Pub Date : 2024-08-21DOI: 10.1016/j.proci.2024.105700
Alfaisal M. Albalawi, Ayman M. Elbaz, Mahmoud M.A. Ahmed, Zubayr O. Hassan, William L. Roberts
Inspired by the attractiveness of ammonia as an energy carrier coupled with the relative lack of experimental data at industrially-relevant conditions for ammonia/ammonia-blended flames, the current work was undertaken to help fill gaps in our understanding. This study reports the structure and stability of non-premixed, simulated cracked ammonia jet flames at three different cracking ratios (CR) (40%, 50%, and 60%) and pressures (1, 2, and 3 bar), and two different co-flow temperatures (295 and 573 K) using a newly commissioned high-pressure and temperature combustion duct. Measurements of qualitative OH and NO via PLIF were conducted to study the near-field flame structure. The results revealed that the detachment velocity increases monotonically with CR, however for a given CR, the detachment velocity decreases with pressure. For CR 55%, the jet flame exhibits a stable lifted flame behavior whereas blowout occurs directly after detachment for CR 55%. The visible flame length/size tends to slightly increase with pressure for the unheated co-flow cases, while the opposite trend was observed for the heated co-flow cases. As CR increases, the flame length/size slightly decreases regardless the pressure and co-flow temperature. It was observed that increasing CR increases the intensity of OH radicals while the NO intensity is reduced. It is suggested that the mismatch between peak NO and OH locations, which increases with CR, promotes the thermal-NO pathway rather than the fuel-NO pathway. Overall, increasing the pressure and co-flow temperature leads to a significant decrease in the peak NO and OH mismatch. Furthermore, as the pressure increases, both OH and NO intensities decrease when the co-flow is at room temperature. Nevertheless, increasing the pressure in the heated co-flow flames results in decreasing OH intensity while increasing that of the NO. This discrepancy between co-flow temperatures with pressure indicates the need for further investigation.
氨作为一种能量载体极具吸引力，但在氨/氨混合火焰的工业相关条件下却相对缺乏实验数据，受此启发，我们开展了当前的研究工作，以帮助填补我们的认识空白。本研究报告了在三种不同的裂解率（CR）（40%、50% 和 60%）和压力（1、2 和 3 巴）以及两种不同的共流温度（295 和 573 K）条件下，使用新调试的高压和高温燃烧管道模拟的非预混合裂解氨喷射火焰的结构和稳定性。通过 PLIF 对定性 OH 和 NO 进行了测量，以研究近场火焰结构。结果表明，脱离速度随 CR 的增加而单调增加，但对于给定的 CR，脱离速度随压力的增加而降低。对于 CR 55%，喷射火焰表现出稳定的抬升火焰行为，而对于 CR 55%，脱离后会直接喷出。在未加热的同流情况下，可见火焰的长度/大小随着压力的增加而略有增加，而在加热的同流情况下则出现相反的趋势。随着 CR 的增加，无论压力和同流温度如何，火焰长度/大小都会略微减小。据观察，CR 的增加会增加 OH 自由基的强度，而 NO 的强度则会降低。这表明，随着 CR 的增加，NO 和 OH 的峰值位置不匹配，促进了热-NO 途径，而不是燃料-NO 途径。总体而言，提高压力和共流温度会显著降低 NO 和 OH 的峰值错配。此外，随着压力的增加，当共流物处于室温时，OH 和 NO 的强度都会降低。然而，在加热的同流火焰中增加压力会导致 OH 强度下降，而 NO 强度上升。共流体温度与压力之间的这种差异表明需要进一步研究。
{"title":"Investigation of the near-field structure and stability of non-premixed NH[formula omitted]/H[formula omitted]/N[formula omitted] jet flames at various pressure and co-flow conditions","authors":"Alfaisal M. Albalawi, Ayman M. Elbaz, Mahmoud M.A. Ahmed, Zubayr O. Hassan, William L. Roberts","doi":"10.1016/j.proci.2024.105700","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105700","url":null,"abstract":"Inspired by the attractiveness of ammonia as an energy carrier coupled with the relative lack of experimental data at industrially-relevant conditions for ammonia/ammonia-blended flames, the current work was undertaken to help fill gaps in our understanding. This study reports the structure and stability of non-premixed, simulated cracked ammonia jet flames at three different cracking ratios (CR) (40%, 50%, and 60%) and pressures (1, 2, and 3 bar), and two different co-flow temperatures (295 and 573 K) using a newly commissioned high-pressure and temperature combustion duct. Measurements of qualitative OH and NO via PLIF were conducted to study the near-field flame structure. The results revealed that the detachment velocity increases monotonically with CR, however for a given CR, the detachment velocity decreases with pressure. For CR 55%, the jet flame exhibits a stable lifted flame behavior whereas blowout occurs directly after detachment for CR 55%. The visible flame length/size tends to slightly increase with pressure for the unheated co-flow cases, while the opposite trend was observed for the heated co-flow cases. As CR increases, the flame length/size slightly decreases regardless the pressure and co-flow temperature. It was observed that increasing CR increases the intensity of OH radicals while the NO intensity is reduced. It is suggested that the mismatch between peak NO and OH locations, which increases with CR, promotes the thermal-NO pathway rather than the fuel-NO pathway. Overall, increasing the pressure and co-flow temperature leads to a significant decrease in the peak NO and OH mismatch. Furthermore, as the pressure increases, both OH and NO intensities decrease when the co-flow is at room temperature. Nevertheless, increasing the pressure in the heated co-flow flames results in decreasing OH intensity while increasing that of the NO. This discrepancy between co-flow temperatures with pressure indicates the need for further investigation.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180208","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.2024.105594
Hua Hong, Stephen D. Tse
Graphene films are grown in an open atmosphere on metal substrates using a modified multiple inverse-diffusion flame (m-IDF) burner with hydrogen as fuel and hydrocarbon as precursor (delivered by multiple distinct tubes staged above the m-IDF burner surface). The flame synthesis procedure uses three stages consisting of () pretreatment, () growth, and () hydrogen etching and produces monolayer graphene (MLG) films with methane as a precursor on copper substrates at 1000 °C. Substrate material (e.g., copper, nickel, silicon), purity, and smoothness (i.e., unpolished, electropolished); precursor composition (i.e., CH, CH, CH); substrate orientation (i.e., parallel, perpendicular, tilted 45˚) with respect to the post-flame flow field; and post-growth in-situ hydrogen etching are investigated for their impact on the quality (i.e., defect level, graphitic structure), uniformity, and number of layers of the as-synthesized graphene films. On low-purity Cu Substrates, defects are observed because of the impurity content. Interestingly, on smooth electropolished Cu substrates, high defect levels are produced presumably because of the high nucleation rates and density from the higher flow rates used in flame synthesis. When using CH and CH as precursors versus CH, growth rates are slower although the graphene film characteristics are similar. The small substrate sizes used are not in the boundary-layer regime, so the substrate orientation does not affect the characteristics of the film. The initial quality of graphene films and the substrate materials are the two key factors controlling the hydrogen etching effect and the healing effect because of thermal recrystallization. Hydrogen annealing can remove adlayers and improve the quality of graphene on Cu but has minimal or detrimental effects on films on other substrate materials.
{"title":"Influence of substrate, precursor, flow field, and hydrogen etching on the flame synthesis of monolayer graphene films","authors":"Hua Hong, Stephen D. Tse","doi":"10.1016/j.proci.2024.105594","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105594","url":null,"abstract":"Graphene films are grown in an open atmosphere on metal substrates using a modified multiple inverse-diffusion flame (m-IDF) burner with hydrogen as fuel and hydrocarbon as precursor (delivered by multiple distinct tubes staged above the m-IDF burner surface). The flame synthesis procedure uses three stages consisting of () pretreatment, () growth, and () hydrogen etching and produces monolayer graphene (MLG) films with methane as a precursor on copper substrates at 1000 °C. Substrate material (e.g., copper, nickel, silicon), purity, and smoothness (i.e., unpolished, electropolished); precursor composition (i.e., CH, CH, CH); substrate orientation (i.e., parallel, perpendicular, tilted 45˚) with respect to the post-flame flow field; and post-growth in-situ hydrogen etching are investigated for their impact on the quality (i.e., defect level, graphitic structure), uniformity, and number of layers of the as-synthesized graphene films. On low-purity Cu Substrates, defects are observed because of the impurity content. Interestingly, on smooth electropolished Cu substrates, high defect levels are produced presumably because of the high nucleation rates and density from the higher flow rates used in flame synthesis. When using CH and CH as precursors versus CH, growth rates are slower although the graphene film characteristics are similar. The small substrate sizes used are not in the boundary-layer regime, so the substrate orientation does not affect the characteristics of the film. The initial quality of graphene films and the substrate materials are the two key factors controlling the hydrogen etching effect and the healing effect because of thermal recrystallization. Hydrogen annealing can remove adlayers and improve the quality of graphene on Cu but has minimal or detrimental effects on films on other substrate materials.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180231","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.2024.105693
Cameron Verwey, Arash Arabkhalaj, Madjid Birouk
Despite the enduring popularity of single-droplet vaporization studies, few researchers have systematically examined the influence of turbulence on droplet burning dynamics. Existing investigations have looked exclusively at large droplets or porous spheres while utilizing thermally conductive suspension schemes. To further understand how turbulence affects normal-gravity droplet burning, single droplets of heptane were suspended at the center of a fan-stirred chamber on a horizontal microfiber, rapidly ignited, and burned to completion. The experimental conditions were parametrically varied across 112 unique combinations of initial diameter, ambient pressure, turbulence intensity, and background oxygen content. The primary quantity of interest is the burning rate, and how individual and average burning rates are affected by the various parameters. To help interpret the results, the radiant soot emission was recorded alongside the temporal evolution of the droplet diameter. The burning rates of droplets in the super-millimeter range are up to 32% lower than those collected in otherwise identical conditions but with large fiber suspenders. Turbulence has little effect on the droplet burning rate until the ambient pressure is elevated. In these cases, turbulence initially augments the burning rate until a critical turbulence level is reached, after which the burning rate quickly falls. The reduction in the burning rate corresponds to the reoccurring appearance of temporary luminous extinction (TLE), where the hot incandescent region that normally surrounds the droplet disappears for a short period, thus tempering the overall burning rate. The cause of, and behavior during, TLE is contrasted with similar phenomena from the literature. Smaller, sub-millimeter droplets behave in largely the same manner, but with lower peak burning rates and greater run-to-run variation. Modest increases to the background oxygen content, from the baseline 21% up to 25% and 30%, delay the onset of TLE to higher turbulence levels. At the highest pressures, turbulent droplet burning rates of the oxygen-enriched cases can double their counterparts in ambient oxygen levels—a synergistic effect with turbulence playing a critical role.
尽管单液滴汽化研究一直很受欢迎，但很少有研究人员系统地研究过湍流对液滴燃烧动力学的影响。现有的研究只关注大液滴或多孔球体，同时采用导热悬浮方案。为了进一步了解湍流如何影响正重力液滴燃烧，研究人员将单个庚烷液滴悬浮在水平微纤维上的扇形搅拌室中心，迅速点燃并燃烧至完全。实验条件在 112 种不同的初始直径、环境压力、湍流强度和背景氧含量组合中进行了参数变化。主要关注点是燃烧速率，以及各种参数对单个和平均燃烧速率的影响。为了帮助解释结果，在记录液滴直径的时间演变的同时，还记录了辐射烟尘排放。超毫米范围内液滴的燃烧速率比在其他相同条件下收集的大纤维悬浮液低 32%。在环境压力升高之前，湍流对液滴燃烧速率的影响很小。在这种情况下，湍流最初会提高燃烧速率，直到达到临界湍流水平，之后燃烧速率会迅速下降。燃烧速率的降低与再次出现的暂时性发光熄灭（TLE）相对应，在这种情况下，通常围绕液滴的热炽热区域会在短时间内消失，从而降低了整体燃烧速率。我们将 TLE 的成因和表现与文献中的类似现象进行了对比。更小的亚毫米液滴的行为方式大致相同，但峰值燃烧速率更低，运行之间的变化更大。背景氧含量的适度增加（从基准的 21% 增加到 25% 和 30%）会将 TLE 的发生时间推迟到更高的湍流水平。在最高压力下，富氧情况下的湍流液滴燃烧速率是环境含氧量情况下的两倍--这是一种协同效应，湍流起到了关键作用。
{"title":"Droplet combustion in a turbulent, elevated-pressure environment","authors":"Cameron Verwey, Arash Arabkhalaj, Madjid Birouk","doi":"10.1016/j.proci.2024.105693","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105693","url":null,"abstract":"Despite the enduring popularity of single-droplet vaporization studies, few researchers have systematically examined the influence of turbulence on droplet burning dynamics. Existing investigations have looked exclusively at large droplets or porous spheres while utilizing thermally conductive suspension schemes. To further understand how turbulence affects normal-gravity droplet burning, single droplets of heptane were suspended at the center of a fan-stirred chamber on a horizontal microfiber, rapidly ignited, and burned to completion. The experimental conditions were parametrically varied across 112 unique combinations of initial diameter, ambient pressure, turbulence intensity, and background oxygen content. The primary quantity of interest is the burning rate, and how individual and average burning rates are affected by the various parameters. To help interpret the results, the radiant soot emission was recorded alongside the temporal evolution of the droplet diameter. The burning rates of droplets in the super-millimeter range are up to 32% lower than those collected in otherwise identical conditions but with large fiber suspenders. Turbulence has little effect on the droplet burning rate until the ambient pressure is elevated. In these cases, turbulence initially augments the burning rate until a critical turbulence level is reached, after which the burning rate quickly falls. The reduction in the burning rate corresponds to the reoccurring appearance of temporary luminous extinction (TLE), where the hot incandescent region that normally surrounds the droplet disappears for a short period, thus tempering the overall burning rate. The cause of, and behavior during, TLE is contrasted with similar phenomena from the literature. Smaller, sub-millimeter droplets behave in largely the same manner, but with lower peak burning rates and greater run-to-run variation. Modest increases to the background oxygen content, from the baseline 21% up to 25% and 30%, delay the onset of TLE to higher turbulence levels. At the highest pressures, turbulent droplet burning rates of the oxygen-enriched cases can double their counterparts in ambient oxygen levels—a synergistic effect with turbulence playing a critical role.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180226","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.2024.105658
Shashank S. Nagaraja, S. Mani Sarathy, Balaji Mohan, Junseok Chang
Fuel design aims to develop and optimize fuels to meet specific performance, environmental, and economic objectives. It encompasses a range of considerations, including selecting appropriate feedstocks, adjusting molecular structures, and incorporating additives to achieve desired characteristics. One critical aspect of fuel design is its relevance to addressing environmental concerns, such as reducing greenhouse gas emissions and air pollutants. In a spark-ignition engine, increasing engine efficiency leads to a reduction in CO2 emissions. The composition of the fuel plays a vital role in enhancing engine efficiency. Anti-knock properties, latent heat of vaporization (HoV), and laminar flame speed (LFS) are some of the fuel properties that can influence engine operating regimes. In the current study, we explore additives that can improve the efficiency of spark-ignition engines. Machine learning-based quantitative structure-property relationship (QSPR) models are developed to predict research and motor octane numbers, HoV, and LFS of 379,500 hydrocarbons containing only carbon, hydrogen, and oxygen atoms. The molecules are ranked based on an established merit function, and the top five candidates are selected. Methanol is the most promising additive candidate, allowing for the highest degree of efficiency enhancement among the screened candidates. Other potential candidates are substituted furans and tetrahydrofuran.
{"title":"Machine learning-driven screening of fuel additives for increased spark-ignition engine efficiency","authors":"Shashank S. Nagaraja, S. Mani Sarathy, Balaji Mohan, Junseok Chang","doi":"10.1016/j.proci.2024.105658","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105658","url":null,"abstract":"Fuel design aims to develop and optimize fuels to meet specific performance, environmental, and economic objectives. It encompasses a range of considerations, including selecting appropriate feedstocks, adjusting molecular structures, and incorporating additives to achieve desired characteristics. One critical aspect of fuel design is its relevance to addressing environmental concerns, such as reducing greenhouse gas emissions and air pollutants. In a spark-ignition engine, increasing engine efficiency leads to a reduction in CO2 emissions. The composition of the fuel plays a vital role in enhancing engine efficiency. Anti-knock properties, latent heat of vaporization (HoV), and laminar flame speed (LFS) are some of the fuel properties that can influence engine operating regimes. In the current study, we explore additives that can improve the efficiency of spark-ignition engines. Machine learning-based quantitative structure-property relationship (QSPR) models are developed to predict research and motor octane numbers, HoV, and LFS of 379,500 hydrocarbons containing only carbon, hydrogen, and oxygen atoms. The molecules are ranked based on an established merit function, and the top five candidates are selected. Methanol is the most promising additive candidate, allowing for the highest degree of efficiency enhancement among the screened candidates. Other potential candidates are substituted furans and tetrahydrofuran.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The cornerstone of chemical looping combustion (CLC) is oxygen carriers (OCs), and most OCs have one or more ever-present problems with performance, cost, stability, and service life. It is vital to develop OCs with balanced performance. A novel CMTF-Mg OC is proposed in this study via B-site elemental substitution of CaMnO perovskite. Systematic experiments using a thermogravimetric analyzer (TGA), a batch fluidized bed reactor, a fixed bed reactor, and an air jet attrition apparatus are performed to evaluate various aspects of the performance of the OC manufactured by the hydraulic molding method. First, in isothermal TGA redox cycles, CMTF-Mg OC exhibits a high oxygen donation ratio (∼5.0 wt.%) and excellent cyclic stability. Mg substitution eliminates the activation effect and promotes lattice oxygen release. Then, the CH-fueled CLC experiments on a batch fluidized bed demonstrate that Mg B-site substitution promotes oxygen uncoupling (0.2 wt.% gaseous oxygen) and significantly improves its reactivity with CH. Following that, an agglomeration resistance test on a packed bed reveals that CMTF-Mg OC particles expand slightly yet exhibit remarkable agglomeration resistance. Further characterization results from SEM, EDS, and XRD analysis show that the perovskite phase is formed in fresh CMTF-Mg OC via solid-phase synthesis at 1350 °C, and OC has high thermal and chemical stability during the multiple redox cycles. According to the attrition test results, CMTF-Mg OC has an 8333-hour service life. Last, CMTF-Mg OC has a material cost of $0.892/kg and a use cost of 0.00217 ($/kg[O]/h). In summary, this CMTF-Mg OC has excellent and balanced performance in reactivity, stability, agglomeration resistance, attrition resistance, and cost, which is of great value for industrial demonstration of CLC in the later stage.
{"title":"Design a novel Ca-Mn perovskite oxygen carrier with balanced performance in chemical looping combustion","authors":"Xin Wu, Xianyu Liu, Guangsheng Zou, Jinchen Ma, Cao Kuang, Haibo Zhao","doi":"10.1016/j.proci.2024.105645","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105645","url":null,"abstract":"The cornerstone of chemical looping combustion (CLC) is oxygen carriers (OCs), and most OCs have one or more ever-present problems with performance, cost, stability, and service life. It is vital to develop OCs with balanced performance. A novel CMTF-Mg OC is proposed in this study via B-site elemental substitution of CaMnO perovskite. Systematic experiments using a thermogravimetric analyzer (TGA), a batch fluidized bed reactor, a fixed bed reactor, and an air jet attrition apparatus are performed to evaluate various aspects of the performance of the OC manufactured by the hydraulic molding method. First, in isothermal TGA redox cycles, CMTF-Mg OC exhibits a high oxygen donation ratio (∼5.0 wt.%) and excellent cyclic stability. Mg substitution eliminates the activation effect and promotes lattice oxygen release. Then, the CH-fueled CLC experiments on a batch fluidized bed demonstrate that Mg B-site substitution promotes oxygen uncoupling (0.2 wt.% gaseous oxygen) and significantly improves its reactivity with CH. Following that, an agglomeration resistance test on a packed bed reveals that CMTF-Mg OC particles expand slightly yet exhibit remarkable agglomeration resistance. Further characterization results from SEM, EDS, and XRD analysis show that the perovskite phase is formed in fresh CMTF-Mg OC via solid-phase synthesis at 1350 °C, and OC has high thermal and chemical stability during the multiple redox cycles. According to the attrition test results, CMTF-Mg OC has an 8333-hour service life. Last, CMTF-Mg OC has a material cost of $0.892/kg and a use cost of 0.00217 ($/kg[O]/h). In summary, this CMTF-Mg OC has excellent and balanced performance in reactivity, stability, agglomeration resistance, attrition resistance, and cost, which is of great value for industrial demonstration of CLC in the later stage.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180229","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 : 2024-08-19DOI: 10.1016/j.proci.2024.105724
Shixing Wang, Ayman M. Elbaz, Zhihua Wang, William L. Roberts
Ammonia (NH) is considered a promising carbon-free fuel in the context of carbon neutrality. However, the emission characteristics of NH swirling flames respond strongly to the influence of heat loss and fuel staging. This study investigated the NO emissions of NH/CH/air mixtures in an air-staging swirling combustor. The ammonia mole fractions range from = 0.3, 0.6, to 1.0, with the primary and overall equivalence ratios ranging from = 0.7 to 1.7 and = 0.5 to 0.7, respectively. Four different secondary air injection strategies and three heat losses rates were adopted to differentiate the thermal and chemical effects on NO emissions. O, NO, and CO emissions were measured using a flue gas analyzer. In-flame temperature was measured by fine-wire thermocouples, and chemiluminescence (OH*, NH*) was captured by an intensified CCD camera. The chemical reactor network approach was used to simulate the two-stage combustion. Secondary gas injection initially has a thermal effect by cooling the downstream flame temperature on the lean side. After = 1.3, the chemical effect dominated while the flame was challenged by lift-off instability. = 1.3 showed the minimum NO emission, while = 1.1, = 0.7 with cooling exhibited low NO levels and high flame stability. Flame at > 1.3 tended to lift-off and merge with secondary air, diminishing the air-staging effect. NH* and OH* indicate the flame lift-off and secondary flame formation. Simulation results show that NO removal is favored at cooling conditions in the primary stage and NO production is suppressed at thermal-insulation conditions in the secondary stage. To ensure low NO emissions, complete ammonia oxidation, and flame stability, stabilizing the primary flame zone close to = 1.0 and overall equivalence ratio close to = 0.7 in combination with the cooling strategy is effective.
在碳中和的背景下，氨（NH）被认为是一种前景广阔的无碳燃料。然而，NH 旋转火焰的排放特性受热损失和燃料分级的影响很大。本研究调查了空气分级漩涡燃烧器中 NH/CH/ 空气混合物的氮氧化物排放情况。氨的摩尔分数从 = 0.3、0.6 到 1.0 不等，一次当量比和总当量比分别从 = 0.7 到 1.7 和 = 0.5 到 0.7 不等。为了区分热效应和化学效应对 NO 排放的影响，采用了四种不同的二次空气喷射策略和三种热损失率。O 、NO 和 CO 的排放是通过烟气分析仪测量的。火焰内温度由细线热电偶测量，化学发光（OH*、NH*）由增强型 CCD 相机捕捉。化学反应器网络法用于模拟两级燃烧。二次气体注入最初会产生热效应，冷却贫气侧的下游火焰温度。在 = 1.3 后，化学效应占主导地位，而火焰则面临升空不稳定性的挑战。 = 1.3 显示了最低的 NO 排放，而 = 1.1、= 0.7 的冷却则显示了较低的 NO 水平和较高的火焰稳定性。大于 1.3 的火焰倾向于升空并与二次空气合并，从而降低了空气分级效果。NH* 和 OH* 表示火焰腾空和二次火焰形成。模拟结果表明，在一级冷却条件下，有利于去除 NO，而在二级隔热条件下，抑制了 NO 的产生。为确保低 NO 排放、氨完全氧化和火焰稳定性，将一级火焰区稳定在 = 1.0 附近，将总当量比稳定在 = 0.7 附近，并结合冷却策略是有效的。
{"title":"Effects of air-staging and heat losses on NO emissions of NH3/CH4/air swirling flames","authors":"Shixing Wang, Ayman M. Elbaz, Zhihua Wang, William L. Roberts","doi":"10.1016/j.proci.2024.105724","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105724","url":null,"abstract":"Ammonia (NH) is considered a promising carbon-free fuel in the context of carbon neutrality. However, the emission characteristics of NH swirling flames respond strongly to the influence of heat loss and fuel staging. This study investigated the NO emissions of NH/CH/air mixtures in an air-staging swirling combustor. The ammonia mole fractions range from = 0.3, 0.6, to 1.0, with the primary and overall equivalence ratios ranging from = 0.7 to 1.7 and = 0.5 to 0.7, respectively. Four different secondary air injection strategies and three heat losses rates were adopted to differentiate the thermal and chemical effects on NO emissions. O, NO, and CO emissions were measured using a flue gas analyzer. In-flame temperature was measured by fine-wire thermocouples, and chemiluminescence (OH*, NH*) was captured by an intensified CCD camera. The chemical reactor network approach was used to simulate the two-stage combustion. Secondary gas injection initially has a thermal effect by cooling the downstream flame temperature on the lean side. After = 1.3, the chemical effect dominated while the flame was challenged by lift-off instability. = 1.3 showed the minimum NO emission, while = 1.1, = 0.7 with cooling exhibited low NO levels and high flame stability. Flame at > 1.3 tended to lift-off and merge with secondary air, diminishing the air-staging effect. NH* and OH* indicate the flame lift-off and secondary flame formation. Simulation results show that NO removal is favored at cooling conditions in the primary stage and NO production is suppressed at thermal-insulation conditions in the secondary stage. To ensure low NO emissions, complete ammonia oxidation, and flame stability, stabilizing the primary flame zone close to = 1.0 and overall equivalence ratio close to = 0.7 in combination with the cooling strategy is effective.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180232","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 : 2024-08-19DOI: 10.1016/j.proci.2024.105727
Guoqing Wang, Abel Faure-Beaulieu, Bruno Schuermans, Nicolas Noiray
This paper investigates the first Flame Transfer Functions (FTFs) of hydrogen diffusion swirl flames, which are crucial for predicting and mitigating thermoacoustic instabilities. Given the need to develop new combustion technologies for hydrogen, it is therefore essential to accurately measure and analyze these FTFs. Employing acoustic and optical methods, we obtained the FTFs over a wide frequency range from 50 to 1000 Hz. Using the acoustic method, the FTFs are deduced from the flame transfer matrices. The FTFs exhibit a low-pass filter behavior with gains decreasing significantly above 150 Hz. Strouhal number normalization effectively collapses the FTFs across various thermal powers, bulk mass flow rates and global equivalence ratios. This result suggests that a generic flame response to acoustic perturbations exists and that the FTF can be interpolated over a range of operating conditions. This study identifies two dominant combustion modes in these hydrogen diffusion swirl flames: a diffusion-mode thin reaction layer near the nozzle and a partially premixed thicker reaction layer downstream. Phase-averaged OH* and OH-PLIF imaging revealed non-uniform transversal oscillations of the reaction zone, offering key insights into the complex swirling flow and the convective wavelength of the coherent heat release rate oscillations along these turbulent hydrogen diffusion swirl flames.
{"title":"Flame transfer function analysis of hydrogen diffusion swirl flames","authors":"Guoqing Wang, Abel Faure-Beaulieu, Bruno Schuermans, Nicolas Noiray","doi":"10.1016/j.proci.2024.105727","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105727","url":null,"abstract":"This paper investigates the first Flame Transfer Functions (FTFs) of hydrogen diffusion swirl flames, which are crucial for predicting and mitigating thermoacoustic instabilities. Given the need to develop new combustion technologies for hydrogen, it is therefore essential to accurately measure and analyze these FTFs. Employing acoustic and optical methods, we obtained the FTFs over a wide frequency range from 50 to 1000 Hz. Using the acoustic method, the FTFs are deduced from the flame transfer matrices. The FTFs exhibit a low-pass filter behavior with gains decreasing significantly above 150 Hz. Strouhal number normalization effectively collapses the FTFs across various thermal powers, bulk mass flow rates and global equivalence ratios. This result suggests that a generic flame response to acoustic perturbations exists and that the FTF can be interpolated over a range of operating conditions. This study identifies two dominant combustion modes in these hydrogen diffusion swirl flames: a diffusion-mode thin reaction layer near the nozzle and a partially premixed thicker reaction layer downstream. Phase-averaged OH* and OH-PLIF imaging revealed non-uniform transversal oscillations of the reaction zone, offering key insights into the complex swirling flow and the convective wavelength of the coherent heat release rate oscillations along these turbulent hydrogen diffusion swirl flames.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180230","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 : 2024-08-07DOI: 10.1016/j.proci.2024.105673
Vinzenz Schuh, Christian Hasse, Hendrik Nicolai
Despite the growing interest in hydrogen as a fuel, current combustion models are still incapable of considering the effects of intrinsic flame instabilities, such as increased flame surface area and local stratification. A significant challenge arises due to the substantial impact on the laminar flame consumption speed, complicating the transfer of established combustion models. This study proposes an extension of the artificially thickened flame (ATF) approach to encompass laminar self-wrinkling flames subject to intrinsic instabilities, serving as a foundation for advancing turbulent combustion models. Several 2D numerical simulations were conducted to analyze the interaction of ATF and thermodiffusive instabilities in unstable lean hydrogen flames. The assessment of characteristic length scales revealed a linear scaling relationship with the thickening factor , causing the domain size at which instabilities manifest to expand and modify the consumption speed of the thickened flame. To compensate for these deviations, a novel efficiency function is derived from the fractal characteristics of the flame front. Using the critical wavelength and a geometric length scale as inner and outer cut-offs, respectively, the improved ATF model was evaluated successfully in fully coupled simulations of the 2D planar flames. To facilitate the use of the new model, a practical on-the-fly procedure for estimating a characteristic geometric length scale required for the efficiency function is proposed and successfully employed.
{"title":"An extension of the artificially thickened flame approach for premixed hydrogen flames with intrinsic instabilities","authors":"Vinzenz Schuh, Christian Hasse, Hendrik Nicolai","doi":"10.1016/j.proci.2024.105673","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105673","url":null,"abstract":"Despite the growing interest in hydrogen as a fuel, current combustion models are still incapable of considering the effects of intrinsic flame instabilities, such as increased flame surface area and local stratification. A significant challenge arises due to the substantial impact on the laminar flame consumption speed, complicating the transfer of established combustion models. This study proposes an extension of the artificially thickened flame (ATF) approach to encompass laminar self-wrinkling flames subject to intrinsic instabilities, serving as a foundation for advancing turbulent combustion models. Several 2D numerical simulations were conducted to analyze the interaction of ATF and thermodiffusive instabilities in unstable lean hydrogen flames. The assessment of characteristic length scales revealed a linear scaling relationship with the thickening factor , causing the domain size at which instabilities manifest to expand and modify the consumption speed of the thickened flame. To compensate for these deviations, a novel efficiency function is derived from the fractal characteristics of the flame front. Using the critical wavelength and a geometric length scale as inner and outer cut-offs, respectively, the improved ATF model was evaluated successfully in fully coupled simulations of the 2D planar flames. To facilitate the use of the new model, a practical on-the-fly procedure for estimating a characteristic geometric length scale required for the efficiency function is proposed and successfully employed.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946255","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 : 2024-08-06DOI: 10.1016/j.proci.2024.105666
Enrique Flores-Montoya, Pierre-Alexandre Masset, Thierry Schuller, Laurent Selle
An experimental study on the influence of porosity and hydrogen enrichment on the stabilization of premixed -Air flames in Porous Media Burners (PMBs) is presented. Flame stabilization is analyzed via direct flame front tracking, which is made possible by a novel experimental apparatus. The use of additive manufacturing for computer-generated topologies allows making optically-accessible PMBs featuring see-through directions. This methodology also enables topology tailoring which is here exploited to study the influence of porosity on the performance of the burner. Flame front tracking reveals a different stabilization trend in highly -enriched flames. A comparison with a theoretical model is used to remove the effect of preheating and focus on other fuel properties. This suggests a flame-speed enhancement mechanism driven by Lewis number effects in mixtures. Together with recent 3D Direct Numerical Simulations, these results provide evidence that preferential diffusion effects are key in the stabilization of flames in PMBs. These phenomena, not considered in state-of-the art 1D-Volume Averaged Models, remain crucial for the design of efficient PMB using hydrogen as a fuel.
{"title":"Speed-up drivers for [formula omitted]-enriched flames in Porous Media Burners","authors":"Enrique Flores-Montoya, Pierre-Alexandre Masset, Thierry Schuller, Laurent Selle","doi":"10.1016/j.proci.2024.105666","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105666","url":null,"abstract":"An experimental study on the influence of porosity and hydrogen enrichment on the stabilization of premixed -Air flames in Porous Media Burners (PMBs) is presented. Flame stabilization is analyzed via direct flame front tracking, which is made possible by a novel experimental apparatus. The use of additive manufacturing for computer-generated topologies allows making optically-accessible PMBs featuring see-through directions. This methodology also enables topology tailoring which is here exploited to study the influence of porosity on the performance of the burner. Flame front tracking reveals a different stabilization trend in highly -enriched flames. A comparison with a theoretical model is used to remove the effect of preheating and focus on other fuel properties. This suggests a flame-speed enhancement mechanism driven by Lewis number effects in mixtures. Together with recent 3D Direct Numerical Simulations, these results provide evidence that preferential diffusion effects are key in the stabilization of flames in PMBs. These phenomena, not considered in state-of-the art 1D-Volume Averaged Models, remain crucial for the design of efficient PMB using hydrogen as a fuel.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946247","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 : 2024-08-05DOI: 10.1016/j.proci.2024.105688
Yutao Zheng, Pervez Ahmed, Simone Hochgreb
We analyze 3D reconstructed surfaces based on previously reported high frequency measurements of flame edge location across expanding flames using Mie scatter. For the first time, principal curvatures of flame surfaces are estimated from eigenvalues of the second fundamental forms of the reconstructed surfaces, allowing the determination of the statistics of mean and Gaussian curvatures as a function of time and thus flame mean radius. Measurements and analysis were made for both lean methane and hydrogen mixtures as a function of time and turbulence levels. The mean 3D flame curvature was found to be inversely proportional to flame radius, and relatively insensitive to turbulence intensity, even in the case of larger, more planar flames. Mean 3D curvatures across the flame brush were determined to be positive (convex) towards the reactant mixture at the leading edge, and negative (concave) towards the trailing edge, as predicted from DNS measurements. The mean and probability distributions of 3D mean curvatures were found to be significantly different than 2D curvatures extracted from the central planes, with the 3D measurements showing much narrower distributions and lower values. Differences between 3D and 2D measurements were different by an order of magnitude in the case of hydrogen flames, possibly owing to the onset of thermodiffusive instabilities which affect the local fine structure of the flame.
我们根据之前报道的利用米氏散射对膨胀火焰的火焰边缘位置进行的高频测量，对三维重建表面进行了分析。我们首次从重建表面的第二基本形式特征值估算出火焰表面的主曲率，从而确定了平均曲率和高斯曲率随时间变化的统计量，进而确定了火焰平均半径。测量和分析了贫甲烷和氢气混合物与时间和湍流水平的函数关系。结果发现，平均三维火焰曲率与火焰半径成反比，并且对湍流强度相对不敏感，即使是较大、较平的火焰也是如此。根据 DNS 测量结果的预测，整个火焰刷的平均三维曲率在前缘向反应物混合物方向为正（凸），在后缘为负（凹）。三维平均曲率的平均值和概率分布与从中心平面提取的二维曲率有显著不同，三维测量值的分布更窄，数值更低。在氢火焰的情况下，三维和二维测量结果的差异达到了一个数量级，这可能是由于热扩散不稳定性的出现影响了火焰的局部精细结构。
{"title":"3D flame surface curvature analysis from reconstructed scanning across spherical expanding flames","authors":"Yutao Zheng, Pervez Ahmed, Simone Hochgreb","doi":"10.1016/j.proci.2024.105688","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105688","url":null,"abstract":"We analyze 3D reconstructed surfaces based on previously reported high frequency measurements of flame edge location across expanding flames using Mie scatter. For the first time, principal curvatures of flame surfaces are estimated from eigenvalues of the second fundamental forms of the reconstructed surfaces, allowing the determination of the statistics of mean and Gaussian curvatures as a function of time and thus flame mean radius. Measurements and analysis were made for both lean methane and hydrogen mixtures as a function of time and turbulence levels. The mean 3D flame curvature was found to be inversely proportional to flame radius, and relatively insensitive to turbulence intensity, even in the case of larger, more planar flames. Mean 3D curvatures across the flame brush were determined to be positive (convex) towards the reactant mixture at the leading edge, and negative (concave) towards the trailing edge, as predicted from DNS measurements. The mean and probability distributions of 3D mean curvatures were found to be significantly different than 2D curvatures extracted from the central planes, with the 3D measurements showing much narrower distributions and lower values. Differences between 3D and 2D measurements were different by an order of magnitude in the case of hydrogen flames, possibly owing to the onset of thermodiffusive instabilities which affect the local fine structure of the flame.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946256","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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