Pub Date : 2025-01-01DOI: 10.1016/j.proci.2025.105910
Jie Sun , Salim M. Shaik , Van Bo Nguyen , Huangwei Zhang
Ammonia has relatively low reactivity, making it difficult to initiate and maintain a stable detonation wave. Cracking ammonia into hydrogen and nitrogen can enhance the detonability of the mixture. This study evaluates the influence of ammonia cracking ratio (κ) on the detonation characteristics of partially cracked ammonia and oxygen mixtures (NH3/H2/O2/N2) by numerical simulations considering detailed chemistry. It aims to explain how the initial hydrogen generated from ammonia cracking affects the detonation. First, steady ZND structures and reaction flux paths are analyzed for different κ. The results show that NH3 is primarily consumed via pyrolysis. The initial hydrogen reacts through reactions R3 (O+H2→OH+H), R4 (OH+H2→H+H2O) and R160 (NH3+H→NH2+H2), which releases heat and shortens the induction time. As κ increases, R3 and R4 replace R160 to dominate the initial hydrogen consumption. Besides, increasing κ also favors the pyrolysis of NH3 by NH3→NH2→NH due to more H and OH radicals generated from the initial hydrogen reactions. Subsequently, unsteady pulsating and cellular detonations are simulated. Detonation waves propagate more stably as κ increases. Two re-initiation modes are identified for pulsating detonations. When κ is small, unburned mixture pockets are observed behind the leading shock. The mixtures within the pockets burn, creating pressure waves to interact with the leading shock. The interactions induce new reaction fronts to re-initiate the detonation. As κ increases, the reactivity of the shocked mixture increases, reshaping the reactivity gradient and causing the re-initiation mode to transition to the acceleration of the original reaction front. For cellular detonation, similar unburned gas pockets caused by the decoupling of transverse detonation waves are also observed. As κ increases, more initial hydrogen reacts and enhances the mixture reactivity behind the incident shock waves, leading to transverse detonation waves to propagate without decoupling. Hence the detonation waves become more stable.
{"title":"Detonation chemistry and propagation characteristics in partially cracked ammonia","authors":"Jie Sun , Salim M. Shaik , Van Bo Nguyen , Huangwei Zhang","doi":"10.1016/j.proci.2025.105910","DOIUrl":"10.1016/j.proci.2025.105910","url":null,"abstract":"<div><div>Ammonia has relatively low reactivity, making it difficult to initiate and maintain a stable detonation wave. Cracking ammonia into hydrogen and nitrogen can enhance the detonability of the mixture. This study evaluates the influence of ammonia cracking ratio (<em>κ</em>) on the detonation characteristics of partially cracked ammonia and oxygen mixtures (NH<sub>3</sub>/H<sub>2</sub>/O<sub>2</sub>/N<sub>2</sub>) by numerical simulations considering detailed chemistry. It aims to explain how the initial hydrogen generated from ammonia cracking affects the detonation. First, steady ZND structures and reaction flux paths are analyzed for different <em>κ</em>. The results show that NH<sub>3</sub> is primarily consumed via pyrolysis. The initial hydrogen reacts through reactions R3 (O+H<sub>2</sub>→OH+H), R4 (OH+H<sub>2</sub>→H+H<sub>2</sub>O) and R160 (NH<sub>3</sub>+H→NH<sub>2</sub>+H<sub>2</sub>), which releases heat and shortens the induction time. As <em>κ</em> increases, R3 and R4 replace R160 to dominate the initial hydrogen consumption. Besides, increasing <em>κ</em> also favors the pyrolysis of NH<sub>3</sub> by NH<sub>3</sub>→NH<sub>2</sub>→NH due to more H and OH radicals generated from the initial hydrogen reactions. Subsequently, unsteady pulsating and cellular detonations are simulated. Detonation waves propagate more stably as <em>κ</em> increases. Two re-initiation modes are identified for pulsating detonations. When <em>κ</em> is small, unburned mixture pockets are observed behind the leading shock. The mixtures within the pockets burn, creating pressure waves to interact with the leading shock. The interactions induce new reaction fronts to re-initiate the detonation. As κ increases, the reactivity of the shocked mixture increases, reshaping the reactivity gradient and causing the re-initiation mode to transition to the acceleration of the original reaction front. For cellular detonation, similar unburned gas pockets caused by the decoupling of transverse detonation waves are also observed. As κ increases, more initial hydrogen reacts and enhances the mixture reactivity behind the incident shock waves, leading to transverse detonation waves to propagate without decoupling. Hence the detonation waves become more stable.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105910"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145262473","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105866
Maurus Bauer , Björn Stelzner , Peter Habisreuther , Michael Schneider , Christof Weis , Dimosthenis Trimis
This study presents an experimental investigation of a turbulent premixed hydrogen jet flame operating under high exhaust gas recirculation (EGR) rates. Experiments were conducted at a Reynolds number of 10 000, exploring flames ranging from pure H2–air mixtures to cases with an EGR rate of 0.67. The flames were carefully adjusted to maintain similar laminar burning velocities, enabling consistent comparisons and revealing a systematic increase in the equivalence ratio () with higher EGR rates. These operating conditions were derived through a detailed 1D analysis of H2–air–EGR laminar flames using comprehensive chemical kinetics, complemented with measurements of the laminar burning velocities of premixed H2–air–EGR flames. The flow field of the model burner setup and nozzle design was characterized under both non-reactive and reactive conditions using particle image velocimetry (PIV). OH* chemiluminescence imaging did not reveal significant changes in the overall structure of the flame, even as the equivalence ratio varied from = 0.4 (pure H2–air flame) to near-stoichiometric conditions ( = 0.77). Selected cases were further investigated using OH planar laser-induced fluorescence (OH-LIF), offering detailed visualization of the flame structure and corroborating the observations from OH* chemiluminescence. NOX emissions remained low across all investigated EGR rates, demonstrating robust emission control. These findings enhance the understanding of hydrogen combustion dynamics under high EGR conditions and provide valuable insights for developing low-emission, high-stability combustion strategies.
{"title":"Experimental investigation of turbulent premixed H2-jet flames at high exhaust gas recirculation","authors":"Maurus Bauer , Björn Stelzner , Peter Habisreuther , Michael Schneider , Christof Weis , Dimosthenis Trimis","doi":"10.1016/j.proci.2025.105866","DOIUrl":"10.1016/j.proci.2025.105866","url":null,"abstract":"<div><div>This study presents an experimental investigation of a turbulent premixed hydrogen jet flame operating under high exhaust gas recirculation (EGR) rates. Experiments were conducted at a Reynolds number of 10<!--> <!-->000, exploring flames ranging from pure H<sub>2</sub>–air mixtures to cases with an EGR rate of 0.67. The flames were carefully adjusted to maintain similar laminar burning velocities, enabling consistent comparisons and revealing a systematic increase in the equivalence ratio (<span><math><mi>Φ</mi></math></span>) with higher EGR rates. These operating conditions were derived through a detailed 1D analysis of H<sub>2</sub>–air–EGR laminar flames using comprehensive chemical kinetics, complemented with measurements of the laminar burning velocities of premixed H<sub>2</sub>–air–EGR flames. The flow field of the model burner setup and nozzle design was characterized under both non-reactive and reactive conditions using particle image velocimetry (PIV). OH* chemiluminescence imaging did not reveal significant changes in the overall structure of the flame, even as the equivalence ratio varied from <span><math><mi>Φ</mi></math></span> = 0.4 (pure H<sub>2</sub>–air flame) to near-stoichiometric conditions (<span><math><mi>Φ</mi></math></span> = 0.77). Selected cases were further investigated using OH planar laser-induced fluorescence (OH-LIF), offering detailed visualization of the flame structure and corroborating the observations from OH* chemiluminescence. NO<sub>X</sub> emissions remained low across all investigated EGR rates, demonstrating robust emission control. These findings enhance the understanding of hydrogen combustion dynamics under high EGR conditions and provide valuable insights for developing low-emission, high-stability combustion strategies.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105866"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145262475","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105787
Christian P. Bjork , Mahmoud K. Ashour , Evangelos K. Stefanidis , Chiara Saggese , Scott W. Wagnon , Francesco Carbone
Synthetic Aviation Turbine Fuels (SATFs) are promising for reducing soot emissions from the aviation sector and diversifying Jet Fuel (JF) sources. Accurately predicting the combustion and emissions behavior of SATFs (and other JFs) necessitates robust experimental databases to elucidate the chemistry of long-chain iso-paraffins, which can compose up to two-thirds of SATF blends and whose behavior is considered to be well-represented by that of iso-dodecane isomers. This study characterizes two laminar non-premixed Planar Mixing Layer Flames (PMLFs) with mild soot loads fueled by nitrogen-diluted ethylene, pure and doped with 2,2,4,6,6-pentamethyl-heptane, respectively. The two PMLFs have the same stoichiometric mixture fraction and total hydrocarbon mole fraction in the fuel stream (XF,F=XC2H4,F+XC12H26,F = 0.260), resulting in nearly the same maximum temperature (Tmax≈1800 K) and simple identification of the effects of doping. Importantly, any horizontal PMLF cross-section has a self-similar structure that can be modeled as an equivalent One-Dimensional Counterflow Flame (1D-CF) with vanishingly small strain rate (a). The cross-section at a Height Above the Burner (HAB) of 50 mm is characterized in terms of C0-C18 gas species using capillary sampling followed by GC-MS analyses. Laser-Induced Emission Spectroscopy (LIES) quantifies the soot volume fraction (fv) profiles at HAB=25 and 50 mm where Elastic Laser Light Scattering (E-LLS) is performed to determine the a of the equivalent 1D-CFs and the profile of the E-LLS equivalent diameter (d6,3) of soot. The substitution of 1500 ppm of ethylene with 2,2,4,6,6-pentamethyl-heptane causes an increase of ≈1.5 in the concentrations of several polycyclic aromatic hydrocarbons and fv. Concurrently, the measured d6,3 doubles in the oxidizer stream, yet remains the same in the fuel stream, at HAB=50 mm. Instead, at HAB= 25 mm, the iso-dodecane doping does not affect the d6,3 profile in either stream. The experimental results partially validate the chemical reactions and soot formation kinetic model developed at Lawrence Livermore National Laboratory and provide directions to further improve its predictions.
{"title":"The effect on soot and its gas precursors of doping ethylene with 2,2,4,6,6-pentamethyl-heptane in the nitrogen-fuel stream of a laminar non-premixed Planar Mixing Layer Flame (PMLF)","authors":"Christian P. Bjork , Mahmoud K. Ashour , Evangelos K. Stefanidis , Chiara Saggese , Scott W. Wagnon , Francesco Carbone","doi":"10.1016/j.proci.2025.105787","DOIUrl":"10.1016/j.proci.2025.105787","url":null,"abstract":"<div><div>Synthetic Aviation Turbine Fuels (SATFs) are promising for reducing soot emissions from the aviation sector and diversifying Jet Fuel (JF) sources. Accurately predicting the combustion and emissions behavior of SATFs (and other JFs) necessitates robust experimental databases to elucidate the chemistry of long-chain iso-paraffins, which can compose up to two-thirds of SATF blends and whose behavior is considered to be well-represented by that of iso-dodecane isomers. This study characterizes two laminar non-premixed Planar Mixing Layer Flames (PMLFs) with mild soot loads fueled by nitrogen-diluted ethylene, pure and doped with 2,2,4,6,6-pentamethyl-heptane, respectively. The two PMLFs have the same stoichiometric mixture fraction and total hydrocarbon mole fraction in the fuel stream (<em>X<sub>F,F</sub></em>=<em>X<sub>C2H4,F</sub></em>+<em>X<sub>C12H26,F</sub></em> = 0.260), resulting in nearly the same maximum temperature (<em>T<sub>max</sub></em>≈1800 K) and simple identification of the effects of doping. Importantly, any horizontal PMLF cross-section has a self-similar structure that can be modeled as an equivalent One-Dimensional Counterflow Flame (1D-CF) with vanishingly small strain rate (<em>a</em>). The cross-section at a Height Above the Burner (HAB) of 50 mm is characterized in terms of C<sub>0</sub>-C<sub>18</sub> gas species using capillary sampling followed by GC-MS analyses. Laser-Induced Emission Spectroscopy (LIES) quantifies the soot volume fraction (<em>f<sub>v</sub></em>) profiles at HAB=25 and 50 mm where Elastic Laser Light Scattering (E-LLS) is performed to determine the <em>a</em> of the equivalent 1D-CFs and the profile of the E-LLS equivalent diameter (<em>d<sub>6,3</sub></em>) of soot. The substitution of 1500 ppm of ethylene with 2,2,4,6,6-pentamethyl-heptane causes an increase of ≈1.5 in the concentrations of several polycyclic aromatic hydrocarbons and <em>f<sub>v</sub></em>. Concurrently, the measured <em>d<sub>6,</sub></em><sub>3</sub> doubles in the oxidizer stream, yet remains the same in the fuel stream, at HAB=50 mm. Instead, at HAB= 25 mm, the iso-dodecane doping does not affect the <em>d<sub>6,</sub></em><sub>3</sub> profile in either stream. The experimental results partially validate the chemical reactions and soot formation kinetic model developed at Lawrence Livermore National Laboratory and provide directions to further improve its predictions.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105787"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144841803","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105828
Jesus Caravaca-Vilchez, Malte Döntgen, Karl Alexander Heufer
Understanding the combustion chemistry of acetaldehyde, a carcinogenic by-product formed during the low-temperature oxidation of various hydrocarbons, is essential for reducing harmful emissions in engines. Previous acetaldehyde experimental works have largely focused on low-pressure conditions, with a few exceptions. Some studies report a clear negative temperature coefficient (NTC) behavior for acetaldehyde and highlight the need for further low-temperature, high-pressure experiments to fully characterize it. In this context, acetaldehyde ignition delay times were measured using a rapid compression machine and a shock tube over a wide range of conditions (580–1410 K, 10–40 bar, and equivalence ratios of 0.5–1.5), significantly extending the very limited IDT data available in the literature at 10 bar. At low temperatures, the most comprehensive kinetic models of acetaldehyde greatly underestimate its reactivity, even those that show reasonable performance for flow reactor species measurements from the literature in the same temperature regime. At high temperatures, model predictions were generally in better agreement with the measured data. To improve prediction accuracy, refinements were made within GalwayMech1.0 model, incorporating recently calculated thermochemistry from the literature and modified reaction rate parameters based on direct analogies and literature information. The resulting chemistry revealed that the acetyl peroxy radical is the primary driver of low-temperature reactivity at high pressures through a closed-loop fuel consumption pathway. Further adjustments in the peroxyl radicals chemistry, which is less relevant under low-pressure conditions, successfully separate first-stage and main ignition in the NTC region. At high temperatures, revised H-atom abstraction by and O rates improved high-temperature predictions. Overall, the proposed model outperforms existing mechanisms over a wide range of conditions, but retains uncertainties in the formation of a few minor intermediates. This work highlights the importance of using high-pressure validation targets for comprehensive kinetic modeling and provides a solid foundation for future studies on acetaldehyde oxidation.
乙醛是各种碳氢化合物在低温氧化过程中形成的一种致癌副产物，了解乙醛的燃烧化学性质对减少发动机的有害排放至关重要。以前的乙醛实验工作主要集中在低压条件下，只有少数例外。一些研究报告了乙醛明显的负温度系数（NTC）行为，并强调需要进一步的低温高压实验来充分表征它。在这种情况下，使用快速压缩机和激波管在广泛的条件下（580-1410 K, 10 - 40 bar, 0.5-1.5的等效比）测量乙醛点火延迟时间，显着扩展了文献中非常有限的IDT数据，可用于10 bar。在低温下，最全面的乙醛动力学模型大大低估了它的反应性，即使是那些在相同温度下从文献中显示出流动反应器物种测量的合理性能的模型。在高温下，模式预测通常更符合实测数据。为了提高预测精度，对GalwayMech1.0模型进行了改进，结合了最近从文献中计算的热化学和基于直接类比和文献信息的修正反应速率参数。结果表明，乙酰过氧自由基是通过闭环燃料消耗途径在高压下进行低温反应的主要驱动因素。在低压条件下不太相关的过氧基化学进一步调整，成功地分离了NTC区域的一级和主点火。在高温下，通过Ḣ和O2速率修正的h原子提取改进了高温预测。总的来说，提出的模型在广泛的条件下优于现有的机制，但在一些次要中间产物的形成中保留了不确定性。这项工作强调了使用高压验证目标进行综合动力学建模的重要性，并为乙醛氧化的未来研究提供了坚实的基础。
{"title":"Acetaldehyde reactivity at engine-relevant conditions: An experimental and kinetic modeling study","authors":"Jesus Caravaca-Vilchez, Malte Döntgen, Karl Alexander Heufer","doi":"10.1016/j.proci.2025.105828","DOIUrl":"10.1016/j.proci.2025.105828","url":null,"abstract":"<div><div>Understanding the combustion chemistry of acetaldehyde, a carcinogenic by-product formed during the low-temperature oxidation of various hydrocarbons, is essential for reducing harmful emissions in engines. Previous acetaldehyde experimental works have largely focused on low-pressure conditions, with a few exceptions. Some studies report a clear negative temperature coefficient (NTC) behavior for acetaldehyde and highlight the need for further low-temperature, high-pressure experiments to fully characterize it. In this context, acetaldehyde ignition delay times were measured using a rapid compression machine and a shock tube over a wide range of conditions (580–1410 K, 10–40 bar, and equivalence ratios of 0.5–1.5), significantly extending the very limited IDT data available in the literature at 10 bar. At low temperatures, the most comprehensive kinetic models of acetaldehyde greatly underestimate its reactivity, even those that show reasonable performance for flow reactor species measurements from the literature in the same temperature regime. At high temperatures, model predictions were generally in better agreement with the measured data. To improve prediction accuracy, refinements were made within GalwayMech1.0 model, incorporating recently calculated thermochemistry from the literature and modified reaction rate parameters based on direct analogies and literature information. The resulting chemistry revealed that the acetyl peroxy radical is the primary driver of low-temperature reactivity at high pressures through a closed-loop fuel consumption pathway. Further adjustments in the peroxyl radicals chemistry, which is less relevant under low-pressure conditions, successfully separate first-stage and main ignition in the NTC region. At high temperatures, revised H-atom abstraction by <span><math><mover><mrow><mi>H</mi></mrow><mrow><mo>̇</mo></mrow></mover></math></span> and O<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> rates improved high-temperature predictions. Overall, the proposed model outperforms existing mechanisms over a wide range of conditions, but retains uncertainties in the formation of a few minor intermediates. This work highlights the importance of using high-pressure validation targets for comprehensive kinetic modeling and provides a solid foundation for future studies on acetaldehyde oxidation.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105828"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145104440","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105862
Jeong Park , Chun Sang Yoo , Suk Ho Chung
This study reviews recent findings on the dynamic behaviors of flame and molten insulation material observed in spreading flames over electrical wires under applied electric fields, which is a relevant scenario in electrical wire safety. The important roles of various unique dynamic behaviors in flame spreads are discussed, including fuel-vapor jet ejection from molten polyethylene (PE) surface, internal circulation of molten PE driven by Marangoni convection, dripping of molten PE, electrospray ejecting multiple small droplets from molten PE surface, and lateral dielectrophoresis by migrating a part of main molten PE toward the burnt wire side by forming a secondary molten PE or a liquid film of molten PE and sometimes leading to a formation of splitting flame. Additional behaviors such as vibration/rotation of molten PE due to a vertical dielectrophoresis, flame-leaning toward the burnt wire side caused by ionic wind, and magnetic field induced flame vortices near flame edges are also reviewed. The physical mechanisms of these dynamic behaviors are explained. Various regimes are identified depending on the occurrence of abovementioned phenomena. The dependence of flame spread rate on relevant physical parameters is reviewed, revealing a non-monotonic response to applied AC voltage and frequency, due to the intricate interactions among various dynamic phenomena. Phenomenological correlations are established for the FSR using key physical parameters including wire diameter, wire core diameter, applied voltage and frequency, and radial electric field gradient. To better understand the dynamic behaviors of molten insulation, the combustion of a droplet suspended on a wire was investigated, isolating the effects of solid-to-liquid phase change and the asymmetric distribution of molten PE between the burnt and unburned sides of the wire. The dynamic behaviors of such burning droplets under applied electric fields, along with their underlying mechanisms, are also reviewed and discussed.
{"title":"Dynamic behaviors of flame and molten insulation in electrical wire fire under applied electric field","authors":"Jeong Park , Chun Sang Yoo , Suk Ho Chung","doi":"10.1016/j.proci.2025.105862","DOIUrl":"10.1016/j.proci.2025.105862","url":null,"abstract":"<div><div>This study reviews recent findings on the dynamic behaviors of flame and molten insulation material observed in spreading flames over electrical wires under applied electric fields, which is a relevant scenario in electrical wire safety. The important roles of various unique dynamic behaviors in flame spreads are discussed, including fuel-vapor jet ejection from molten polyethylene (PE) surface, internal circulation of molten PE driven by Marangoni convection, dripping of molten PE, electrospray ejecting multiple small droplets from molten PE surface, and lateral dielectrophoresis by migrating a part of main molten PE toward the burnt wire side by forming a secondary molten PE or a liquid film of molten PE and sometimes leading to a formation of splitting flame. Additional behaviors such as vibration/rotation of molten PE due to a vertical dielectrophoresis, flame-leaning toward the burnt wire side caused by ionic wind, and magnetic field induced flame vortices near flame edges are also reviewed. The physical mechanisms of these dynamic behaviors are explained. Various regimes are identified depending on the occurrence of abovementioned phenomena. The dependence of flame spread rate on relevant physical parameters is reviewed, revealing a non-monotonic response to applied AC voltage and frequency, due to the intricate interactions among various dynamic phenomena. Phenomenological correlations are established for the FSR using key physical parameters including wire diameter, wire core diameter, applied voltage and frequency, and radial electric field gradient. To better understand the dynamic behaviors of molten insulation, the combustion of a droplet suspended on a wire was investigated, isolating the effects of solid-to-liquid phase change and the asymmetric distribution of molten PE between the burnt and unburned sides of the wire. The dynamic behaviors of such burning droplets under applied electric fields, along with their underlying mechanisms, are also reviewed and discussed.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105862"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145104448","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105848
B. Aravind , Ziyu Wang , Syed Mashruk , Deanna A. Lacoste , Agustin Valera-Medina
This study investigates the impact of gliding arc plasma (GAP) on the stability and emissions characteristics of a partially premixed ammonia (NH₃)-air swirling flames for wide ranges of global equivalence ratios (ϕg). A novel dual-swirl GAP combustor, incorporating conical central electrode serving as a bluff body, is used to generate a rotating gliding arc plasma within the fuel lance. The plasma power is maintained below 1.4 % of the thermal power of the flame across all experimental conditions. This is the first study to apply GAP directly to the fuel side, facilitating premixing immediately after plasma interaction. The results reveal that plasma significantly enhances lean and rich blowout limits by 15–20 % and 30–35 %, respectively. This is mainly due to the continuous local ignition effect through heating and the generation of active species pools. Plasma actuation also results in a substantial reduction in NO and NO₂ emissions, decreasing by 40–80 % and 30–50 %, respectively, depending on ϕg in the range of 0.76 to 1.05. Simultaneously, OH* and NH₂* intensities increase by 30–60 % and 70–80 %, respectively. This could indicate an increased NH₂ production favouring NO consumption reactions. A notable NH₃ slip occurs at ϕg values exceeding 0.93 and 0.76, indicating incomplete combustion. Numerical results suggest that NO formation predominantly occurs via the HNO pathway, and that plasma conditions promote thermal De-NOx reactions, notably through NH₂ + NO → NNH + OH and NH₂ + NO → N₂ + H₂O reactions. This study provides critical insights into the potential of GAP technique for advancing NH₃ combustion technologies, offering promising applications for sustainable energy systems.
{"title":"Novel strategy for combustion enhancement of NH3-air mixture using gliding arc plasma","authors":"B. Aravind , Ziyu Wang , Syed Mashruk , Deanna A. Lacoste , Agustin Valera-Medina","doi":"10.1016/j.proci.2025.105848","DOIUrl":"10.1016/j.proci.2025.105848","url":null,"abstract":"<div><div>This study investigates the impact of gliding arc plasma (GAP) on the stability and emissions characteristics of a partially premixed ammonia (NH₃)-air swirling flames for wide ranges of global equivalence ratios (ϕ<sub>g</sub>). A novel dual-swirl GAP combustor, incorporating conical central electrode serving as a bluff body, is used to generate a rotating gliding arc plasma within the fuel lance. The plasma power is maintained below 1.4 % of the thermal power of the flame across all experimental conditions. This is the first study to apply GAP directly to the fuel side, facilitating premixing immediately after plasma interaction. The results reveal that plasma significantly enhances lean and rich blowout limits by 15–20 % and 30–35 %, respectively. This is mainly due to the continuous local ignition effect through heating and the generation of active species pools. Plasma actuation also results in a substantial reduction in NO and NO₂ emissions, decreasing by 40–80 % and 30–50 %, respectively, depending on ϕ<sub>g</sub> in the range of 0.76 to 1.05. Simultaneously, OH* and NH₂* intensities increase by 30–60 % and 70–80 %, respectively. This could indicate an increased NH₂ production favouring NO consumption reactions. A notable NH₃ slip occurs at ϕ<sub>g</sub> values exceeding 0.93 and 0.76, indicating incomplete combustion. Numerical results suggest that NO formation predominantly occurs via the HNO pathway, and that plasma conditions promote thermal De-NO<sub>x</sub> reactions, notably through NH₂ + NO → NNH + OH and NH₂ + NO → N₂ + H₂O reactions. This study provides critical insights into the potential of GAP technique for advancing NH₃ combustion technologies, offering promising applications for sustainable energy systems.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105848"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145104548","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105859
Zhaohan Chu , Zhongkai Liu , Changyang Wang , Long Zhao , Bin Yang
An experimental study was conducted to investigate the weight growth routes from o-methylphenyl radical (o-CH3C6H4) to indene. o-Nitrosotoluene served as the precursor for o-methylphenyl radicals in this study. Co-pyrolysis of o-methylphenyl radical/C2H2 and o-methylphenyl radical/C2H4 was investigated utilizing the chemical microreactor and synchrotron vacuum ultraviolet photoionization mass spectrometry. Sampled mass-specific photoionization efficiency (PIE) curves were employed to identify the aromatic species, elucidating interactions between o-methylphenyl radicals and C2 species. The species detected at m/z = 116 and 118, essential for understanding the reaction mechanism, were identified via matching photoionization cross-sections and adiabatic ionization energies with literature and theoretical values. Specifically, indene and its isomer o-methylphenylacetylene (m/z = 116) were determined in the reaction of o-methylphenyl radical with C2H2, while indene and o-methylstyrene (m/z = 118) were identified in the reaction of o-methylphenyl radical with C2H4. By combining the identified intermediate species with previous literature basis, the formation pathways for indene, originating from o-methylphenyl radical were discussed in both reaction systems, providing further insights for understanding the indene formation pathways.
{"title":"Experimental evidence for indene formation from o-methylphenyl radical + C2H2/C2H4 reactions","authors":"Zhaohan Chu , Zhongkai Liu , Changyang Wang , Long Zhao , Bin Yang","doi":"10.1016/j.proci.2025.105859","DOIUrl":"10.1016/j.proci.2025.105859","url":null,"abstract":"<div><div>An experimental study was conducted to investigate the weight growth routes from <em>o</em>-methylphenyl radical (<em>o</em>-CH<sub>3</sub>C<sub>6</sub>H<sub>4</sub>) to indene. <em>o</em>-Nitrosotoluene served as the precursor for <em>o</em>-methylphenyl radicals in this study. Co-pyrolysis of <em>o</em>-methylphenyl radical/C<sub>2</sub>H<sub>2</sub> and <em>o</em>-methylphenyl radical/C<sub>2</sub>H<sub>4</sub> was investigated utilizing the chemical microreactor and synchrotron vacuum ultraviolet photoionization mass spectrometry. Sampled mass-specific photoionization efficiency (PIE) curves were employed to identify the aromatic species, elucidating interactions between <em>o</em>-methylphenyl radicals and C<sub>2</sub> species. The species detected at <em>m/z</em> = 116 and 118, essential for understanding the reaction mechanism, were identified via matching photoionization cross-sections and adiabatic ionization energies with literature and theoretical values. Specifically, indene and its isomer <em>o</em>-methylphenylacetylene (<em>m/z</em> = 116) were determined in the reaction of <em>o</em>-methylphenyl radical with C<sub>2</sub>H<sub>2</sub>, while indene and <em>o</em>-methylstyrene (<em>m/z</em> = 118) were identified in the reaction of <em>o</em>-methylphenyl radical with C<sub>2</sub>H<sub>4</sub>. By combining the identified intermediate species with previous literature basis, the formation pathways for indene, originating from <em>o</em>-methylphenyl radical were discussed in both reaction systems, providing further insights for understanding the indene formation pathways.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105859"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145109371","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105882
Matteo Impagnatiello, Nicolas Noiray
This study investigates the influence of Nanosecond Repetitively Pulsed Discharges (NRPDs) on the acoustic response of the second stage of a Constant Pressure Sequential Combustor (CPSC) operating at atmospheric pressure. NRPDs are applied upstream of the second-stage combustion chamber to modify the autoignition process, thereby altering the combustor’s acoustic scattering properties. Large Eddy Simulations (LES) combined with System Identification (SI) methods are employed to better understand the NRPD-flame-acoustic interactions in the sequential flame across three different Plasma Repetition Frequencies (PRF), namely 20, 40, and 60 kHz. Results show that, while NRPDs always improve the overall acoustic scattering properties of the system compared to the combustion without NRPDs, the improvement is non-monotonic with respect to PRF. The most favorable acoustic characteristics are observed at kHz. Analysis of local Rayleigh index fields, reconstructed from broadband-forced simulation data, reveals that variations in PRF alter the physical mechanism by which plasma discharges influence system acoustics. Plasma-generated kernels can either directly induce heat release rate fluctuations and act as acoustic energy sources or sinks, or indirectly affect the system’s acoustics by interacting with the main flame brush and modifying its response. The ability to influence the interaction between autoignition kernels and acoustics by simply adjusting the PRF underscores the potential of NRPDs as a versatile tool for controlling the acoustic behavior of sequential combustors, enabling adaptation to the varying operational needs of real gas turbines.
{"title":"Local Rayleigh index reconstruction: Application to plasma-assisted sequential combustion under varying pulse repetition frequency","authors":"Matteo Impagnatiello, Nicolas Noiray","doi":"10.1016/j.proci.2025.105882","DOIUrl":"10.1016/j.proci.2025.105882","url":null,"abstract":"<div><div>This study investigates the influence of Nanosecond Repetitively Pulsed Discharges (NRPDs) on the acoustic response of the second stage of a Constant Pressure Sequential Combustor (CPSC) operating at atmospheric pressure. NRPDs are applied upstream of the second-stage combustion chamber to modify the autoignition process, thereby altering the combustor’s acoustic scattering properties. Large Eddy Simulations (LES) combined with System Identification (SI) methods are employed to better understand the NRPD-flame-acoustic interactions in the sequential flame across three different Plasma Repetition Frequencies (PRF), namely 20, 40, and 60 kHz. Results show that, while NRPDs always improve the overall acoustic scattering properties of the system compared to the combustion without NRPDs, the improvement is non-monotonic with respect to PRF. The most favorable acoustic characteristics are observed at <span><math><mrow><mtext>PRF</mtext><mo>=</mo><mtext>20</mtext></mrow></math></span> kHz. Analysis of local Rayleigh index fields, reconstructed from broadband-forced simulation data, reveals that variations in PRF alter the physical mechanism by which plasma discharges influence system acoustics. Plasma-generated kernels can either directly induce heat release rate fluctuations and act as acoustic energy sources or sinks, or indirectly affect the system’s acoustics by interacting with the main flame brush and modifying its response. The ability to influence the interaction between autoignition kernels and acoustics by simply adjusting the PRF underscores the potential of NRPDs as a versatile tool for controlling the acoustic behavior of sequential combustors, enabling adaptation to the varying operational needs of real gas turbines.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105882"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145216306","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105867
Can Shao , Meysam Khademorezaeian , Jürgen Herzler , Greg J. Smallwood , Thomas Dreier , Torsten Endres , Mustapha Fikri , Christof Schulz
Particle inception remains the most enigmatic stage of the formation process of carbonaceous particles. Detailed knowledge of the evolution of optical properties during the transition from molecular species to particles is essential for unraveling this phenomenon and enabling accurate particle volume fraction measurements of freshly formed particles in combustion environments. This study monitors the transition from molecular precursors to incipient soot particles during toluene pyrolysis behind reflected shock waves by laser-induced emission spectroscopy. Time-resolved and spectrally-resolved measurements of laser-induced emission were performed with excitation at 266, 355, 532, or 1064 nm. Microsecond time resolution was provided upon laser-pulse excitation via simultaneous measurements at various spatial locations behind the reflected shock wave, using the reaction-time-resolved detection concept. These measurements trace the evolution of different stages of the carbonaceous species evolving from red-shifted laser-induced fluorescence (LIF) progressing from toluene decomposition and polycyclic aromatic hydrocarbon (PAH) formation to the onset of incipient soot and subsequent laser-induced incandescence (LII) from refractory soot. LII signals recorded after 1064-nm excitation were utilized to identify initial particle formation, while time-resolved LII measurements provided insight into particle-size evolution. These findings contribute to a deeper understanding of soot inception and provide optical properties of the early stage of soot particles.
{"title":"Monitoring carbonaceous species in the transition from molecules to particles in shock-tube pyrolysis of toluene by laser induced emission spectroscopy","authors":"Can Shao , Meysam Khademorezaeian , Jürgen Herzler , Greg J. Smallwood , Thomas Dreier , Torsten Endres , Mustapha Fikri , Christof Schulz","doi":"10.1016/j.proci.2025.105867","DOIUrl":"10.1016/j.proci.2025.105867","url":null,"abstract":"<div><div>Particle inception remains the most enigmatic stage of the formation process of carbonaceous particles. Detailed knowledge of the evolution of optical properties during the transition from molecular species to particles is essential for unraveling this phenomenon and enabling accurate particle volume fraction measurements of freshly formed particles in combustion environments. This study monitors the transition from molecular precursors to incipient soot particles during toluene pyrolysis behind reflected shock waves by laser-induced emission spectroscopy. Time-resolved and spectrally-resolved measurements of laser-induced emission were performed with excitation at 266, 355, 532, or 1064 nm. Microsecond time resolution was provided upon laser-pulse excitation via simultaneous measurements at various spatial locations behind the reflected shock wave, using the reaction-time-resolved detection concept. These measurements trace the evolution of different stages of the carbonaceous species evolving from red-shifted laser-induced fluorescence (LIF) progressing from toluene decomposition and polycyclic aromatic hydrocarbon (PAH) formation to the onset of incipient soot and subsequent laser-induced incandescence (LII) from refractory soot. LII signals recorded after 1064-nm excitation were utilized to identify initial particle formation, while time-resolved LII measurements provided insight into particle-size evolution. These findings contribute to a deeper understanding of soot inception and provide optical properties of the early stage of soot particles.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105867"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145216398","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 : 2025-01-01DOI: 10.1016/j.proci.2025.105893
Nicolas Vaysse, Daniel Durox, Ronan Vicquelin, Sébastien Candel, Antoine Renaud
Hydrogen is currently considered as a possible fuel substitute for gas turbines and aeroengines in the context of decarbonizing transportation and energy industries. However, its combustion raises scientific challenges due to its broad flammability domain and propensity to combustion instabilities. To ensure safe operation of hydrogen fueled systems, it is mandatory to study hydrogen combustion in industrially-relevant annular configurations that are typically found in applications. The present investigation is carried out in the MICCA facility equipped with 16 hydrogen injection units. In each injector, hydrogen is delivered in cross-flow in a swirled air flow. The aim of this investigation is to study the light-round ignition dynamics of a hydrogen-fueled annular combustor. The ignition sequence is observed with a high-speed camera equipped with an OH filter. The light-round delays are determined for a range of injection velocities and for equivalence ratios between 0.29 to 0.72. The relatively short light-round delays (from 18 ms to 35 ms), are considerably lower than those found for hydrocarbon flames. It is also found that at low equivalence ratios, the light-round proceeds but does not establish all the flames. The light-round delay is shown to decrease when the equivalence ratio is increased, and also when the inlet velocity is augmented at constant equivalence ratio. A link is made between the average flame displacement velocity and the turbulent burning velocity taking into account the thermal expansion. It is found that this can be achieved with a model combining two expressions for the turbulent burning velocity, corresponding to high and low values of the laminar burning velocity. The model captures the influence of injection velocity and equivalence ratio on the flame displacement velocity during light round. It is thus possible to derive a correlation for the reduced light-round delay that suitably retrieves experimental data.
{"title":"Ignition dynamics of a hydrogen-fueled annular combustor","authors":"Nicolas Vaysse, Daniel Durox, Ronan Vicquelin, Sébastien Candel, Antoine Renaud","doi":"10.1016/j.proci.2025.105893","DOIUrl":"10.1016/j.proci.2025.105893","url":null,"abstract":"<div><div>Hydrogen is currently considered as a possible fuel substitute for gas turbines and aeroengines in the context of decarbonizing transportation and energy industries. However, its combustion raises scientific challenges due to its broad flammability domain and propensity to combustion instabilities. To ensure safe operation of hydrogen fueled systems, it is mandatory to study hydrogen combustion in industrially-relevant annular configurations that are typically found in applications. The present investigation is carried out in the MICCA facility equipped with 16 hydrogen injection units. In each injector, hydrogen is delivered in cross-flow in a swirled air flow. The aim of this investigation is to study the light-round ignition dynamics of a hydrogen-fueled annular combustor. The ignition sequence is observed with a high-speed camera equipped with an OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> filter. The light-round delays are determined for a range of injection velocities and for equivalence ratios between 0.29 to 0.72. The relatively short light-round delays (from 18 ms to 35 ms), are considerably lower than those found for hydrocarbon flames. It is also found that at low equivalence ratios, the light-round proceeds but does not establish all the flames. The light-round delay is shown to decrease when the equivalence ratio is increased, and also when the inlet velocity is augmented at constant equivalence ratio. A link is made between the average flame displacement velocity and the turbulent burning velocity taking into account the thermal expansion. It is found that this can be achieved with a model combining two expressions for the turbulent burning velocity, corresponding to high and low values of the laminar burning velocity. The model captures the influence of injection velocity and equivalence ratio on the flame displacement velocity during light round. It is thus possible to derive a correlation for the reduced light-round delay that suitably retrieves experimental data.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"41 ","pages":"Article 105893"},"PeriodicalIF":5.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145319801","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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