Pub Date : 2024-07-30DOI: 10.1016/j.proci.2024.105452
Harikrishna Tummalapalli, Evatt R. Hawkes, Bruno Savard, Ji-Woong Park, Tianfeng Lu
We report a large-scale direct numerical simulation (DNS) of a highly-lifted premixed methane–air jet flame in a hot cross flow, relevant to axially staged gas-turbine combustion systems. The jet Reynolds number is 17,938 and the cross flow Reynolds number is 28,822. Apart from pressure, the thermochemical parameters closely match practical axially staged combustors. A premixed methane–air jet with an equivalence ratio of 0.7 is injected into a vitiated cross flow comprising combustion products from a methane–air mixture at an equivalence ratio of 0.5 and atmospheric pressure. The DNS is analysed to understand the stabilisation mechanism of the flame. The DNS reveals a lifted flame quasi-statically anchored on the leeward side. Time scale and OH budget analyses demonstrate that autoignition is the dominant stabilisation mechanism, and the leeward side anchoring is explained with reference to residence time and scalar dissipation rate. The study also shows that the interaction between the counter-rotating vortex pair and leeward ignition kernels results in a premixed flame in the jet core.
我们报告了对热交叉流中高扬程预混合甲烷-空气喷射火焰的大规模直接数值模拟（DNS），该火焰与轴向分段燃气轮机燃烧系统相关。射流雷诺数为 17938，横流雷诺数为 28822。除压力外，热化学参数与实际的轴向分段燃烧器非常吻合。将等效比为 0.7 的预混合甲烷-空气射流喷射到由等效比为 0.5 和大气压力下的甲烷-空气混合物燃烧产物组成的虚化横流中。对 DNS 进行分析，以了解火焰的稳定机制。DNS 显示了一个准静态锚定在背风面的抬升火焰。时间尺度和羟基预算分析表明，自燃是主要的稳定机制，而背风面的锚定则可参照停留时间和标量耗散率来解释。研究还表明，反向旋转涡对和背风点火核之间的相互作用导致了喷流核心的预混合火焰。
{"title":"Flame stabilisation in a highly-lifted premixed jet flame in a hot cross flow","authors":"Harikrishna Tummalapalli, Evatt R. Hawkes, Bruno Savard, Ji-Woong Park, Tianfeng Lu","doi":"10.1016/j.proci.2024.105452","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105452","url":null,"abstract":"We report a large-scale direct numerical simulation (DNS) of a highly-lifted premixed methane–air jet flame in a hot cross flow, relevant to axially staged gas-turbine combustion systems. The jet Reynolds number is 17,938 and the cross flow Reynolds number is 28,822. Apart from pressure, the thermochemical parameters closely match practical axially staged combustors. A premixed methane–air jet with an equivalence ratio of 0.7 is injected into a vitiated cross flow comprising combustion products from a methane–air mixture at an equivalence ratio of 0.5 and atmospheric pressure. The DNS is analysed to understand the stabilisation mechanism of the flame. The DNS reveals a lifted flame quasi-statically anchored on the leeward side. Time scale and OH budget analyses demonstrate that autoignition is the dominant stabilisation mechanism, and the leeward side anchoring is explained with reference to residence time and scalar dissipation rate. The study also shows that the interaction between the counter-rotating vortex pair and leeward ignition kernels results in a premixed flame in the jet core.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"55 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886433","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 : 2024-07-30DOI: 10.1016/j.proci.2024.105506
Ioannis Kavroulakis, Dimitris Papageorgiou, Christos E. Frouzakis, Paul Fischer, Ananias Tomboulides
Overlapping-domain methods together with current exascale computing capabilities can provide significant speedup to large-scale direct numerical simulations (DNS). The objective of this work is to examine the accuracy and performance of the non-conforming Schwarz method for the simulation of low Mach number reacting flows using the spectral element solver Nek5000. The overlapping-domain approach already implemented in Nek5000 for incompressible non-reacting scenarios is extended to reacting flows in open domains. First, the spatial and temporal convergence properties of the method were tested using the analytical solution for a 1-D reacting transient model problem developed for this purpose. The results show that the method preserves the exponential convergence in space with respect to polynomial order and exhibits a third-order accuracy in time, when the flame front is located away from the interdomain boundaries.When the flame approaches the interdomain boundaries, a first-order accuracy in time is observed, similar to non-reacting flows in overlapping domains when no sub-iterations are performed. Additionally, a simulation of a propagating turbulent lean premixed H-air flame in a 2-D circular domain was conducted, demonstrating that with adequate resolution in both overlapping domains, the flame transitions smoothly from the inner to the outer domain. Subsequently, a DNS of a 3-D early flame kernel development (EFKD) in decaying homogeneous isotropic turbulence (HIT) was carried out to assess accuracy and performance of the method under turbulent conditions, closely resembling scenarios during the initial phase of internal combustion engines (ICEs). Temperature and species profiles, flame consumption speed, as well as other quantities of interest, were found to be in very good agreement with single-domain results, showing that the method retains its accuracy. Finally, a strong scaling study of the EFKD configuration reveals that the parallel performance and speedup show the expected behavior of the overlapping-domain method for low Mach number reacting flows.
{"title":"Non-conforming Schwarz-spectral element method for low Mach number reacting flows","authors":"Ioannis Kavroulakis, Dimitris Papageorgiou, Christos E. Frouzakis, Paul Fischer, Ananias Tomboulides","doi":"10.1016/j.proci.2024.105506","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105506","url":null,"abstract":"Overlapping-domain methods together with current exascale computing capabilities can provide significant speedup to large-scale direct numerical simulations (DNS). The objective of this work is to examine the accuracy and performance of the non-conforming Schwarz method for the simulation of low Mach number reacting flows using the spectral element solver Nek5000. The overlapping-domain approach already implemented in Nek5000 for incompressible non-reacting scenarios is extended to reacting flows in open domains. First, the spatial and temporal convergence properties of the method were tested using the analytical solution for a 1-D reacting transient model problem developed for this purpose. The results show that the method preserves the exponential convergence in space with respect to polynomial order and exhibits a third-order accuracy in time, when the flame front is located away from the interdomain boundaries.When the flame approaches the interdomain boundaries, a first-order accuracy in time is observed, similar to non-reacting flows in overlapping domains when no sub-iterations are performed. Additionally, a simulation of a propagating turbulent lean premixed H-air flame in a 2-D circular domain was conducted, demonstrating that with adequate resolution in both overlapping domains, the flame transitions smoothly from the inner to the outer domain. Subsequently, a DNS of a 3-D early flame kernel development (EFKD) in decaying homogeneous isotropic turbulence (HIT) was carried out to assess accuracy and performance of the method under turbulent conditions, closely resembling scenarios during the initial phase of internal combustion engines (ICEs). Temperature and species profiles, flame consumption speed, as well as other quantities of interest, were found to be in very good agreement with single-domain results, showing that the method retains its accuracy. Finally, a strong scaling study of the EFKD configuration reveals that the parallel performance and speedup show the expected behavior of the overlapping-domain method for low Mach number reacting flows.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"366 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886435","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 : 2024-07-30DOI: 10.1016/j.proci.2024.105473
A. Cuoci, G. Bucci, M. Sutti, T. Faravelli, A. Frassoldati
Hydrogen is recognized as a promising resource for decarbonizing not only the industrial sector, but also the domestic heating systems. Through the partial substitution of natural gas with hydrogen, domestic combustion-based conversion systems can potentially offer improved efficiency, reduced carbon emissions, and cleaner combustion, i.e., lower levels of particulate matter. However, hydrogen exhibits properties that are significantly different from natural gas: (i) because of its higher laminar flame speed, hydrogen is more susceptible to flashback, which may pose significant concerns from the safety point of view; (ii) because of its higher adiabatic temperature, NOx emissions are expected to increase. Thus, experimental and numerical investigations are needed to better understand how the addition of hydrogen to the fuel mixture modifies the combustion process and how to mitigate/control the higher propensity to flashback and NOx formation within domestic devices.
{"title":"Experimental and numerical study of pollutant emissions from a domestic condensing boiler fed with natural gas enriched with H[formula omitted]","authors":"A. Cuoci, G. Bucci, M. Sutti, T. Faravelli, A. Frassoldati","doi":"10.1016/j.proci.2024.105473","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105473","url":null,"abstract":"Hydrogen is recognized as a promising resource for decarbonizing not only the industrial sector, but also the domestic heating systems. Through the partial substitution of natural gas with hydrogen, domestic combustion-based conversion systems can potentially offer improved efficiency, reduced carbon emissions, and cleaner combustion, i.e., lower levels of particulate matter. However, hydrogen exhibits properties that are significantly different from natural gas: (i) because of its higher laminar flame speed, hydrogen is more susceptible to flashback, which may pose significant concerns from the safety point of view; (ii) because of its higher adiabatic temperature, NOx emissions are expected to increase. Thus, experimental and numerical investigations are needed to better understand how the addition of hydrogen to the fuel mixture modifies the combustion process and how to mitigate/control the higher propensity to flashback and NOx formation within domestic devices.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886436","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 : 2024-07-29DOI: 10.1016/j.proci.2024.105557
Giovanni Di Cristina, Rodney A. Bryant
Bi-directional probes are utilized throughout fire science to measure fire-induced flows due to their ability to measure flow which changes direction, and to withstand hostile environments. However, they are not available commercially and researchers must take it upon themselves to make and manufacture them. S-type pitot probes (S-probes) work on the same principle as bi-directional probes, measuring the differential pressure between two openings, thereby offering the same benefits. However, S-probes also feature reliable manufacturing and calibration standards. In this study, the performance of bi-directional and S-probes is characterized against pitot-static probes in two scenarios. First, measurements of a steady, smooth flow in a well-characterized wind tunnel are examined. Second, the probes are used to measure the velocity profile across a turbulent jet from a blower fan. In both scenarios, the S-probe performed comparable to or better than the bi-directional probe in terms of accuracy. It is found that S-probes have similar performance to bi-directional probes in well conditioned flows. In the turbulent jet flow measurements, S-probe measurements are within 2% of pitot-static measurements in the core region of the jet, while bi-directional probes are within 6%.
{"title":"Comparison of two flow measurement devices for use in fire experiments","authors":"Giovanni Di Cristina, Rodney A. Bryant","doi":"10.1016/j.proci.2024.105557","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105557","url":null,"abstract":"Bi-directional probes are utilized throughout fire science to measure fire-induced flows due to their ability to measure flow which changes direction, and to withstand hostile environments. However, they are not available commercially and researchers must take it upon themselves to make and manufacture them. S-type pitot probes (S-probes) work on the same principle as bi-directional probes, measuring the differential pressure between two openings, thereby offering the same benefits. However, S-probes also feature reliable manufacturing and calibration standards. In this study, the performance of bi-directional and S-probes is characterized against pitot-static probes in two scenarios. First, measurements of a steady, smooth flow in a well-characterized wind tunnel are examined. Second, the probes are used to measure the velocity profile across a turbulent jet from a blower fan. In both scenarios, the S-probe performed comparable to or better than the bi-directional probe in terms of accuracy. It is found that S-probes have similar performance to bi-directional probes in well conditioned flows. In the turbulent jet flow measurements, S-probe measurements are within 2% of pitot-static measurements in the core region of the jet, while bi-directional probes are within 6%.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"10 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886437","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 : 2024-07-26DOI: 10.1016/j.proci.2024.105420
Ketana Teav, Adam M. Steinberg
This paper presents spectral measurements of Rayleigh-Brillouin scattering (RBS) spectra in binary mixtures of and at a number of mixture ratios at 300 K, and pressures ranging from 4 to 60 atm. To identify trends in lineshape changes associated with addition, measured spectra of pure and at 300 K and similar pressures are included. These measurements were acquired with a custom spectrometer based on an air-spaced virtually-imaged phased array whose resolving power was on the order of 10. Improvements upon previous work to the data processing procedure, including revised implementation of the scalar envelope correction, and the addition of a dispersion correction, are described. Measurements of RBS spectra in pure and are compared to their counterparts modelled by Tenti S6. Good agreement is observed in pressures up to 20 atm, and discrepancies at higher pressure are attributable to known limitations in the measurements and model. Attenuation and broadening of the Brillouin and central Rayleigh peaks, as well as an outward shift of the Brillouin doublet, are observed with addition. These trends are related to the dissipative role of on thermodynamic fluctuations in the fluid medium, enhanced by its mass disparity with the host species. Analysis of spectral energy distribution in mixture spectra at 20+ atm reveals a net transfer of spectral energy from the Brillouin doublet towards the central Rayleigh peak with increasing dilution. Experimental and modelled RBS spectra, and a model I filter, are used to test the validity, at elevated pressure, of approximating a mixture filtered Rayleigh scattering (FRS) signal by a mole fraction-weighted sum of isolated FRS signals from mixture constituents. FRS signals calculated from measured mixture spectra are compared to their approximations calculated from modelled pure gas spectra. Results show limited and inconsistent agreement. Where agreement is strong, further analysis reveals a sensitive counterbalance of factors affecting FRS signal generation that is not reliable for robust FRS signal inversion. The work demonstrates the need for improved spectral models to support the application of FRS diagnostics to fluid mixtures at elevated pressure.
{"title":"Rayleigh-Brillouin scattering from [formula omitted] and [formula omitted] mixtures at elevated pressures","authors":"Ketana Teav, Adam M. Steinberg","doi":"10.1016/j.proci.2024.105420","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105420","url":null,"abstract":"This paper presents spectral measurements of Rayleigh-Brillouin scattering (RBS) spectra in binary mixtures of and at a number of mixture ratios at 300 K, and pressures ranging from 4 to 60 atm. To identify trends in lineshape changes associated with addition, measured spectra of pure and at 300 K and similar pressures are included. These measurements were acquired with a custom spectrometer based on an air-spaced virtually-imaged phased array whose resolving power was on the order of 10. Improvements upon previous work to the data processing procedure, including revised implementation of the scalar envelope correction, and the addition of a dispersion correction, are described. Measurements of RBS spectra in pure and are compared to their counterparts modelled by Tenti S6. Good agreement is observed in pressures up to 20 atm, and discrepancies at higher pressure are attributable to known limitations in the measurements and model. Attenuation and broadening of the Brillouin and central Rayleigh peaks, as well as an outward shift of the Brillouin doublet, are observed with addition. These trends are related to the dissipative role of on thermodynamic fluctuations in the fluid medium, enhanced by its mass disparity with the host species. Analysis of spectral energy distribution in mixture spectra at 20+ atm reveals a net transfer of spectral energy from the Brillouin doublet towards the central Rayleigh peak with increasing dilution. Experimental and modelled RBS spectra, and a model I filter, are used to test the validity, at elevated pressure, of approximating a mixture filtered Rayleigh scattering (FRS) signal by a mole fraction-weighted sum of isolated FRS signals from mixture constituents. FRS signals calculated from measured mixture spectra are compared to their approximations calculated from modelled pure gas spectra. Results show limited and inconsistent agreement. Where agreement is strong, further analysis reveals a sensitive counterbalance of factors affecting FRS signal generation that is not reliable for robust FRS signal inversion. The work demonstrates the need for improved spectral models to support the application of FRS diagnostics to fluid mixtures at elevated pressure.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"26 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886605","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 : 2024-07-25DOI: 10.1016/j.proci.2024.105399
Giovanni Di Cristina, Ryan Falkenstein-Smith, Ickchan Kim, Savannah Wessies, Matthew Bundy, Mauro Zammarano
Upholstered furniture persists as the leading item in deadly US home fires. New state regulations that restrict the use of flame retardants have been introduced across the nation, and the development of flaming tests for upholstered furniture ( National Fire Protection Agency 266) has been halted. In this work, the ability of an open-flame barrier fabric to suppress fire growth initiated from an upholstered sofa in a fully furnished living room-like compartment is demonstrated. The open-flame barrier was specifically developed for this application based on ASTM E 3367 test protocol. The barrier did not contain flame retardants and was made of intrinsically fire-resistant fibers and a para-aramid scrim. No other component of the sofa contained flame retardants. Experiments were conducted under a 10 MW exhaust hood equipped with an oxygen consumption calorimetry system that provides real-time heat release rate measurements. The room was instrumented with various temperature, heat flux, and gas analyzing sensors. Gas analysis of species, such as oxygen, carbon monoxide, and hydrogen cyanide, was carried out on gas samples extracted from the room to determine tenability and the exhaust duct of the hood to estimate species yields. The experiment with full-barrier coverage on the sofa showed no flashover and reduced the total heat release by approximately 44%, compared to the no-barrier coverage experiment. Based on the fractional effective dose, tenability time in the room increased from about 4 min for the no-barrier to 19 min for the partial-barrier and 25 min for the full-barrier. Overall, the application of the barrier fabric extended the tenability and delayed or suppressed flashover, giving more time in any life threatening fire scenario hence remarkably increasing egress time and survival rate without potential health or environmental hazards associated with the use of flame retardants.
{"title":"Towards fire safe and flame-retardant-free upholstered furniture","authors":"Giovanni Di Cristina, Ryan Falkenstein-Smith, Ickchan Kim, Savannah Wessies, Matthew Bundy, Mauro Zammarano","doi":"10.1016/j.proci.2024.105399","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105399","url":null,"abstract":"Upholstered furniture persists as the leading item in deadly US home fires. New state regulations that restrict the use of flame retardants have been introduced across the nation, and the development of flaming tests for upholstered furniture ( National Fire Protection Agency 266) has been halted. In this work, the ability of an open-flame barrier fabric to suppress fire growth initiated from an upholstered sofa in a fully furnished living room-like compartment is demonstrated. The open-flame barrier was specifically developed for this application based on ASTM E 3367 test protocol. The barrier did not contain flame retardants and was made of intrinsically fire-resistant fibers and a para-aramid scrim. No other component of the sofa contained flame retardants. Experiments were conducted under a 10 MW exhaust hood equipped with an oxygen consumption calorimetry system that provides real-time heat release rate measurements. The room was instrumented with various temperature, heat flux, and gas analyzing sensors. Gas analysis of species, such as oxygen, carbon monoxide, and hydrogen cyanide, was carried out on gas samples extracted from the room to determine tenability and the exhaust duct of the hood to estimate species yields. The experiment with full-barrier coverage on the sofa showed no flashover and reduced the total heat release by approximately 44%, compared to the no-barrier coverage experiment. Based on the fractional effective dose, tenability time in the room increased from about 4 min for the no-barrier to 19 min for the partial-barrier and 25 min for the full-barrier. Overall, the application of the barrier fabric extended the tenability and delayed or suppressed flashover, giving more time in any life threatening fire scenario hence remarkably increasing egress time and survival rate without potential health or environmental hazards associated with the use of flame retardants.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"299 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886606","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 : 2024-07-24DOI: 10.1016/j.proci.2024.105616
Siyan Wang, Bryce L. Bathras, Wuquan Cui, Priya Garg, Shaorun Lin, Michael J. Gollner
A linear tube heater apparatus was used to simulate the non-ideal burning commonly encountered in real wildland fire scenarios, such as limited oxygen conditions. Recently live and dead vegetative fuels were tested under oxygen concentrations varied between 0 and 21 % with applied external heat fluxes ranging from 25 to 50 kW/m. Utilizing Fourier-transform infrared spectrometry (FTIR) and a cascade impactor, both gaseous and particulate effluents produced during combustion were characterized. The results revealed a significant correlation between emission factors of various species and oxygen concentrations, external heat fluxes and fuel moisture contents. As oxygen concentration increased from 0 % to 10 %, emission factors (EFs) of CO and CO significantly increased, while CO EFs decreased under flaming conditions but slightly increased under smoldering conditions with further increases in oxygen concentration. Emission of unburnt hydrocarbons, predominantly methane (CH) and butane (CH), increased with additional available oxygen due to char oxidation at a lower heat flux, evidenced by an approximately 18 % rise in total hydrocarbon emission factors from 10.71 ± 1.5 to 12.61 ± 3.8 g/kg for dead fuels and 10.61 ± 1.0 to 14.85 ± 2.1 g/kg for recently live fuels as oxygen concentrations increased from 0 to 10 %. Accelerated thermal cracking in heavier hydrocarbons (i.e., butane) due to a stronger smoldering process and greater oxygen supply was also observed. Additionally, increasing oxygen concentrations favored the production of NO while reduced acrolein emissions under flaming conditions. TPM emissions reduced with higher heat flux and oxygen concentration, and the difference in chemical composition associated with PM size was noted. This study has important implications on efforts to model emissions from wildland fuels, as a broader understanding of the processes driving emissions production considering variations in FMC, oxygen supply concentration and combustion modes is needed to better inform future emission management and wildfire management strategies.
{"title":"Flaming vs. smoldering emissions of pine needles under limited oxygen and fuel moisture conditions","authors":"Siyan Wang, Bryce L. Bathras, Wuquan Cui, Priya Garg, Shaorun Lin, Michael J. Gollner","doi":"10.1016/j.proci.2024.105616","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105616","url":null,"abstract":"A linear tube heater apparatus was used to simulate the non-ideal burning commonly encountered in real wildland fire scenarios, such as limited oxygen conditions. Recently live and dead vegetative fuels were tested under oxygen concentrations varied between 0 and 21 % with applied external heat fluxes ranging from 25 to 50 kW/m. Utilizing Fourier-transform infrared spectrometry (FTIR) and a cascade impactor, both gaseous and particulate effluents produced during combustion were characterized. The results revealed a significant correlation between emission factors of various species and oxygen concentrations, external heat fluxes and fuel moisture contents. As oxygen concentration increased from 0 % to 10 %, emission factors (EFs) of CO and CO significantly increased, while CO EFs decreased under flaming conditions but slightly increased under smoldering conditions with further increases in oxygen concentration. Emission of unburnt hydrocarbons, predominantly methane (CH) and butane (CH), increased with additional available oxygen due to char oxidation at a lower heat flux, evidenced by an approximately 18 % rise in total hydrocarbon emission factors from 10.71 ± 1.5 to 12.61 ± 3.8 g/kg for dead fuels and 10.61 ± 1.0 to 14.85 ± 2.1 g/kg for recently live fuels as oxygen concentrations increased from 0 to 10 %. Accelerated thermal cracking in heavier hydrocarbons (i.e., butane) due to a stronger smoldering process and greater oxygen supply was also observed. Additionally, increasing oxygen concentrations favored the production of NO while reduced acrolein emissions under flaming conditions. TPM emissions reduced with higher heat flux and oxygen concentration, and the difference in chemical composition associated with PM size was noted. This study has important implications on efforts to model emissions from wildland fuels, as a broader understanding of the processes driving emissions production considering variations in FMC, oxygen supply concentration and combustion modes is needed to better inform future emission management and wildfire management strategies.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"26 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886608","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 : 2024-07-24DOI: 10.1016/j.proci.2024.105509
Tong Jiang, Yanjun Sun, Lingfeng Dai, Weihao Zeng, Yingju Yang, Chun Zou
Ammonia (NH) is now attracting attention in the energy field due to its hydrogen-containing and carbon-free, vast infrastructure, safe utilization and longstanding storage. Nevertheless, NH combustion is usually associated with low flame instability and high NO emissions due to its low laminar flame speed and nitrogen content. The partial catalytic cracking of NH offers an economical strategy to improve combustion stability. However, the significant limitations of this strategy include high NO emissions. Therefore, the MILD combustion of partial catalytic cracking of NH is an excellent method to address the challenge. In this work, a novel trimetallic catalyst (Fe, Co, and Ni) was developed, and the MILD combustion of partially catalyzed NH and NH/N was performed in a novel burner. The effects of the NH conversion, N addition and NH power on pollutant emissions were experimental investigated. Numerical simulations were carried out to analyze the characteristics in the MILD combustion of partially catalyzed NH and NH/N observed in the experiments.
{"title":"MILD combustion of partially catalyzed NH3 and NH3/N2 in a novel burner","authors":"Tong Jiang, Yanjun Sun, Lingfeng Dai, Weihao Zeng, Yingju Yang, Chun Zou","doi":"10.1016/j.proci.2024.105509","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105509","url":null,"abstract":"Ammonia (NH) is now attracting attention in the energy field due to its hydrogen-containing and carbon-free, vast infrastructure, safe utilization and longstanding storage. Nevertheless, NH combustion is usually associated with low flame instability and high NO emissions due to its low laminar flame speed and nitrogen content. The partial catalytic cracking of NH offers an economical strategy to improve combustion stability. However, the significant limitations of this strategy include high NO emissions. Therefore, the MILD combustion of partial catalytic cracking of NH is an excellent method to address the challenge. In this work, a novel trimetallic catalyst (Fe, Co, and Ni) was developed, and the MILD combustion of partially catalyzed NH and NH/N was performed in a novel burner. The effects of the NH conversion, N addition and NH power on pollutant emissions were experimental investigated. Numerical simulations were carried out to analyze the characteristics in the MILD combustion of partially catalyzed NH and NH/N observed in the experiments.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"33 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886609","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 : 2024-07-24DOI: 10.1016/j.proci.2024.105629
Ye Wang, Mamoru Tanahashi
The three-dimensional geometric structure of near-wall flame and its effect on the near-wall flame quenching characteristics have been investigated using direct numerical simulation data of a V-shaped H-air flame in turbulent channel flow. The principal curvatures of the flame are calculated to categorize various flame structures. Additionally, the quenching status of the near-wall flame is evaluated based on a local fuel consumption speed, derived by integrating the fuel reaction rate across the local flame element. The results show that, there is a significant change in the statistical characteristics of the flame’s structure as it approaches the wall: flat flames predominate in the far-wall region, while cylindrical-shaped flames are more prevalent in the near-wall regions which align with the buffer layer and linear sublayer of the corresponding non-reacting turbulent boundary layer. A notable transition is observed from a turbulence-driven to a wall-driven influence on the flame’s geometric structure within the buffer layer. Meanwhile, the spherical and cylindrical flames convex towards the burned side, which are initially characterized by high reactivity in the far-wall area, exhibit a significant reduction in reaction rate within buffer layer. This leads to a shift in the general relationship between flame curvature and reactivity from a positive to a negative correlation. Furthermore, it has been found that the flame gets near-wall quenched mostly with a cylindrical surface. And, the flame elements convex towards the burned gas exhibit longer quenching distances and lower levels of wall heat flux compared to those with other geometric structures. The current results underscore the impact of flame’s geometric structure on its near-wall quenching characteristics. Future work will focus on investigating these findings in near-wall combustion under various turbulent conditions and different wall-bounded combustion configurations.
利用湍流通道流中 V 形 H 空气火焰的直接数值模拟数据，研究了近壁火焰的三维几何结构及其对近壁火焰熄灭特性的影响。通过计算火焰的主曲率，对各种火焰结构进行了分类。此外，还根据局部燃料消耗速度评估了近壁火焰的熄灭状态，该速度是通过对局部火焰元素的燃料反应速率进行积分而得出的。结果表明，当火焰接近壁面时，其结构的统计特征发生了显著变化：扁平火焰在远壁区域占主导地位，而圆柱形火焰在近壁区域更为普遍，近壁区域与相应的非反应湍流边界层的缓冲层和线性子层相一致。在缓冲层内，火焰的几何结构明显从湍流驱动过渡到壁面驱动。同时，凸向燃烧侧的球形和圆柱形火焰最初在远壁区域具有高反应性，但在缓冲层内的反应速率显著降低。这导致火焰曲率与反应率之间的一般关系从正相关转变为负相关。此外，研究还发现，近壁淬火的火焰多为圆柱形表面。而且，与其他几何结构的火焰相比，凸向燃烧气体的火焰元素表现出更长的淬火距离和更低的壁面热通量水平。目前的研究结果强调了火焰的几何结构对其近壁淬火特性的影响。未来的工作将重点研究在各种湍流条件和不同壁面燃烧配置下的近壁燃烧中的这些发现。
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Pub Date : 2024-07-24DOI: 10.1016/j.proci.2024.105537
Marco Davidovic, Heinz Pitsch
Mixture fraction-based models, such as non-premixed flamelet or Conditional Moment Closure (CMC) models, find widespread application in the investigation of turbulent combustion and pollutant formation. These models solve for the mixing field in physical space, while the chemistry solution is obtained in mixture fraction space. The coupling between the two fields is accomplished by two flow-dependent parameters governing the transport in mixture fraction space. These parameters must be computed consistently with the mixture fraction field evolution in order to preserve scalar mass conservation. Analytic expressions can be derived for obtaining these flow parameters consistently to the widely applied presumed Filtered Density Function (FDF) approach. Two approaches are considered in this paper: the local model formulates the local flow parameters consistently with the local FDF evolution before determining the global flow parameters through volume averaging. The global model integrates the FDF in physical space first and then determines the global flow parameter directly from the global mixture distribution evolution. These two models are employed in Large Eddy Simulations (LES) of an auto-igniting -dodecane spray. The simulation results are compared with each other and to a conventional flow parameters model, with a specific focus on scalar mass conservation. Both new models outperform the conventional model in terms of scalar mass conservation, with the most pronounced effect observed for soot. Furthermore, it is demonstrated that, although both new models are analytically equal, numerical errors arising from scalar convection terms in the LES solver impact mass conservation properties differently. The local model accurately predicts conditional flow parameters but suffers from numerical inconsistencies within discretized equations, resulting in scalar mass conservation errors, particularly for highly-diffusive numerical schemes. In contrast, the global model incorporates numerical errors from the flow solver within the flow parameters, thus yielding small conservation errors for all considered scalar convection schemes.
基于混合物分数的模型，如非预混合火焰模型或条件矩闭合（CMC）模型，广泛应用于研究湍流燃烧和污染物的形成。这些模型在物理空间中求解混合场，而在混合物分数空间中求解化学场。这两个场之间的耦合是通过两个与流动有关的参数来实现的，这两个参数控制着混合物分数空间的传输。这些参数的计算必须与混合分数场的演化保持一致，以保持标量质量守恒。根据广泛应用的滤波密度函数（FDF）方法，可以推导出获得这些流动参数的解析表达式。本文考虑了两种方法：局部模型在通过体积平均法确定全局流动参数之前，先根据局部 FDF 演化确定局部流动参数。全局模型则是先在物理空间整合 FDF，然后直接根据全局混合物分布演化确定全局流动参数。这两种模型被用于自燃十二烷喷雾的大涡流模拟（LES）。模拟结果与传统的流动参数模型进行了比较，重点是标量质量守恒。两种新模型在标量质量守恒方面都优于传统模型，其中对烟尘的影响最为明显。此外，研究还表明，尽管两种新模型在分析上是相同的，但 LES 求解器中的标量对流项产生的数值误差对质量守恒特性的影响是不同的。局部模型能准确预测条件流参数，但受离散方程中数值不一致的影响，导致标量质量守恒误差，特别是对于高扩散数值方案。与此相反，全局模型将流动求解器的数值误差纳入流动参数中，因此对所有考虑的标量对流方案来说，质量守恒误差都很小。
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