Pub Date : 2024-08-22DOI: 10.1016/j.proci.2024.105748
Leilei Xu, Ayman M. Elbaz, Emre Cenker, Jaeheon Sim, Xue-Song Bai, William L. Roberts
Ammonia is a carbon-free fuel that can be produced from renewable energy sources and has the potential to replace fossil fuels, exerting a significant impact on the decarbonization of power production and propulsion industries. However, the challenge lies in the high NO emissions, narrow flammability, and low flame speed of ammonia/air mixtures. In this paper, we study a novel concept of double-flame premixed co-combustion (DFPC) of ammonia and methane in a double-swirl premixed combustion burner, which results in low NO emissions and high flame stabilization. Large eddy simulations using a detailed chemical kinetic mechanism and planar laser-induced fluorescence imaging of OH and exhaust gas NO emission measurements are employed to investigate the fundamental mechanisms behind flame/flame interactions and NO emissions. The main findings are: (a) NO emissions can be reduced by 90% using the DFPC concept along with a significant broadening of flammability; (b) the outer methane/air flame stabilizes the inner ammonia flame in the shear layer of the two flames; (c) combustion products and excess oxygen leaked across the shear layer decrease the equivalence ratio of the inner ammonia/air mixture, reducing the NO formation of close-to-stoichiometric ammonia/air flame but increasing the NO formation in the fuel-rich ammonia/air flames; (d) mixing of the combustion products from the inner and outer flames reduces the NO emissions in the flue exhaust gas.
氨是一种可利用可再生能源生产的无碳燃料，具有替代化石燃料的潜力，对电力生产和推进行业的去碳化具有重大影响。然而，氨/空气混合物的高氮氧化物排放、窄可燃性和低火焰速度是其面临的挑战。本文研究了氨气和甲烷在双漩涡预混合燃烧器中进行双火焰预混合共燃（DFPC）的新概念，该概念可实现低氮氧化物排放和高火焰稳定性。利用详细的化学动力学机制和平面激光诱导荧光成像对 OH 和废气 NO 排放测量进行了大涡流模拟，以研究火焰/火焰相互作用和 NO 排放背后的基本机制。主要发现有(a) 使用 DFPC 概念可将氮氧化物排放量减少 90%，同时显著拓宽可燃性；(b) 甲烷/空气外焰可在两个火焰的剪切层中稳定氨气内焰；(c) 穿过剪切层泄漏的燃烧产物和过量氧气降低了内部氨/空气混合物的当量比，从而减少了接近均匀度的氨/空气火焰的氮氧化物形成，但增加了富燃料的氨/空气火焰的氮氧化物形成；(d) 内部和外部火焰的燃烧产物混合减少了烟道废气中的氮氧化物排放。
{"title":"Reduction of NO[formula omitted] emissions in ammonia combustion using a double-flame premixed co-combustion concept","authors":"Leilei Xu, Ayman M. Elbaz, Emre Cenker, Jaeheon Sim, Xue-Song Bai, William L. Roberts","doi":"10.1016/j.proci.2024.105748","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105748","url":null,"abstract":"Ammonia is a carbon-free fuel that can be produced from renewable energy sources and has the potential to replace fossil fuels, exerting a significant impact on the decarbonization of power production and propulsion industries. However, the challenge lies in the high NO emissions, narrow flammability, and low flame speed of ammonia/air mixtures. In this paper, we study a novel concept of double-flame premixed co-combustion (DFPC) of ammonia and methane in a double-swirl premixed combustion burner, which results in low NO emissions and high flame stabilization. Large eddy simulations using a detailed chemical kinetic mechanism and planar laser-induced fluorescence imaging of OH and exhaust gas NO emission measurements are employed to investigate the fundamental mechanisms behind flame/flame interactions and NO emissions. The main findings are: (a) NO emissions can be reduced by 90% using the DFPC concept along with a significant broadening of flammability; (b) the outer methane/air flame stabilizes the inner ammonia flame in the shear layer of the two flames; (c) combustion products and excess oxygen leaked across the shear layer decrease the equivalence ratio of the inner ammonia/air mixture, reducing the NO formation of close-to-stoichiometric ammonia/air flame but increasing the NO formation in the fuel-rich ammonia/air flames; (d) mixing of the combustion products from the inner and outer flames reduces the NO emissions in the flue exhaust gas.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"29 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180201","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.2024.105728
Alessandro Porcarelli, Ivan Langella
The interplay between strain and preferential diffusion in lean premixed hydrogen flamelets is investigated numerically. Lean conditions are established at an equivalence ratio of 0.5. Detailed chemistry, one-dimensional simulations are performed on a reactants-to-products counterflow configuration, both including and artificially excluding preferential diffusion effects. A comprehensive analysis of the flame physical properties is performed, showing that preferential diffusion tends to weaken the flame as compared to the case where it is artificially suppressed, as it triggers a local leaning of the mixture ahead of the flame front. Counterintuitively, strain is observed to counteract or limit this preferential diffusion effect, with the peaks of radicals and reaction rate, flame thickness, and consumption speed, progressively approaching and in some cases overtaking the corresponding solution obtained with equal diffusivities as strain increases. This is shown to be a consequence of the fluid elements being increasingly preferentially transported in the flame tangential direction rather than diffusing in the flame normal direction. Hence, the flame weakening effect due to different diffusive fluxes of fuel and oxidizer across the flame front is progressively compensated by their differential transport on the flame tangential direction triggered by increasing applied strain rate, which instead enables an overall enrichment of the burning mixture. This analysis provides a different view as compared to previous studies attributing to strain an enhancing influence on the effects of preferential diffusion. In this work the opposite interpretation is proposed instead, where strain acts as a limiting factor to the weakening effect of preferential diffusion on lean hydrogen flames.
{"title":"Mitigation of preferential diffusion effects by intensive strain in lean premixed hydrogen flamelets","authors":"Alessandro Porcarelli, Ivan Langella","doi":"10.1016/j.proci.2024.105728","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105728","url":null,"abstract":"The interplay between strain and preferential diffusion in lean premixed hydrogen flamelets is investigated numerically. Lean conditions are established at an equivalence ratio of 0.5. Detailed chemistry, one-dimensional simulations are performed on a reactants-to-products counterflow configuration, both including and artificially excluding preferential diffusion effects. A comprehensive analysis of the flame physical properties is performed, showing that preferential diffusion tends to weaken the flame as compared to the case where it is artificially suppressed, as it triggers a local leaning of the mixture ahead of the flame front. Counterintuitively, strain is observed to counteract or limit this preferential diffusion effect, with the peaks of radicals and reaction rate, flame thickness, and consumption speed, progressively approaching and in some cases overtaking the corresponding solution obtained with equal diffusivities as strain increases. This is shown to be a consequence of the fluid elements being increasingly preferentially transported in the flame tangential direction rather than diffusing in the flame normal direction. Hence, the flame weakening effect due to different diffusive fluxes of fuel and oxidizer across the flame front is progressively compensated by their differential transport on the flame tangential direction triggered by increasing applied strain rate, which instead enables an overall enrichment of the burning mixture. This analysis provides a different view as compared to previous studies attributing to strain an enhancing influence on the effects of preferential diffusion. In this work the opposite interpretation is proposed instead, where strain acts as a limiting factor to the weakening effect of preferential diffusion on lean hydrogen flames.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"59 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180202","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.2024.105716
Hassan F. Ahmed, R. Stewart Cant
The mechanism of propagation close to flame–flame interaction events is analysed using direct numerical simulation of a turbulent premixed methane–air flame. Four canonical local topologies arising from flame–flame interaction are identified in the vicinity of critical points. These correspond to reactant pocket, tunnel closure, tunnel formation and product pocket. The two spherical topologies (reactant and product pockets) are found to propagate consistently with no change in direction. Reactant pockets tend to propagate in the direction normal to the flame while product pockets tend to diffuse in the counter–normal direction. In contrast, both cylindrical topologies (tunnel closure and formation) may propagate either normally or counter–normally. It is shown that the direction of propagation for these topologies is strongly linked to principal curvatures of the flame surface. In such cases, the direction of propagation may reverse as the topology evolves and the principal curvatures change over time. Thus the conditioning on topology allows for more accurate estimation of displacement speed which is central to modelling turbulent flame speed.
{"title":"Propagation and topology in turbulent premixed flames","authors":"Hassan F. Ahmed, R. Stewart Cant","doi":"10.1016/j.proci.2024.105716","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105716","url":null,"abstract":"The mechanism of propagation close to flame–flame interaction events is analysed using direct numerical simulation of a turbulent premixed methane–air flame. Four canonical local topologies arising from flame–flame interaction are identified in the vicinity of critical points. These correspond to reactant pocket, tunnel closure, tunnel formation and product pocket. The two spherical topologies (reactant and product pockets) are found to propagate consistently with no change in direction. Reactant pockets tend to propagate in the direction normal to the flame while product pockets tend to diffuse in the counter–normal direction. In contrast, both cylindrical topologies (tunnel closure and formation) may propagate either normally or counter–normally. It is shown that the direction of propagation for these topologies is strongly linked to principal curvatures of the flame surface. In such cases, the direction of propagation may reverse as the topology evolves and the principal curvatures change over time. Thus the conditioning on topology allows for more accurate estimation of displacement speed which is central to modelling turbulent flame speed.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"31 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180204","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.2024.105751
Leilei Xu, Pengbo Dong, Zhenxian Zhang, Jingqi Bu, Jiangping Tian, Wuqiang Long, Haifeng Liu, Xue-Song Bai
This study investigates the combustion characteristics of ammonia and diesel sprays in a constant-volume vessel under conditions typical of internal combustion engines, focusing on the interplay between evaporation dynamics and flame interactions within the framework of the Direct Dual Fuel Stratification (DDFS) concept. Under non-evaporation conditions, ammonia and diesel sprays exhibit comparable evaporation profiles, but under evaporation scenarios, ammonia’s higher evaporation rate results in faster mixing with ambient gas than diesel despite the similar liquid penetration lengths of these two fuels. By utilizing meticulously designed arrangements of diesel and ammonia spray injectors, two distinct interaction scenarios between diesel spray and ammonia spray, early and late interaction, are explored. In the early interaction scenario, fuel-rich ammonia-air mixtures ignite directly by the diesel flame, achieving self-sustained propagation and significant heat release, thereby maintaining a high-temperature region for continuous combustion. Conversely, in late interaction scenarios, rapid ammonia evaporation leads to a fuel-lean ammonia/air mixture that cannot be ignited by the diesel flame, eventually leading to ammonia flame extinction. The study reveals that NOx and NO emissions are sensitive to the diesel/ammonia flame interaction. NO emissions, formed predominantly at the forefront of the quenching ammonia flame, pose a significant challenge due to the fast evaporation rate and slow oxidation rate in fuel-lean mixtures. These findings provide insights into the physics of ammonia–diesel combustion, highlighting the challenges and potential strategies for efficient and clean combustion in ammonia-fueled DDFS engines.
{"title":"Impact of spray interaction on ammonia/diesel dual-fuel combustion and emission under engine relevant conditions","authors":"Leilei Xu, Pengbo Dong, Zhenxian Zhang, Jingqi Bu, Jiangping Tian, Wuqiang Long, Haifeng Liu, Xue-Song Bai","doi":"10.1016/j.proci.2024.105751","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105751","url":null,"abstract":"This study investigates the combustion characteristics of ammonia and diesel sprays in a constant-volume vessel under conditions typical of internal combustion engines, focusing on the interplay between evaporation dynamics and flame interactions within the framework of the Direct Dual Fuel Stratification (DDFS) concept. Under non-evaporation conditions, ammonia and diesel sprays exhibit comparable evaporation profiles, but under evaporation scenarios, ammonia’s higher evaporation rate results in faster mixing with ambient gas than diesel despite the similar liquid penetration lengths of these two fuels. By utilizing meticulously designed arrangements of diesel and ammonia spray injectors, two distinct interaction scenarios between diesel spray and ammonia spray, early and late interaction, are explored. In the early interaction scenario, fuel-rich ammonia-air mixtures ignite directly by the diesel flame, achieving self-sustained propagation and significant heat release, thereby maintaining a high-temperature region for continuous combustion. Conversely, in late interaction scenarios, rapid ammonia evaporation leads to a fuel-lean ammonia/air mixture that cannot be ignited by the diesel flame, eventually leading to ammonia flame extinction. The study reveals that NOx and NO emissions are sensitive to the diesel/ammonia flame interaction. NO emissions, formed predominantly at the forefront of the quenching ammonia flame, pose a significant challenge due to the fast evaporation rate and slow oxidation rate in fuel-lean mixtures. These findings provide insights into the physics of ammonia–diesel combustion, highlighting the challenges and potential strategies for efficient and clean combustion in ammonia-fueled DDFS engines.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"21 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180196","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.2024.105708
Kuppuraj Rajamanickam, Ariff Magdoom Mahuthannan, Corine Lacour, Said Idlahcen, Armelle Cessou, David Honoré, Bertrand Lecordier
This study discusses fundamental turbulence-chemistry interactions in a canonical non-premixed bluff body burner fueled with 100% methane or hydrogen. Simultaneous time-resolved PIV&OH-PLIF and 1D Spontaneous Raman Scattering (SRS) have been employed to provide deeper insights into the difference in combustion regimes between CH and H operations. The analysis of the instantaneous time-resolved PIV and OH-PLIF datasets reveals the presence and absence of local extinctions in methane and hydrogen flames despite the mean flow topology being similar across the test cases. The instantaneous scatter plots of 1D Raman data in the mixture fraction space further quantified the spatial evolution of temperature and major species. Finally, the regime identification scheme is implemented over instantaneous 1D SRS data to identify the different flame/mixture regimes. The change in combustion regime is observed even very close to the burner exit while switching between CH and H, which is attributed to the probability of localized flame extinctions. Overall, this study provides detailed interlinks between flow field aerodynamics and scalar structures in the two different flames whose thermo physical properties are entirely different and form a comprehensive database for cornerstone computational model validation.
{"title":"Insights into the flow and scalar structures when shifting from methane to hydrogen turbulent flames using simultaneous PIV – OH PLIF and spontaneous Raman scattering","authors":"Kuppuraj Rajamanickam, Ariff Magdoom Mahuthannan, Corine Lacour, Said Idlahcen, Armelle Cessou, David Honoré, Bertrand Lecordier","doi":"10.1016/j.proci.2024.105708","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105708","url":null,"abstract":"This study discusses fundamental turbulence-chemistry interactions in a canonical non-premixed bluff body burner fueled with 100% methane or hydrogen. Simultaneous time-resolved PIV&OH-PLIF and 1D Spontaneous Raman Scattering (SRS) have been employed to provide deeper insights into the difference in combustion regimes between CH and H operations. The analysis of the instantaneous time-resolved PIV and OH-PLIF datasets reveals the presence and absence of local extinctions in methane and hydrogen flames despite the mean flow topology being similar across the test cases. The instantaneous scatter plots of 1D Raman data in the mixture fraction space further quantified the spatial evolution of temperature and major species. Finally, the regime identification scheme is implemented over instantaneous 1D SRS data to identify the different flame/mixture regimes. The change in combustion regime is observed even very close to the burner exit while switching between CH and H, which is attributed to the probability of localized flame extinctions. Overall, this study provides detailed interlinks between flow field aerodynamics and scalar structures in the two different flames whose thermo physical properties are entirely different and form a comprehensive database for cornerstone computational model validation.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"84 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180203","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.2024.105701
M. Vabre, Z. Li, S. Jella, P. Versailles, G. Bourque, M. Day, B. Savard
With the increasing need for fuel flexibility, mitigation of auto-ignition (AI) inside gas turbine (GT) premixers becomes crucial. They must be designed to yield a sufficiently homogeneous fuel–air mixture to achieve low emissions while at the same time avoiding the occurrence of AI and subsequent flame stabilization. This challenge requires a detailed understanding of turbulent mixing and chemistry interactions. In the present work, a direct numerical simulation (DNS) of an array of jets in crossflow (JICF), representative of an industrial GT premixer, is reported to shed light on these complex phenomena. It is found that AI kernels form in the aft part of the premixer and coalesce into a flame front that then propagates upstream, mainly through the boundary layer, and successively engulfs the jets. This, therefore, suggests a significant role of the jet array pattern on the flame stabilization. It is noted that AI kernels continue to form independently during the whole time of the simulation. To clarify the contribution of AI and diffusion in the ignition kernels and the main flame, chemical explosive mode analysis (CEMA) is employed jointly with a kernel tracking algorithm. It is found that during the initial formation of the flame, many ignition kernels form in mixtures with low scalar dissipation rate and large contribution from AI mode. As they quickly grow, they merge into a single flame front that becomes increasingly more diffusion-assisted over time, balancing the AI mode. Turbulence is shown to have a significant enhancing effect in lean premixed flames, but further analysis is required to fully characterize it. These findings are relevant for the industrial premixer studied, and also for novel micromix concepts that may be used in the next generation of GT combustion systems.
{"title":"DNS of ignition and flame stabilization in a simplified gas turbine premixer","authors":"M. Vabre, Z. Li, S. Jella, P. Versailles, G. Bourque, M. Day, B. Savard","doi":"10.1016/j.proci.2024.105701","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105701","url":null,"abstract":"With the increasing need for fuel flexibility, mitigation of auto-ignition (AI) inside gas turbine (GT) premixers becomes crucial. They must be designed to yield a sufficiently homogeneous fuel–air mixture to achieve low emissions while at the same time avoiding the occurrence of AI and subsequent flame stabilization. This challenge requires a detailed understanding of turbulent mixing and chemistry interactions. In the present work, a direct numerical simulation (DNS) of an array of jets in crossflow (JICF), representative of an industrial GT premixer, is reported to shed light on these complex phenomena. It is found that AI kernels form in the aft part of the premixer and coalesce into a flame front that then propagates upstream, mainly through the boundary layer, and successively engulfs the jets. This, therefore, suggests a significant role of the jet array pattern on the flame stabilization. It is noted that AI kernels continue to form independently during the whole time of the simulation. To clarify the contribution of AI and diffusion in the ignition kernels and the main flame, chemical explosive mode analysis (CEMA) is employed jointly with a kernel tracking algorithm. It is found that during the initial formation of the flame, many ignition kernels form in mixtures with low scalar dissipation rate and large contribution from AI mode. As they quickly grow, they merge into a single flame front that becomes increasingly more diffusion-assisted over time, balancing the AI mode. Turbulence is shown to have a significant enhancing effect in lean premixed flames, but further analysis is required to fully characterize it. These findings are relevant for the industrial premixer studied, and also for novel micromix concepts that may be used in the next generation of GT combustion systems.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"10 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180205","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.2024.105749
Chongpeng Chen, Cheng Chi, Dominique Thévenin, Wang Han, Lijun Yang
As a carbon-free fuel, hydrogen (H) is of increasing importance in the development of low-emission engines. Due to a low volumetric energy density, H is preferably stored at cryogenic temperatures ( K). In this context, it is indispensable to investigate the combustion behavior of hydrogen at such low temperatures. Although some studies focused on the ignition and detonation of hydrogen, investigations about premixed H/air flame propagation interacting with turbulence at cryogenic temperatures are rather scarce. In this work, stoichiometric turbulent premixed /air flames are studied at cryogenic temperature () and normal temperature (), using three-dimensional direct numerical simulations with detailed chemistry and transport. It is found that at cryogenic temperature, dimensionless turbulent flame speed and flame surface area increase significantly due to Darrieus–Landau instability (DLI) induced by a large expansion ratio. Since the effective Lewis numbers of the two cases are close to unity, the diffusive-thermal instability (DTI) is negligible in the cases. Furthermore, it is found that there are substantial differences in the peaks of and mass fractions between the two cases, probably due to smaller local flame curvatures at cryogenic temperature. Moreover, the results indicate that the flame response to stretch is not sensitive to the change of the initial temperature. A larger fractal inner cutoff scale is found at K, suggesting that the flame exhibits more large-scale flame wrinkling than that at K due to the impact of DLI. All these facts lead to the conclusion that cryogenic temperature can significantly promote large-scale flame wrinkling, increase turbulent flame speed and flame surface area, and affect intermediate species distribution. This suggests that combustion of cryogenic H may have a high risk of flashback.
作为一种无碳燃料，氢气（H）在低排放发动机的开发中越来越重要。由于氢的体积能量密度较低，因此最好在低温（K）下储存。在这种情况下，研究氢气在这种低温下的燃烧行为是必不可少的。虽然一些研究侧重于氢气的点燃和爆燃，但有关低温下氢气/空气预混合火焰传播与湍流相互作用的研究却非常少。在这项工作中，利用三维直接数值模拟，结合详细的化学和传输，研究了低温（）和常温（）下的化学湍流预混氢气/空气火焰。研究发现，在低温条件下，由于大膨胀比引起的达里厄斯-朗道不稳定性（DLI），无量纲湍流火焰速度和火焰表面积显著增加。由于两种情况下的有效路易斯数都接近于统一，因此扩散-热不稳定性（DTI）在这两种情况下都可以忽略不计。此外，研究还发现，两种情况下火焰的峰值和质量分数存在很大差异，这可能是由于低温下火焰的局部曲率较小。此外，结果表明，火焰对拉伸的响应对初始温度的变化并不敏感。在 K 温度下，分形内截止尺度较大，这表明由于 DLI 的影响，火焰比 K 温度下的火焰表现出更大尺度的火焰皱缩。所有这些事实都表明，低温能显著促进大尺度火焰皱缩，增加湍流火焰速度和火焰表面积，并影响中间物质的分布。这表明，低温 H 的燃烧可能具有很高的回火风险。
{"title":"Effects of cryogenic temperature on turbulent premixed hydrogen/air flames","authors":"Chongpeng Chen, Cheng Chi, Dominique Thévenin, Wang Han, Lijun Yang","doi":"10.1016/j.proci.2024.105749","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105749","url":null,"abstract":"As a carbon-free fuel, hydrogen (H) is of increasing importance in the development of low-emission engines. Due to a low volumetric energy density, H is preferably stored at cryogenic temperatures ( K). In this context, it is indispensable to investigate the combustion behavior of hydrogen at such low temperatures. Although some studies focused on the ignition and detonation of hydrogen, investigations about premixed H/air flame propagation interacting with turbulence at cryogenic temperatures are rather scarce. In this work, stoichiometric turbulent premixed /air flames are studied at cryogenic temperature () and normal temperature (), using three-dimensional direct numerical simulations with detailed chemistry and transport. It is found that at cryogenic temperature, dimensionless turbulent flame speed and flame surface area increase significantly due to Darrieus–Landau instability (DLI) induced by a large expansion ratio. Since the effective Lewis numbers of the two cases are close to unity, the diffusive-thermal instability (DTI) is negligible in the cases. Furthermore, it is found that there are substantial differences in the peaks of and mass fractions between the two cases, probably due to smaller local flame curvatures at cryogenic temperature. Moreover, the results indicate that the flame response to stretch is not sensitive to the change of the initial temperature. A larger fractal inner cutoff scale is found at K, suggesting that the flame exhibits more large-scale flame wrinkling than that at K due to the impact of DLI. All these facts lead to the conclusion that cryogenic temperature can significantly promote large-scale flame wrinkling, increase turbulent flame speed and flame surface area, and affect intermediate species distribution. This suggests that combustion of cryogenic H may have a high risk of flashback.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"6 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180198","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.2024.105738
Yue Zhang, Xuanye Liang, Zixuan Wang, Lijun Yang, Jingxuan Li
In this paper, the dynamic responses of a laminar diffusion flame subjected to acoustic disturbances in the fuel line (ADF) and surrounded air flow (ADA) were experimentally studied. Experiments were conducted at different frequencies by keeping the velocity perturbation amplitudes for both ADF and ADA the same. Chemiluminescence data (CH* and OH*) measured by an intensified high-speed camera and density perturbations measured by a Mach–Zehnder interferometer (MZI) were used to identify the flame dynamic responses in detail. Results show that both ADF and ADA can induce flame oscillations by stimulating disturbances in the fuel flow but in different manners. The perturbations led by the ADF propagate along the flame front with a hydrodynamic wavelength, while those driven by the ADA are more likely to periodically squeeze and extend the flame region from the lateral interfaces, leading to a global periodic motion along the longitudinal direction. Both types of perturbation are difficult to propagate downstream due to the damping of flow perturbation. In addition, the flame oscillation patterns driven by the ADA remain the same under different disturbance frequencies. When the diffusion flame is simultaneously subjected to both ADF and ADA, the perturbations of them are mutually coupled at this time, but the oscillation patterns of the flame are dominated by the ADF. Due to the different mechanisms of two disturbances, the oscillation patterns after coupling are related to the disturbance frequency. Based on the above results, a model of the diffusion flame oscillation subjected to ADF and ADA was proposed.
本文通过实验研究了层流扩散火焰在燃料管（ADF）和环绕气流（ADA）受到声学干扰时的动态响应。通过保持 ADF 和 ADA 的速度扰动振幅相同，在不同频率下进行了实验。利用高速强化照相机测量的化学发光数据（CH* 和 OH*）和马赫-泽恩德干涉仪（MZI）测量的密度扰动来详细识别火焰的动态响应。结果表明，ADF 和 ADA 都能通过刺激燃料流中的扰动引起火焰振荡，但方式不同。由 ADF 引发的扰动以流体动力波长沿火焰前沿传播，而由 ADA 引发的扰动则更有可能从横向界面周期性地挤压和扩展火焰区域，从而导致沿纵向的整体周期性运动。由于流动扰动的阻尼作用，这两种扰动都很难向下游传播。此外，在不同的扰动频率下，由 ADA 驱动的火焰振荡模式保持不变。当扩散火焰同时受到 ADF 和 ADA 扰动时，此时两者的扰动是相互耦合的，但火焰的振荡模式是由 ADF 主导的。由于两种扰动的机理不同，耦合后的振荡模式与扰动频率有关。根据上述结果，提出了受 ADF 和 ADA 影响的扩散火焰振荡模型。
{"title":"Comparisons of the dynamic responses of diffusion flames subjected to acoustic disturbances in the fuel and air lines","authors":"Yue Zhang, Xuanye Liang, Zixuan Wang, Lijun Yang, Jingxuan Li","doi":"10.1016/j.proci.2024.105738","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105738","url":null,"abstract":"In this paper, the dynamic responses of a laminar diffusion flame subjected to acoustic disturbances in the fuel line (ADF) and surrounded air flow (ADA) were experimentally studied. Experiments were conducted at different frequencies by keeping the velocity perturbation amplitudes for both ADF and ADA the same. Chemiluminescence data (CH* and OH*) measured by an intensified high-speed camera and density perturbations measured by a Mach–Zehnder interferometer (MZI) were used to identify the flame dynamic responses in detail. Results show that both ADF and ADA can induce flame oscillations by stimulating disturbances in the fuel flow but in different manners. The perturbations led by the ADF propagate along the flame front with a hydrodynamic wavelength, while those driven by the ADA are more likely to periodically squeeze and extend the flame region from the lateral interfaces, leading to a global periodic motion along the longitudinal direction. Both types of perturbation are difficult to propagate downstream due to the damping of flow perturbation. In addition, the flame oscillation patterns driven by the ADA remain the same under different disturbance frequencies. When the diffusion flame is simultaneously subjected to both ADF and ADA, the perturbations of them are mutually coupled at this time, but the oscillation patterns of the flame are dominated by the ADF. Due to the different mechanisms of two disturbances, the oscillation patterns after coupling are related to the disturbance frequency. Based on the above results, a model of the diffusion flame oscillation subjected to ADF and ADA was proposed.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"2012 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180200","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}
Compartment fire has been studied extensively based on the no wind condition, as well as using the gas fuel to achieve the “controllable” fire growth under the wind. However, no work reported on the compartment fire evolution with fire growth using the liquid as fuel considering the real accident. In the present study, ethanol (liquid) pool fire behavior inside a 30 cm cubic compartment with an opening was investigated experimentally under facing wind condition considering the “uncontrollable” real compartment fire scenario. The burning rate and flame behavior inside the compartment was recorded and measured. It is found that: (1) The stable mass loss rate inside the compartment could be divided into three types according to its evolution with facing wind speed, (I) it first increases or decreases a little, and then flame extinction occurs for lower ventilation factor; (II) it first changes a little and then increases, finally decreases for medium ventilation factor; (III) it first changes a little then increases monotonously for larger ventilation factor of over-ventilated condition. (2) The mass loss rate could be described well by the wind Froude number based on the opening flowing length scale. The mass loss rate ratio between the fuel combustion inside compartment and free condition first changes a little, then decreases with wind speed. This could be well explained as a function of the wind Froude number at the opening and wall heat losses characterizing the temperature rise. These new findings and proposed models provide a basis for understanding compartment fire evolution with liquid fuel combustion inside under the wind effect.
{"title":"An experimental study of the liquid fire evolution inside the compartment under the facing wind condition","authors":"Xiepeng Sun, Yu Han, Fei Ren, Xiaolei Zhang, Fei Tang, Longhua Hu","doi":"10.1016/j.proci.2024.105661","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105661","url":null,"abstract":"Compartment fire has been studied extensively based on the no wind condition, as well as using the gas fuel to achieve the “controllable” fire growth under the wind. However, no work reported on the compartment fire evolution with fire growth using the liquid as fuel considering the real accident. In the present study, ethanol (liquid) pool fire behavior inside a 30 cm cubic compartment with an opening was investigated experimentally under facing wind condition considering the “uncontrollable” real compartment fire scenario. The burning rate and flame behavior inside the compartment was recorded and measured. It is found that: (1) The stable mass loss rate inside the compartment could be divided into three types according to its evolution with facing wind speed, (I) it first increases or decreases a little, and then flame extinction occurs for lower ventilation factor; (II) it first changes a little and then increases, finally decreases for medium ventilation factor; (III) it first changes a little then increases monotonously for larger ventilation factor of over-ventilated condition. (2) The mass loss rate could be described well by the wind Froude number based on the opening flowing length scale. The mass loss rate ratio between the fuel combustion inside compartment and free condition first changes a little, then decreases with wind speed. This could be well explained as a function of the wind Froude number at the opening and wall heat losses characterizing the temperature rise. These new findings and proposed models provide a basis for understanding compartment fire evolution with liquid fuel combustion inside under the wind effect.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"7 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180227","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 : 2024-08-21DOI: 10.1016/j.proci.2024.105746
Luqing Zhu, James L. Urban
Firebrand spotting is a significant mechanism for structure losses in wildland–urban interface (WUI) fires. In this work, the ability of firebrand accumulations to cause flaming ignition of an engineered wood material, Oriented Strand Board (OSB), under different flow conditions was experimentally studied. The firebrands were emulated by burning wooden dowels of two sizes, 6.35 & 12.7 mm. Firebrands were dropped onto on the fuel to form accumulations, with the coverage densities of 0.06 to on the fuel surface. The surface temperature of glowing combustion on the firebrands was measured with color ratio pyrometry. The ignition outcome results show a similar hyperbolic relationship between air flow and coverage density for both firebrand sizes although accumulations of small firebrands can cause the ignition faster. A firebrand combustion model was adopted to predict the surface temperature of accumulated firebrands considering re-radiation between nearby firebrands. A correlation between the ignition time and characteristics of accumulations was also established based on a theoretical combustion and heat transfer analysis.
{"title":"Analyzing the ignition capabilities of glowing firebrand accumulations","authors":"Luqing Zhu, James L. Urban","doi":"10.1016/j.proci.2024.105746","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105746","url":null,"abstract":"Firebrand spotting is a significant mechanism for structure losses in wildland–urban interface (WUI) fires. In this work, the ability of firebrand accumulations to cause flaming ignition of an engineered wood material, Oriented Strand Board (OSB), under different flow conditions was experimentally studied. The firebrands were emulated by burning wooden dowels of two sizes, 6.35 & 12.7 mm. Firebrands were dropped onto on the fuel to form accumulations, with the coverage densities of 0.06 to on the fuel surface. The surface temperature of glowing combustion on the firebrands was measured with color ratio pyrometry. The ignition outcome results show a similar hyperbolic relationship between air flow and coverage density for both firebrand sizes although accumulations of small firebrands can cause the ignition faster. A firebrand combustion model was adopted to predict the surface temperature of accumulated firebrands considering re-radiation between nearby firebrands. A correlation between the ignition time and characteristics of accumulations was also established based on a theoretical combustion and heat transfer analysis.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"7 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180206","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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