Spot fire is an important ignition pathway in the rapid spread of wildland and wildland-urban interface (WUI) fires. Firebrand combustion regime (flaming or glowing) and flame characteristics (flame tilt angle, flame length, and flame duration) are critical in predicting firebrand burning rate, spotting distance, and ignition hazard. Experiments were conducted to study firebrand combustion with various firebrand diameters ( = 10 to 20 mm) and wind speeds ( = 0 to 6 m s). The effects of the cross-wind on the pyrolysis rate, flame tilt angle (), flame length, and flame duration are investigated before the transition from flaming to glowing combustion ( 5 m s in this work). The pyrolysis rate is derived, showing it is proportional to ( is pyrolysis diameter). Then, the tan, flame length, and flame duration models are proposed based on the pyrolysis rate model. The tan is determined by wind speed and flame uprising speed (a speed controlled by the pyrolysis rate). The wind speed has a noticeable effect on the flame tilt angle. The derived flame length positively correlates with the volatile combustion rate, which is related to the pyrolysis rate. The flame length is proportional to and inversely proportional to for < 90°. The flame duration model is also derived, showing that the flame duration is related to the reduction rate of and is thus also affected by the pyrolysis rate. The flame duration is proportional to and inversely proportional to . The model predictions in tan, flame length, and flame duration agree well with the experimental data. Finally, a correlation equation of flame extinction ( 5 m s in this work) is related to critical wind speed and firebrand diameter.
点火是野地和野地-城市界面（WUI）火灾迅速蔓延的重要引燃途径。火种燃烧机制（燃烧或发光）和火焰特征（火焰倾斜角、火焰长度和火焰持续时间）对于预测火种燃烧速度、点火距离和点火危险至关重要。实验研究了不同火苗直径（= 10 至 20 毫米）和风速（= 0 至 6 米秒）下的火苗燃烧情况。在从火焰燃烧过渡到发光燃烧之前（5 m s），研究了横风对热分解率、火焰倾斜角（）、火焰长度和火焰持续时间的影响。推导出热解速率，表明它与 （为热解直径）成正比。然后，根据热解速率模型提出了 tan 值、火焰长度和火焰持续时间模型。tan 由风速和火焰上升速度（由热解速率控制的速度）决定。风速对火焰倾斜角有明显影响。得出的火焰长度与挥发燃烧速率呈正相关，而挥发燃烧速率与热解速率相关。火焰长度与 < 90° 成正比，与 < 90° 成反比。还推导出了火焰持续时间模型，表明火焰持续时间与火焰的还原率有关，因此也受热解率的影响。火焰持续时间与 tan 值、火焰长度和火焰持续时间成正比，与实验数据成反比。最后，火焰熄灭（本研究中为 5 m s）的相关方程与临界风速和火焰直径有关。
{"title":"Effect of cross-wind on firebrand flame: An experimental study and scaling analysis","authors":"Weidong Yan, Naian Liu, Hong Zhu, Haixiang Chen, Xiaodong Xie, Linhe Zhang","doi":"10.1016/j.proci.2024.105621","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105621","url":null,"abstract":"Spot fire is an important ignition pathway in the rapid spread of wildland and wildland-urban interface (WUI) fires. Firebrand combustion regime (flaming or glowing) and flame characteristics (flame tilt angle, flame length, and flame duration) are critical in predicting firebrand burning rate, spotting distance, and ignition hazard. Experiments were conducted to study firebrand combustion with various firebrand diameters ( = 10 to 20 mm) and wind speeds ( = 0 to 6 m s). The effects of the cross-wind on the pyrolysis rate, flame tilt angle (), flame length, and flame duration are investigated before the transition from flaming to glowing combustion ( 5 m s in this work). The pyrolysis rate is derived, showing it is proportional to ( is pyrolysis diameter). Then, the tan, flame length, and flame duration models are proposed based on the pyrolysis rate model. The tan is determined by wind speed and flame uprising speed (a speed controlled by the pyrolysis rate). The wind speed has a noticeable effect on the flame tilt angle. The derived flame length positively correlates with the volatile combustion rate, which is related to the pyrolysis rate. The flame length is proportional to and inversely proportional to for < 90°. The flame duration model is also derived, showing that the flame duration is related to the reduction rate of and is thus also affected by the pyrolysis rate. The flame duration is proportional to and inversely proportional to . The model predictions in tan, flame length, and flame duration agree well with the experimental data. Finally, a correlation equation of flame extinction ( 5 m s in this work) is related to critical wind speed and firebrand diameter.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"78 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886571","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 : 2024-08-02DOI: 10.1016/j.proci.2024.105609
Alexander J. Eder, Bayu Dharmaputra, Alex M. Garcia, Camilo F. Silva, Wolfgang Polifke
Unsteady combustion generates not only acoustic waves, but also fluctuations of the burnt gas temperature — referred to as entropy waves. These waves are convected by the mean flow through the combustor and result in conversion to acoustic energy when accelerated in an exit nozzle. The upstream traveling acoustic wave can then couple with the unsteady heat release of the flame and cause self-excited thermoacoustic instability, particularly at low frequencies (“rumble”). In this work, large eddy simulation (LES) is combined with system identification (SI) to determine the entropy transfer function (ETF) of a partially premixed, swirl-stabilized flame with hydrogen enrichment. We compare the single-input single-output (SISO) entropy transfer function identified from a broadband-forced LES with air mass flow modulation to the one obtained experimentally through tunable diode laser absorption spectroscopy with wavelength modulation spectroscopy (TDLAS-WMS) to measure temperature fluctuations. Then, multiple-input single-output (MISO) identification is applied to time series data obtained from simultaneous modulation of air and fuel mass flow to estimate the individual contributions of perturbations in velocity and equivalence ratio to entropy response. Equivalence ratio fluctuations are found to be the dominant generation mechanism of entropy waves. Finally, the entropy transfer function is identified at various positions in the combustion chamber to analyze the decay of entropy waves governed by convective dispersion.
非稳态燃烧不仅会产生声波，还会产生燃烧气体温度的波动，即熵波。这些波由通过燃烧器的平均气流对流，在出口喷嘴中加速后转化为声能。然后，上游行进的声波会与火焰的不稳定热释放耦合，导致自激热声不稳定性，尤其是在低频（"隆隆声"）时。在这项研究中，大涡流模拟（LES）与系统识别（SI）相结合，确定了氢气富集的部分预混漩涡稳定火焰的熵传递函数（ETF）。我们将通过空气质量流量调制宽带强迫 LES 确定的单输入单输出（SISO）熵传递函数与通过可调谐二极管激光吸收光谱与波长调制光谱（TDLAS-WMS）测量温度波动实验获得的熵传递函数进行了比较。然后，对同时调制空气和燃料质量流量获得的时间序列数据进行多输入单输出（MISO）识别，以估算速度和等效比扰动对熵响应的单独贡献。结果发现，等效比波动是熵波的主要产生机制。最后，确定了燃烧室中不同位置的熵传递函数，以分析对流扩散所控制的熵波衰减。
{"title":"Identification of entropy waves in a partially premixed combustor","authors":"Alexander J. Eder, Bayu Dharmaputra, Alex M. Garcia, Camilo F. Silva, Wolfgang Polifke","doi":"10.1016/j.proci.2024.105609","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105609","url":null,"abstract":"Unsteady combustion generates not only acoustic waves, but also fluctuations of the burnt gas temperature — referred to as entropy waves. These waves are convected by the mean flow through the combustor and result in conversion to acoustic energy when accelerated in an exit nozzle. The upstream traveling acoustic wave can then couple with the unsteady heat release of the flame and cause self-excited thermoacoustic instability, particularly at low frequencies (“rumble”). In this work, large eddy simulation (LES) is combined with system identification (SI) to determine the entropy transfer function (ETF) of a partially premixed, swirl-stabilized flame with hydrogen enrichment. We compare the single-input single-output (SISO) entropy transfer function identified from a broadband-forced LES with air mass flow modulation to the one obtained experimentally through tunable diode laser absorption spectroscopy with wavelength modulation spectroscopy (TDLAS-WMS) to measure temperature fluctuations. Then, multiple-input single-output (MISO) identification is applied to time series data obtained from simultaneous modulation of air and fuel mass flow to estimate the individual contributions of perturbations in velocity and equivalence ratio to entropy response. Equivalence ratio fluctuations are found to be the dominant generation mechanism of entropy waves. Finally, the entropy transfer function is identified at various positions in the combustion chamber to analyze the decay of entropy waves governed by convective dispersion.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"99 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886572","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}
Reducing the environmental impact of aircraft engines could be achieved in particular through the use of drop-in sustainable aviation fuels. However, changing the fuel composition could give rise to operating issues, among which are transverse/azimuthal thermoacoustic combustion instabilities. In this context, the paper aims at characterizing the effect of two-component liquid fuel mixtures of n-heptane and dodecane on the dynamics of swirl-stabilized spray flames in a forced transverse acoustic mode of the combustion chamber. This is done by using a linear array of three flames, TACC-Spray, in which the central flame is placed at a pressure antinode. Analyses of the flame dynamics through the downstream-pressure-based Flame Describing Function, and of the thermoacoustic coupling qualified by a Rayleigh index show that increasing the proportion of n-heptane favors the propensity to instabilities. Flame dynamics is typified by the propagation of longitudinal flame intensity waves, whose amplitude significantly increases with the proportion of n-heptane. The fuel spray dynamics participates in the flame dynamics through the presence of droplet number waves and the oscillations of the Sauter mean diameter. The propagation of droplet number waves correlates well with that of flame intensity waves, indicating that the former waves are a fundamental mechanism at the basis of the swirl-stabilized spray flames dynamics. The decrease of the evaporation rate as the proportion of dodecane is increased appears as an essential feature which induces a weaker flame dynamics.
{"title":"Effect of two-component liquid fuel mixtures on the dynamics of a swirl-stabilized spray flames array subjected to a forced transverse acoustic mode","authors":"Abdallah Alhaffar, Clément Patat, Jean-Bernard Blaisot, Éric Domingues, Françoise Baillot","doi":"10.1016/j.proci.2024.105566","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105566","url":null,"abstract":"Reducing the environmental impact of aircraft engines could be achieved in particular through the use of drop-in sustainable aviation fuels. However, changing the fuel composition could give rise to operating issues, among which are transverse/azimuthal thermoacoustic combustion instabilities. In this context, the paper aims at characterizing the effect of two-component liquid fuel mixtures of n-heptane and dodecane on the dynamics of swirl-stabilized spray flames in a forced transverse acoustic mode of the combustion chamber. This is done by using a linear array of three flames, TACC-Spray, in which the central flame is placed at a pressure antinode. Analyses of the flame dynamics through the downstream-pressure-based Flame Describing Function, and of the thermoacoustic coupling qualified by a Rayleigh index show that increasing the proportion of n-heptane favors the propensity to instabilities. Flame dynamics is typified by the propagation of longitudinal flame intensity waves, whose amplitude significantly increases with the proportion of n-heptane. The fuel spray dynamics participates in the flame dynamics through the presence of droplet number waves and the oscillations of the Sauter mean diameter. The propagation of droplet number waves correlates well with that of flame intensity waves, indicating that the former waves are a fundamental mechanism at the basis of the swirl-stabilized spray flames dynamics. The decrease of the evaporation rate as the proportion of dodecane is increased appears as an essential feature which induces a weaker flame dynamics.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"220 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886421","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 : 2024-08-01DOI: 10.1016/j.proci.2024.105610
Chao Peng, Chun Zou, Jiacheng Liu, Lingfeng Dai, Wenxiang Xia
Ammonia is a promising alternative clean fuel due to its carbon-free, high energy density and well-established infrastructure of storage and distribution. The co-combustion with reactive fuels improves the NH combustion stability. Moreover, CH is an important intermediate product in the oxidation of many hydrocarbon fuels. Therefore, some researchers focused the fundamental study and soot formation of NH/CH combustion. A reliable combustion model of NH/CH advances the understanding of the interaction between NH and CH. The key to develop the model of NH /CH is the cross reactions between N-containing species and C-containing species. In this work, the ignition delay times of NH/CH mixtures were measured at three blending ratios (95 %, 90 %, 70 % NH) at 1.75atm and 10atm in a shock tube at the temperature range of 1247 K to 1786 K. A detailed chemical kinetic model was developed on the base of our previous optimizing NH model and the CC sub-model of NUIGMECH1.1, and some new cross reactions between N-containing species and hydrocarbon species were considered in the model. The NH-CH model is validated by the current experimental data, the laminar flame speeds of NH/CH mixtures and the species profiles of NH/CH mixtures oxidation. The cross reactions considered in this work significantly improve the prediction. The disproportionation reactions, CH + NH <=> CH + NH (R1466) and HCO + NH <=> CO + NH (R1465), significantly inhibit the ignition and the flame propagation, and cause the increase in the formation of HCO and HCCO with the increase of NH content, which facilitates the reduction of the soot formation.
氨是一种前景广阔的替代清洁燃料，因为它不含碳、能量密度高，而且具有完善的储存和分配基础设施。与活性燃料共燃可提高 NH 燃烧的稳定性。此外，CH 是许多碳氢化合物燃料氧化过程中的重要中间产物。因此，一些研究人员将 NH/CH 燃烧的基础研究和烟尘形成作为重点。一个可靠的 NH/CH 燃烧模型可以加深对 NH 和 CH 之间相互作用的理解。建立 NH /CH 燃烧模型的关键在于含 N 物种和含 C 物种之间的交叉反应。在这项工作中，我们在 1.75atm 和 10atm 的冲击管中，在 1247 K 到 1786 K 的温度范围内，测量了 NH/CH 混合物在三种混合比（95%、90%、70% NH）下的点火延迟时间。在我们之前优化的 NH 模型和 NUIGMECH1.1 的 CC 子模型的基础上，建立了一个详细的化学动力学模型，并在模型中考虑了含 N 物种和碳氢化合物物种之间的一些新的交叉反应。NH-CH 模型通过当前的实验数据、NH/CH 混合物的层流火焰速度和 NH/CH 混合物氧化的物种分布图进行了验证。本研究中考虑的交叉反应大大提高了预测效果。歧化反应 CH + NH CH + NH (R1466) 和 HCO + NH CO + NH (R1465) 显著抑制了点火和火焰传播，并导致 HCO 和 HCCO 的形成随 NH 含量的增加而增加，从而有利于减少烟尘的形成。
{"title":"Shock tube and modeling study on the ignition delay times of ammonia/ethylene mixtures at high temperatures","authors":"Chao Peng, Chun Zou, Jiacheng Liu, Lingfeng Dai, Wenxiang Xia","doi":"10.1016/j.proci.2024.105610","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105610","url":null,"abstract":"Ammonia is a promising alternative clean fuel due to its carbon-free, high energy density and well-established infrastructure of storage and distribution. The co-combustion with reactive fuels improves the NH combustion stability. Moreover, CH is an important intermediate product in the oxidation of many hydrocarbon fuels. Therefore, some researchers focused the fundamental study and soot formation of NH/CH combustion. A reliable combustion model of NH/CH advances the understanding of the interaction between NH and CH. The key to develop the model of NH /CH is the cross reactions between N-containing species and C-containing species. In this work, the ignition delay times of NH/CH mixtures were measured at three blending ratios (95 %, 90 %, 70 % NH) at 1.75atm and 10atm in a shock tube at the temperature range of 1247 K to 1786 K. A detailed chemical kinetic model was developed on the base of our previous optimizing NH model and the CC sub-model of NUIGMECH1.1, and some new cross reactions between N-containing species and hydrocarbon species were considered in the model. The NH-CH model is validated by the current experimental data, the laminar flame speeds of NH/CH mixtures and the species profiles of NH/CH mixtures oxidation. The cross reactions considered in this work significantly improve the prediction. The disproportionation reactions, CH + NH <=> CH + NH (R1466) and HCO + NH <=> CO + NH (R1465), significantly inhibit the ignition and the flame propagation, and cause the increase in the formation of HCO and HCCO with the increase of NH content, which facilitates the reduction of the soot formation.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"30 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886577","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}
Chemical looping combustion (CLC) reactors have developed into megawatt units, calling for industrial-scale oxygen carriers (OCs). Four typical OCs with potential for industrial-scale applications are quantitatively evaluated in terms of reactivity and attrition, including ilmenite (labeled as Ilm-NO), Cu-Fe bi-ore OC through hydroforming (labeled as CuFe-Hy), perovskite through spray drying (labeled as Per-SD), and Cu-based OC through impregnation (labeled as CuAl-Im). The 20-cycle reactivity test is operated in a batch fluidized bed reactor, while the 5-hour attrition test is conducted in an air jet attrition reactor. With the determined reduction durations via breakthrough testing, all OCs show no decrease in methane combustion performance. CuAl-Im demonstrates the highest instantaneous oxygen transferring rate of ca. 19.5 × 10 wt.%/s and the second maximum accumulated oxygen transferring amount of 3.74 wt.%. The OC reactivity follows the order of CuAl-Im > Per-SD > CuFe-Im > Ilm-NO. The attrition test results indicate that the attrition indexes, inversely proportional to the lifetimes of OCs, are 0.04 wt.% for Ilm-NO, 0.32 wt.% for CuFe-Hy, 0.20 wt.% for Per-SD, and 0.04 wt.% for CuAl-Im. Characterization results demonstrate all OCs get developed in pore structures except CuAl-Im due to its severe sintering after the reactivity test, which suppresses the regeneration of minor CuAlO. Reduced crushing strengths of four OCs are observed. Additionally, their phases are relatively stable, except for the migration of iron in Ilm-NO and CuFe-Hy, and the copper migration in CuAl-Im. The proposed method can be a preliminary standard to screen appropriate OC for industrial CLC units. The cycle number can be further reduced to 10 according to the reactivity tests, while the benchmark test details such the concentration of testing gases, reaction temperature, and reduction duration may need further consideration. Anyway, the obtained results are beneficial to the selection of OC for CLC of methane.
{"title":"Quantitative evaluation of four oxygen carriers for natural gas chemical looping combustion","authors":"Xianyu Liu, Zhenshan Li, Laihong Shen, Jinchen Ma, Xinhe Liu, Diwen He, Haibo Zhao","doi":"10.1016/j.proci.2024.105641","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105641","url":null,"abstract":"Chemical looping combustion (CLC) reactors have developed into megawatt units, calling for industrial-scale oxygen carriers (OCs). Four typical OCs with potential for industrial-scale applications are quantitatively evaluated in terms of reactivity and attrition, including ilmenite (labeled as Ilm-NO), Cu-Fe bi-ore OC through hydroforming (labeled as CuFe-Hy), perovskite through spray drying (labeled as Per-SD), and Cu-based OC through impregnation (labeled as CuAl-Im). The 20-cycle reactivity test is operated in a batch fluidized bed reactor, while the 5-hour attrition test is conducted in an air jet attrition reactor. With the determined reduction durations via breakthrough testing, all OCs show no decrease in methane combustion performance. CuAl-Im demonstrates the highest instantaneous oxygen transferring rate of ca. 19.5 × 10 wt.%/s and the second maximum accumulated oxygen transferring amount of 3.74 wt.%. The OC reactivity follows the order of CuAl-Im > Per-SD > CuFe-Im > Ilm-NO. The attrition test results indicate that the attrition indexes, inversely proportional to the lifetimes of OCs, are 0.04 wt.% for Ilm-NO, 0.32 wt.% for CuFe-Hy, 0.20 wt.% for Per-SD, and 0.04 wt.% for CuAl-Im. Characterization results demonstrate all OCs get developed in pore structures except CuAl-Im due to its severe sintering after the reactivity test, which suppresses the regeneration of minor CuAlO. Reduced crushing strengths of four OCs are observed. Additionally, their phases are relatively stable, except for the migration of iron in Ilm-NO and CuFe-Hy, and the copper migration in CuAl-Im. The proposed method can be a preliminary standard to screen appropriate OC for industrial CLC units. The cycle number can be further reduced to 10 according to the reactivity tests, while the benchmark test details such the concentration of testing gases, reaction temperature, and reduction duration may need further consideration. Anyway, the obtained results are beneficial to the selection of OC for CLC of methane.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"82 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886418","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 : 2024-08-01DOI: 10.1016/j.proci.2024.105644
Ayman M. Elbaz, Zubayr O. Hassan, William L. Roberts
Ammonia's appeal as a clean, carbon-free fuel is marred by its low reactivity and high NOx emissions, limiting its practical use. Understanding swirl intensity's influence on ammonia flame stabilization and emissions remains a gap. This study endeavors to explore the impact of swirl intensity on stabilization, NO/NH emissions, and the spatial distribution of NO and OH radicals in non-premixed NH/CH swirling flames. The burner consists of a central fuel jet (with a fuel jet velocity, U) surrounded by swirling airflow (of an air velocity, U). A blend of NH/CH, with ammonia mole fraction (: 0 to 0.85), was supplied to the central jet. The stability map, comparing U versus U, revealed that at the same swirl number (S), as U increased, a higher U became necessary to extinguish the flame, while, the higher levels amplified the sensitivity of U to U. For ≤ 0.25, an increase in S elevated the U required for the flame to blowout. However, this impact of S diminishes as increases until it starts to adversely reduce the blowout limits at = 0.85. At ≥ 0.75, adjusting Φ (the global mixture equivalence ratio) towards stoichiometry alongside increased S effectively lowers NO emissions and limits NH slip into the exhaust. The OH/NO-PLIF measurements highlight conical OH/NO layers near the burner exit. This conical NO layer transforms into a broader and more uniformly downstream, where the intensity of NO within this area likely mirrors the NO levels measured in the exhaust. Increasing at low S flames elongates both the OH/NO structure and intensifies the NO gradient in downstream distances. Conversely, an increase in S enhances fuel/air mixing and diminishes the impact of increased and Φ on the flame structure. A reduced sensitivity of NO emissions to Φ is observed with increasing S.
氨作为一种清洁的无碳燃料，其低反应性和高氮氧化物排放量使其吸引力大打折扣，限制了其实际应用。了解漩涡强度对氨火焰稳定和排放的影响仍然是一个空白。本研究试图探索漩涡强度对稳定、NO/NH 排放以及非预混合 NH/CH 漩涡火焰中 NO 和 OH 自由基空间分布的影响。燃烧器由中心燃料喷射（燃料喷射速度为 U）和漩涡气流（气流速度为 U）组成。氨分子分数（：0 至 0.85）的 NH/CH 混合物被提供给中央射流。通过比较 U 与 U 的稳定性图可以发现，在相同的漩涡数（S）下，随着 U 的增加，熄灭火焰所需的 U 越高，同时，较高的水平放大了 U 对 U 的敏感性。然而，S 的影响随着 S 的增加而减小，直到 = 0.85 时才开始不利地降低喷火极限。在 ≥ 0.75 时，在增加 S 的同时，将 Φ（全局混合物当量比）调整为化学计量，可有效降低 NO 排放量并限制 NH 滑入排气管。OH/NO-PLIF 测量结果突出显示了燃烧器出口附近的锥形 OH/NO 层。锥形 NO 层转变为更宽广、更均匀的下游，该区域内的 NO 强度可能反映了排气中测得的 NO 水平。在低 S 条件下，火焰温度升高会拉长 OH/NO 结构，并加剧下游距离的 NO 梯度。相反，S 的增加会加强燃料/空气的混合，并减弱增加和 Φ 对火焰结构的影响。随着 S 的增加，NO 排放对 Φ 的敏感性也会降低。
{"title":"Exploring the influence of swirl intensity on stability, emissions, and flame structure in non-premixed NH3/CH4 swirling flames","authors":"Ayman M. Elbaz, Zubayr O. Hassan, William L. Roberts","doi":"10.1016/j.proci.2024.105644","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105644","url":null,"abstract":"Ammonia's appeal as a clean, carbon-free fuel is marred by its low reactivity and high NOx emissions, limiting its practical use. Understanding swirl intensity's influence on ammonia flame stabilization and emissions remains a gap. This study endeavors to explore the impact of swirl intensity on stabilization, NO/NH emissions, and the spatial distribution of NO and OH radicals in non-premixed NH/CH swirling flames. The burner consists of a central fuel jet (with a fuel jet velocity, U) surrounded by swirling airflow (of an air velocity, U). A blend of NH/CH, with ammonia mole fraction (: 0 to 0.85), was supplied to the central jet. The stability map, comparing U versus U, revealed that at the same swirl number (S), as U increased, a higher U became necessary to extinguish the flame, while, the higher levels amplified the sensitivity of U to U. For ≤ 0.25, an increase in S elevated the U required for the flame to blowout. However, this impact of S diminishes as increases until it starts to adversely reduce the blowout limits at = 0.85. At ≥ 0.75, adjusting Φ (the global mixture equivalence ratio) towards stoichiometry alongside increased S effectively lowers NO emissions and limits NH slip into the exhaust. The OH/NO-PLIF measurements highlight conical OH/NO layers near the burner exit. This conical NO layer transforms into a broader and more uniformly downstream, where the intensity of NO within this area likely mirrors the NO levels measured in the exhaust. Increasing at low S flames elongates both the OH/NO structure and intensifies the NO gradient in downstream distances. Conversely, an increase in S enhances fuel/air mixing and diminishes the impact of increased and Φ on the flame structure. A reduced sensitivity of NO emissions to Φ is observed with increasing S.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"75 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886417","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 : 2024-08-01DOI: 10.1016/j.proci.2024.105619
Chonglv Cheng, Conghui Shan, Baopeng Xu, Jennifer X. Wen
Dynamic predictions of the mass burning rate of pool fires under different burner conditions are essential to facilitate pool fire simulations without the need for artificially setting the inlet boundary conditions for the fuel surface. Such capability can remove the need for prescribed mass burning rates of pool fires in quantified assessment of the fire hazards. A fully coupled three-dimensional (3-D) model based on a multi-zone approach has been developed. In the gas-phase region, a compressible solver was employed. In the liquid-phase region, an incompressible solver with temperature-dependent thermophysical properties was utilized to directly solve fuel flow, accounting for the Marangoni effect, buoyancy effect, and incident radiation. In the solid-phase region, the 3-D heat transfer equation was resolved. The heat and mass transfer processes between different regions were simulated using conjugate heat transfer and an evaporation model based on "film theory". The proposed model has been validated through comparison with the 9 cm diameter methanol pool fire experiments. The predictions showed promising agreement with experimental measurements and empirical corrections, with the error in mass burn rate being within 3.1 %. Additionally, the predictions have captured a pair of vortices in sizes and directions closely resembling experimental observations. The sizes of the predicted vortices increased with the rising temperature at the base of the pool due to buoyancy and shear force. The analysis revealed that the wall effect not only leads to differences in the number of vortices and Marangoni velocity but also leads to a smaller mass burning rate in the burner with a high thermal conductivity than in the one with a poor thermal conductivity in the 9 cm diameter methanol pool fire. Neglecting the wall heat transfer would result in up to 18 % underprediction of the mass burning rate.
{"title":"Numerical study of the wall effect on the mass burning rate of small-scale methanol pool fires","authors":"Chonglv Cheng, Conghui Shan, Baopeng Xu, Jennifer X. Wen","doi":"10.1016/j.proci.2024.105619","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105619","url":null,"abstract":"Dynamic predictions of the mass burning rate of pool fires under different burner conditions are essential to facilitate pool fire simulations without the need for artificially setting the inlet boundary conditions for the fuel surface. Such capability can remove the need for prescribed mass burning rates of pool fires in quantified assessment of the fire hazards. A fully coupled three-dimensional (3-D) model based on a multi-zone approach has been developed. In the gas-phase region, a compressible solver was employed. In the liquid-phase region, an incompressible solver with temperature-dependent thermophysical properties was utilized to directly solve fuel flow, accounting for the Marangoni effect, buoyancy effect, and incident radiation. In the solid-phase region, the 3-D heat transfer equation was resolved. The heat and mass transfer processes between different regions were simulated using conjugate heat transfer and an evaporation model based on \"film theory\". The proposed model has been validated through comparison with the 9 cm diameter methanol pool fire experiments. The predictions showed promising agreement with experimental measurements and empirical corrections, with the error in mass burn rate being within 3.1 %. Additionally, the predictions have captured a pair of vortices in sizes and directions closely resembling experimental observations. The sizes of the predicted vortices increased with the rising temperature at the base of the pool due to buoyancy and shear force. The analysis revealed that the wall effect not only leads to differences in the number of vortices and Marangoni velocity but also leads to a smaller mass burning rate in the burner with a high thermal conductivity than in the one with a poor thermal conductivity in the 9 cm diameter methanol pool fire. Neglecting the wall heat transfer would result in up to 18 % underprediction of the mass burning rate.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"55 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886419","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 : 2024-08-01DOI: 10.1016/j.proci.2024.105648
Fiorella Massa, Elisabetta Maria Cepollaro, Stefano Cimino, Antonio Coppola, Fabrizio Scala
CO capture from combustion flue gas combined to its catalytic hydrogenation to synthetic methane is considered as a promising technology in the field of Carbon Capture and Utilization (CCU). In this work, the integrated CO capture and methanation process was investigated in an innovative chemical looping configuration using dual function materials (DFMs) recirculated alternately between two interconnected bubbling fluidized bed reactors. By physically separating the CO capture step and the catalytic hydrogenation reaction in two coupled fluidized bed reactors it is possible to effectively control and independently optimize the operating temperature of each half cycle while running the process continuously. A high-performing Lithium-Ruthenium/AlO was selected to investigate the effect of the specific temperature level for the CO capture and the methanation phases in the range 200 - 400 °C, checking the stability and repeatability of the CO sorption and catalytic performance over 5 repeated cycles for each operating condition. Subsequently, under the best conditions in terms of methanation performance, a similar Na-promoted dual function material was also tested. The DFMs performance appeared to be quite reproducible over the cycles, but it was subject to kinetic limitations, especially in the case of Na-Ru/AlO. Interestingly, the methane yield approached 100 % under the highest tested temperatures for the Li-based DFM. Despite some limitations due to the experimental purge phases of the lab-scale system, the study provides the proof-of-concept of the process which enables the possibility of decoupling the two steps with the aim of a large potential intensification.
从燃烧烟道气中捕集一氧化碳并将其催化加氢转化为合成甲烷被认为是碳捕集与利用（CCU）领域一项前景广阔的技术。本研究采用创新的化学循环配置，在两个相互连接的鼓泡流化床反应器之间交替循环使用双功能材料 (DFM)，对一氧化碳捕集和甲烷化综合工艺进行了研究。通过在两个耦合流化床反应器中物理分离一氧化碳捕集步骤和催化加氢反应，可以在连续运行工艺的同时有效控制和独立优化每个半循环的工作温度。我们选择了一种高性能的锂-钌/氧化铝来研究 200 - 400 °C 范围内特定温度水平对一氧化碳捕集和甲烷化阶段的影响，检查每个操作条件下重复 5 个循环的一氧化碳吸附和催化性能的稳定性和可重复性。随后，在甲烷化性能最佳的条件下，还测试了类似的 Na 促进双功能材料。双功能材料在循环过程中的性能似乎具有相当高的可重复性，但受到动力学的限制，尤其是在 Na-Ru/AlO 的情况下。有趣的是，在最高测试温度下，锂基 DFM 的甲烷产量接近 100%。尽管实验室规模系统的实验净化阶段存在一些限制，但这项研究提供了该工艺的概念验证，使得将这两个步骤解耦成为可能，从而实现大幅提高潜力的目标。
{"title":"Fluidized bed chemical looping for CO2 capture and catalytic methanation using dual function materials","authors":"Fiorella Massa, Elisabetta Maria Cepollaro, Stefano Cimino, Antonio Coppola, Fabrizio Scala","doi":"10.1016/j.proci.2024.105648","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105648","url":null,"abstract":"CO capture from combustion flue gas combined to its catalytic hydrogenation to synthetic methane is considered as a promising technology in the field of Carbon Capture and Utilization (CCU). In this work, the integrated CO capture and methanation process was investigated in an innovative chemical looping configuration using dual function materials (DFMs) recirculated alternately between two interconnected bubbling fluidized bed reactors. By physically separating the CO capture step and the catalytic hydrogenation reaction in two coupled fluidized bed reactors it is possible to effectively control and independently optimize the operating temperature of each half cycle while running the process continuously. A high-performing Lithium-Ruthenium/AlO was selected to investigate the effect of the specific temperature level for the CO capture and the methanation phases in the range 200 - 400 °C, checking the stability and repeatability of the CO sorption and catalytic performance over 5 repeated cycles for each operating condition. Subsequently, under the best conditions in terms of methanation performance, a similar Na-promoted dual function material was also tested. The DFMs performance appeared to be quite reproducible over the cycles, but it was subject to kinetic limitations, especially in the case of Na-Ru/AlO. Interestingly, the methane yield approached 100 % under the highest tested temperatures for the Li-based DFM. Despite some limitations due to the experimental purge phases of the lab-scale system, the study provides the proof-of-concept of the process which enables the possibility of decoupling the two steps with the aim of a large potential intensification.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"36 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886576","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 : 2024-08-01DOI: 10.1016/j.proci.2024.105487
Sven Eckart, Krishna P. Shrestha, Binod R. Giri, Qilong Fang, Chen Chen, Wei Li, Hartmut Krause, Fabian Mauss, Dong Liu, Yuyang Li
Oxygenated fuels, such as alcohols, ethers, and esters, are promising alternatives to conventional fuels. These fuels can help reduce detrimental emissions like carbon monoxide and unburned hydrocarbons and enhance octane ratings. Among these oxygenates, ethyl acetate (EA), a small alkyl ester sourced from biomass, emerges as a clean, promising energy carrier. It serves as a surrogate fuel to facilitate investigations into the combustion behaviours of biodiesel. Despite its importance, the literature knowledge of EA combustion characteristics is limited. Therefore, this study aims to broaden the knowledge of the combustion behaviour of this type of oxygenated fuel compound. In this study, we measured the laminar burning velocities of EA by employing a heat flux burner and a closed combustion vessel over the equivalence ratios of 0.7 – 1.7, pressures of 1 – 10 bar and temperatures ranging from 353 – 423 K. Further, we also measured the NO emissions in exhaust gas of the premixed flames fueled by EA/air for the first time over the equivalence ratio of 0.8 – 1.2. Additionally, we employed a non-premixed counterflow flame setup for extensive characterisation of species and their concentration under diverse conditions encompassing various strain rates and oxygen concentrations. Finally, we utilized these newly measured data to construct and validate a detailed kinetic model developed as part of this work. The newly developed model will help characterize the combustion properties of EA.
醇类、醚类和酯类等含氧燃料是很有前途的传统燃料替代品。这些燃料有助于减少一氧化碳和未燃烧碳氢化合物等有害气体的排放，并提高辛烷值。在这些含氧化合物中，醋酸乙酯（EA）是一种来自生物质的小烷基酯，是一种清洁、有前途的能源载体。乙酸乙酯是一种替代燃料，有助于研究生物柴油的燃烧行为。尽管它很重要，但有关 EA 燃烧特性的文献知识却很有限。因此，本研究旨在拓宽对这类含氧燃料化合物燃烧特性的认识。在这项研究中，我们采用热通量燃烧器和封闭式燃烧容器，在当量比为 0.7 - 1.7、压力为 1 - 10 巴、温度为 353 - 423 K 的条件下测量了 EA 的层燃速度。此外，我们还首次在当量比为 0.8 - 1.2 的条件下测量了以 EA/空气为燃料的预混合火焰废气中的氮氧化物排放量。此外，我们还采用了非预混合逆流火焰装置，在包括各种应变率和氧气浓度在内的不同条件下，对物种及其浓度进行了广泛表征。最后，我们利用这些新测量的数据，构建并验证了在这项工作中开发的详细动力学模型。新开发的模型将有助于描述 EA 的燃烧特性。
{"title":"Chemical insights into ethyl acetate flames from experiment and kinetic modeling: Laminar burning velocity, speciation and NOx emission","authors":"Sven Eckart, Krishna P. Shrestha, Binod R. Giri, Qilong Fang, Chen Chen, Wei Li, Hartmut Krause, Fabian Mauss, Dong Liu, Yuyang Li","doi":"10.1016/j.proci.2024.105487","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105487","url":null,"abstract":"Oxygenated fuels, such as alcohols, ethers, and esters, are promising alternatives to conventional fuels. These fuels can help reduce detrimental emissions like carbon monoxide and unburned hydrocarbons and enhance octane ratings. Among these oxygenates, ethyl acetate (EA), a small alkyl ester sourced from biomass, emerges as a clean, promising energy carrier. It serves as a surrogate fuel to facilitate investigations into the combustion behaviours of biodiesel. Despite its importance, the literature knowledge of EA combustion characteristics is limited. Therefore, this study aims to broaden the knowledge of the combustion behaviour of this type of oxygenated fuel compound. In this study, we measured the laminar burning velocities of EA by employing a heat flux burner and a closed combustion vessel over the equivalence ratios of 0.7 – 1.7, pressures of 1 – 10 bar and temperatures ranging from 353 – 423 K. Further, we also measured the NO emissions in exhaust gas of the premixed flames fueled by EA/air for the first time over the equivalence ratio of 0.8 – 1.2. Additionally, we employed a non-premixed counterflow flame setup for extensive characterisation of species and their concentration under diverse conditions encompassing various strain rates and oxygen concentrations. Finally, we utilized these newly measured data to construct and validate a detailed kinetic model developed as part of this work. The newly developed model will help characterize the combustion properties of EA.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"34 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886422","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 : 2024-08-01DOI: 10.1016/j.proci.2024.105591
Jingru Zheng, Fei Tang, Suk Ho Chung, Longhua Hu
The effect of ammonia addition on the characteristics of liftoff, blowout, and instability is investigated experimentally in nonpremixed jet flames with NH/CH mixture fuels by the varying mole fraction of ammonia (). Both laminar and turbulent lifted flames are observed and the lifted flame for = 0.3 has a transition from laminar to turbulent lifted flame, when the jet flow is in the laminar-to-turbulent transition regime. The results demonstrate that, for ≤ 0.3, only turbulent lifted flame exists and the liftoff height increases linearly with the fuel jet velocity , as well as the ammonia mole fraction. A satisfactory linear relationship between nondimensional turbulent lifted flame height and nondimensional flow velocity can be obtained, based on the turbulent intensity theory. For > 0.3, only laminar lifted flame exists and the liftoff height increases reasonably linearly with , which is stabilized in the jet developing region. Both the critical liftoff () and blowout () velocities decrease with the increase in . When is scaled with laminar burning velocity , / is insensitive to for ≤ 0.3, having / ≈ 50, while it decreases linearly for > 0.3. While / decreases linearly with the increase in . These critical velocities show that no flame can be stabilized for > 0.5. The oscillation frequency of laminar nozzle-attached flame for CH/NH mixture fuel slightly increases with , while the critical Froude number (Fr) for the transition from sinuous to varicose modes of oscillation increases with ammonia addition. The flame oscillation frequency can be characterized by the Strouhal number St having a power law relationship of St ∝ (1/Fr).
{"title":"Characteristics of liftoff, blowout and instability in nonpremixed jet flames with NH3/CH4 mixture fuels","authors":"Jingru Zheng, Fei Tang, Suk Ho Chung, Longhua Hu","doi":"10.1016/j.proci.2024.105591","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105591","url":null,"abstract":"The effect of ammonia addition on the characteristics of liftoff, blowout, and instability is investigated experimentally in nonpremixed jet flames with NH/CH mixture fuels by the varying mole fraction of ammonia (). Both laminar and turbulent lifted flames are observed and the lifted flame for = 0.3 has a transition from laminar to turbulent lifted flame, when the jet flow is in the laminar-to-turbulent transition regime. The results demonstrate that, for ≤ 0.3, only turbulent lifted flame exists and the liftoff height increases linearly with the fuel jet velocity , as well as the ammonia mole fraction. A satisfactory linear relationship between nondimensional turbulent lifted flame height and nondimensional flow velocity can be obtained, based on the turbulent intensity theory. For > 0.3, only laminar lifted flame exists and the liftoff height increases reasonably linearly with , which is stabilized in the jet developing region. Both the critical liftoff () and blowout () velocities decrease with the increase in . When is scaled with laminar burning velocity , / is insensitive to for ≤ 0.3, having / ≈ 50, while it decreases linearly for > 0.3. While / decreases linearly with the increase in . These critical velocities show that no flame can be stabilized for > 0.5. The oscillation frequency of laminar nozzle-attached flame for CH/NH mixture fuel slightly increases with , while the critical Froude number (Fr) for the transition from sinuous to varicose modes of oscillation increases with ammonia addition. The flame oscillation frequency can be characterized by the Strouhal number St having a power law relationship of St ∝ (1/Fr).","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"34 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141886420","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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