Pub Date : 2025-11-24DOI: 10.1016/j.combustflame.2025.114662
Alain Brillard , Andre Molina , Evgeny Shafirovich , Cornelius Schönnenbeck , Jean-François Brilhac , Valérie Tschamber
Fluidized bed reactors could be used for combustion of iron powder, a promising recyclable metal fuel. The modeling and development of such reactors will be facilitated if a simple kinetic model for the oxidation of iron particles in air is available. However, there are discrepancies in the literature on the oxidation of iron powders, including different kinetic models developed to describe the experimental data obtained. In the present study, isothermal oxidation of iron particles (size: 50–70 µm) in an O2/N2 (20:80 mole ratio) mixture at temperatures of 500–800 °C was studied using a laboratory-scale fluidized bed reactor and a thermogravimetric analyzer (TGA). X-ray diffraction analysis of the oxidized samples has shown that with increasing the temperature, the content of magnetite decreases, while that of hematite increases. Scanning electron microscopy revealed a porous surface of the oxidized particles. The mass gain profiles obtained in both fluidized bed and TGA show a rapid first stage and a slow second stage. The profiles were used in a model-fitting analysis that assumed a two-stage conversion of a spherical iron particle into a hematite one and inward transport of oxygen through the growing oxide layer. The use of a three-dimensional diffusion-controlled reaction function resulted in an excellent correlation between the simulated and experimental mass gain profiles. The values of the apparent activation energy obtained for fluidized bed at temperatures of 600–800 °C are close to the literature data on the activation energy of flat iron oxidation.
{"title":"Oxidation of iron particles for energy storage: Experiments in a fluidized bed reactor and kinetic modeling","authors":"Alain Brillard , Andre Molina , Evgeny Shafirovich , Cornelius Schönnenbeck , Jean-François Brilhac , Valérie Tschamber","doi":"10.1016/j.combustflame.2025.114662","DOIUrl":"10.1016/j.combustflame.2025.114662","url":null,"abstract":"<div><div>Fluidized bed reactors could be used for combustion of iron powder, a promising recyclable metal fuel. The modeling and development of such reactors will be facilitated if a simple kinetic model for the oxidation of iron particles in air is available. However, there are discrepancies in the literature on the oxidation of iron powders, including different kinetic models developed to describe the experimental data obtained. In the present study, isothermal oxidation of iron particles (size: 50–70 µm) in an O<sub>2</sub>/N<sub>2</sub> (20:80 mole ratio) mixture at temperatures of 500–800 °C was studied using a laboratory-scale fluidized bed reactor and a thermogravimetric analyzer (TGA). X-ray diffraction analysis of the oxidized samples has shown that with increasing the temperature, the content of magnetite decreases, while that of hematite increases. Scanning electron microscopy revealed a porous surface of the oxidized particles. The mass gain profiles obtained in both fluidized bed and TGA show a rapid first stage and a slow second stage. The profiles were used in a model-fitting analysis that assumed a two-stage conversion of a spherical iron particle into a hematite one and inward transport of oxygen through the growing oxide layer. The use of a three-dimensional diffusion-controlled reaction function resulted in an excellent correlation between the simulated and experimental mass gain profiles. The values of the apparent activation energy obtained for fluidized bed at temperatures of 600–800 °C are close to the literature data on the activation energy of flat iron oxidation.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114662"},"PeriodicalIF":6.2,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145621519","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 : 2025-11-24DOI: 10.1016/j.combustflame.2025.114651
Xiang Gao , Du Wang , Hong-Qing Shi , Xu-Peng Yu , Ya-Ning Zhang , Zhen-Yu Tian
This study aims to guide the optimization of surrogate fuels and reduce development time and experimental costs by investigating the effect of three C9H12 isomers as aromatic components on the high-pressure oxidation of a surrogate fuel for RP-3 kerosene. Consistent with Part I, the surrogate fuel consists of 66.2 % n-dodecane, 18.0 % 1,3,5-trimethylcyclohexane, and 15.8 % aromatic compounds (in mole fraction). The three C9H12 isomers are n-propylbenzene (A1C3H7), 1,3,5-trimethylbenzene (T135MB), and 1,2,4-trimethylbenzene (T124MB). The oxidation experiments were conducted in a jet-stirred reactor at an equivalence ratio of 0.4, temperatures ranging from 500 to 1020 K, and a pressure of 12.0 atm. A comprehensive kinetic model comprising 1596 species and 8376 reactions was developed to elucidate the influence of aromatic components. As observed in Part I, the surrogate fuel exhibits a three-stage oxidation phenomenon, regardless of the aromatic component. Aromatic components minimally affect the mole fraction profiles of n-dodecane and 1,3,5-trimethylcyclohexane due to their low concentration and reactivity. Interestingly, A1C3H7, the most reactive aromatic component, is consumed slower than T135MB and T124MB during the oxidation of the surrogate fuel in Stages II and III. This behavior is attributed to A1C3H7 being more readily regenerated via reactions of fuel radicals with HȮ2, and radicals such as HȮ2 in the surrogate fuel oxidation depending on n-dodecane. The impact of aromatic components on products is primarily seen in aromatic products, with minimal effects on CO, CO2, and light hydrocarbons. A1C3H7 predominantly produces unsaturated mono-substituted benzene, T135MB primarily forms m-xylene, and T124MB produces o-/m-/p-xylene. The fuel consumption pathways align closely with ȮH radical generation. A1C3H7 and T124MB exhibit pronounced low-temperature chain-branching oxidation, whereas T135MB does not. Considering the molecular structure of aromatic components is essential for more accurate prediction of aromatic consumption, product formation, and ignition behavior of real RP-3 kerosene.
{"title":"Experimental and kinetic modeling studies on high-pressure oxidation of RP-3 surrogate fuel. Part Ⅱ: The effect of aromatic component","authors":"Xiang Gao , Du Wang , Hong-Qing Shi , Xu-Peng Yu , Ya-Ning Zhang , Zhen-Yu Tian","doi":"10.1016/j.combustflame.2025.114651","DOIUrl":"10.1016/j.combustflame.2025.114651","url":null,"abstract":"<div><div>This study aims to guide the optimization of surrogate fuels and reduce development time and experimental costs by investigating the effect of three C<sub>9</sub>H<sub>12</sub> isomers as aromatic components on the high-pressure oxidation of a surrogate fuel for RP-3 kerosene. Consistent with Part I, the surrogate fuel consists of 66.2 % <em>n</em>-dodecane, 18.0 % 1,3,5-trimethylcyclohexane, and 15.8 % aromatic compounds (in mole fraction). The three C<sub>9</sub>H<sub>12</sub> isomers are <em>n</em>-propylbenzene (A1C<sub>3</sub>H<sub>7</sub>), 1,3,5-trimethylbenzene (T135MB), and 1,2,4-trimethylbenzene (T124MB). The oxidation experiments were conducted in a jet-stirred reactor at an equivalence ratio of 0.4, temperatures ranging from 500 to 1020 K, and a pressure of 12.0 atm. A comprehensive kinetic model comprising 1596 species and 8376 reactions was developed to elucidate the influence of aromatic components. As observed in Part I, the surrogate fuel exhibits a three-stage oxidation phenomenon, regardless of the aromatic component. Aromatic components minimally affect the mole fraction profiles of <em>n</em>-dodecane and 1,3,5-trimethylcyclohexane due to their low concentration and reactivity. Interestingly, A1C<sub>3</sub>H<sub>7</sub>, the most reactive aromatic component, is consumed slower than T135MB and T124MB during the oxidation of the surrogate fuel in Stages II and III. This behavior is attributed to A1C<sub>3</sub>H<sub>7</sub> being more readily regenerated via reactions of fuel radicals with HȮ<sub>2</sub>, and radicals such as HȮ<sub>2</sub> in the surrogate fuel oxidation depending on <em>n</em>-dodecane. The impact of aromatic components on products is primarily seen in aromatic products, with minimal effects on CO, CO<sub>2</sub>, and light hydrocarbons. A1C<sub>3</sub>H<sub>7</sub> predominantly produces unsaturated mono-substituted benzene, T135MB primarily forms <em>m</em>-xylene, and T124MB produces <em>o</em>-/<em>m</em>-/<em>p</em>-xylene. The fuel consumption pathways align closely with ȮH radical generation. A1C<sub>3</sub>H<sub>7</sub> and T124MB exhibit pronounced low-temperature chain-branching oxidation, whereas T135MB does not. Considering the molecular structure of aromatic components is essential for more accurate prediction of aromatic consumption, product formation, and ignition behavior of real RP-3 kerosene.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114651"},"PeriodicalIF":6.2,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145621399","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 : 2025-11-24DOI: 10.1016/j.combustflame.2025.114632
Jia Xu , Yuhang Chen , Miao Han , Jiang Lv , Yuxuan Ma , Suk Ho Chung , Longhua Hu
This work explores the combustion characteristics of candle flames with various wick diameters and lengths for the gravity level of 3 − 9 g by utilizing a centrifuge. Results show that the burning rate and flame height decrease with increasing gravity, as the suppression of capillary action inside the wick reduces the fuel supply. There exists a critical gravity level Gcr to determine whether the liquid wax can reach the wick tip. When G > Gcr at hypergravity, the liquefied wax cannot reach the wick tip, resulting in reduced flame height and burning rate, whereas at G < Gcr, sufficient liquid wax is supplied to generate higher flame height. The candle flame has a transition from a stable laminar to oscillating flame, because of the enhanced buoyancy-induced velocity in hypergravity. However, a flame extinction is observed at 9 g due to minimized fuel supply rate. Considering the capillary-driven fuel supply mechanism and enhanced buoyant flow, flame oscillation frequency and amplitude are found to initially increase and then decrease with two oscillation modes (bulk flickering and tip flickering). The oscillation frequencies can well be described in terms of the Strouhal and Froude number relationship incorporating the change of burning rate. A physical model of burning rate is established considering the variation of characteristic length. The flame height in hypergravity is well predicted based on the Roper’s model by adopting the "apparent port burner" concept, taking into account the effect of fuel supply rate. This paper provides comprehensive experimental data and facilitates fundamental understanding regarding the candle flames in hypergravity.
{"title":"An experimental study on combustion behavior of candle flames in hypergravity","authors":"Jia Xu , Yuhang Chen , Miao Han , Jiang Lv , Yuxuan Ma , Suk Ho Chung , Longhua Hu","doi":"10.1016/j.combustflame.2025.114632","DOIUrl":"10.1016/j.combustflame.2025.114632","url":null,"abstract":"<div><div>This work explores the combustion characteristics of candle flames with various wick diameters and lengths for the gravity level of 3 − 9 g by utilizing a centrifuge. Results show that the burning rate and flame height decrease with increasing gravity, as the suppression of capillary action inside the wick reduces the fuel supply. There exists a critical gravity level <em>G</em><sub>cr</sub> to determine whether the liquid wax can reach the wick tip. When <em>G</em> > <em>G</em><sub>cr</sub> at hypergravity, the liquefied wax cannot reach the wick tip, resulting in reduced flame height and burning rate, whereas at <em>G</em> < <em>G</em><sub>cr</sub>, sufficient liquid wax is supplied to generate higher flame height. The candle flame has a transition from a stable laminar to oscillating flame, because of the enhanced buoyancy-induced velocity in hypergravity. However, a flame extinction is observed at 9 g due to minimized fuel supply rate. Considering the capillary-driven fuel supply mechanism and enhanced buoyant flow, flame oscillation frequency and amplitude are found to initially increase and then decrease with two oscillation modes (bulk flickering and tip flickering). The oscillation frequencies can well be described in terms of the Strouhal and Froude number relationship incorporating the change of burning rate. A physical model of burning rate is established considering the variation of characteristic length. The flame height in hypergravity is well predicted based on the Roper’s model by adopting the \"apparent port burner\" concept, taking into account the effect of fuel supply rate. This paper provides comprehensive experimental data and facilitates fundamental understanding regarding the candle flames in hypergravity.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114632"},"PeriodicalIF":6.2,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145621518","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 : 2025-11-23DOI: 10.1016/j.combustflame.2025.114652
Shu Zheng, Mingyang Na, Xinyue Zhang, Yan Lv, Hao Liu, Qiang Lu
CO2 mole fraction is a key indicator on evaluating combustion parameters including heat release, burning degree, and combustion efficiency. In this study, a new method based on the adaptive weight particle swarm optimization algorithm (AWPSO) in conjunction with the line-by-line model (LBL) was developed to measure the CO2 mole fraction and flame temperature in premixed laminar methane/air flat flames by using the mid-infrared (MIR) emission spectrum. The relative error of the spectral radiative intensity reconstructed by the AWPSO-LBL method was <0.1 %, which verified the accuracy and reasonability of the AWPSO-LBL method. The CO2 mole fraction and temperature distributions were measured at different heights above the burner (HAB) at different equivalence ratios (Φ = 1.0, 1.1, and 1.2). The results showed that the maximum relative error between the measured and simulated CO2 mole fraction was 4.03 %, and that of temperature was 2.56 %. Meanwhile, the effect of chemical reactions on CO2 mole fraction at different equivalence ratios was discussed. Under fuel-rich conditions, the O2 concentration in the premixed fuel decreased as the equivalence ratio increased, which led to a decrease of OH radical via H + O2 ≤> OH + O, inhibiting the CO2 production through CO + OH ≤> CO2 + H. Consequently, the CO2 mole fraction in the downstream of the reaction region decreased by 24.14 % as the equivalence ratio increased from 1.0 to 1.2.
{"title":"A new method for measuring the CO2 mole fraction and flame temperature in premixed laminar methane/air flames based on MIR emission spectrum","authors":"Shu Zheng, Mingyang Na, Xinyue Zhang, Yan Lv, Hao Liu, Qiang Lu","doi":"10.1016/j.combustflame.2025.114652","DOIUrl":"10.1016/j.combustflame.2025.114652","url":null,"abstract":"<div><div>CO<sub>2</sub> mole fraction is a key indicator on evaluating combustion parameters including heat release, burning degree, and combustion efficiency. In this study, a new method based on the adaptive weight particle swarm optimization algorithm (AWPSO) in conjunction with the line-by-line model (LBL) was developed to measure the CO<sub>2</sub> mole fraction and flame temperature in premixed laminar methane/air flat flames by using the mid-infrared (MIR) emission spectrum. The relative error of the spectral radiative intensity reconstructed by the AWPSO-LBL method was <0.1 %, which verified the accuracy and reasonability of the AWPSO-LBL method. The CO<sub>2</sub> mole fraction and temperature distributions were measured at different heights above the burner (HAB) at different equivalence ratios (Φ = 1.0, 1.1, and 1.2). The results showed that the maximum relative error between the measured and simulated CO<sub>2</sub> mole fraction was 4.03 %, and that of temperature was 2.56 %. Meanwhile, the effect of chemical reactions on CO<sub>2</sub> mole fraction at different equivalence ratios was discussed. Under fuel-rich conditions, the O<sub>2</sub> concentration in the premixed fuel decreased as the equivalence ratio increased, which led to a decrease of OH radical via <em>H</em> + O<sub>2</sub> ≤> OH + <em>O</em>, inhibiting the CO<sub>2</sub> production through CO + OH ≤> CO<sub>2</sub> + <em>H</em>. Consequently, the CO<sub>2</sub> mole fraction in the downstream of the reaction region decreased by 24.14 % as the equivalence ratio increased from 1.0 to 1.2.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114652"},"PeriodicalIF":6.2,"publicationDate":"2025-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145621618","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 : 2025-11-22DOI: 10.1016/j.combustflame.2025.114630
Qiao Wang , Peng Zhang , Chengcheng Liu , Bin Yang
The co-firing of ammonia (NH3) with hydrocarbon fuels represents an important application solution for low-carbon operation in various combustion devices. This approach enables enhanced NH3 combustion without requiring extensive modifications to the devices. However, the underlying kinetic interactions between NH3 and hydrocarbons remain poorly understood, impeding the advancement of tailored combustion technologies. In this study, co-oxidation of NH3 with ethylene (C2H4) and acetylene (C2H2), key intermediates in the combustion of larger hydrocarbons, was experimentally and modeling investigated. The experiments were conducted in a jet-stirred reactor (JSR) at atmospheric pressure over a temperature range of 600–1200 K. Stable products were quantified at different equivalence ratios, including hydrocarbons, aldehydes, NOx, and CN cross-reaction species such as HCN. A detailed kinetic model was developed based on Glarborg et al. (2018), with substantial updates implemented to both the N/H/O sub-mechanism and the CN interaction sub-mechanism. The updated model satisfactorily predicts both mid-to-low temperature experimental data from this work and high-temperature results reported in the literature. The results reveal that NH3 consumption in both NH3C2H4 and NH3C2H2 co-oxidation systems displays distinct two-stage characteristics, including pronounced negative temperature coefficient (NTC) behavior. This is attributed to the synergistic effects of intensified chain-termination and competitive fuel chemistry. Specifically, the dominant chain-terminating reaction NH2 + HO2 → NH3 + O2, coupled with the effective OH-scavenging by NH3 which suppresses C2H4/C2H2 oxidation, collectively quench the system's reactivity within the intermediate temperature range. Significant HCN formation was observed in both systems, particularly under fuel-rich conditions. Kinetic analysis demonstrates that HCN formation strongly correlates with amine intermediates in the reaction pathways. In NH3C2H4 systems, HCN is produced through sequential dehydrogenation of methylamine (CH3NH2), formed via CH3 + NH2 recombination. In NH3C2H2 systems, the consumption pathways of 1-ethyleneimine (CH2CNH), formed via NH₂ + C₂H₂ addition, predominantly determine the distribution of nitrogen-containing products (e.g., HCN, HNCO, CH₃CN). Further experimental and theoretical investigations are required to fully elucidate the reaction networks involving these amine intermediates.
{"title":"Co-oxidation of ammonia with ethylene and acetylene: An experimental and kinetic modeling study","authors":"Qiao Wang , Peng Zhang , Chengcheng Liu , Bin Yang","doi":"10.1016/j.combustflame.2025.114630","DOIUrl":"10.1016/j.combustflame.2025.114630","url":null,"abstract":"<div><div>The co-firing of ammonia (NH<sub>3</sub>) with hydrocarbon fuels represents an important application solution for low-carbon operation in various combustion devices. This approach enables enhanced NH<sub>3</sub> combustion without requiring extensive modifications to the devices. However, the underlying kinetic interactions between NH<sub>3</sub> and hydrocarbons remain poorly understood, impeding the advancement of tailored combustion technologies. In this study, co-oxidation of NH<sub>3</sub> with ethylene (C<sub>2</sub>H<sub>4</sub>) and acetylene (C<sub>2</sub>H<sub>2</sub>), key intermediates in the combustion of larger hydrocarbons, was experimentally and modeling investigated. The experiments were conducted in a jet-stirred reactor (JSR) at atmospheric pressure over a temperature range of 600–1200 K. Stable products were quantified at different equivalence ratios, including hydrocarbons, aldehydes, NOx, and C<img>N cross-reaction species such as HCN. A detailed kinetic model was developed based on Glarborg et al. (2018), with substantial updates implemented to both the N/H/O sub-mechanism and the C<img>N interaction sub-mechanism. The updated model satisfactorily predicts both mid-to-low temperature experimental data from this work and high-temperature results reported in the literature. The results reveal that NH<sub>3</sub> consumption in both NH<sub>3</sub><img>C<sub>2</sub>H<sub>4</sub> and NH<sub>3</sub><img>C<sub>2</sub>H<sub>2</sub> co-oxidation systems displays distinct two-stage characteristics, including pronounced negative temperature coefficient (NTC) behavior. This is attributed to the synergistic effects of intensified chain-termination and competitive fuel chemistry. Specifically, the dominant chain-terminating reaction NH<sub>2</sub> + HO<sub>2</sub> → NH<sub>3</sub> + O<sub>2</sub>, coupled with the effective OH-scavenging by NH<sub>3</sub> which suppresses C<sub>2</sub>H<sub>4</sub>/C<sub>2</sub>H<sub>2</sub> oxidation, collectively quench the system's reactivity within the intermediate temperature range. Significant HCN formation was observed in both systems, particularly under fuel-rich conditions. Kinetic analysis demonstrates that HCN formation strongly correlates with amine intermediates in the reaction pathways. In NH<sub>3</sub><img>C<sub>2</sub>H<sub>4</sub> systems, HCN is produced through sequential dehydrogenation of methylamine (CH<sub>3</sub>NH<sub>2</sub>), formed via CH<sub>3</sub> + NH<sub>2</sub> recombination. In NH<sub>3</sub><img>C<sub>2</sub>H<sub>2</sub> systems, the consumption pathways of 1-ethyleneimine (CH<sub>2</sub><img><em>C</em><img>NH), formed via NH₂ + <em>C</em>₂H₂ addition, predominantly determine the distribution of nitrogen-containing products (e.g., HCN, HNCO, CH₃CN). Further experimental and theoretical investigations are required to fully elucidate the reaction networks involving these amine intermediates.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114630"},"PeriodicalIF":6.2,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578348","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 : 2025-11-22DOI: 10.1016/j.combustflame.2025.114643
Yuto Akiyama, Rikuma Nomoto, Bungo Ito, Jun Hayashi, Hiroshi Kawanabe
Nanosecond repetitively pulsed discharge (NRPD) is a promising ignition technique, which is distinguished among methods that generate non-equilibrium plasma using a high reduced electric field and a strong discharge-induced flow. In this study, the NRPD ignition process was investigated using quiescent CH4-air (ϕ = 0.75) mixtures and pure air. To investigate the effect of the NRPD-induced flow formed in high input energy per pulse, the discharge gap distance (dgap) and pulse repetition frequency (PRF) were set as variables. The measurement of the ignition probability (Pig) and simultaneous imaging of Schlieren and chemiluminescence provided knowledge about the ignition process and performance of NRPD ignition. The results showed a non-monotonic trend in Pig versus PRF, which can be attributed to flow induced by a strong discharge pulse. Additionally, a significant mismatch between the Schlieren-based kernel region and the residence of chemiluminescence was observed. This can be associated with a unique kernel formation and propagation process in which a flame kernel was initiated apart from the discharge gap. This process was prone to occur when the dgap was smaller than 1.4 mm and PRF was lower than 10 kHz. When a heat loss to the electrodes is high or PRF is low, the flame kernel could be partially quenched between the electrodes by the heat loss, resulting in displaced, vulnerable flame kernel initiation. In this process, flow induced by subsequent pulse could have a negative interference phenomenon, destroying these vulnerable flame kernels. Therefore, a PRF of 5 kHz, which does not offer sufficiently high chemical activeness but triggers the pulse-to-kernel interference phenomenon, had difficulty in stable ignition. However, a positive correlation was observed between flame kernel development and PRF in successful ignition cases. This finding clarifies that the initial flame kernel development, namely the initial flame kernel size does not necessarily correlate with ignition probability in NRPD ignition.
{"title":"Interferences on flame kernel development by nano-second repetitively pulsed discharges (NRPD) in ignition processes of CH4-air mixture","authors":"Yuto Akiyama, Rikuma Nomoto, Bungo Ito, Jun Hayashi, Hiroshi Kawanabe","doi":"10.1016/j.combustflame.2025.114643","DOIUrl":"10.1016/j.combustflame.2025.114643","url":null,"abstract":"<div><div>Nanosecond repetitively pulsed discharge (NRPD) is a promising ignition technique, which is distinguished among methods that generate non-equilibrium plasma using a high reduced electric field and a strong discharge-induced flow. In this study, the NRPD ignition process was investigated using quiescent CH<sub>4</sub>-air (<em>ϕ</em> = 0.75) mixtures and pure air. To investigate the effect of the NRPD-induced flow formed in high input energy per pulse, the discharge gap distance (<em>d<sub>gap</sub></em>) and pulse repetition frequency (PRF) were set as variables. The measurement of the ignition probability (<em>P<sub>ig</sub></em>) and simultaneous imaging of Schlieren and chemiluminescence provided knowledge about the ignition process and performance of NRPD ignition. The results showed a non-monotonic trend in <em>P<sub>ig</sub></em> versus PRF, which can be attributed to flow induced by a strong discharge pulse. Additionally, a significant mismatch between the Schlieren-based kernel region and the residence of chemiluminescence was observed. This can be associated with a unique kernel formation and propagation process in which a flame kernel was initiated apart from the discharge gap. This process was prone to occur when the <em>d<sub>gap</sub></em> was smaller than 1.4 mm and PRF was lower than 10 kHz. When a heat loss to the electrodes is high or PRF is low, the flame kernel could be partially quenched between the electrodes by the heat loss, resulting in displaced, vulnerable flame kernel initiation. In this process, flow induced by subsequent pulse could have a negative interference phenomenon, destroying these vulnerable flame kernels. Therefore, a PRF of 5 kHz, which does not offer sufficiently high chemical activeness but triggers the pulse-to-kernel interference phenomenon, had difficulty in stable ignition. However, a positive correlation was observed between flame kernel development and PRF in successful ignition cases. This finding clarifies that the initial flame kernel development, namely the initial flame kernel size does not necessarily correlate with ignition probability in NRPD ignition.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114643"},"PeriodicalIF":6.2,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578289","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 : 2025-11-21DOI: 10.1016/j.combustflame.2025.114622
Qianwen Jiang , Junhong Chen , Zhiyuan Guan , Zhongbo Han , Changkun Song , Chunpei Yu , Jianyong Xu , Pengfei Cui , Wenchao Zhang
Micron-sized aluminum (mAl) is a cost-effective and environmentally friendly metal fuel that holds great potential for combustion applications. mAl, as the main raw material of microthermite, has shown tremendous potential in aerospace, military, and energy fields. However, the presence of a natural oxide (Al2O3) layer around the active Al core limits its performance. Recent studies have focused on enhancing mAl reactivity by incorporating fluorinated polymers as coatings or additives. However, excessive F content introduced may reduce the thermal conductivity of the microthermite. Therefore, the content of F has also become a key issue in regulating the combustion process of Al/CuO micro-thermites. In this paper, fluorinated acrylate was used for the first time to in-situ coat polymers with different F contents on the surface of mAl to regulate the performance of thermite. Analysis shows that the fluorinated coating can accelerate the etching of the high-melting Al2O3 shell and accelerate the mass transfer between the oxidant and the reducing agent. More importantly, the combustion rate and combustion duration of Al/CuO microthermite were successfully controlled by changing the F content in the modified raw material. This novel approach is scalable and offers a viable pathway for optimizing energetic material performance.
{"title":"Gradient fluorine content in fluorinated interfacial layer regulates the combustion reaction of Al/CuO microthermite","authors":"Qianwen Jiang , Junhong Chen , Zhiyuan Guan , Zhongbo Han , Changkun Song , Chunpei Yu , Jianyong Xu , Pengfei Cui , Wenchao Zhang","doi":"10.1016/j.combustflame.2025.114622","DOIUrl":"10.1016/j.combustflame.2025.114622","url":null,"abstract":"<div><div>Micron-sized aluminum (mAl) is a cost-effective and environmentally friendly metal fuel that holds great potential for combustion applications. mAl, as the main raw material of microthermite, has shown tremendous potential in aerospace, military, and energy fields. However, the presence of a natural oxide (Al<sub>2</sub>O<sub>3</sub>) layer around the active Al core limits its performance. Recent studies have focused on enhancing mAl reactivity by incorporating fluorinated polymers as coatings or additives. However, excessive F content introduced may reduce the thermal conductivity of the microthermite. Therefore, the content of F has also become a key issue in regulating the combustion process of Al/CuO micro-thermites. In this paper, fluorinated acrylate was used for the first time to in-situ coat polymers with different F contents on the surface of mAl to regulate the performance of thermite. Analysis shows that the fluorinated coating can accelerate the etching of the high-melting Al<sub>2</sub>O<sub>3</sub> shell and accelerate the mass transfer between the oxidant and the reducing agent. More importantly, the combustion rate and combustion duration of Al/CuO microthermite were successfully controlled by changing the F content in the modified raw material. This novel approach is scalable and offers a viable pathway for optimizing energetic material performance.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114622"},"PeriodicalIF":6.2,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578343","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 : 2025-11-21DOI: 10.1016/j.combustflame.2025.114623
Dengke Chen , Chang Xing , Linyao Zhang , Penghua Qiu , Li Liu , Yijun Zhao , Jingyu Guan , Rui Sun
Micro-mixing (MM) combustion technology offers advantages such as enhanced flame stability and reduced pollutant emissions. Experimental investigations are conducted on a typical low heating value syngas under varying inlet air pressures (P3) ranging from 0.1 to 0.6 MPa and equivalence ratios (φ) spanning 0.52 to 0.73. This study provides an in-depth analysis of combustion dynamics, flame structure,and pollutant emission characteristics. The findings reveal that the MM flame mode predominantly resides within the continuous stirred reaction zone, with a local curvature radius on the millimeter scale, indicating the presence of numerous small-scale wrinkles across the flame front. With the increase of P3, the OH distribution area markedly contracts and concentrates toward the combustion chamber head. The flame width exhibits only a slight fluctuation of <5 % throughout the entire pressure variation range, indicating that axial compression is the dominant mechanism by which pressure affects flame morphology, and the coefficient of variation (CV) of OH spatial distribution uniformity (SDU) exhibits non-monotonic pressure dependence, undergoing critical behavioral transition at P3 = 0.3 MPa. NO emission exhibits a rapid increase with rising P3 and φ, however, under the tested conditions, NO level remains below 5 ppm (@15 %O2).
{"title":"Investigation of elevated pressure effects on combustion characteristics of combined micro-mixing flames","authors":"Dengke Chen , Chang Xing , Linyao Zhang , Penghua Qiu , Li Liu , Yijun Zhao , Jingyu Guan , Rui Sun","doi":"10.1016/j.combustflame.2025.114623","DOIUrl":"10.1016/j.combustflame.2025.114623","url":null,"abstract":"<div><div>Micro-mixing (MM) combustion technology offers advantages such as enhanced flame stability and reduced pollutant emissions. Experimental investigations are conducted on a typical low heating value syngas under varying inlet air pressures (<em>P</em><sub>3</sub>) ranging from 0.1 to 0.6 MPa and equivalence ratios (<em>φ</em>) spanning 0.52 to 0.73. This study provides an in-depth analysis of combustion dynamics, flame structure,and pollutant emission characteristics. The findings reveal that the MM flame mode predominantly resides within the continuous stirred reaction zone, with a local curvature radius on the millimeter scale, indicating the presence of numerous small-scale wrinkles across the flame front. With the increase of <em>P</em><sub>3</sub>, the OH distribution area markedly contracts and concentrates toward the combustion chamber head. The flame width exhibits only a slight fluctuation of <5 % throughout the entire pressure variation range, indicating that axial compression is the dominant mechanism by which pressure affects flame morphology, and the coefficient of variation (<em>CV</em>) of OH spatial distribution uniformity (<em>SDU</em>) exhibits non-monotonic pressure dependence, undergoing critical behavioral transition at <em>P</em><sub>3</sub> = 0.3 MPa. NO emission exhibits a rapid increase with rising <em>P</em><sub>3</sub> and <em>φ</em>, however, under the tested conditions, NO level remains below 5 ppm (@15 %O<sub>2</sub>).</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114623"},"PeriodicalIF":6.2,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578344","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 : 2025-11-21DOI: 10.1016/j.combustflame.2025.114666
Hongchao Chu, Heinz Pitsch
The flame front curvature distribution is critically important for premixed flames, particularly for flames with non-unity Lewis numbers, such as lean hydrogen flames, where differential diffusion effects are strongly correlated with flame curvature. Although the statistics and evolution of the curvature of premixed flames have garnered considerable interest in recent literature, a rigorous mathematical framework for quantitatively studying the evolution of the curvature probability density function (PDF) has yet to be developed. This paper presents a rigorous derivation of the equation governing the curvature PDF of instantaneous flame fronts. The derived theory is applied to analyze a premixed developing turbulent planar flame. It is revealed that the evolution of the curvature PDF is governed by (i) a drift in curvature space caused by the curvature evolution, and (ii) the non-uniform surface area evolution associated with various curvatures. A focus in the analysis is placed on the initial transition of the planar flame to a fully developed turbulent surface. During and after this transition, distinctly different effects of flow and flame propagation on the evolution of curvature and curvature PDF are identified. These findings enhance the understanding of curvature dynamics and offer new perspectives for modeling turbulent premixed combustion based on the curvature PDF. Furthermore, the derived PDF equation can equivalently be written for other scalar quantities defined on a moving surface, offering a general framework for analyzing scalar statistics on evolving surfaces, such as displacement speed, which plays a critical role in scalar mixing and turbulent combustion.
Novelty and significance statement
This work presents a novel equation for the evolution of the flame curvature probability density function (PDF) and provides the first quantitative analysis of the mechanisms governing the curvature PDF evolution of instantaneous flame fronts. The significance lies in two main aspects. First, the study advances the understanding of curvature dynamics and offers new insights for modeling curvature effects in turbulent premixed combustion. Second, the derived PDF equation can be equivalently formulated for other scalar quantities defined on a moving surface. Hence, the proposed framework holds strong potential for analyzing scalar statistics on evolving surfaces, such as displacement speed, thereby improving the understanding of turbulent combustion and scalar mixing in turbulent flows.
{"title":"An equation for the curvature probability density function of instantaneous flame fronts","authors":"Hongchao Chu, Heinz Pitsch","doi":"10.1016/j.combustflame.2025.114666","DOIUrl":"10.1016/j.combustflame.2025.114666","url":null,"abstract":"<div><div>The flame front curvature distribution is critically important for premixed flames, particularly for flames with non-unity Lewis numbers, such as lean hydrogen flames, where differential diffusion effects are strongly correlated with flame curvature. Although the statistics and evolution of the curvature of premixed flames have garnered considerable interest in recent literature, a rigorous mathematical framework for quantitatively studying the evolution of the curvature probability density function (PDF) has yet to be developed. This paper presents a rigorous derivation of the equation governing the curvature PDF of instantaneous flame fronts. The derived theory is applied to analyze a premixed developing turbulent planar flame. It is revealed that the evolution of the curvature PDF is governed by (i) a drift in curvature space caused by the curvature evolution, and (ii) the non-uniform surface area evolution associated with various curvatures. A focus in the analysis is placed on the initial transition of the planar flame to a fully developed turbulent surface. During and after this transition, distinctly different effects of flow and flame propagation on the evolution of curvature and curvature PDF are identified. These findings enhance the understanding of curvature dynamics and offer new perspectives for modeling turbulent premixed combustion based on the curvature PDF. Furthermore, the derived PDF equation can equivalently be written for other scalar quantities defined on a moving surface, offering a general framework for analyzing scalar statistics on evolving surfaces, such as displacement speed, which plays a critical role in scalar mixing and turbulent combustion.</div><div><strong>Novelty and significance statement</strong></div><div>This work presents a novel equation for the evolution of the flame curvature probability density function (PDF) and provides the first quantitative analysis of the mechanisms governing the curvature PDF evolution of instantaneous flame fronts. The significance lies in two main aspects. First, the study advances the understanding of curvature dynamics and offers new insights for modeling curvature effects in turbulent premixed combustion. Second, the derived PDF equation can be equivalently formulated for other scalar quantities defined on a moving surface. Hence, the proposed framework holds strong potential for analyzing scalar statistics on evolving surfaces, such as displacement speed, thereby improving the understanding of turbulent combustion and scalar mixing in turbulent flows.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114666"},"PeriodicalIF":6.2,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578212","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 : 2025-11-21DOI: 10.1016/j.combustflame.2025.114646
Shuainan Yang , Chenyang Fan , Zheng Fu , Ye Liu , Huiyong Du , Bin Xu , Yidu Tong , Mingliang Wei
Co-combustion of ammonia with hydrocarbon fuels and its effect on soot emission characteristics have garnered interest. In this study, the oxidation kinetics of soot generated in a laminar co-flow acetylene diffusion flame were investigated under 30 –800 °C temperature-programmed oxidation and isothermal oxidation at 500°C, 600°C, and 700°C using thermogravimetric analysis (TGA). The evolution of functional groups on soot surfaces and gaseous products were monitored by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis coupled with infrared spectroscopy (TG-IR), respectively. Results indicate that the activation energy for soot oxidation increases with higher NH3 substitution ratios (XNH₃) and elevated temperatures. Isothermal oxidation tests also show that the oxidation rate constant increases with increasing XNH₃. FTIR results show that increasing XNH₃ reduces aliphatic C–H groups and increases oxygenated groups on soot surfaces. The detected C–N bonds are attributed to dehydrogenation of aliphatic carbon atoms on polycyclic aromatic hydrocarbons (PAHs) surfaces. TG-IR analysis revealed the C–N bonds in urethanes on soot surfaces may release as the gaseous C–N species during low-temperature (500 °C) oxidation of soot particles. Nevertheless, the higher-temperature facilitated the cleavage of C–N bonds, and then the generated NH₂ radicals react with oxygen radicals, leading to the formation of HNO on the soot surface.
{"title":"Oxidation kinetic of soot generated from ammonia-acetylene laminar diffusion flame","authors":"Shuainan Yang , Chenyang Fan , Zheng Fu , Ye Liu , Huiyong Du , Bin Xu , Yidu Tong , Mingliang Wei","doi":"10.1016/j.combustflame.2025.114646","DOIUrl":"10.1016/j.combustflame.2025.114646","url":null,"abstract":"<div><div>Co-combustion of ammonia with hydrocarbon fuels and its effect on soot emission characteristics have garnered interest. In this study, the oxidation kinetics of soot generated in a laminar co-flow acetylene diffusion flame were investigated under 30 –800 °C temperature-programmed oxidation and isothermal oxidation at 500°C, 600°C, and 700°C using thermogravimetric analysis (TGA). The evolution of functional groups on soot surfaces and gaseous products were monitored by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis coupled with infrared spectroscopy (TG-IR), respectively. Results indicate that the activation energy for soot oxidation increases with higher NH<sub>3</sub> substitution ratios (X<sub>NH₃</sub>) and elevated temperatures. Isothermal oxidation tests also show that the oxidation rate constant increases with increasing X<sub>NH₃</sub>. FTIR results show that increasing X<sub>NH₃</sub> reduces aliphatic C–H groups and increases oxygenated groups on soot surfaces. The detected C–N bonds are attributed to dehydrogenation of aliphatic carbon atoms on polycyclic aromatic hydrocarbons (PAHs) surfaces. TG-IR analysis revealed the C–N bonds in urethanes on soot surfaces may release as the gaseous C–N species during low-temperature (500 °C) oxidation of soot particles. Nevertheless, the higher-temperature facilitated the cleavage of C–N bonds, and then the generated NH₂ radicals react with oxygen radicals, leading to the formation of HNO on the soot surface.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"284 ","pages":"Article 114646"},"PeriodicalIF":6.2,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145578347","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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