Pub Date : 2024-08-29DOI: 10.1016/j.proci.2024.105736
Ruslan Khamedov, Mohammad Rafi Malik, Francisco E. Hernández-Pérez, Hong G. Im
Direct numerical simulations (DNS) of fuel-lean turbulent premixed NH-H-N-air flames are analyzed to investigate propagation and flame structural characteristics under fixed velocity and length ratios. To comprehensively assess the impact of diffusive-thermal imbalances on hydrogen–enriched ammonia flames, additional solutions with unity-Lewis-number transport were analyzed and compared with those obtained using the mixture-averaged transport model. The increase of H fraction in the fuel leads to elevated mean turbulent flame speed and stretch factor, indicating the impact of thermal-diffusive instability. The turbulent flame speed of the 60%NH-25%H-15%N-air flame displays pronounced oscillations, a phenomenon absent in other mixtures considered in the current study. This behavior is attributed to the preferential diffusion of H mixed with the low-reactive NH in moderate quantities, resulting in higher generation of flame elements extending into the product side and dynamic evolution of H. The flame structure analysis, in terms of conditional averages, revealed a distinctive variation in H and H atom distributions. The flames with a higher H fraction (40%NH-45%H-15%N-air) produced a second peak of HO in the trailing edge region, indicating additional production in the intense reaction zone. Additionally, in the 60%NH-25%H-15%N-air flame, the reaction rate of H exhibited a unique behavior, with H being produced in the intermediate flame zone and rapidly consumed in the reaction zone, differing from other cases.
分析了燃料倾斜湍流预混合 NH-H-N-air 火焰的直接数值模拟 (DNS)，以研究固定速度和长度比下的传播和火焰结构特征。为了全面评估扩散-热失衡对富氢氨火焰的影响，还分析了单路易斯数输运的附加解，并与使用混合物平均输运模型得到的解进行了比较。燃料中氢含量的增加导致平均湍流火焰速度和拉伸系数的上升，表明热扩散不稳定性的影响。60%NH-25%H-15%N-空气火焰的湍流火焰速度显示出明显的振荡，这是本次研究中考虑的其他混合物所没有的现象。这种行为归因于 H 与适量低反应性 NH 混合后的优先扩散，导致火焰元素向生成物一侧延伸，H 的动态演化也随之增加。H 含量较高的火焰（40%NH-45%H-15%N-空气）在后缘区域产生了第二个 HO 峰，表明在强烈反应区产生了额外的 H。此外，在 60%NH-25%H-15%N-air 的火焰中，H 的反应速率表现出独特的行为，H 在中间火焰区产生，在反应区迅速消耗，这与其他情况不同。
{"title":"Propagation characteristics of lean turbulent premixed ammonia–hydrogen flames","authors":"Ruslan Khamedov, Mohammad Rafi Malik, Francisco E. Hernández-Pérez, Hong G. Im","doi":"10.1016/j.proci.2024.105736","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105736","url":null,"abstract":"Direct numerical simulations (DNS) of fuel-lean turbulent premixed NH-H-N-air flames are analyzed to investigate propagation and flame structural characteristics under fixed velocity and length ratios. To comprehensively assess the impact of diffusive-thermal imbalances on hydrogen–enriched ammonia flames, additional solutions with unity-Lewis-number transport were analyzed and compared with those obtained using the mixture-averaged transport model. The increase of H fraction in the fuel leads to elevated mean turbulent flame speed and stretch factor, indicating the impact of thermal-diffusive instability. The turbulent flame speed of the 60%NH-25%H-15%N-air flame displays pronounced oscillations, a phenomenon absent in other mixtures considered in the current study. This behavior is attributed to the preferential diffusion of H mixed with the low-reactive NH in moderate quantities, resulting in higher generation of flame elements extending into the product side and dynamic evolution of H. The flame structure analysis, in terms of conditional averages, revealed a distinctive variation in H and H atom distributions. The flames with a higher H fraction (40%NH-45%H-15%N-air) produced a second peak of HO in the trailing edge region, indicating additional production in the intense reaction zone. Additionally, in the 60%NH-25%H-15%N-air flame, the reaction rate of H exhibited a unique behavior, with H being produced in the intermediate flame zone and rapidly consumed in the reaction zone, differing from other cases.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180168","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}
Fuel-lean combustion is challenging because of the difficulty in successful ignition-to-flame propagation transition in intense turbulence conditions. This study aims to elucidate the governing factor of fuel dependence on the lean limit through fundamental ignition experiments and numerical simulations. Previous scaling analysis has reported strong correlations between lean engine operation limit and Minimum Ignition Energy (MIE) transitions. Additionally, the temporal evolution of turbulent intensity in the engine cylinder plotted on Peters diagram suggested that the flame kernel growth occurs only in relatively weak turbulent intensity, , the condition under which is lower than the MIE transition. To investigate the behavior of flame kernel growth in the vicinity of the MIE transition condition, we conducted ignition experiments under both laminar and turbulent conditions utilizing a constant volume chamber with counter-rotating fans. Flame initiation was achieved by spark discharge at various turbulent intensities. The results showed notable distinctions in flame kernel growth processes between below and above the MIE transition condition. For MIE transition, flame kernel development is governed by molecular transports showing an apparent Lewis number effect, whereas for MIE transition, the effect seems to disappear. Subsequently, experiments and numerical simulations on spherically propagating flames in quiescent mixtures with various blended fuels were conducted. The results indicated that fuels facilitating rapid flame kernel growth generally exhibited leaner engine operation limits, regardless of engine specifications. The present study successfully demonstrated that the fuels suitable for lean combustion could be predicted by investigation of spherically propagating flames in quiescent mixtures.
{"title":"Fundamental study on lean operation limit of super lean-burn spark ignition engines: MIE transition and limit prediction","authors":"Takashi Kakizawa, Yoshiki Hirano, Taichi Mukoyama, Ayaka Hashimoto, Haru Okada, Keisuke Akita, Takuya Tezuka, Youhi Morii, Hisashi Nakamura, Kaoru Maruta","doi":"10.1016/j.proci.2024.105718","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105718","url":null,"abstract":"Fuel-lean combustion is challenging because of the difficulty in successful ignition-to-flame propagation transition in intense turbulence conditions. This study aims to elucidate the governing factor of fuel dependence on the lean limit through fundamental ignition experiments and numerical simulations. Previous scaling analysis has reported strong correlations between lean engine operation limit and Minimum Ignition Energy (MIE) transitions. Additionally, the temporal evolution of turbulent intensity in the engine cylinder plotted on Peters diagram suggested that the flame kernel growth occurs only in relatively weak turbulent intensity, , the condition under which is lower than the MIE transition. To investigate the behavior of flame kernel growth in the vicinity of the MIE transition condition, we conducted ignition experiments under both laminar and turbulent conditions utilizing a constant volume chamber with counter-rotating fans. Flame initiation was achieved by spark discharge at various turbulent intensities. The results showed notable distinctions in flame kernel growth processes between below and above the MIE transition condition. For MIE transition, flame kernel development is governed by molecular transports showing an apparent Lewis number effect, whereas for MIE transition, the effect seems to disappear. Subsequently, experiments and numerical simulations on spherically propagating flames in quiescent mixtures with various blended fuels were conducted. The results indicated that fuels facilitating rapid flame kernel growth generally exhibited leaner engine operation limits, regardless of engine specifications. The present study successfully demonstrated that the fuels suitable for lean combustion could be predicted by investigation of spherically propagating flames in quiescent mixtures.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180169","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 utilization of liquid ammonia in gas turbines can reduce energy loss and start-up time. However, the flash boiling phenomenon and the high latent heat of liquid ammonia make the spray flame difficult to stabilize. Increasing the preheated air temperature or adding a small amount of hydrogen as a piloted fuel are considered as effective methods to enhance the stability. To understand the flame topological structure, simultaneous Mie scattering and planar laser-induced fluorescence of OH (OH-PLIF) techniques were used to visualize the liquid ammonia spray structure and flame region information. Results show that the liquid ammonia swirl spray flame exhibits the flame topological structure of distinct zoning characteristics, including the droplet zone, the mixing zone, and the flame zone. Increasing the preheated air temperature accelerates the evaporation of liquid ammonia, leading to an increase in the local equivalence ratio and radial flame splitting. At lower air temperature conditions, increasing the hydrogen blending ratio has minimal impact on the flame topological structure. However, at higher temperature conditions, hydrogen blending significantly promotes reaction intensity upstream and reduces the flame lift-off height, which makes the mixing zone smaller. In general, to achieve a better flame stability effect, the two factors need to be reasonably matched, which has important reference value for the development of liquid ammonia fueled gas turbine combustors.
{"title":"Topology characteristics of liquid ammonia swirl spray flame","authors":"Ruixiang Wang, Meng Zhang, Zhenhua An, Xiao Cai, Jiawen Liu, Jinhua Wang, Zuohua Huang","doi":"10.1016/j.proci.2024.105740","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105740","url":null,"abstract":"The utilization of liquid ammonia in gas turbines can reduce energy loss and start-up time. However, the flash boiling phenomenon and the high latent heat of liquid ammonia make the spray flame difficult to stabilize. Increasing the preheated air temperature or adding a small amount of hydrogen as a piloted fuel are considered as effective methods to enhance the stability. To understand the flame topological structure, simultaneous Mie scattering and planar laser-induced fluorescence of OH (OH-PLIF) techniques were used to visualize the liquid ammonia spray structure and flame region information. Results show that the liquid ammonia swirl spray flame exhibits the flame topological structure of distinct zoning characteristics, including the droplet zone, the mixing zone, and the flame zone. Increasing the preheated air temperature accelerates the evaporation of liquid ammonia, leading to an increase in the local equivalence ratio and radial flame splitting. At lower air temperature conditions, increasing the hydrogen blending ratio has minimal impact on the flame topological structure. However, at higher temperature conditions, hydrogen blending significantly promotes reaction intensity upstream and reduces the flame lift-off height, which makes the mixing zone smaller. In general, to achieve a better flame stability effect, the two factors need to be reasonably matched, which has important reference value for the development of liquid ammonia fueled gas turbine combustors.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180173","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 ignition dynamic of liquid fuel droplets impacting hot surfaces is critical for fire-safety analysis in engineering systems, as well as for controlling wall-filming effects in IC engines. The scenario of slow fuel-leakage rates poses challenges associated with the stochastic processes of droplet splashing, break-up, turbulent mixing, and combustion. To address this, we conduct controlled experiments of liquid n-heptane droplets impacting a heated surface in the Leidenfrost regime, targeting the individual-droplet-deposition conditions. The experiment encompasses a range of surface temperatures and droplet-deposition rates. The experiments are complemented by theoretical analysis, where we developed a stochastic low-order numerical model, demonstrating good accuracy for predicting ignition probability and overall combustion dynamics. Notably, we observe a broad region of intermittent combustion behavior, with ignition probability varying based on surface temperature and droplet deposition rate. Additionally, we find that the transition to consistent ignition relies heavily on both surface temperature and deposition rate. Experimental and numerical model results shed light on the roles of the complex interplay between droplet breakup, chemical kinetics, and evaporation and mixing time scales, as well as the interaction among subsequent droplet combustion events, in governing the ignition and combustion of impacting droplet trains. The revealed dynamic of droplet/hot-surface ignition and the proposed stochastic model hold promise for advancing predictive capabilities of hot-surface-induced ignition and combustion arising from accidental leaks in flammable-liquid piping and wall-filming, particularly in the stochasticity-dominated individual-droplet-deposition regime.
{"title":"Experiment and modeling of stochastic ignition and combustion of fuel droplets impacting a hot surface","authors":"Nguyen Ly, Yichi Ma, Guillaume Vignat, Nozomu Hashimoto, Matthias Ihme","doi":"10.1016/j.proci.2024.105747","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105747","url":null,"abstract":"The ignition dynamic of liquid fuel droplets impacting hot surfaces is critical for fire-safety analysis in engineering systems, as well as for controlling wall-filming effects in IC engines. The scenario of slow fuel-leakage rates poses challenges associated with the stochastic processes of droplet splashing, break-up, turbulent mixing, and combustion. To address this, we conduct controlled experiments of liquid n-heptane droplets impacting a heated surface in the Leidenfrost regime, targeting the individual-droplet-deposition conditions. The experiment encompasses a range of surface temperatures and droplet-deposition rates. The experiments are complemented by theoretical analysis, where we developed a stochastic low-order numerical model, demonstrating good accuracy for predicting ignition probability and overall combustion dynamics. Notably, we observe a broad region of intermittent combustion behavior, with ignition probability varying based on surface temperature and droplet deposition rate. Additionally, we find that the transition to consistent ignition relies heavily on both surface temperature and deposition rate. Experimental and numerical model results shed light on the roles of the complex interplay between droplet breakup, chemical kinetics, and evaporation and mixing time scales, as well as the interaction among subsequent droplet combustion events, in governing the ignition and combustion of impacting droplet trains. The revealed dynamic of droplet/hot-surface ignition and the proposed stochastic model hold promise for advancing predictive capabilities of hot-surface-induced ignition and combustion arising from accidental leaks in flammable-liquid piping and wall-filming, particularly in the stochasticity-dominated individual-droplet-deposition regime.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180171","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 : 2024-08-28DOI: 10.1016/j.proci.2024.105741
Amitesh S. Jayaraman, Ethan S. Genter, Wendi Dong, Hai Wang
Conventional assumption in gas-phase detonations, where shock compression is decoupled from chemical kinetics, predicates on the shock and triple point structures being treated as perfect discontinuities. However, the shock is a region of high translational nonequilibrium three to five mean free paths in thickness. In this study, we use molecular dynamics simulations to probe Ar and N shocks focusing on the collision statistics in the shock front. Translationally superheated molecules were identified, as suggested by Zeldovich ( 248 (1979) 349–351), which raise the collision temperature and potentially enhance chemical reaction rates within and ahead of the shock front. We evaluated this reaction rate enhancement effect on stoichiometric H/O ZND detonation and found the effect to be negligible. The triple point region is observed to have a similar distribution of translationally superheated molecules. The temperature in the triple point region in Ar is substantially higher than that in N; the difference could impact detonation and deflagration-to-detonation characteristics due to diluent differences.
{"title":"Collision enhancement in shocks and its implication on gas-phase detonations: A molecular dynamics and gas-kinetic theory study","authors":"Amitesh S. Jayaraman, Ethan S. Genter, Wendi Dong, Hai Wang","doi":"10.1016/j.proci.2024.105741","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105741","url":null,"abstract":"Conventional assumption in gas-phase detonations, where shock compression is decoupled from chemical kinetics, predicates on the shock and triple point structures being treated as perfect discontinuities. However, the shock is a region of high translational nonequilibrium three to five mean free paths in thickness. In this study, we use molecular dynamics simulations to probe Ar and N shocks focusing on the collision statistics in the shock front. Translationally superheated molecules were identified, as suggested by Zeldovich ( 248 (1979) 349–351), which raise the collision temperature and potentially enhance chemical reaction rates within and ahead of the shock front. We evaluated this reaction rate enhancement effect on stoichiometric H/O ZND detonation and found the effect to be negligible. The triple point region is observed to have a similar distribution of translationally superheated molecules. The temperature in the triple point region in Ar is substantially higher than that in N; the difference could impact detonation and deflagration-to-detonation characteristics due to diluent differences.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180172","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 : 2024-08-28DOI: 10.1016/j.proci.2024.105719
Claudio Munoz-Herrera, O. Skurtys, Petr Nikrityuk, Robert E. Hayes, Mario Toledo
The energy transition process triggered by the threat of climate change has created the need for cleaner heat generating systems. Using blends of hydrocarbons with increasing presence of green fuels, such as green hydrogen, has been proposed as an initial step of this process. The present study aims to investigate methane–hydrogen flames stabilized inside a divergent inert porous media burner. Experimentally, four stable operating points were found for the considered burner with a hydrogen presence between 0% and 30% in the fuel mixture at a constant thermal output of 2 kW. Temperatures are presented for each condition, noticing a decreasing trend as hydrogen presence was increased, since the equivalence ratio was gradually reduced to achieve stabilization. CO and NO emissions were below 15 ppm for all studied cases. A 2-dimensional numerical model incorporating the GRI-Mech 3.0 mechanism was developed and validated against experimental data.The model revealed that the stabilized flame front is observed as a straight line that runs parallel to the radial coordinate. This line exhibits a slight curvature close to the burner wall, which is caused by heat losses and the influence of the divergent geometry. Solid surface temperature was not constant due to the reduced convective heat exchange with flue gases in the periphery of the burner. To reduce this issue a lower expansion angle is proposed as an alternative. In addition, changes in the chemical kinetics due to H addition were also evaluated. As results, a general trend towards reaction shifting was found with a 56% of the reactions being strongly promoted by H presence, which is associated with an increase in radical concentration in the flame front due to H decomposition.
气候变化的威胁所引发的能源转型过程需要更清洁的供热系统。有人建议使用碳氢化合物混合物，并增加绿色燃料（如绿色氢气）的含量，作为这一过程的第一步。本研究旨在研究在发散惰性多孔介质燃烧器内稳定的甲烷-氢火焰。实验发现，在恒定热输出为 2 千瓦的条件下，燃料混合物中的氢含量在 0% 至 30% 之间时，所考虑的燃烧器有四个稳定的工作点。每个条件下的温度都有显示，注意到随着氢气含量的增加，温度呈下降趋势，因为等量比逐渐降低以达到稳定。在所有研究案例中，CO 和 NO 排放量均低于 15 ppm。该模型显示，稳定的火焰前沿是一条平行于径向坐标的直线。模型显示，稳定的火焰前沿呈平行于径向坐标的直线，在靠近燃烧器壁的地方有轻微的弯曲，这是由于热损失和发散几何形状的影响造成的。由于燃烧器外围与烟气的对流热交换减少，固体表面温度并不恒定。为减少这一问题，建议采用较低的膨胀角作为替代方案。此外，还评估了因添加 H 而引起的化学动力学变化。结果发现，总体趋势是反应转移，56% 的反应因 H 的存在而得到强烈促进，这与 H 分解导致火焰前沿自由基浓度增加有关。
{"title":"Stabilization of methane–hydrogen flames inside a divergent porous media reactor","authors":"Claudio Munoz-Herrera, O. Skurtys, Petr Nikrityuk, Robert E. Hayes, Mario Toledo","doi":"10.1016/j.proci.2024.105719","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105719","url":null,"abstract":"The energy transition process triggered by the threat of climate change has created the need for cleaner heat generating systems. Using blends of hydrocarbons with increasing presence of green fuels, such as green hydrogen, has been proposed as an initial step of this process. The present study aims to investigate methane–hydrogen flames stabilized inside a divergent inert porous media burner. Experimentally, four stable operating points were found for the considered burner with a hydrogen presence between 0% and 30% in the fuel mixture at a constant thermal output of 2 kW. Temperatures are presented for each condition, noticing a decreasing trend as hydrogen presence was increased, since the equivalence ratio was gradually reduced to achieve stabilization. CO and NO emissions were below 15 ppm for all studied cases. A 2-dimensional numerical model incorporating the GRI-Mech 3.0 mechanism was developed and validated against experimental data.The model revealed that the stabilized flame front is observed as a straight line that runs parallel to the radial coordinate. This line exhibits a slight curvature close to the burner wall, which is caused by heat losses and the influence of the divergent geometry. Solid surface temperature was not constant due to the reduced convective heat exchange with flue gases in the periphery of the burner. To reduce this issue a lower expansion angle is proposed as an alternative. In addition, changes in the chemical kinetics due to H addition were also evaluated. As results, a general trend towards reaction shifting was found with a 56% of the reactions being strongly promoted by H presence, which is associated with an increase in radical concentration in the flame front due to H decomposition.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180174","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 : 2024-08-28DOI: 10.1016/j.proci.2024.105759
Tao Li, Mahmut Doğrudil, Andreas Dreizler
The current experimental investigation focuses on the macroscopic structures of CH/air and H/air flames operated on the Darmstadt multi-regime burner adapted for hydrogen operation. Building upon previous research on lean-burn limits, this study utilizes simultaneous PIV and OH-PLIF measurements to examine notable differences in flame and flow structures. Six flame cases are studied, focusing on CH/air and H/air jet flames at equivalence ratios of 1.4, 2.2, and 3.5. It is observed that the hydrogen slot 2 flames exhibit unique behavior under ultra-lean conditions, demonstrating thermodiffusive effects that generate finger-like structures. Despite receiving less thermal support from the slot 2 flame, hydrogen jet flames burn faster and resist flame extinction in high-velocity regions. The extensive heat release from fuel-rich H jets maintains a stable location compared to CH jets at the same equivalence ratio, altering local flow dynamics. Additionally, the study identifies a reshaped primary inner recirculation zone (IRZ) and a secondary IRZ in H/air flame cases, which is absent in CH flames. The interplay between the jet flame and the primary IRZ results in visible flame enhancement in slot 2, indicating preheating and fuel enrichment effects. Overall, this research provides comprehensive insights into the distinct combustion behavior and flow structures of CH and H flames on a multi-regime burner.
{"title":"Macroscopic flame and flow structures in hydrogen and methane multi-regime combustion","authors":"Tao Li, Mahmut Doğrudil, Andreas Dreizler","doi":"10.1016/j.proci.2024.105759","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105759","url":null,"abstract":"The current experimental investigation focuses on the macroscopic structures of CH/air and H/air flames operated on the Darmstadt multi-regime burner adapted for hydrogen operation. Building upon previous research on lean-burn limits, this study utilizes simultaneous PIV and OH-PLIF measurements to examine notable differences in flame and flow structures. Six flame cases are studied, focusing on CH/air and H/air jet flames at equivalence ratios of 1.4, 2.2, and 3.5. It is observed that the hydrogen slot 2 flames exhibit unique behavior under ultra-lean conditions, demonstrating thermodiffusive effects that generate finger-like structures. Despite receiving less thermal support from the slot 2 flame, hydrogen jet flames burn faster and resist flame extinction in high-velocity regions. The extensive heat release from fuel-rich H jets maintains a stable location compared to CH jets at the same equivalence ratio, altering local flow dynamics. Additionally, the study identifies a reshaped primary inner recirculation zone (IRZ) and a secondary IRZ in H/air flame cases, which is absent in CH flames. The interplay between the jet flame and the primary IRZ results in visible flame enhancement in slot 2, indicating preheating and fuel enrichment effects. Overall, this research provides comprehensive insights into the distinct combustion behavior and flow structures of CH and H flames on a multi-regime burner.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180170","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 : 2024-08-24DOI: 10.1016/j.proci.2024.105664
Erik L. Braun, Stephen D. Hammack, Timothy M. Ombrello, Philip Lax, Sergey B. Leonov
The ability to achieve stable heat release from fuel injected into high-speed air-breathing propulsion systems (such as scramjets) operating at supersonic speeds across a wide range of inlet conditions is crucial for hypersonic applications. Energetic enhancement using plasma is an attractive method of active flameholding and provides the potential for enhancing combustion in scramjet systems. Plasma injection modules (PIMs) have been used previously for flameholding and flow control and this work extends the application of PIMs to combustion enhancement in a stably burning, axisymmetric scramjet combustor. A narrow range of operating conditions, where the engine had an excess of unburned fuel and was on the verge of transitioning from scram-mode to ram-mode operation, generated local conditions in the flameholder where improvements to a specific stream thrust metric of up to 42.1 % during actuation of the PIMs was possible. The requirement for low operating efficiency in the system in order to leverage energy from the PIMs to improve performance is discussed, as well as the effect of modifying the upstream fuel injection scheme. A comparison of the thermal power required to match the result of adding ∼8 kW of power from the PIMs is presented and indicates that the PIMs can successfully improve the performance of a stably burning scramjet combustor, albeit over a narrow range of inefficient operating conditions.
{"title":"Enhancement of chemical heat release in a generic scramjet combustor using plasma injection modules","authors":"Erik L. Braun, Stephen D. Hammack, Timothy M. Ombrello, Philip Lax, Sergey B. Leonov","doi":"10.1016/j.proci.2024.105664","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105664","url":null,"abstract":"The ability to achieve stable heat release from fuel injected into high-speed air-breathing propulsion systems (such as scramjets) operating at supersonic speeds across a wide range of inlet conditions is crucial for hypersonic applications. Energetic enhancement using plasma is an attractive method of active flameholding and provides the potential for enhancing combustion in scramjet systems. Plasma injection modules (PIMs) have been used previously for flameholding and flow control and this work extends the application of PIMs to combustion enhancement in a stably burning, axisymmetric scramjet combustor. A narrow range of operating conditions, where the engine had an excess of unburned fuel and was on the verge of transitioning from scram-mode to ram-mode operation, generated local conditions in the flameholder where improvements to a specific stream thrust metric of up to 42.1 % during actuation of the PIMs was possible. The requirement for low operating efficiency in the system in order to leverage energy from the PIMs to improve performance is discussed, as well as the effect of modifying the upstream fuel injection scheme. A comparison of the thermal power required to match the result of adding ∼8 kW of power from the PIMs is presented and indicates that the PIMs can successfully improve the performance of a stably burning scramjet combustor, albeit over a narrow range of inefficient operating conditions.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180197","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 : 2024-08-22DOI: 10.1016/j.proci.2024.105717
Yue Qiu, Sheng Feng, Zhiyong Wu, Shijie Xu, Can Ruan, Xue-Song Bai, Elna J.K. Nilsson, Marcus Aldén, Zhongshan Li
Detailed numerical simulations are conducted in comparison with experimental results to study the flame structure and burning rate of a steadily burning aluminum droplet in hot steam-dominated environments. The droplet surface temperature, flame temperature, and flame stabilization position are measured along with the droplet burning rate estimated from the droplet size evolution. A numerical model accounting for detailed transport properties and chemical kinetics is presented and applied to unveil the flame structure, species and temperature distributions, and heat/mass transfer between the droplet and the surrounding gas. The numerical results of the temperature, velocity, and species distribution profiles demonstrate that the aluminum vapor flame is of classical diffusion flame structure, where near the droplet, there is a non-negligible amount of AlOAl apart from the main product AlO. This supports the deposition and formation of an alumina cap on the surface proposed in the literature. The simulation correctly captured the flame temperature and flame stabilization distance for a range of droplet sizes. Net heat flux analysis shows that conduction heat from the flame front accounts for less than 30% of the heat needed in aluminum evaporation, which warrants further quantification on other heat sources. The experimental and numerical results enrich the knowledge of the heat/mass transfer and chemical reactions near the droplet, which helps deepen the understanding of aluminum droplet burning.
{"title":"Detailed numerical simulation and experiments of a steadily burning micron-sized aluminum droplet in hot steam-dominated flows","authors":"Yue Qiu, Sheng Feng, Zhiyong Wu, Shijie Xu, Can Ruan, Xue-Song Bai, Elna J.K. Nilsson, Marcus Aldén, Zhongshan Li","doi":"10.1016/j.proci.2024.105717","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105717","url":null,"abstract":"Detailed numerical simulations are conducted in comparison with experimental results to study the flame structure and burning rate of a steadily burning aluminum droplet in hot steam-dominated environments. The droplet surface temperature, flame temperature, and flame stabilization position are measured along with the droplet burning rate estimated from the droplet size evolution. A numerical model accounting for detailed transport properties and chemical kinetics is presented and applied to unveil the flame structure, species and temperature distributions, and heat/mass transfer between the droplet and the surrounding gas. The numerical results of the temperature, velocity, and species distribution profiles demonstrate that the aluminum vapor flame is of classical diffusion flame structure, where near the droplet, there is a non-negligible amount of AlOAl apart from the main product AlO. This supports the deposition and formation of an alumina cap on the surface proposed in the literature. The simulation correctly captured the flame temperature and flame stabilization distance for a range of droplet sizes. Net heat flux analysis shows that conduction heat from the flame front accounts for less than 30% of the heat needed in aluminum evaporation, which warrants further quantification on other heat sources. The experimental and numerical results enrich the knowledge of the heat/mass transfer and chemical reactions near the droplet, which helps deepen the understanding of aluminum droplet burning.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180199","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 : 2024-08-22DOI: 10.1016/j.proci.2024.105414
Mithuun Kanapathipillai, Kenneth H. Yu
Dual-mode scramjets can operate efficiently over a range of flight speeds from moderate supersonic to hypersonic conditions. Depending on the fueling and flight conditions, the combustion mode operates in either a thermally-choked mode or a supersonic combustion mode. Direct-connect experiments were conducted using a laboratory-scale scramjet combustor with hydrogen as fuel, and its combustion mode transition behavior was characterized over various equivalence ratios. It was observed that the combustor became susceptible to combustion instability when mode transition was occurring naturally. To explore the possibility of actively triggering combustion mode transition while alleviating the combustion instability concerns, a new strategy of changing fuel injection distribution was formulated and a series of spatially distributed fuel injection experiments were conducted. The results showed that the critical amount of fueling for mode transition depends on the degree of fuel distribution. Subsequent experiments demonstrated that the combustion mode transition timing could be effectively controlled by scheduling spatial distribution of fuel injection. When fuel was injected at one location, most of heat release was concentrated near the cavity flame-holder, leading to thermal choking at a relatively low equivalence ratio. With distributed fuel injection, heat release became more evenly distributed across the expanding portion of the combustor, effectively delaying the mode transition to a higher equivalence ratio. Through the use of fast-acting solenoid valves, it was shown that changing fuel injection distribution could be used to trigger a timely combustor mode transition while holding the total fuel flow rate unchanged. When mode transition was actively triggered, the entire transition process occurred over a significantly shorter time scale compared to the natural mode transition process. The results indicate that combustion mode transition process could be controlled at the desired timing by actively scheduling fuel injection distribution, with reduced risks of encountering combustion instabilities while transitioning.
{"title":"Regulating scramjet combustor mode transition using fuel distribution control","authors":"Mithuun Kanapathipillai, Kenneth H. Yu","doi":"10.1016/j.proci.2024.105414","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105414","url":null,"abstract":"Dual-mode scramjets can operate efficiently over a range of flight speeds from moderate supersonic to hypersonic conditions. Depending on the fueling and flight conditions, the combustion mode operates in either a thermally-choked mode or a supersonic combustion mode. Direct-connect experiments were conducted using a laboratory-scale scramjet combustor with hydrogen as fuel, and its combustion mode transition behavior was characterized over various equivalence ratios. It was observed that the combustor became susceptible to combustion instability when mode transition was occurring naturally. To explore the possibility of actively triggering combustion mode transition while alleviating the combustion instability concerns, a new strategy of changing fuel injection distribution was formulated and a series of spatially distributed fuel injection experiments were conducted. The results showed that the critical amount of fueling for mode transition depends on the degree of fuel distribution. Subsequent experiments demonstrated that the combustion mode transition timing could be effectively controlled by scheduling spatial distribution of fuel injection. When fuel was injected at one location, most of heat release was concentrated near the cavity flame-holder, leading to thermal choking at a relatively low equivalence ratio. With distributed fuel injection, heat release became more evenly distributed across the expanding portion of the combustor, effectively delaying the mode transition to a higher equivalence ratio. Through the use of fast-acting solenoid valves, it was shown that changing fuel injection distribution could be used to trigger a timely combustor mode transition while holding the total fuel flow rate unchanged. When mode transition was actively triggered, the entire transition process occurred over a significantly shorter time scale compared to the natural mode transition process. The results indicate that combustion mode transition process could be controlled at the desired timing by actively scheduling fuel injection distribution, with reduced risks of encountering combustion instabilities while transitioning.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180207","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：