire; neck formation—melted downstream material merges with the tip droplet, creating a characteristic neck structure; droplet jumping—rapid droplet movement (<1 ms) driven by surface tension, leaving partially unmelted microwire behind; tip retraction—post-jump combustion completes melting of the residual solid microwire through heat release. Furthermore, the microwire’s cross-sectional area significantly influences the combustion dynamics, with thicker microwires exhibiting slower average propagation speed, reduced “jumping” frequency, and shorter quenching distances, attributed to the size-dependent heat capacity and heat loss.
{"title":"“Jumping flame propagation”: Almost-periodic combustion dynamics of iron microwires","authors":"Zeying Hu, Hecong Liu, Peng Zhang","doi":"10.1016/j.combustflame.2025.114628","DOIUrl":"10.1016/j.combustflame.2025.114628","url":null,"abstract":"<div><div>A “jumping” combustion phenomenon of iron microwires was discovered and characterized by using an advanced optical diagnostic setup capable of 10k fps shadowgraph imaging and synchronized two-color thermometry. We systematically examined the iron microwires with a fixed length (6 mm) but varying cross-sectional areas (3000–23400 µm<sup>2</sup>). The results reveal that all the tested cases exhibit an almost-periodic “jumping” combustion propagation, which can be divided into four distinct phases: tip combustion—continuous heat release from the molten droplet melts the downstream microwire; neck formation—melted downstream material merges with the tip droplet, creating a characteristic neck structure; droplet jumping—rapid droplet movement (<1 ms) driven by surface tension, leaving partially unmelted microwire behind; tip retraction—post-jump combustion completes melting of the residual solid microwire through heat release. Furthermore, the microwire’s cross-sectional area significantly influences the combustion dynamics, with thicker microwires exhibiting slower average propagation speed, reduced “jumping” frequency, and shorter quenching distances, attributed to the size-dependent heat capacity and heat loss.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114628"},"PeriodicalIF":6.2,"publicationDate":"2025-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578346","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}
扫码关注我们
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号