Pub Date : 2025-12-26DOI: 10.1016/j.combustflame.2025.114733
Jumeng Fan , Xiangyu Zhang , Huahua Xiao , Longhua Hu , Luqing Wang , Honghao Ma , Xinming Qin , Yundong Zhang , Chao Wu
Numerical simulation of the formation and evolution of distorted tulip flame (DTF) requires solving the three-dimensional (3D), fully-compressible, and reactive Navier-Stokes equations using a high-order numerical method and adaptive mesh refinement. In this work, a dynamically thickened flame model coupled with a chemical-diffusive model was employed to achieve efficient and accurate resolution of 3D DTF structures. Validation against prior experiments, theories, and simulations confirms the numerical method’s reliability. The 3D results reveal noteworthy differences from two-dimensional (2D) simulations in flame evolution and pressure dynamics. A key observation in 3D simulation is the progressive shallowing of the primary central cusp without collapse, contrasting with the collapse-regeneration cycles observed in 2D During exponential flame acceleration, the acceleration rate is proportional to the ratio of flame surface area to the burned volume, leading to higher propagation speed and reduced distortion frequency. While both 2D and 3D models predict the same peak pressure, the 2D case underestimates the pressure growth rate due to slower flame acceleration. Linear Rayleigh-Taylor instability (RTI) analysis indicates that the larger RTI growth rate and time-scale in 3D leads to greater flame distortions and deeper cusps, and consequently larger flame surface area that causes higher flame speed and pressure growth rate in the later stage.
{"title":"Three- versus two-dimensional numerical simulation of distorted tulip flame in stoichiometric hydrogen-air mixture","authors":"Jumeng Fan , Xiangyu Zhang , Huahua Xiao , Longhua Hu , Luqing Wang , Honghao Ma , Xinming Qin , Yundong Zhang , Chao Wu","doi":"10.1016/j.combustflame.2025.114733","DOIUrl":"10.1016/j.combustflame.2025.114733","url":null,"abstract":"<div><div>Numerical simulation of the formation and evolution of distorted tulip flame (DTF) requires solving the three-dimensional (3D), fully-compressible, and reactive Navier-Stokes equations using a high-order numerical method and adaptive mesh refinement. In this work, a dynamically thickened flame model coupled with a chemical-diffusive model was employed to achieve efficient and accurate resolution of 3D DTF structures. Validation against prior experiments, theories, and simulations confirms the numerical method’s reliability. The 3D results reveal noteworthy differences from two-dimensional (2D) simulations in flame evolution and pressure dynamics. A key observation in 3D simulation is the progressive shallowing of the primary central cusp without collapse, contrasting with the collapse-regeneration cycles observed in 2D During exponential flame acceleration, the acceleration rate is proportional to the ratio of flame surface area to the burned volume, leading to higher propagation speed and reduced distortion frequency. While both 2D and 3D models predict the same peak pressure, the 2D case underestimates the pressure growth rate due to slower flame acceleration. Linear Rayleigh-Taylor instability (RTI) analysis indicates that the larger RTI growth rate and time-scale in 3D leads to greater flame distortions and deeper cusps, and consequently larger flame surface area that causes higher flame speed and pressure growth rate in the later stage.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114733"},"PeriodicalIF":6.2,"publicationDate":"2025-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837902","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 : 2025-12-25DOI: 10.1016/j.combustflame.2025.114737
Hao-Dong Liu , Bo Gong , Hang Zhang , Jie-Ping Wang , Jin-Xiao Dou , Rui Guo , Guang-Yue Li , Ying-Hua Liang
While the integration of real-time experimental monitoring and molecular dynamics simulations offers new insights into coal pyrolysis, it is still constrained by inadequate force field parameter accuracy, excessively large molecular scale and long computation times. To overcome this challenge, we propose an innovative method that combines the Metropolis Monte Carlo algorithm and ClipIRMol (MMCClipIRMol) to simulate the pyrolysis process of coal. This method is based on elementary reactions and their corresponding bond energy information in coal pyrolysis, using the Monte Carlo algorithm to randomly sample reaction processes and simulate the entire reaction network. First, elemental analysis, IR spectroscopy, and 13C NMR, providing the basis for constructing three macromolecular models of bituminous coal with different degrees of coalification (C809H783N13O71S, C819H645N13O19S, C808H516N10O17S). Subsequently, the pyrolysis process of this molecular model was simulated by Monte Carlo and ReaxFF molecular dynamics respectively. The Monte Carlo objective function incorporated structure characterization information from in-situ DRIFTS and the data relevant to volatile generation (such as H2, CH4, and CH3 radicals) from TG-MS experiments as constraints. By comparing the reaction intermediates generated by both simulation methods, similar molecular structures were found, which validated the effectiveness of the proposed method.
{"title":"Prediction of structural evolution during coal pyrolysis with metropolis Monte Carlo and deep learning","authors":"Hao-Dong Liu , Bo Gong , Hang Zhang , Jie-Ping Wang , Jin-Xiao Dou , Rui Guo , Guang-Yue Li , Ying-Hua Liang","doi":"10.1016/j.combustflame.2025.114737","DOIUrl":"10.1016/j.combustflame.2025.114737","url":null,"abstract":"<div><div>While the integration of real-time experimental monitoring and molecular dynamics simulations offers new insights into coal pyrolysis, it is still constrained by inadequate force field parameter accuracy, excessively large molecular scale and long computation times. To overcome this challenge, we propose an innovative method that combines the Metropolis Monte Carlo algorithm and ClipIRMol (MMC<img>ClipIRMol) to simulate the pyrolysis process of coal. This method is based on elementary reactions and their corresponding bond energy information in coal pyrolysis, using the Monte Carlo algorithm to randomly sample reaction processes and simulate the entire reaction network. First, elemental analysis, IR spectroscopy, and <sup>13</sup>C NMR, providing the basis for constructing three macromolecular models of bituminous coal with different degrees of coalification (C<sub>809</sub>H<sub>783</sub>N<sub>13</sub>O<sub>71</sub>S, C<sub>819</sub>H<sub>645</sub>N<sub>13</sub>O<sub>19</sub>S, C<sub>808</sub>H<sub>516</sub>N<sub>10</sub>O<sub>17</sub>S). Subsequently, the pyrolysis process of this molecular model was simulated by Monte Carlo and ReaxFF molecular dynamics respectively. The Monte Carlo objective function incorporated structure characterization information from in-situ DRIFTS and the data relevant to volatile generation (such as H<sub>2</sub>, CH<sub>4</sub>, and CH<sub>3</sub> radicals) from TG-MS experiments as constraints. By comparing the reaction intermediates generated by both simulation methods, similar molecular structures were found, which validated the effectiveness of the proposed method.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114737"},"PeriodicalIF":6.2,"publicationDate":"2025-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837900","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 : 2025-12-24DOI: 10.1016/j.combustflame.2025.114738
Hanzheng Shi , Wanhui Zhao , Ying Wang , Zongkuan Liu , Tao Wang , Zhiqiang Niu , Lei Zhou , Haiqiao Wei
Pyrolysis and coking of aviation fuels under high-temperature conditions are critical to the performance and longevity of aero-engines. Reactive force field molecular dynamics (ReaxFF MD) was used to investigate the atomic-scale pyrolysis and coking behavior of a four-component RP-3 surrogate fuel and the inhibitory effects of methanol (CH₃OH) and ammonia (NH₃) additives. Results showed that pyrolysis was initiated via C–C bond cleavage in alkanes and cycloalkanes, followed by radical-mediated chain elongation and cyclization into polycyclic aromatic hydrocarbons (PAHs), forming layered coke structures. Methanol suppressed coke formation by generating OH radicals that intercept unsaturated intermediates, while ammonia introduced C–N species (e.g., HCN) that hinder PAH growth through nitrogen-doped ring formation and carbon chain shortening. Notably, NH₃ exhibited superior inhibition, reducing the maximum carbon atoms in coke (Cmax) from 898 (Additive-free system) to 670, compared to methanol’s reduction to 745. CH₃OH shortens the carbon chain length by attacking the unsaturated carbon chain through the formation of stabilizing CO products by -OH, while NH₃ reduces the number of unsaturated small molecules through the formation of CN products, and the inhibitory mechanism of the carbon chain lengthening process by the CN species in the growth process of PAH has been revealed for the first time. This study systematically elucidates the different mechanisms of methanol and ammonia blending to inhibit coking of RP-3 fuel from the atomic scale, which provides an important theoretical basis for the optimization of aviation fuel formulations and the design of coking prevention of engine thermal management systems for low-carbon fuels.
{"title":"A ReaxFF molecular dynamics study of pyrolysis and coking inhibition by low/zero-carbon fuel additives in aviation fuels","authors":"Hanzheng Shi , Wanhui Zhao , Ying Wang , Zongkuan Liu , Tao Wang , Zhiqiang Niu , Lei Zhou , Haiqiao Wei","doi":"10.1016/j.combustflame.2025.114738","DOIUrl":"10.1016/j.combustflame.2025.114738","url":null,"abstract":"<div><div>Pyrolysis and coking of aviation fuels under high-temperature conditions are critical to the performance and longevity of aero-engines. Reactive force field molecular dynamics (ReaxFF MD) was used to investigate the atomic-scale pyrolysis and coking behavior of a four-component RP-3 surrogate fuel and the inhibitory effects of methanol (CH₃OH) and ammonia (NH₃) additives. Results showed that pyrolysis was initiated via C–C bond cleavage in alkanes and cycloalkanes, followed by radical-mediated chain elongation and cyclization into polycyclic aromatic hydrocarbons (PAHs), forming layered coke structures. Methanol suppressed coke formation by generating OH radicals that intercept unsaturated intermediates, while ammonia introduced C–N species (e.g., HCN) that hinder PAH growth through nitrogen-doped ring formation and carbon chain shortening. Notably, NH₃ exhibited superior inhibition, reducing the maximum carbon atoms in coke (C<sub>max</sub>) from 898 (Additive-free system) to 670, compared to methanol’s reduction to 745. CH₃OH shortens the carbon chain length by attacking the unsaturated carbon chain through the formation of stabilizing C<img>O products by -OH, while NH₃ reduces the number of unsaturated small molecules through the formation of C<img>N products, and the inhibitory mechanism of the carbon chain lengthening process by the C<img>N species in the growth process of PAH has been revealed for the first time. This study systematically elucidates the different mechanisms of methanol and ammonia blending to inhibit coking of RP-3 fuel from the atomic scale, which provides an important theoretical basis for the optimization of aviation fuel formulations and the design of coking prevention of engine thermal management systems for low-carbon fuels.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114738"},"PeriodicalIF":6.2,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837899","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 : 2025-12-23DOI: 10.1016/j.combustflame.2025.114725
Nicolas Vaysse, Daniel Durox, Ronan Vicquelin, Sébastien Candel, Antoine Renaud
<div><div>One issue in the operation of annular combustors is to ensure a reliable light-round ignition that will establish flames on all injector units without excessive pressure excursion and in a relatively short period of time. This issue is here examined in the case where the annular system is fed with pure hydrogen by combining experimentation and reduced order modeling. Systematic experiments are carried out in a model scale configuration equipped with multiple injectors, in which pure hydrogen is delivered in cross-flow in a swirling stream of air. In this large set of experiments, ignition initiated by a single spark plug gives rise to a couple of flames traveling in clockwise and counterclockwise directions which at a later stage, propagate head-on and merge. It is found that the duration of this process is much shorter when the combustor is fed with pure H2 than when it is operated with gaseous propane–air mixtures or liquid sprays of heptane or dodecane. Systematic observations of the final stage before flame merging indicates that a layer of fresh reactants is formed between the two flame branches which slows down the flame propagation. This flame deceleration is here documented in the case of hydrogen flames. A reduced order model, that accounts for this final stage, is shown to suitably capture effects of global equivalence ratio and injection velocity on the light-round time delay. Experiments also provide indications on effects of injector swirl number and preheating of the chamber walls. In contrast with previous experiments with hydrocarbon flames, it is found that preheating has only a marginal effect on the light-round time. An examination of pressure records during ignition is finally carried out to quantify the amplitude of the ignition-induced pressure excursion. A novel scaling law is derived to estimate the corresponding pressure peaks and this model is shown to be consistent with experimental data. It is also found that under certain conditions, the ignition is followed by a cyclic regime corresponding to a thermoacoustic oscillation that is shown to be coupled by the first azimuthal mode of the chamber.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this research lies in the experimental investigation of light-round ignition in an annular combustor fed with pure hydrogen, a case not well documented in the literature. The broad set of experiments reported in this article provides a comprehensive view of the influence of global equivalence ratio, injection velocity, swirl number and wall preheating on the light-round characteristic time in the case of pure H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> injection and probably constitutes the only data set that fills an identified gap of knowledge. The flames slowdown in their head-on merging is also analyzed for the first time in the hydrogen case. A reduced-order model of the light-round ignition accou
{"title":"Light-round ignition dynamics of a hydrogen-fueled annular combustor: Parametric effects and reduced-order modeling","authors":"Nicolas Vaysse, Daniel Durox, Ronan Vicquelin, Sébastien Candel, Antoine Renaud","doi":"10.1016/j.combustflame.2025.114725","DOIUrl":"10.1016/j.combustflame.2025.114725","url":null,"abstract":"<div><div>One issue in the operation of annular combustors is to ensure a reliable light-round ignition that will establish flames on all injector units without excessive pressure excursion and in a relatively short period of time. This issue is here examined in the case where the annular system is fed with pure hydrogen by combining experimentation and reduced order modeling. Systematic experiments are carried out in a model scale configuration equipped with multiple injectors, in which pure hydrogen is delivered in cross-flow in a swirling stream of air. In this large set of experiments, ignition initiated by a single spark plug gives rise to a couple of flames traveling in clockwise and counterclockwise directions which at a later stage, propagate head-on and merge. It is found that the duration of this process is much shorter when the combustor is fed with pure H2 than when it is operated with gaseous propane–air mixtures or liquid sprays of heptane or dodecane. Systematic observations of the final stage before flame merging indicates that a layer of fresh reactants is formed between the two flame branches which slows down the flame propagation. This flame deceleration is here documented in the case of hydrogen flames. A reduced order model, that accounts for this final stage, is shown to suitably capture effects of global equivalence ratio and injection velocity on the light-round time delay. Experiments also provide indications on effects of injector swirl number and preheating of the chamber walls. In contrast with previous experiments with hydrocarbon flames, it is found that preheating has only a marginal effect on the light-round time. An examination of pressure records during ignition is finally carried out to quantify the amplitude of the ignition-induced pressure excursion. A novel scaling law is derived to estimate the corresponding pressure peaks and this model is shown to be consistent with experimental data. It is also found that under certain conditions, the ignition is followed by a cyclic regime corresponding to a thermoacoustic oscillation that is shown to be coupled by the first azimuthal mode of the chamber.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this research lies in the experimental investigation of light-round ignition in an annular combustor fed with pure hydrogen, a case not well documented in the literature. The broad set of experiments reported in this article provides a comprehensive view of the influence of global equivalence ratio, injection velocity, swirl number and wall preheating on the light-round characteristic time in the case of pure H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> injection and probably constitutes the only data set that fills an identified gap of knowledge. The flames slowdown in their head-on merging is also analyzed for the first time in the hydrogen case. A reduced-order model of the light-round ignition accou","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114725"},"PeriodicalIF":6.2,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837863","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 : 2025-12-22DOI: 10.1016/j.combustflame.2025.114708
Sandeep Jella , Jeffrey Bergthorson
Flameholding has been studied for decades but premixed flame-flow interaction near the point of blow-off, in practical combustion devices, still raises interesting questions. While theoretical ideas about blow-off generally consider the disruption of a reaction–diffusion balance (e.g., strain-based extinction) or a convection–reaction balance (well-stirred reactor), these balances have not been quantified previously during an actual blow-off event. In this work, strain-flame alignment and enstrophy budgets are investigated far from, near, and during total blow-off for a swirl injector. To quantify these, a two-flame, periodic model of interacting methane–air flames is constructed, fully resolving the flame structure using adaptive mesh refinement and detailed chemical kinetics. The flow is resolved down to twice the estimated Kolmogorov length scale in the reactant stream. Near blow-off, the Reynolds (Re), Damköhler (Da) and Karlovitz (Ka) numbers are estimated to be 24400, 0.1 and 250 respectively, which places the blow-off condition in the distributed/broken-reaction zones regime. Results indicate that the flame is passive with respect to alignment to the fluid-dynamic strain rate field but not with respect to vorticity dynamics and baroclinic torque may compete with or even exceed vortex-stretching as a source or sink of enstrophy. Species transport budgets, extracted during the final moments of total blow-off, indicate reaction–diffusion balances persist to the end. Scalar gradients are not observed to thicken to the point of distributing but exhibit complex dependencies on stretch effects.
{"title":"Flame–turbulence interaction near and during blow-off of lean premixed flames","authors":"Sandeep Jella , Jeffrey Bergthorson","doi":"10.1016/j.combustflame.2025.114708","DOIUrl":"10.1016/j.combustflame.2025.114708","url":null,"abstract":"<div><div>Flameholding has been studied for decades but premixed flame-flow interaction near the point of blow-off, in practical combustion devices, still raises interesting questions. While theoretical ideas about blow-off generally consider the disruption of a reaction–diffusion balance (e.g., strain-based extinction) or a convection–reaction balance (well-stirred reactor), these balances have not been quantified previously during an actual blow-off event. In this work, strain-flame alignment and enstrophy budgets are investigated far from, near, and during total blow-off for a swirl injector. To quantify these, a two-flame, periodic model of interacting methane–air flames is constructed, fully resolving the flame structure using adaptive mesh refinement and detailed chemical kinetics. The flow is resolved down to twice the estimated Kolmogorov length scale in the reactant stream. Near blow-off, the Reynolds (Re), Damköhler (Da) and Karlovitz (Ka) numbers are estimated to be 24400, 0.1 and 250 respectively, which places the blow-off condition in the distributed/broken-reaction zones regime. Results indicate that the flame is passive with respect to alignment to the fluid-dynamic strain rate field but not with respect to vorticity dynamics and baroclinic torque may compete with or even exceed vortex-stretching as a source or sink of enstrophy. Species transport budgets, extracted during the final moments of total blow-off, indicate reaction–diffusion balances persist to the end. Scalar gradients are not observed to thicken to the point of distributing but exhibit complex dependencies on stretch effects.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114708"},"PeriodicalIF":6.2,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837895","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 : 2025-12-22DOI: 10.1016/j.combustflame.2025.114710
Arthur Péquin , Erica Quadarella , James C. Massey , Riccardo Malpica Galassi , Salvatore Iavarone , Hong G. Im , Alessandro Parente , Nedunchezhian Swaminathan
Turbulent reacting flows are described as multi-scale processes with characteristic flow and chemical timescales spanning several orders of magnitude. Species source term closure models that rely on the description of such systems through a single scale make a strong assumption, failing to provide accurate estimations for chemical processes with significantly different characteristic timescales. The modal Partially Stirred Reactor (mPaSR) model overcomes this limitation by accounting for all chemical system dynamics through the modal decomposition of the Jacobian matrix of the species source terms. Following a priori testing on direct numerical simulation data and simulations using the Reynolds-averaged Navier–Stokes approach, this work details the first mPaSR model assessment in the context of Large Eddy Simulation (LES). Model validation is achieved through a series of LES of the Darmstadt Multi-Regime Burner (MRB). Attention is paid to the quality of temperature and carbon monoxide estimations in comparison to the measurements. Insights into the model are provided by assessing the resulting flow fields with tools from the Computational Singular Perturbation (CSP) theory. The study supports the use of the mPaSR model for the numerical investigation of complex turbulent reacting flows with the LES approach.
Novelty and significance
The novelty of this work lies in the first a posteriori testing, in the context of Large Eddy Simulation, of an innovative combustion model accounting for several timescales of dynamical chemical systems. This represents an important step towards developing well-suited approaches for modelling multi-regime combustion and multi-scale processes, such as pollutant formation in turbulent flames. The model demonstrates promising predictive capabilities in the investigated cases, motivating further studies across a broader range of combustion scenarios.
{"title":"Large eddy simulation of multi-regime turbulent combustion with modal partially stirred reactor models","authors":"Arthur Péquin , Erica Quadarella , James C. Massey , Riccardo Malpica Galassi , Salvatore Iavarone , Hong G. Im , Alessandro Parente , Nedunchezhian Swaminathan","doi":"10.1016/j.combustflame.2025.114710","DOIUrl":"10.1016/j.combustflame.2025.114710","url":null,"abstract":"<div><div>Turbulent reacting flows are described as multi-scale processes with characteristic flow and chemical timescales spanning several orders of magnitude. Species source term closure models that rely on the description of such systems through a single scale make a strong assumption, failing to provide accurate estimations for chemical processes with significantly different characteristic timescales. The modal Partially Stirred Reactor (mPaSR) model overcomes this limitation by accounting for all chemical system dynamics through the modal decomposition of the Jacobian matrix of the species source terms. Following <em>a priori</em> testing on direct numerical simulation data and simulations using the Reynolds-averaged Navier–Stokes approach, this work details the first mPaSR model assessment in the context of Large Eddy Simulation (LES). Model validation is achieved through a series of LES of the Darmstadt Multi-Regime Burner (MRB). Attention is paid to the quality of temperature and carbon monoxide estimations in comparison to the measurements. Insights into the model are provided by assessing the resulting flow fields with tools from the Computational Singular Perturbation (CSP) theory. The study supports the use of the mPaSR model for the numerical investigation of complex turbulent reacting flows with the LES approach.</div><div><strong>Novelty and significance</strong></div><div>The novelty of this work lies in the first <em>a posteriori</em> testing, in the context of Large Eddy Simulation, of an innovative combustion model accounting for several timescales of dynamical chemical systems. This represents an important step towards developing well-suited approaches for modelling multi-regime combustion and multi-scale processes, such as pollutant formation in turbulent flames. The model demonstrates promising predictive capabilities in the investigated cases, motivating further studies across a broader range of combustion scenarios.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114710"},"PeriodicalIF":6.2,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837898","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 : 2025-12-22DOI: 10.1016/j.combustflame.2025.114732
A. Perrier , M. Bouvier , F. Collin-Bastiani , G. Cabot , J. Yon , F. Grisch
Two measurement diagnostics were developed to study soot production in swirl stratified premixed ethylene/air flames. The first one measures the spatially-resolved mobility diameter and number density distributions of soot using a dual-port dilution sampling probe connected with a second dilution system and a Scanning Mobility Particle Sizer (SMPS). The second technique relies on high-speed 2D multi-angle light scattering diagnostic (2D-MALS) enabling the measurement of 2D spatially-resolved distributions of soot gyration diameter and number density. The gyration diameter is derived from the data processing of scattering images collected by CMOS cameras located at 45° and 135° around the flame while the data recorded at 90° with another CMOS camera combined to the knowledge of the gyration diameter, enables the determination of the soot number density. Performances of both diagnostics were compared by measuring in various operating conditions of swirl stratified premixed ethylene/air flames, the mean mobility diameter and particles’ number density by SMPS, then by recording the single-shot 2D distributions of gyration diameter and particles’ number density, under given assumptions on the diameter of primary spheres, at a repetition rate of 800 Hz by 2D-MALS. Because the SMPS system reports mobility diameters and 2D-MALS provides gyration diameters, a conversion procedure of mobility diameter into gyration diameter was developed to compare effectively the mean soot size and number density distributions recorded by both diagnostics. The good agreement between the results indicates that the dual-port dilution sampling probe coupled to the SMPS provides accurate measurements of mean particle size and number density distributions in turbulent flames, with the exception of high-gradient regions adjacent to the flame front and ambient air, where disturbances in flame properties and soot oxidation can be observed. Furthermore, 2D-MALS offers the additional advantage of recording the temporal and 2D spatial evolution of soot properties (size and number density) in turbulent flames.
{"title":"Comparison between ex-situ and in-situ soot particle size and number density distributions in swirl stratified turbulent premixed ethylene/air flames","authors":"A. Perrier , M. Bouvier , F. Collin-Bastiani , G. Cabot , J. Yon , F. Grisch","doi":"10.1016/j.combustflame.2025.114732","DOIUrl":"10.1016/j.combustflame.2025.114732","url":null,"abstract":"<div><div>Two measurement diagnostics were developed to study soot production in swirl stratified premixed ethylene/air flames. The first one measures the spatially-resolved mobility diameter and number density distributions of soot using a dual-port dilution sampling probe connected with a second dilution system and a Scanning Mobility Particle Sizer (SMPS). The second technique relies on high-speed 2D multi-angle light scattering diagnostic (2D-MALS) enabling the measurement of 2D spatially-resolved distributions of soot gyration diameter and number density. The gyration diameter is derived from the data processing of scattering images collected by CMOS cameras located at 45° and 135° around the flame while the data recorded at 90° with another CMOS camera combined to the knowledge of the gyration diameter, enables the determination of the soot number density. Performances of both diagnostics were compared by measuring in various operating conditions of swirl stratified premixed ethylene/air flames, the mean mobility diameter and particles’ number density by SMPS, then by recording the single-shot 2D distributions of gyration diameter and particles’ number density, under given assumptions on the diameter of primary spheres, at a repetition rate of 800 Hz by 2D-MALS. Because the SMPS system reports mobility diameters and 2D-MALS provides gyration diameters, a conversion procedure of mobility diameter into gyration diameter was developed to compare effectively the mean soot size and number density distributions recorded by both diagnostics. The good agreement between the results indicates that the dual-port dilution sampling probe coupled to the SMPS provides accurate measurements of mean particle size and number density distributions in turbulent flames, with the exception of high-gradient regions adjacent to the flame front and ambient air, where disturbances in flame properties and soot oxidation can be observed. Furthermore, 2D-MALS offers the additional advantage of recording the temporal and 2D spatial evolution of soot properties (size and number density) in turbulent flames.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114732"},"PeriodicalIF":6.2,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837896","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 : 2025-12-22DOI: 10.1016/j.combustflame.2025.114734
Yanggang Huang , Yong Kou , Ting Chang , Jiaqi Wei , Hongfei Liu , Lei Xiao , Wei Jiang , Gazi Hao
Aiming at the critical issues of uneven dispersion, inadequate interfacial contact, and significant mass/heat transfer resistance inherent in the mechanical mixing process for traditional solid propellant charging, this study proposes a novel strategy for constructing energetic micro-units through core-shell structural design, with the aim of achieving highly reactive and integrated composites tailored for practical solid propellant applications. Using etched aluminum (Al) powder as the core and ammonium perchlorate (AP) together with hexanitrohexaazaisowurtzitane (CL-20) as the composite shell, Al@AP/CL-20 micro-units with uniform coatings of AP/CL-20 and well-defined core-shell structures were successfully fabricated via solvent evaporation. The thermogravimetric-differential scanning calorimetry (TG-DSC) and combustion analyses indicate that Al@AP/CL-20 energetic micro-units exhibit significantly earlier decomposition peak temperature compared to pure AP, larger and more concentrated exothermic peaks, as well as stronger combustion intensity and higher flame temperature than the Al/AP/CL-20 composite in the physical mixture. The result confirms that the Al@AP/CL-20 composite structure can effectively enhance the synergistic effect between components, thereby improving the performance of the micro-units. Moreover, as the etching time increases, the porosity of the Al powder surface rises, leading to a further enhancement in the combustion performance of the Al@AP/CL-20 energetic micro-unit. In particular, when the Al powder etching time reached 5 h and the mass ratio of Al/AP/CL-20 was 1:2:2, the Al@AP/CL-20 micro-units demonstrated the best combustion performance, with the highest light intensity and a maximum flame temperature of 1094 °C — a 49 % improvement over the physically blended sample (PAAC-2) with the same mass ratio. This is attributed to the well-defined core-shell structure, which significantly shortens mass and heat transfer distances between components, and a better-matched oxygen balance that imparts the best combustion efficiency. The study affirms that the core-shell energetic micro-unit strategy effectively overcomes the limitations of conventional mixing methods and provides a pathway for formulating highly reactive solid propellant with enhanced energy release efficiency.
{"title":"High-reactivity energetic micro-units achieved by tightly packing AP and CL-20 onto etched porous Al powder","authors":"Yanggang Huang , Yong Kou , Ting Chang , Jiaqi Wei , Hongfei Liu , Lei Xiao , Wei Jiang , Gazi Hao","doi":"10.1016/j.combustflame.2025.114734","DOIUrl":"10.1016/j.combustflame.2025.114734","url":null,"abstract":"<div><div>Aiming at the critical issues of uneven dispersion, inadequate interfacial contact, and significant mass/heat transfer resistance inherent in the mechanical mixing process for traditional solid propellant charging, this study proposes a novel strategy for constructing energetic micro-units through core-shell structural design, with the aim of achieving highly reactive and integrated composites tailored for practical solid propellant applications. Using etched aluminum (Al) powder as the core and ammonium perchlorate (AP) together with hexanitrohexaazaisowurtzitane (CL-20) as the composite shell, Al@AP/CL-20 micro-units with uniform coatings of AP/CL-20 and well-defined core-shell structures were successfully fabricated via solvent evaporation. The thermogravimetric-differential scanning calorimetry (TG-DSC) and combustion analyses indicate that Al@AP/CL-20 energetic micro-units exhibit significantly earlier decomposition peak temperature compared to pure AP, larger and more concentrated exothermic peaks, as well as stronger combustion intensity and higher flame temperature than the Al/AP/CL-20 composite in the physical mixture. The result confirms that the Al@AP/CL-20 composite structure can effectively enhance the synergistic effect between components, thereby improving the performance of the micro-units. Moreover, as the etching time increases, the porosity of the Al powder surface rises, leading to a further enhancement in the combustion performance of the Al@AP/CL-20 energetic micro-unit. In particular, when the Al powder etching time reached 5 h and the mass ratio of Al/AP/CL-20 was 1:2:2, the Al@AP/CL-20 micro-units demonstrated the best combustion performance, with the highest light intensity and a maximum flame temperature of 1094 °C — a 49 % improvement over the physically blended sample (PAAC-2) with the same mass ratio. This is attributed to the well-defined core-shell structure, which significantly shortens mass and heat transfer distances between components, and a better-matched oxygen balance that imparts the best combustion efficiency. The study affirms that the core-shell energetic micro-unit strategy effectively overcomes the limitations of conventional mixing methods and provides a pathway for formulating highly reactive solid propellant with enhanced energy release efficiency.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114734"},"PeriodicalIF":6.2,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837897","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 : 2025-12-20DOI: 10.1016/j.combustflame.2025.114714
Amir H. Mahdipour , Fekadu Mosisa Wako , Cécile Devaud , W. Kendal Bushe
This study presents a numerical investigation of conditional source-term estimation (CSE) with direct integration of chemical kinetics, applied to one turbulent DME jet flame. This new CSE framework eliminates the need for pre-tabulated chemistry, therefore greater flexibility and accuracy are added when more complex fuels are considered. Two chemical mechanisms are considered: a detailed mechanism with 42 species and a tailored 21-species reduced mechanism. Both simulations are evaluated against a comprehensive experimental dataset including temperature and species concentration fields. Results show that simulations using both mechanisms yield nearly identical predictions for major scalars, with only minor differences observed in the conditional and Favre-averaged profiles. Discrepancies in peak temperature and species concentrations correlate with local deviations in predicted mixing statistics. While the detailed mechanism increases computational cost by nearly tenfold, the reduced mechanism retains accuracy at a fraction of the expense. These findings confirm that direct chemistry integration CSE, when combined with an optimized skeletal mechanism, offers an accurate and computationally efficient approach for modeling DME combustion in turbulent flows.
Novelty and significance statement
This study includes two novel components. One is focused on the assessment of a recent conditional source-term estimation (CSE) formulation with direct chemistry integration, in principle, capable of dealing with any chemical kinetics, without pre-tabulated chemistry. For the first time, this method is applied to the simulation of a turbulent flame burning DME with two different chemical mechanisms including over 20 species. A suitable stiff solver is added. A rigorous analysis is performed using experimental data. The second novelty is the derivation of a new reduced mechanism for DME, consisting of only 21 species, thoroughly validated over a range of combustion conditions for laminar flame speeds, species concentrations and ignition delays, and included in the CSE turbulent flame simulations, with excellent performance. This study, including direct chemistry integration CSE and optimized skeletal DME kinetics, provides significant contributions towards the advancement of accurate and efficient combustion simulation tools for industry-relevant conditions.
{"title":"Assessment of conditional source-term estimation (CSE) with direct chemistry integration including detailed and reduced kinetics for the simulation of a turbulent DME flame","authors":"Amir H. Mahdipour , Fekadu Mosisa Wako , Cécile Devaud , W. Kendal Bushe","doi":"10.1016/j.combustflame.2025.114714","DOIUrl":"10.1016/j.combustflame.2025.114714","url":null,"abstract":"<div><div>This study presents a numerical investigation of conditional source-term estimation (CSE) with direct integration of chemical kinetics, applied to one turbulent DME jet flame. This new CSE framework eliminates the need for pre-tabulated chemistry, therefore greater flexibility and accuracy are added when more complex fuels are considered. Two chemical mechanisms are considered: a detailed mechanism with 42 species and a tailored 21-species reduced mechanism. Both simulations are evaluated against a comprehensive experimental dataset including temperature and species concentration fields. Results show that simulations using both mechanisms yield nearly identical predictions for major scalars, with only minor differences observed in the conditional and Favre-averaged profiles. Discrepancies in peak temperature and species concentrations correlate with local deviations in predicted mixing statistics. While the detailed mechanism increases computational cost by nearly tenfold, the reduced mechanism retains accuracy at a fraction of the expense. These findings confirm that direct chemistry integration CSE, when combined with an optimized skeletal mechanism, offers an accurate and computationally efficient approach for modeling DME combustion in turbulent flows.</div><div><strong>Novelty and significance statement</strong></div><div>This study includes two novel components. One is focused on the assessment of a recent conditional source-term estimation (CSE) formulation with direct chemistry integration, in principle, capable of dealing with any chemical kinetics, without pre-tabulated chemistry. For the first time, this method is applied to the simulation of a turbulent flame burning DME with two different chemical mechanisms including over 20 species. A suitable stiff solver is added. A rigorous analysis is performed using experimental data. The second novelty is the derivation of a new reduced mechanism for DME, consisting of only 21 species, thoroughly validated over a range of combustion conditions for laminar flame speeds, species concentrations and ignition delays, and included in the CSE turbulent flame simulations, with excellent performance. This study, including direct chemistry integration CSE and optimized skeletal DME kinetics, provides significant contributions towards the advancement of accurate and efficient combustion simulation tools for industry-relevant conditions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114714"},"PeriodicalIF":6.2,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789261","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}
The experiments on the pyrolysis of methane, ethane, ethylene, diethyl ether, acetylene, and benzene mixtures were conducted in a shock tube behind reflected shock waves. The spectra and time-resolved laser-induced fluorescence of a chemically reacting mixture were measured upon excitation a 266 nm picosecond laser pulse with varying temperature and reaction time. The measurements were carried out under conditions preceding the appearance of a condensed phase actively absorbing radiation in the UV and visible spectrum. The time resolution made it possible to distinguish the LIF from gas molecules and incipient soot particles. The lifetime of the LIF signals found was 2–9 ns, which is much longer than expected for PAH molecules at high pyrolysis temperature, but much shorter and spectrally different from the laser-induced incandescence of soot particles. Obtained results showed that fluorescence was caused by condensed aromatic rings in the incipient soot particles. Comparison of in situ LIF measurements with the results of modeling shows that the kinetic path of PAH formation and soot nucleation depends on the fuel composition and temperature conditions of pyrolysis.
{"title":"Experimental study of PAH and incipient soot particles formation in hydrocarbons pyrolysis behind shock waves","authors":"Alexander Eremin , Mayya Korshunova , Ekaterina Mikheyeva , Vasily Zolotarenko","doi":"10.1016/j.combustflame.2025.114719","DOIUrl":"10.1016/j.combustflame.2025.114719","url":null,"abstract":"<div><div>The experiments on the pyrolysis of methane, ethane, ethylene, diethyl ether, acetylene, and benzene mixtures were conducted in a shock tube behind reflected shock waves. The spectra and time-resolved laser-induced fluorescence of a chemically reacting mixture were measured upon excitation a 266 nm picosecond laser pulse with varying temperature and reaction time. The measurements were carried out under conditions preceding the appearance of a condensed phase actively absorbing radiation in the UV and visible spectrum. The time resolution made it possible to distinguish the LIF from gas molecules and incipient soot particles. The lifetime of the LIF signals found was 2–9 ns, which is much longer than expected for PAH molecules at high pyrolysis temperature, but much shorter and spectrally different from the laser-induced incandescence of soot particles. Obtained results showed that fluorescence was caused by condensed aromatic rings in the incipient soot particles. Comparison of in situ LIF measurements with the results of modeling shows that the kinetic path of PAH formation and soot nucleation depends on the fuel composition and temperature conditions of pyrolysis.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"285 ","pages":"Article 114719"},"PeriodicalIF":6.2,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145789265","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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