The diffusion jet flame is a high-speed flow gas ignited at the outlet, a common combustion behavior in fundamental science of combustion, including applications in the industrial exhaust gas treatment torches and engines. This paper investigates experimentally the downward jet flame characteristics from the laminar to the turbulent, which has not been reported comprehensively yet. The overall jet flame length, jet flame downward distance, temperature and flame radiation heat flux profile are studied, as important characteristic parameters determining the flame boundary in vertical direction, the farthest distance that the flame could travel, as well as the thermal effect on the surrounding, respectively. Experiments were conducted to explore the global evolutionary process of downward jet flame with increasing initial fuel jet velocity for various circle nozzle diameters (3 mm, 4 mm and 5 mm), fuel types (pure fuel and blended fuel), and Reynolds numbers widely ranging from 65 to 97,209 involving laminar, transition and turbulent combustion regimes before reaching the flame blowout limit. The downward jet flame length and the downward distance show a non-monotonic evolution with the Reynolds number or heat release rate, i.e., first increase at the laminar combustion regime, change a little at the transition regime, and finally increase significantly after reaching fully turbulent combustion regime. The vertical temperature profile along the centerline of the downward jet flame is associated with the downward jet flame morphologic characteristic parameters, it decreases significantly with the non-dimensional height at the intermittent region compared to the upward jet flame. The flame radiation fraction of the downward jet flame based on the measured flame radiation heat fluxes first changes a little and then decreases with the Reynolds number as a power function. The flame length could be well correlated by the non-dimensional heat release rate, the flame Froude number as well as the non-dimensional volumetric flow rate based on the air entrainment dynamics. The jet flame downward distance could be well correlated by the momentum-buoyancy length scale at the turbulent combustion regime. A non-dimensional global model involving the momentum-buoyancy length, flow rate length scale and the stoichiometric air-fuel ratio is developed to describe the global jet flame downward distance evolution. This work provides essential and fundamental knowledge about the dynamic evolution of downward jet flame in designing rocket propulsion/combustor structures, combustion and evolution characteristics.
{"title":"A global evolution of the downward jet flame behavior: From the laminar to the turbulent","authors":"Xiepeng Sun, Jiang Lv, Yu Han, Xiaolei Zhang, Fei Tang, Longhua Hu","doi":"10.1016/j.combustflame.2024.113906","DOIUrl":"10.1016/j.combustflame.2024.113906","url":null,"abstract":"<div><div>The diffusion jet flame is a high-speed flow gas ignited at the outlet, a common combustion behavior in fundamental science of combustion, including applications in the industrial exhaust gas treatment torches and engines. This paper investigates experimentally the downward jet flame characteristics from the laminar to the turbulent, which has not been reported comprehensively yet. The overall jet flame length, jet flame downward distance, temperature and flame radiation heat flux profile are studied, as important characteristic parameters determining the flame boundary in vertical direction, the farthest distance that the flame could travel, as well as the thermal effect on the surrounding, respectively. Experiments were conducted to explore the global evolutionary process of downward jet flame with increasing initial fuel jet velocity for various circle nozzle diameters (3 mm, 4 mm and 5 mm), fuel types (pure fuel and blended fuel), and Reynolds numbers widely ranging from 65 to 97,209 involving laminar, transition and turbulent combustion regimes before reaching the flame blowout limit. The downward jet flame length and the downward distance show a non-monotonic evolution with the Reynolds number or heat release rate, <em>i.e.</em>, first increase at the laminar combustion regime, change a little at the transition regime, and finally increase significantly after reaching fully turbulent combustion regime. The vertical temperature profile along the centerline of the downward jet flame is associated with the downward jet flame morphologic characteristic parameters, it decreases significantly with the non-dimensional height at the intermittent region compared to the upward jet flame. The flame radiation fraction of the downward jet flame based on the measured flame radiation heat fluxes first changes a little and then decreases with the Reynolds number as a power function. The flame length could be well correlated by the non-dimensional heat release rate, the flame Froude number as well as the non-dimensional volumetric flow rate based on the air entrainment dynamics. The jet flame downward distance could be well correlated by the momentum-buoyancy length scale at the turbulent combustion regime. A non-dimensional global model involving the momentum-buoyancy length, flow rate length scale and the stoichiometric air-fuel ratio is developed to describe the global jet flame downward distance evolution. This work provides essential and fundamental knowledge about the dynamic evolution of downward jet flame in designing rocket propulsion/combustor structures, combustion and evolution characteristics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113906"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143103024","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 : 2025-02-01DOI: 10.1016/j.combustflame.2024.113889
Chengcheng Shan , Haogang Wei , Jiefeng Wan , Zijian Zhang , Philip De Goey , Lei Zhou
This study utilizes a simplified one-dimensional discrete model to analyze the characteristic parameters involved in the flame propagation of iron particles. It focuses on the influence of dispersive "micro flames" within these flames on propagation dynamics, investigating stable and unstable scenarios. The model adopts the form of particle suspension delineating alternant reaction intervals and inert intervals. The spatial dispersion rate (Γ) which describes the spatial extent of the "micro flames" is introduced, with Γ = 1 for the continuum model and Γ > 1 for the discrete model. Theoretical equations, combining kinetic and diffusion equations, are solved with the finite difference method. The solution is evaluated preliminarily to distinguish numerical instability and thermodynamic instability. Additionally, in the preset time and space range, conditions for different equivalence ratios, particle radius and spatial dispersion rates are analyzed emphatically, with a comparison of typical simulation results and experimental data. As shown in the numerical simulation, the flame maintains stable propagation when ϕ≥0.7. The flame front, where the particle temperature rises above the gas temperature, extends backward with the increase of particle radius. The increase of Γ tends to extend the flame front of the fuel-lean flame and constringe that of the fuel-rich flame. Thermodynamic instability occurs in fuel-lean suspension with its manifestation preliminarily classified to distinct fluctuation, faint fluctuation and the final cessation. The increase of Γ also extends the flame propagation time under the dominance of thermodynamic instability, indicating different temperature structure evolution from the continuum model.
{"title":"The influence of spatial dispersion on the steady-state characteristics and thermodynamic instability fluctuations of one-dimensional iron particle flames","authors":"Chengcheng Shan , Haogang Wei , Jiefeng Wan , Zijian Zhang , Philip De Goey , Lei Zhou","doi":"10.1016/j.combustflame.2024.113889","DOIUrl":"10.1016/j.combustflame.2024.113889","url":null,"abstract":"<div><div>This study utilizes a simplified one-dimensional discrete model to analyze the characteristic parameters involved in the flame propagation of iron particles. It focuses on the influence of dispersive \"micro flames\" within these flames on propagation dynamics, investigating stable and unstable scenarios. The model adopts the form of particle suspension delineating alternant reaction intervals and inert intervals. The spatial dispersion rate (Γ) which describes the spatial extent of the \"micro flames\" is introduced, with Γ = 1 for the continuum model and Γ > 1 for the discrete model. Theoretical equations, combining kinetic and diffusion equations, are solved with the finite difference method. The solution is evaluated preliminarily to distinguish numerical instability and thermodynamic instability. Additionally, in the preset time and space range, conditions for different equivalence ratios, particle radius and spatial dispersion rates are analyzed emphatically, with a comparison of typical simulation results and experimental data. As shown in the numerical simulation, the flame maintains stable propagation when <em>ϕ</em>≥0.7. The flame front, where the particle temperature rises above the gas temperature, extends backward with the increase of particle radius. The increase of Γ tends to extend the flame front of the fuel-lean flame and constringe that of the fuel-rich flame. Thermodynamic instability occurs in fuel-lean suspension with its manifestation preliminarily classified to distinct fluctuation, faint fluctuation and the final cessation. The increase of Γ also extends the flame propagation time under the dominance of thermodynamic instability, indicating different temperature structure evolution from the continuum model.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113889"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143102426","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 : 2025-02-01DOI: 10.1016/j.combustflame.2024.113876
Mark Kelly , G. Bourque , M. Hase , S. Dooley
A novel data-intensive methodology to produce a high fidelity, extremely-reduced “compact” kinetic model for a high boiling point complex liquid fuel is proposed and demonstrated. A five-component surrogate definition for the liquid fuel is developed that displays a high accuracy to the experimentally-derived combustion property targets. The calculations of the Lawrence Livermore National Lab diesel surrogate model containing 6476 species are used to serve as gas turbine industry-defined performance targets for this surrogate.
Acknowledging that the retention of a multi-component surrogate definition is a limitation on the size of the model, the surrogate fuel is consolidated into a single virtual molecule. Subsequently, the reaction mechanism is simplified by replacing high carbon number chemistry with a virtual scheme. This scheme links the virtual fuel molecule to low carbon number chemistry using four virtual species and forty-four virtual reactions, resulting in a reduction to 429 species in the model.
The Machine Learned Optimisation of Chemical Kinetics (MLOCK) algorithm is adapted to “compact” this model. Compaction is the over-reduction and optimisation of a kinetic model. Path flux analysis generates an overly-reduced model with 31 species that has a poor replication of the detailed model calculations. To address this, virtual reaction rate constants of important virtual reactions are numerically optimized to detailed model high temperature calculations. MLOCK systematically perturbs all three virtual Arrhenius reaction rate constant parameters to generate and evaluate numerous model candidates, refining the search space based on prior results, finding better models. A low temperature virtual reaction network, comprising one new virtual species and three new virtual reactions, is appended to the high temperature compact model. MLOCK is employed to reoptimize the model to calculations at low and intermediate temperatures.
The application of this methodology results in a 32-species compact model in ChemKin/Cantera format, which retains fidelities in the range of 76 to 92 % across a comprehensive range of gas-turbine relevant performance calculations for low, intermediate and high temperatures.
{"title":"Machine learned compact kinetic model for liquid fuel combustion","authors":"Mark Kelly , G. Bourque , M. Hase , S. Dooley","doi":"10.1016/j.combustflame.2024.113876","DOIUrl":"10.1016/j.combustflame.2024.113876","url":null,"abstract":"<div><div>A novel data-intensive methodology to produce a high fidelity, extremely-reduced “compact” kinetic model for a high boiling point complex liquid fuel is proposed and demonstrated. A five-component surrogate definition for the liquid fuel is developed that displays a high accuracy to the experimentally-derived combustion property targets. The calculations of the Lawrence Livermore National Lab diesel surrogate model containing 6476 species are used to serve as gas turbine industry-defined performance targets for this surrogate.</div><div>Acknowledging that the retention of a multi-component surrogate definition is a limitation on the size of the model, the surrogate fuel is consolidated into a single virtual molecule. Subsequently, the reaction mechanism is simplified by replacing high carbon number chemistry with a virtual scheme. This scheme links the virtual fuel molecule to low carbon number chemistry using four virtual species and forty-four virtual reactions, resulting in a reduction to 429 species in the model.</div><div>The Machine Learned Optimisation of Chemical Kinetics (MLOCK) algorithm is adapted to “compact” this model. Compaction is the over-reduction and optimisation of a kinetic model. Path flux analysis generates an overly-reduced model with 31 species that has a poor replication of the detailed model calculations. To address this, virtual reaction rate constants of important virtual reactions are numerically optimized to detailed model high temperature calculations. MLOCK systematically perturbs all three virtual Arrhenius reaction rate constant parameters to generate and evaluate numerous model candidates, refining the search space based on prior results, finding better models. A low temperature virtual reaction network, comprising one new virtual species and three new virtual reactions, is appended to the high temperature compact model. MLOCK is employed to reoptimize the model to calculations at low and intermediate temperatures.</div><div>The application of this methodology results in a 32-species compact model in ChemKin/Cantera format, which retains fidelities in the range of 76 to 92 % across a comprehensive range of gas-turbine relevant performance calculations for low, intermediate and high temperatures.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113876"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143102427","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 : 2025-02-01DOI: 10.1016/j.combustflame.2024.113901
Jiasen Wei, Alessandro Bottaro, Jan O. Pralits
Clean combustion, particularly premixed hydrogen combustion aimed at reducing NOx emissions, is prone to thermoacoustic instabilities that can cause structural vibrations and equipment failures. This study focuses on a low-order model for a thermoacoustic prototype, a simple quasi-one-dimensional combustor comprising a plenum, premixing duct, and combustion chamber. Resonant modes of the combustor are identified by solving a nonlinear eigenvalue problem. Using an adjoint-based sensitivity analysis, the impact of uncertainties in base flow parameters on resonant frequencies and linear growth rates is assessed. The results obtained highlight the significant influence of variations in cold gas density within the plenum and premixing duct on the linear growth rates, potentially explaining discrepancies with literature data. Additionally, structural sensitivities in both the base and the perturbation flow are examined to evaluate the effects of a generic feedback mechanism on the eigenvalues. Structural sensitivities at the base-flow level are evaluated as a function of the flame position, identifying effective stabilizing mechanisms such as heat addition and mass flow rate reduction at duct intersections. The most stabilizing feedback mechanism is identified as mass fluctuations proportional to pressure perturbation at the end of the plenum, an effect achievable with Helmholtz resonators. Adjoint analyses permit uncertainty quantification of base-state parameters and gradient information for optimization strategies aimed at mitigating thermoacoustic instabilities through efficient and low-cost calculations.
Novelty and significance statement
The novelty of this research lies in its development of a comprehensive adjoint analysis framework for three types of sensitivity analyses within a thermoacoustic premixed combustor model. This paper uses base-state sensitivity to quantify the significant effect of base flow uncertainties, such as cold gas properties in the premixer, on the unstable resonant mode growth rates. In addition to structural perturbation sensitivity analysis, it uniquely applies structural sensitivity to base flow modifications, uncovering effective steady control mechanisms like mass suction and heating. The findings identify efficient approaches to mitigate thermoacoustic instabilities in premixed combustion systems and broaden the scope of potential control strategies.
{"title":"Adjoint-based mean-flow uncertainty and feedback-forcing analyses of a thermoacoustic model system","authors":"Jiasen Wei, Alessandro Bottaro, Jan O. Pralits","doi":"10.1016/j.combustflame.2024.113901","DOIUrl":"10.1016/j.combustflame.2024.113901","url":null,"abstract":"<div><div>Clean combustion, particularly premixed hydrogen combustion aimed at reducing NOx emissions, is prone to thermoacoustic instabilities that can cause structural vibrations and equipment failures. This study focuses on a low-order model for a thermoacoustic prototype, a simple quasi-one-dimensional combustor comprising a plenum, premixing duct, and combustion chamber. Resonant modes of the combustor are identified by solving a nonlinear eigenvalue problem. Using an adjoint-based sensitivity analysis, the impact of uncertainties in base flow parameters on resonant frequencies and linear growth rates is assessed. The results obtained highlight the significant influence of variations in cold gas density within the plenum and premixing duct on the linear growth rates, potentially explaining discrepancies with literature data. Additionally, structural sensitivities in both the base and the perturbation flow are examined to evaluate the effects of a generic feedback mechanism on the eigenvalues. Structural sensitivities at the base-flow level are evaluated as a function of the flame position, identifying effective stabilizing mechanisms such as heat addition and mass flow rate reduction at duct intersections. The most stabilizing feedback mechanism is identified as mass fluctuations proportional to pressure perturbation at the end of the plenum, an effect achievable with Helmholtz resonators. Adjoint analyses permit uncertainty quantification of base-state parameters and gradient information for optimization strategies aimed at mitigating thermoacoustic instabilities through efficient and low-cost calculations.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this research lies in its development of a comprehensive adjoint analysis framework for three types of sensitivity analyses within a thermoacoustic premixed combustor model. This paper uses base-state sensitivity to quantify the significant effect of base flow uncertainties, such as cold gas properties in the premixer, on the unstable resonant mode growth rates. In addition to structural perturbation sensitivity analysis, it uniquely applies structural sensitivity to base flow modifications, uncovering effective steady control mechanisms like mass suction and heating. The findings identify efficient approaches to mitigate thermoacoustic instabilities in premixed combustion systems and broaden the scope of potential control strategies.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113901"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143102611","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/j.combustflame.2024.113905
Siqi Cai, Wenquan Yang, Jianlong Wan
The lean premixed combustion LPC can achieve clean combustion of natural gas and reduce emissions of harmful gases. However, this combustion mode is usually difficult to sustain. To improve the anchoring performance of lean premixed flame LPF, the high-temperature bluff-body HTB with 900 K is employed in this work. Unexpectedly, a stable residual flame of the methane-air ultra-lean premixed mixture is found experimentally and computationally near the blow-off limit. A deeper insight into its anchoring mechanism is necessary to further promote the LPF stability. At first, the residual flame structure is revealed quantitatively, and it is found that the diffusion dominates the reactant flux which arrives at the residual flame rather than the convection. Then, the anchoring mechanism of the ultra-lean residual flame is revealed in terms of the effects of the preferential transport, stretch, and conjugate heat exchange. The recirculation zone right behind the HTB provides a good anchoring location for the residual flame base. The small value of the stretch rate contributes to the residence of the residual flame tip. The enhanced preferential transport effect by the HTB contributes to maintaining the residual flame by generating a relatively fuel-richer region compared with the incoming fresh mixture around it. In addition, the enhanced pre-heated fresh reactants by the HTB provide good ignition and combustion conditions around the residual flame, which contributes to its residence. To the best of our knowledge, such a detailed visualization of the main factors responsible for anchoring the residual flame stabilized by the HTB has not been reported yet. This study provides a new scheme to improve LPC performance. This study expands our understanding of the LPF dynamics stabilized by the bluff-body.
{"title":"Insight into the ultra-lean residual flame stabilized on a high-temperature bluff-body","authors":"Siqi Cai, Wenquan Yang, Jianlong Wan","doi":"10.1016/j.combustflame.2024.113905","DOIUrl":"10.1016/j.combustflame.2024.113905","url":null,"abstract":"<div><div>The lean premixed combustion LPC can achieve clean combustion of natural gas and reduce emissions of harmful gases. However, this combustion mode is usually difficult to sustain. To improve the anchoring performance of lean premixed flame LPF, the high-temperature bluff-body HTB with 900 K is employed in this work. Unexpectedly, a stable residual flame of the methane-air ultra-lean premixed mixture is found experimentally and computationally near the blow-off limit. A deeper insight into its anchoring mechanism is necessary to further promote the LPF stability. At first, the residual flame structure is revealed quantitatively, and it is found that the diffusion dominates the reactant flux which arrives at the residual flame rather than the convection. Then, the anchoring mechanism of the ultra-lean residual flame is revealed in terms of the effects of the preferential transport, stretch, and conjugate heat exchange. The recirculation zone right behind the HTB provides a good anchoring location for the residual flame base. The small value of the stretch rate contributes to the residence of the residual flame tip. The enhanced preferential transport effect by the HTB contributes to maintaining the residual flame by generating a relatively fuel-richer region compared with the incoming fresh mixture around it. In addition, the enhanced pre-heated fresh reactants by the HTB provide good ignition and combustion conditions around the residual flame, which contributes to its residence. To the best of our knowledge, such a detailed visualization of the main factors responsible for anchoring the residual flame stabilized by the HTB has not been reported yet. This study provides a new scheme to improve LPC performance. This study expands our understanding of the LPF dynamics stabilized by the bluff-body.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113905"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143102614","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 : 2025-02-01DOI: 10.1016/j.combustflame.2024.113902
Qianlong Wang , Siming Xiong , Zilin Deng , Guillaume legros , Haifeng Liu , Zibang Zhang
This paper initially utilizes a Fourier single-pixel imaging (FSI) optical method to measure the soot volume fraction () field in flames, which is based on the theorems of Fourier transform and Beer-Lambert law. Unlike the conventional two-dimensional sensor used for imaging, a spatially unresolvable detector, such as a photomultiplier tube (PMT), is utilized to reconstruct flame images. The current prototype optical measurement system is detailed and further validated by a proof-of-concept experiment on a benchmark laminar diffusion flame. It is found that the sample rate and the loop number significantly affect the quality of flame image reconstruction, and it is recommended to use thresholds of 25 % and 20 for these two parameters. In addition, the maximum standard deviation of 0.025, as calculated through error propagation in five repeated experiments, demonstrates the robustness of the FSI technique. Nevertheless, the present optical layout could be further optimized in terms of improving the quality of reconstructed images, shortening the sampling duration, and replacing the near-infrared light source to achieve more precise distributions and reduce uncertainties. Moreover, the potential for single-shot resolution improvements deserves further investigation of temporal flame measurements in the near future.
{"title":"A novel single-pixel imaging method for two-dimensional soot volume fraction measurements in axisymmetric flames","authors":"Qianlong Wang , Siming Xiong , Zilin Deng , Guillaume legros , Haifeng Liu , Zibang Zhang","doi":"10.1016/j.combustflame.2024.113902","DOIUrl":"10.1016/j.combustflame.2024.113902","url":null,"abstract":"<div><div>This paper initially utilizes a Fourier single-pixel imaging (FSI) optical method to measure the soot volume fraction (<span><math><msub><mi>f</mi><mi>v</mi></msub></math></span>) field in flames, which is based on the theorems of Fourier transform and Beer-Lambert law. Unlike the conventional two-dimensional sensor used for imaging, a spatially unresolvable detector, such as a photomultiplier tube (PMT), is utilized to reconstruct flame images. The current prototype optical measurement system is detailed and further validated by a proof-of-concept experiment on a benchmark laminar diffusion flame. It is found that the sample rate and the loop number significantly affect the quality of flame image reconstruction, and it is recommended to use thresholds of 25 % and 20 for these two parameters. In addition, the maximum standard deviation <span><math><msub><mi>f</mi><mi>v</mi></msub></math></span> of 0.025, as calculated through error propagation in five repeated experiments, demonstrates the robustness of the FSI technique. Nevertheless, the present optical layout could be further optimized in terms of improving the quality of reconstructed images, shortening the sampling duration, and replacing the near-infrared light source to achieve more precise <span><math><msub><mi>f</mi><mi>v</mi></msub></math></span> distributions and reduce uncertainties. Moreover, the potential for single-shot resolution improvements deserves further investigation of temporal flame measurements in the near future.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113902"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143102615","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}
Measuring the ignition temperature of micron-sized iron particles can verify the ignition mechanism and aid in designing efficient iron powder combustion devices. This study captured the diameter, morphology and ignition status of iron particles with diameter range from 17 to 45 μm entering a stable high-temperature environment by high-speed cameras. The ignition frequency of iron particles at different ambient temperatures and oxygen concentration were recorded. Defining the ignition temperature as the ambient temperature at which the ignition frequency of iron particles exceeds 0.9, it was found that the ignition temperature of iron particles heated from room temperature and closer to a spherical shape is approximately 1140 K, while the non-spherical iron particles is around 1120 K. The ignition temperature is independent of particle diameter and ambient oxygen concentration. The theoretical method for estimating ignition temperature (X.C. Mi, A. Fujinawa, J.M. Bergthorson, 2022) aligns well with the experimental results. Theoretical analysis indicates that the oxidation mechanism at low temperatures (below 800 K) does not affect the ignition temperature, preheating does not effectively reduce the ignition temperature, and iron particles with high specific surface areas, such as sponge iron powder, exhibit significantly lower ignition temperatures.
Novelty and significance statement
This study, for the first time integrates experimental investigation with theoretical models to systematically examine the ignition temperature of individual micron-sized iron particles under diverse conditions. The experimental approach allows precise in-situ characterization of particle diameter, particle morphology in different ambient oxygen concentration, providing insights into their respective effects on ignition temperature. Through comprehensive theoretical discussion and experimental validation, the ignition mechanism of iron particles is verified, offering crucial parameters for the design and optimization of efficient iron particle combustion systems.
{"title":"A detailed experimental and numerical study on the ignition temperature of single micron-sized spherical iron particles","authors":"Liulin Cen , Zekang Lyu , Yong Qian , Wenjun Zhong , Xingcai Lu","doi":"10.1016/j.combustflame.2024.113909","DOIUrl":"10.1016/j.combustflame.2024.113909","url":null,"abstract":"<div><div>Measuring the ignition temperature of micron-sized iron particles can verify the ignition mechanism and aid in designing efficient iron powder combustion devices. This study captured the diameter, morphology and ignition status of iron particles with diameter range from 17 to 45 μm entering a stable high-temperature environment by high-speed cameras. The ignition frequency of iron particles at different ambient temperatures and oxygen concentration were recorded. Defining the ignition temperature as the ambient temperature at which the ignition frequency of iron particles exceeds 0.9, it was found that the ignition temperature of iron particles heated from room temperature and closer to a spherical shape is approximately 1140 K, while the non-spherical iron particles is around 1120 K. The ignition temperature is independent of particle diameter and ambient oxygen concentration. The theoretical method for estimating ignition temperature (X.C. Mi, A. Fujinawa, J.M. Bergthorson, 2022) aligns well with the experimental results. Theoretical analysis indicates that the oxidation mechanism at low temperatures (below 800 K) does not affect the ignition temperature, preheating does not effectively reduce the ignition temperature, and iron particles with high specific surface areas, such as sponge iron powder, exhibit significantly lower ignition temperatures.</div></div><div><h3>Novelty and significance statement</h3><div>This study, for the first time integrates experimental investigation with theoretical models to systematically examine the ignition temperature of individual micron-sized iron particles under diverse conditions. The experimental approach allows precise in-situ characterization of particle diameter, particle morphology in different ambient oxygen concentration, providing insights into their respective effects on ignition temperature. Through comprehensive theoretical discussion and experimental validation, the ignition mechanism of iron particles is verified, offering crucial parameters for the design and optimization of efficient iron particle combustion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113909"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143102616","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 : 2025-02-01DOI: 10.1016/j.combustflame.2024.113887
Mingrui Wang , Ruoyue Tang , Xinrui Ren , Hongqing Wu , Yuxin Dong , Ting Zhang , Song Cheng
Significant efforts have been committed to understanding the fundamental combustion chemistry of ammonia at high-pressure and low-temperature conditions with or without blending with other fuels, as these are promising to improve ammonia combustion performance and reduce NOx emission. A commonly used fundamental reactor is the jet-stirred reactor (JSR). However, modeling of high-pressure JSR experiments has been conducted assuming complete ideal gas behaviors, which might lead to misinterpreted or completely wrong results. Therefore, this study proposes, for the first time, a novel framework coupling high-order Virial equation of state, ab initio multi-body intermolecular potential, and real-fluid governing equations. The framework is further applied to investigate NH3 oxidation under supercritical conditions in jet-stirred reactors, where the real-fluid effects on NH3 oxidation characteristics are quantified and compared, via simulated species profiles and relative changes in simulated mole fractions at various temperatures, pressures, diluents, dilution ratios, equivalence ratios, and with or without blending with H2 and CH4. Strong promoting effects on NH3 oxidation from real-fluid effects are revealed, with significant shifts in simulated species profiles observed for both fuel, intermediates, and product species. Sensitivity analyses are also conducted based on the new framework, with diverse influences of real-fluid effects on the contributions of the most sensitive pathways highlighted. It is found that, without considering real-fluid behaviors, the error introduced in simulated species mole fractions can reach ±85 % at the conditions investigated in this study. Propagation of such levels of error to chemical kinetic mechanisms can disqualify them for any meaningful modeling work. These errors can now be excluded using the framework developed in this study.
{"title":"Investigation of real-fluid effects on NH3 oxidation and blending characteristics at supercritical conditions via high-order Virial equation of state coupled with ab initio intermolecular potentials","authors":"Mingrui Wang , Ruoyue Tang , Xinrui Ren , Hongqing Wu , Yuxin Dong , Ting Zhang , Song Cheng","doi":"10.1016/j.combustflame.2024.113887","DOIUrl":"10.1016/j.combustflame.2024.113887","url":null,"abstract":"<div><div>Significant efforts have been committed to understanding the fundamental combustion chemistry of ammonia at high-pressure and low-temperature conditions with or without blending with other fuels, as these are promising to improve ammonia combustion performance and reduce NOx emission. A commonly used fundamental reactor is the jet-stirred reactor (JSR). However, modeling of high-pressure JSR experiments has been conducted assuming complete ideal gas behaviors, which might lead to misinterpreted or completely wrong results. Therefore, this study proposes, for the first time, a novel framework coupling high-order Virial equation of state, <em>ab initio</em> multi-body intermolecular potential, and real-fluid governing equations. The framework is further applied to investigate NH<sub>3</sub> oxidation under supercritical conditions in jet-stirred reactors, where the real-fluid effects on NH<sub>3</sub> oxidation characteristics are quantified and compared, via simulated species profiles and relative changes in simulated mole fractions at various temperatures, pressures, diluents, dilution ratios, equivalence ratios, and with or without blending with H<sub>2</sub> and CH<sub>4</sub>. Strong promoting effects on NH<sub>3</sub> oxidation from real-fluid effects are revealed, with significant shifts in simulated species profiles observed for both fuel, intermediates, and product species. Sensitivity analyses are also conducted based on the new framework, with diverse influences of real-fluid effects on the contributions of the most sensitive pathways highlighted. It is found that, without considering real-fluid behaviors, the error introduced in simulated species mole fractions can reach ±85 % at the conditions investigated in this study. Propagation of such levels of error to chemical kinetic mechanisms can disqualify them for any meaningful modeling work. These errors can now be excluded using the framework developed in this study.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113887"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143103019","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 : 2025-02-01DOI: 10.1016/j.combustflame.2024.113894
Shangpeng Li, Huangwei Zhang
<div><div>Liquid sprays consisting of interacting droplets with diverse compositions are prevalent in engineering applications and everyday life. Although extensive research has been conducted on multi-droplet interactions, most studies concentrate on scenarios involving identical compositions. In this study, we theoretically investigate the quasi-steady evaporation of compositionally distinct droplet pairs using the mass-flux potential model and a bispherical-coordinate approach. Two droplet temperature models under contrasting conditions – no-mixing and rapid-mixing – are examined. Based on these models, the realistic equilibrium temperatures of droplet pairs, accounting for evaporative cooling effects, are clarified. Asymptotic analysis, conducted for relatively large inter-droplet spacings, yields theoretical solutions for the distributions of potential function, temperature, and various components in the gas phase. The equilibrium droplet temperatures, local and cumulative evaporation rates, and interaction coefficients between droplets are determined. Findings reveal that in dual-droplet systems with varying compositions, the surface evaporation potential, temperature, and vapor mass fraction become non-uniform. This non-uniformity, in contrast to the uniform distribution observed in existing studies on identical compositions, intensifies with greater differences in droplet volatilities or reduced inter-droplet spacing. Furthermore, the equilibrium droplet temperatures and evaporation rates decrease due to the shielding effect from adjacent droplets, with smaller or less volatile droplets experiencing more significant impacts. The theoretical results align well with numerical simulations across a wide range of parameters, including liquid compositions, droplet sizes, and inter-droplet spacings. This study enhances the understanding of realistic evaporation dynamics in multi-droplet systems, especially those with diverse compositions. Additionally, while the current analysis focuses on pure vaporization, the flame-sheet assumption provides a theoretical basis for potentially extending this work to include combustion scenarios.</div><div>Novelty and Significance Statement: This study contributes novel theoretical insights into the quasi-steady evaporation processes of compositionally distinct droplet pairs, a subject that has received less attention compared to the extensive research on identical compositions. It unveils detailed asymptotic solutions that expose the non-uniform distributions of temperatures, vapor concentrations, and evaporation rates on droplet surfaces, presenting a significant contrast to the uniformity observed in prior studies. These findings deepen our understanding of evaporation dynamics in multi-droplet systems with varying compositions, which are prevalent in practical settings. The insights obtained from this study could influence the design and operational strategies of technologies in fields such as spray evapora
{"title":"Theoretical analysis of quasi-steady evaporation in compositionally distinct droplet pairs","authors":"Shangpeng Li, Huangwei Zhang","doi":"10.1016/j.combustflame.2024.113894","DOIUrl":"10.1016/j.combustflame.2024.113894","url":null,"abstract":"<div><div>Liquid sprays consisting of interacting droplets with diverse compositions are prevalent in engineering applications and everyday life. Although extensive research has been conducted on multi-droplet interactions, most studies concentrate on scenarios involving identical compositions. In this study, we theoretically investigate the quasi-steady evaporation of compositionally distinct droplet pairs using the mass-flux potential model and a bispherical-coordinate approach. Two droplet temperature models under contrasting conditions – no-mixing and rapid-mixing – are examined. Based on these models, the realistic equilibrium temperatures of droplet pairs, accounting for evaporative cooling effects, are clarified. Asymptotic analysis, conducted for relatively large inter-droplet spacings, yields theoretical solutions for the distributions of potential function, temperature, and various components in the gas phase. The equilibrium droplet temperatures, local and cumulative evaporation rates, and interaction coefficients between droplets are determined. Findings reveal that in dual-droplet systems with varying compositions, the surface evaporation potential, temperature, and vapor mass fraction become non-uniform. This non-uniformity, in contrast to the uniform distribution observed in existing studies on identical compositions, intensifies with greater differences in droplet volatilities or reduced inter-droplet spacing. Furthermore, the equilibrium droplet temperatures and evaporation rates decrease due to the shielding effect from adjacent droplets, with smaller or less volatile droplets experiencing more significant impacts. The theoretical results align well with numerical simulations across a wide range of parameters, including liquid compositions, droplet sizes, and inter-droplet spacings. This study enhances the understanding of realistic evaporation dynamics in multi-droplet systems, especially those with diverse compositions. Additionally, while the current analysis focuses on pure vaporization, the flame-sheet assumption provides a theoretical basis for potentially extending this work to include combustion scenarios.</div><div>Novelty and Significance Statement: This study contributes novel theoretical insights into the quasi-steady evaporation processes of compositionally distinct droplet pairs, a subject that has received less attention compared to the extensive research on identical compositions. It unveils detailed asymptotic solutions that expose the non-uniform distributions of temperatures, vapor concentrations, and evaporation rates on droplet surfaces, presenting a significant contrast to the uniformity observed in prior studies. These findings deepen our understanding of evaporation dynamics in multi-droplet systems with varying compositions, which are prevalent in practical settings. The insights obtained from this study could influence the design and operational strategies of technologies in fields such as spray evapora","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113894"},"PeriodicalIF":5.8,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143103023","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}
In this work, Mie-scattering imaging, chemiluminescence and PIV are applied in various optically accessible Porous Media Burners (PMBs). The present PMBs are generated using Triply Periodic Minimal Surfaces (TPMS) and produced via Additive Manufacturing (AM). These topologies feature optical pathways that are both orthogonal and coincident, so that one can be used for illumination and the other for imaging. This enables the application of laser diagnostics in fully 3D structures whilst avoiding altering the geometry of the porous medium. These techniques are applied in homogeneous porous burners where the position of the flame is determined by the operating conditions. First, Mie-scattering imaging is combined with chemiluminescence to analyze the influence of the flame position on the preheating distance of the reactants. For that, the flow is seeded with micrometric oil droplets that evaporate at approximately 500 K. The light scattered by these particles delineates an evaporation front in the Mie-scattering images and this can be compared to the actual location of the reaction region, which is deduced from chemiluminescence images. Then, Mie-scattering imaging and PIV are used to obtain the flame shape and the velocity field in the unburned gas region for inlet-anchored flames. The influence of the hydrogen content, the pore-size and the burner topology is analyzed. The topology is found to have a major impact on the interstitial flow and flame stabilization. A new topological parameter, namely the linear porosity, is proposed to quantify the influence of local hydrodynamic effects on flame stabilization.
Novelty and Significance Statement
The novelty of this work is the accomplishment of Mie-scattering imaging and PIV measurements in a Porous Media Burner (PMB). The application of these laser techniques in an homogeneous PMB requires two orthogonal and coincident optical accesses. In this work, this is achieved via TPMS-based topologies and Additive Manufacturing (AM) techniques. It is significant because it opens the door for the application of laser diagnostics in 3D porous structures without altering the topology. Mie-scattering imaging on small oil droplets seeded in the flow offers a new way to study heat recirculation in PMBs via characterization of the solid-diffusion distance. PIV measurements reveal the importance of linear porosity and its influence on the interstitial flow and on the hydrodynamic stabilization of flames within the pores.
{"title":"Mie-scattering imaging and μPIV in porous media burners with TPMS-based topologies","authors":"Enrique Flores-Montoya , Sébastien Cazin , Thierry Schuller , Laurent Selle","doi":"10.1016/j.combustflame.2025.113990","DOIUrl":"10.1016/j.combustflame.2025.113990","url":null,"abstract":"<div><div>In this work, Mie-scattering imaging, <span><math><msup><mrow><mi>CH</mi></mrow><mrow><mi>⋆</mi></mrow></msup></math></span> chemiluminescence and <span><math><mi>μ</mi></math></span>PIV are applied in various optically accessible Porous Media Burners (PMBs). The present PMBs are generated using Triply Periodic Minimal Surfaces (TPMS) and produced via Additive Manufacturing (AM). These topologies feature optical pathways that are both orthogonal and coincident, so that one can be used for illumination and the other for imaging. This enables the application of laser diagnostics in fully 3D structures whilst avoiding altering the geometry of the porous medium. These techniques are applied in homogeneous porous burners where the position of the flame is determined by the operating conditions. First, Mie-scattering imaging is combined with <span><math><msup><mrow><mi>CH</mi></mrow><mrow><mi>⋆</mi></mrow></msup></math></span> chemiluminescence to analyze the influence of the flame position on the preheating distance of the reactants. For that, the flow is seeded with micrometric oil droplets that evaporate at approximately 500 K. The light scattered by these particles delineates an evaporation front in the Mie-scattering images and this can be compared to the actual location of the reaction region, which is deduced from chemiluminescence images. Then, Mie-scattering imaging and <span><math><mi>μ</mi></math></span>PIV are used to obtain the flame shape and the velocity field in the unburned gas region for inlet-anchored flames. The influence of the hydrogen content, the pore-size and the burner topology is analyzed. The topology is found to have a major impact on the interstitial flow and flame stabilization. A new topological parameter, namely the linear porosity, is proposed to quantify the influence of local hydrodynamic effects on flame stabilization.</div><div><strong>Novelty and Significance Statement</strong></div><div>The novelty of this work is the accomplishment of Mie-scattering imaging and <span><math><mi>μ</mi></math></span>PIV measurements in a Porous Media Burner (PMB). The application of these laser techniques in an homogeneous PMB requires two orthogonal and coincident optical accesses. In this work, this is achieved via TPMS-based topologies and Additive Manufacturing (AM) techniques. It is significant because it opens the door for the application of laser diagnostics in 3D porous structures without altering the topology. Mie-scattering imaging on small oil droplets seeded in the flow offers a new way to study heat recirculation in PMBs via characterization of the solid-diffusion distance. <span><math><mi>μ</mi></math></span>PIV measurements reveal the importance of linear porosity and its influence on the interstitial flow and on the hydrodynamic stabilization of flames within the pores.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"274 ","pages":"Article 113990"},"PeriodicalIF":5.8,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143193351","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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