Pub Date : 2024-07-05DOI: 10.1016/j.proci.2024.105278
Quentin Malé, Khushboo Pandey, Nicolas Noiray
The development of low NO hydrogen (H) burners is crucial for the sustainability target of the power/propulsion sector. However, the technical difficulty of burning H at low NO emissions is challenging for the combustion community. Recently, the concept of LEan Azimuthal Flame (LEAF) has demonstrated promising results for low NO kerosene/hydrogen combustion by rapidly diluting the reactants with burnt gas and fresh oxidizer. However, there is a lack of understanding of the flame dynamics and the NO formation routes for H LEAF. We therefore carried out a joint experimental and numerical study of the LEAF combustor at atmospheric pressure fueled with H. Experiments are based on OH-planar laser-induced fluorescence and exhaust gas analysis. Numerical results are based on massively parallel Large Eddy Simulation (LES) with an accurate description of the combustion and NO chemistry. This study focuses on understanding the effects of the Air Ratio (AR), which defines the distribution of the air injected from the top and the bottom of the LEAF combustor. The LES results are in excellent agreement with the experimental data in terms of flame topology and exhaust emissions. A dual flame structure is observed when rich premixed gas is injected from the bottom together with air from the top, leading to the coexistence of premixed and non-premixed combustion regimes. An optimum AR is identified to minimize NO emissions. It is attributed to the enhancement of the azimuthal whirling flow by the air injected from the bottom, having higher momentum than pure H injection only.
开发低氮氧化物（NO）氢（H）燃烧器对于实现电力/推进领域的可持续发展目标至关重要。然而，在低氮氧化物排放条件下燃烧氢气的技术难度对燃烧界来说具有挑战性。最近，"低氮方位火焰"（LEAF）概念通过用燃烧气体和新鲜氧化剂快速稀释反应物，在低氮煤油/氢燃烧方面取得了可喜的成果。然而，人们对 H LEAF 的火焰动力学和 NO 的形成途径还缺乏了解。因此，我们对常压下以 H 为燃料的 LEAF 燃烧器进行了联合实验和数值研究。数值结果基于大规模并行大涡模拟（LES），对燃烧和氮氧化物化学性质进行了精确描述。这项研究的重点是了解空气比（AR）的影响，空气比定义了从 LEAF 燃烧器顶部和底部喷入的空气的分布。在火焰拓扑和废气排放方面，LES 结果与实验数据非常吻合。当从底部喷入富预混气体和从顶部喷入空气时，可观察到双重火焰结构，从而导致预混和非预混燃烧状态共存。确定了一个最佳 AR，以最大限度地减少氮氧化物的排放。这归因于从底部喷入的空气增强了方位旋流，其动量高于仅喷入纯 H 的动量。
{"title":"The LEAF concept operated with hydrogen: Flame topology and NOx formation","authors":"Quentin Malé, Khushboo Pandey, Nicolas Noiray","doi":"10.1016/j.proci.2024.105278","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105278","url":null,"abstract":"The development of low NO hydrogen (H) burners is crucial for the sustainability target of the power/propulsion sector. However, the technical difficulty of burning H at low NO emissions is challenging for the combustion community. Recently, the concept of LEan Azimuthal Flame (LEAF) has demonstrated promising results for low NO kerosene/hydrogen combustion by rapidly diluting the reactants with burnt gas and fresh oxidizer. However, there is a lack of understanding of the flame dynamics and the NO formation routes for H LEAF. We therefore carried out a joint experimental and numerical study of the LEAF combustor at atmospheric pressure fueled with H. Experiments are based on OH-planar laser-induced fluorescence and exhaust gas analysis. Numerical results are based on massively parallel Large Eddy Simulation (LES) with an accurate description of the combustion and NO chemistry. This study focuses on understanding the effects of the Air Ratio (AR), which defines the distribution of the air injected from the top and the bottom of the LEAF combustor. The LES results are in excellent agreement with the experimental data in terms of flame topology and exhaust emissions. A dual flame structure is observed when rich premixed gas is injected from the bottom together with air from the top, leading to the coexistence of premixed and non-premixed combustion regimes. An optimum AR is identified to minimize NO emissions. It is attributed to the enhancement of the azimuthal whirling flow by the air injected from the bottom, having higher momentum than pure H injection only.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551052","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-05DOI: 10.1016/j.proci.2024.105204
Véranika Latour, Daniel Durox, Antoine Renaud, Sébastien Candel
The determination of acoustic source terms and growth rates is of paramount importance in the thermoacoustic stability analysis of combustion systems. This article aims to experimentally quantify the acoustic energy source term in the laboratory-scale annular combustor MICCA-Spray and deduce growth rate estimates from these measurements. MICCA-Spray is equipped with sixteen modular injection units and an original method is used to vary the level of self-sustained pressure oscillations at limit cycle in the system by mixing injectors leading to different flame dynamics, characterized by their flame describing functions (FDFs). Various injectors’ arrangements are explored, and the Rayleigh source terms associated to the different flames are determined from the simultaneous recording of pressure and heat release rate fluctuations that are respectively detected by a set of microphones plugged on the chamber backplane and photomultipliers collecting the light emitted by OH* radicals. The contribution of the different flames to the total acoustic source term is quantified and shown to depend on the flame position with respect to the nodal line and the flame dynamical characteristics (FDF gain and phase). A theoretical expression of the growth rate, based on the FDF data collected in a single-injector test rig, is derived. The analytical results closely match the experimentally determined Rayleigh source terms and provide growth rates that exceed the damping rate, which is in agreement with experimental observations, thus validating the analytical framework and indicating that the model can be used for predictive purposes.
{"title":"Experimental and theoretical estimation of acoustic energy source terms and instability growth rates in an annular combustor","authors":"Véranika Latour, Daniel Durox, Antoine Renaud, Sébastien Candel","doi":"10.1016/j.proci.2024.105204","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105204","url":null,"abstract":"The determination of acoustic source terms and growth rates is of paramount importance in the thermoacoustic stability analysis of combustion systems. This article aims to experimentally quantify the acoustic energy source term in the laboratory-scale annular combustor MICCA-Spray and deduce growth rate estimates from these measurements. MICCA-Spray is equipped with sixteen modular injection units and an original method is used to vary the level of self-sustained pressure oscillations at limit cycle in the system by mixing injectors leading to different flame dynamics, characterized by their flame describing functions (FDFs). Various injectors’ arrangements are explored, and the Rayleigh source terms associated to the different flames are determined from the simultaneous recording of pressure and heat release rate fluctuations that are respectively detected by a set of microphones plugged on the chamber backplane and photomultipliers collecting the light emitted by OH* radicals. The contribution of the different flames to the total acoustic source term is quantified and shown to depend on the flame position with respect to the nodal line and the flame dynamical characteristics (FDF gain and phase). A theoretical expression of the growth rate, based on the FDF data collected in a single-injector test rig, is derived. The analytical results closely match the experimentally determined Rayleigh source terms and provide growth rates that exceed the damping rate, which is in agreement with experimental observations, thus validating the analytical framework and indicating that the model can be used for predictive purposes.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-05DOI: 10.1016/j.proci.2024.105372
Juan F. Alarcon, Alexander N. Morozov, Alexander M. Mebel, Andrea Della Libera, Luna Pratali Maffei, Carlo Cavallotti
Automated reaction path discovery tools have been used to map out the CHO potential energy surface and determine the prevailing channels for oxidation of the propargyl radical with atomic oxygen. The energy of the stationary points was then evaluated at the CCSD(T)/CBS//ωB97X-D/6-311+G(d,p) level of electronic structure theory. The CH + O total and individual product channel rate constants were evaluated with Rice-Ramsperger-Kassel-Marcus Master Equation calculations combined with variable reaction coordinate transition state theory assessment of barrierless entrance channels. The total reaction rate so determined is in quantitative agreement with experiments, highlighting the relevance of accounting for CH + O recombination on the excited electronic state surface. CHCHO (propynal) + H are predicted as the prevailing reaction products, followed by CHCCO (propadienone) + H, with minor contributions from CH + HCO and CH + CO. The calculated rate constants have been utilized in kinetic simulations, which tested the impact of the CH + O reaction on chemical reactivity in premixed laminar flames of acetylene, ethylene, allene, propyne, and benzene. The results displayed macroscopic changes of the model predictions at low pressures (< 0.1 atm) and rich conditions, a reduction in the consumption of propargyl via CH + O, and a substantial decrease in the CH + HCO reactivity to CH + CO. The updated model showed an improved performance in predicting C species in the considered flames.
利用自动反应路径发现工具绘制了 CHO 势能面，并确定了丙炔基与原子氧氧化的主要通道。然后在 CCSD(T)/CBS//ωB97X-D/6-311+G(d,p) 电子结构理论水平上评估了静止点的能量。通过赖斯-拉姆佩尔格-卡塞尔-马库斯主方程（Rice-Ramsperger-Kassel-Marcus Master Equation）计算，结合无障碍入口通道的可变反应坐标过渡态理论评估，对 CH + O 总速率常数和单个产物通道速率常数进行了评估。由此确定的总反应速率与实验结果在数量上是一致的，突出了考虑激发电子态表面 CH + O 重组的相关性。据预测，CHCHO（丙炔醛）+ H 是最主要的反应产物，其次是 CHCCO（丙二烯酮）+ H，CH + HCO 和 CH + CO 的贡献较小。计算出的速率常数被用于动力学模拟，以测试 CH + O 反应对乙炔、乙烯、异戊二烯、丙炔和苯的预混合层流火焰中化学反应活性的影响。结果表明，在低压（< 0.1 atm）和富裕条件下，模型预测值发生了宏观变化，丙炔通过 CH + O 的消耗量减少，CH + HCO 与 CH + CO 的反应性大幅降低。更新后的模型在预测所考虑的火焰中的 C 物种方面表现更佳。
{"title":"Mechanism and kinetics of the oxidation of propargyl radical by atomic oxygen","authors":"Juan F. Alarcon, Alexander N. Morozov, Alexander M. Mebel, Andrea Della Libera, Luna Pratali Maffei, Carlo Cavallotti","doi":"10.1016/j.proci.2024.105372","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105372","url":null,"abstract":"Automated reaction path discovery tools have been used to map out the CHO potential energy surface and determine the prevailing channels for oxidation of the propargyl radical with atomic oxygen. The energy of the stationary points was then evaluated at the CCSD(T)/CBS//ωB97X-D/6-311+G(d,p) level of electronic structure theory. The CH + O total and individual product channel rate constants were evaluated with Rice-Ramsperger-Kassel-Marcus Master Equation calculations combined with variable reaction coordinate transition state theory assessment of barrierless entrance channels. The total reaction rate so determined is in quantitative agreement with experiments, highlighting the relevance of accounting for CH + O recombination on the excited electronic state surface. CHCHO (propynal) + H are predicted as the prevailing reaction products, followed by CHCCO (propadienone) + H, with minor contributions from CH + HCO and CH + CO. The calculated rate constants have been utilized in kinetic simulations, which tested the impact of the CH + O reaction on chemical reactivity in premixed laminar flames of acetylene, ethylene, allene, propyne, and benzene. The results displayed macroscopic changes of the model predictions at low pressures (< 0.1 atm) and rich conditions, a reduction in the consumption of propargyl via CH + O, and a substantial decrease in the CH + HCO reactivity to CH + CO. The updated model showed an improved performance in predicting C species in the considered flames.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141576903","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1016/j.proci.2024.105268
Seong-Young Lee, Timothy M. Ombrello
Utilizing time-resolved CH*/C* and multi-angle color flame imaging recorded at 1 kHz/22.5 kHz frequencies, this study investigates the dynamics and stabilization of supersonic flames in a cavity flameholder combustor at Mach 2, with ethylene fuel and air. A stagnation pressure of 289 kPa was used for the stable cavity burning experiments with fuel flow rates of 30, 60, and 90 slpm and 483 kPa for ignition transient experiments with fuel flow rates of 55 and 90 slpm, injecting fuel at the closeout ramp. The stagnation temperature was 597 K. Chemiluminescence analysis focused on the equivalence ratio (ER) and combustion intensity, while a fiber-based endoscope captured color flame image, informing on premixedness, flame structure, and flame surface density. Results from transient ignition showed that a progression from lean to stoichiometric, and ultimately to fuel-rich conditions was observed, with marked transitions occurring along the cavity floor. High-intensity CH* regions were consistently associated with fuel-rich zones. Digital flame coloration discrimination (DFCD) analysis provided insights into the mixing efficiency, affecting the flame color and structure. Despite reduced fuel flow rates significantly altering flame characteristics, such as thickness and the persistence of a 'W' flame structure, the shear layer remained a focal point for optimal combustion conditions. The study demonstrated that the shear layer's intense turbulent mixing is crucial for flame stability and structure, with chemiluminescence surface density (CSD) profiles suggesting balanced combustion at 60 and 90 slpm flow rates. However, an asymmetry of CSD at 30 slpm indicated a shift towards fuel-rich conditions at the burning surface, indicating potential instability and elevated blowout.
{"title":"Color and multi-band imaging of a cavity-based flameholder in supersonic flow","authors":"Seong-Young Lee, Timothy M. Ombrello","doi":"10.1016/j.proci.2024.105268","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105268","url":null,"abstract":"Utilizing time-resolved CH*/C* and multi-angle color flame imaging recorded at 1 kHz/22.5 kHz frequencies, this study investigates the dynamics and stabilization of supersonic flames in a cavity flameholder combustor at Mach 2, with ethylene fuel and air. A stagnation pressure of 289 kPa was used for the stable cavity burning experiments with fuel flow rates of 30, 60, and 90 slpm and 483 kPa for ignition transient experiments with fuel flow rates of 55 and 90 slpm, injecting fuel at the closeout ramp. The stagnation temperature was 597 K. Chemiluminescence analysis focused on the equivalence ratio (ER) and combustion intensity, while a fiber-based endoscope captured color flame image, informing on premixedness, flame structure, and flame surface density. Results from transient ignition showed that a progression from lean to stoichiometric, and ultimately to fuel-rich conditions was observed, with marked transitions occurring along the cavity floor. High-intensity CH* regions were consistently associated with fuel-rich zones. Digital flame coloration discrimination (DFCD) analysis provided insights into the mixing efficiency, affecting the flame color and structure. Despite reduced fuel flow rates significantly altering flame characteristics, such as thickness and the persistence of a 'W' flame structure, the shear layer remained a focal point for optimal combustion conditions. The study demonstrated that the shear layer's intense turbulent mixing is crucial for flame stability and structure, with chemiluminescence surface density (CSD) profiles suggesting balanced combustion at 60 and 90 slpm flow rates. However, an asymmetry of CSD at 30 slpm indicated a shift towards fuel-rich conditions at the burning surface, indicating potential instability and elevated blowout.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1016/j.proci.2024.105298
Juhan Kim, Huido Lee, Jong Moon Lee, Jeong Park, Suk Ho Chung, Chun Sang Yoo
This study experimentally investigates the effects of secondary air injection on the flame structure and CO/NO emission characteristics of turbulent premixed CH/NH/air flames in a two-stage swirl combustor. The equivalence ratio () and velocity () of the primary fuel/air jet and the injection location () and velocity () of the secondary air jet are varied. The location of the secondary air injection of 30 and 250 mm are adopted to investigate two interaction cases in two-stage combustion (TSC): 1) a strong interaction where the secondary air is directly injected into the primary premixed flame and strongly affects the flame, and 2) a weak interaction where the secondary air is injected after the primary reaction is completed. A single-stage combustion (SSC) is also tested for comparison. It is found from averaged OH-PLIF images that the strong interaction cases of TSC with > 1 can produce a significant amount of NO emissions due to the direct interaction between the primary flame and the secondary air, while the weak interaction cases can produce an appreciable amount of CO emissions due to the incomplete combustion of the secondary flames. This result is further confirmed by CO/NO measurements that the strong interaction cases produce higher NO emissions than the weak interaction cases, while the CO emissions of the weak interaction cases become significant and peak at = 1.1 ∼ 1.2. Based on the OH-PLIF images and CO/NO emission characteristics of TSC, the optimal conditions of the primary and secondary jets are proposed to ensure the reduction of NO emissions with low level of CO emissions.
本研究通过实验研究了二次空气喷射对两级漩涡燃烧器中湍流预混合 CH/NH/ 空气火焰结构和 CO/NO 排放特性的影响。研究改变了一次燃料/空气喷射的等效比（）和速度（）以及二次空气喷射的喷射位置（）和速度（）。采用 30 毫米和 250 毫米的二次空气喷射位置来研究两级燃烧（TSC）中的两种相互作用情况：1) 强交互作用，即二次空气直接喷入一次预混合火焰并对火焰产生强烈影响；以及 2) 弱交互作用，即二次空气在一次反应完成后喷入。为了进行比较，还测试了单级燃烧（SSC）。从平均 OH-PLIF 图像中可以发现，TSC > 1 的强相互作用情况下，由于一次火焰和二次空气之间的直接相互作用，会产生大量的 NO 排放；而弱相互作用情况下，由于二次火焰的不完全燃烧，会产生相当数量的 CO 排放。CO/NO 测量进一步证实了这一结果，即强相互作用情况下产生的 NO 排放量高于弱相互作用情况下的 NO 排放量，而弱相互作用情况下的 CO 排放量变得显著，并在 = 1.1 ∼ 1.2 时达到峰值。根据 TSC 的 OH-PLIF 图像和 CO/NO 排放特征，提出了主喷流和副喷流的最佳条件，以确保在减少 CO 排放的同时减少 NO 排放。
{"title":"Effects of the secondary air on the combustion characteristics of turbulent premixed CH4/NH3/air","authors":"Juhan Kim, Huido Lee, Jong Moon Lee, Jeong Park, Suk Ho Chung, Chun Sang Yoo","doi":"10.1016/j.proci.2024.105298","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105298","url":null,"abstract":"This study experimentally investigates the effects of secondary air injection on the flame structure and CO/NO emission characteristics of turbulent premixed CH/NH/air flames in a two-stage swirl combustor. The equivalence ratio () and velocity () of the primary fuel/air jet and the injection location () and velocity () of the secondary air jet are varied. The location of the secondary air injection of 30 and 250 mm are adopted to investigate two interaction cases in two-stage combustion (TSC): 1) a strong interaction where the secondary air is directly injected into the primary premixed flame and strongly affects the flame, and 2) a weak interaction where the secondary air is injected after the primary reaction is completed. A single-stage combustion (SSC) is also tested for comparison. It is found from averaged OH-PLIF images that the strong interaction cases of TSC with > 1 can produce a significant amount of NO emissions due to the direct interaction between the primary flame and the secondary air, while the weak interaction cases can produce an appreciable amount of CO emissions due to the incomplete combustion of the secondary flames. This result is further confirmed by CO/NO measurements that the strong interaction cases produce higher NO emissions than the weak interaction cases, while the CO emissions of the weak interaction cases become significant and peak at = 1.1 ∼ 1.2. Based on the OH-PLIF images and CO/NO emission characteristics of TSC, the optimal conditions of the primary and secondary jets are proposed to ensure the reduction of NO emissions with low level of CO emissions.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1016/j.proci.2024.105455
Ridong Zhang, Qihang Zhang, Yunliang Qi, Bin Yang, Zhi Wang
Ammonia-hydrogen engine has attracted much attention due to its carbon-free nature. Given that ammonia has high knock resistance (indicated by its high research octane number of nearly 130), researchers are trying to increase the compression ratio (CR) to improve engines’ thermal efficiency. However, knocking cycles can still be detected in ammonia-hydrogen engines under elevated thermodynamic conditions. To further explore the ammonia-hydrogen knocking process, this study conducted a series of spark-ignition combustion experiments focusing on flame propagation and end-gas auto-ignition in a full-field-visualized rapid compression machine. Four ammonia-hydrogen blended fuels with hydrogen energy fractions of 0 % (H0), 10 % (H10), 20 % (H20), and 100 % (H100) were comparatively tested under the thermodynamic conditions of 30 bar and 750–985 K. The experimental results showed that the flame speed of H0, H10, and H20 is around 3–6 m/s under test conditions, much lower than that of H100, which exceeds 37 m/s at 30 bar/750 K. Strong end-gas auto-ignitions with maximum pressure amplitudes of 77 bar and 101 bar were recorded for H0 at 30 bar/985 K and H10 at 30 bar/915 K, respectively. The two auto-ignition events both exhibited detonation characteristics by clear wavefronts with speeds reaching up to 1620 m/s (H0) and 1812 m/s (H10). Based on the experimental results, simulations were carried out to analyze the chemical process during the end-gas auto-ignition. The simulated results showed that for H0 at 30 bar/985 K, the NO-, NO-, and HNO-related reactions contributed most to heat production, which improved the end-gas reactivity and promoted the occurrence of auto-ignition. For H10 at 30 bar/915 K, the H + O (+M) = HO (+M) became the most exothermic reaction, indicating the hydrogen addition significantly promoted the ammonia's end-gas auto-ignition. Additionally, the detonation events observed in this study can be well classified in the -diagram.
{"title":"Investigation on flame propagation and end-gas auto-ignition of ammonia/hydrogen in a full-field-visualized rapid compression machine","authors":"Ridong Zhang, Qihang Zhang, Yunliang Qi, Bin Yang, Zhi Wang","doi":"10.1016/j.proci.2024.105455","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105455","url":null,"abstract":"Ammonia-hydrogen engine has attracted much attention due to its carbon-free nature. Given that ammonia has high knock resistance (indicated by its high research octane number of nearly 130), researchers are trying to increase the compression ratio (CR) to improve engines’ thermal efficiency. However, knocking cycles can still be detected in ammonia-hydrogen engines under elevated thermodynamic conditions. To further explore the ammonia-hydrogen knocking process, this study conducted a series of spark-ignition combustion experiments focusing on flame propagation and end-gas auto-ignition in a full-field-visualized rapid compression machine. Four ammonia-hydrogen blended fuels with hydrogen energy fractions of 0 % (H0), 10 % (H10), 20 % (H20), and 100 % (H100) were comparatively tested under the thermodynamic conditions of 30 bar and 750–985 K. The experimental results showed that the flame speed of H0, H10, and H20 is around 3–6 m/s under test conditions, much lower than that of H100, which exceeds 37 m/s at 30 bar/750 K. Strong end-gas auto-ignitions with maximum pressure amplitudes of 77 bar and 101 bar were recorded for H0 at 30 bar/985 K and H10 at 30 bar/915 K, respectively. The two auto-ignition events both exhibited detonation characteristics by clear wavefronts with speeds reaching up to 1620 m/s (H0) and 1812 m/s (H10). Based on the experimental results, simulations were carried out to analyze the chemical process during the end-gas auto-ignition. The simulated results showed that for H0 at 30 bar/985 K, the NO-, NO-, and HNO-related reactions contributed most to heat production, which improved the end-gas reactivity and promoted the occurrence of auto-ignition. For H10 at 30 bar/915 K, the H + O (+M) = HO (+M) became the most exothermic reaction, indicating the hydrogen addition significantly promoted the ammonia's end-gas auto-ignition. Additionally, the detonation events observed in this study can be well classified in the -diagram.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1016/j.proci.2024.105277
Quentin Malé, Sergey Shcherbanev, Matteo Impagnatiello, Nicolas Noiray
Plasma-assisted combustion using Nanosecond Repetitively Pulsed Discharges (NRPDs) is an emerging technology that enhances the reactivity of fuel–air mixtures, offering significant improvements in operational and fuel flexibility—two crucial features for future sustainable gas turbines. The mechanisms that enable the stabilization of thermoacoustically unstable burners, however, remain unclear. Thus, to investigate the physical phenomena involved, we performed a massively parallel Large Eddy Simulation (LES) of the stabilization of a thermoacoustically unstable sequential combustor by NRPDs at atmospheric pressure. LES is combined with an accurate description of the combustion chemistry and a state-of-the-art phenomenological model for the non-equilibrium plasma effects. In this work, we have validated the simulation framework by comparison with experimental data including acoustic pressure and Heat Release Rate (HRR) signals in both stages of the sequential combustor, and OH-planar laser-induced fluorescence images in the second stage combustion chamber. Hence, this study provides a robust LES framework to study the effects of NRPDs on Thermoacoustic Instabilities (TIs). In addition, the analysis of the LES data reveals a significant decrease of the acoustic energy production in the sequential combustor thanks to the NRPDs. Surprisingly, the steady NRPD actuation generates HRR fluctuations upstream of the combustion chamber, which are in phase opposition to the acoustic pressure, inducing locally a sink term in the acoustic energy balance equation. Moreover, an analysis of the acoustic energy production during the onset of the TI reveals the predominant role of the second stage in developing and sustaining the self-excited TI. The effect of plasma is therefore very effective in stabilizing the system by reducing the acoustic energy production in the sequential stage.
使用纳秒重复脉冲放电（NRPDs）进行等离子体辅助燃烧是一项新兴技术，可提高燃料-空气混合物的反应性，显著改善操作和燃料灵活性--这是未来可持续燃气轮机的两个关键特征。然而，能够稳定热声不稳定燃烧器的机制仍不清楚。因此，为了研究其中涉及的物理现象，我们对 NRPDs 在大气压力下稳定热声不稳定顺序燃烧器的过程进行了大规模并行大涡流模拟（LES）。大涡流模拟结合了对燃烧化学性质的精确描述和最先进的非平衡等离子体效应现象学模型。在这项工作中，我们通过与实验数据（包括序贯燃烧器两级的声压和热释放率（HRR）信号以及第二级燃烧室的 OH 平面激光诱导荧光图像）进行比较，验证了模拟框架。因此，本研究为研究 NRPD 对热声不稳定性（TIs）的影响提供了一个稳健的 LES 框架。此外，对 LES 数据的分析表明，由于 NRPD 的存在，顺序燃烧器中产生的声能显著减少。令人惊讶的是，稳定的 NRPD 驱动会在燃烧室上游产生 HRR 波动，这种波动与声压的相位相反，从而在声能平衡方程中产生局部的汇项。此外，对 TI 开始期间声能产生的分析表明，第二阶段在发展和维持自激 TI 方面起着主导作用。因此，等离子体的作用通过减少连续阶段的声能产生，在稳定系统方面非常有效。
{"title":"Stabilization of a thermoacoustically unstable sequential combustor using non-equilibrium plasma: Large eddy simulation and experiments","authors":"Quentin Malé, Sergey Shcherbanev, Matteo Impagnatiello, Nicolas Noiray","doi":"10.1016/j.proci.2024.105277","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105277","url":null,"abstract":"Plasma-assisted combustion using Nanosecond Repetitively Pulsed Discharges (NRPDs) is an emerging technology that enhances the reactivity of fuel–air mixtures, offering significant improvements in operational and fuel flexibility—two crucial features for future sustainable gas turbines. The mechanisms that enable the stabilization of thermoacoustically unstable burners, however, remain unclear. Thus, to investigate the physical phenomena involved, we performed a massively parallel Large Eddy Simulation (LES) of the stabilization of a thermoacoustically unstable sequential combustor by NRPDs at atmospheric pressure. LES is combined with an accurate description of the combustion chemistry and a state-of-the-art phenomenological model for the non-equilibrium plasma effects. In this work, we have validated the simulation framework by comparison with experimental data including acoustic pressure and Heat Release Rate (HRR) signals in both stages of the sequential combustor, and OH-planar laser-induced fluorescence images in the second stage combustion chamber. Hence, this study provides a robust LES framework to study the effects of NRPDs on Thermoacoustic Instabilities (TIs). In addition, the analysis of the LES data reveals a significant decrease of the acoustic energy production in the sequential combustor thanks to the NRPDs. Surprisingly, the steady NRPD actuation generates HRR fluctuations upstream of the combustion chamber, which are in phase opposition to the acoustic pressure, inducing locally a sink term in the acoustic energy balance equation. Moreover, an analysis of the acoustic energy production during the onset of the TI reveals the predominant role of the second stage in developing and sustaining the self-excited TI. The effect of plasma is therefore very effective in stabilizing the system by reducing the acoustic energy production in the sequential stage.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551116","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1016/j.proci.2024.105274
Tong Xu, Fei Tang, Jianping Zhang
This work was aimed at investigating the temperature profile and flame extension characteristics of the ceiling jet, which was induced by the fire ejected from a carriage in an inclined tunnel. A series of experiments were conducted in a 1 : 6 reduced-scale model, including a compartment with a window in an inclined tunnel (from 0 to 10 %). Tests were conducted with various heat release rates (HRRs) and opening dimensions. Results showed that with the decreasing ventilation factor, the mixing degree of the air and fuel gases is weakened inside the compartment and the average temperature at the continuous flames ejecting stage is also reduced. For a given opening size, the tunnel slope is shown to affect the temperature distribution inside the enclosure only before reaching the steady burning stage, after which the temperature inside the compartment becomes almost uniform independent of the tunnel slope. In the transverse direction, both the temperature profile and flame extension length under the tunnel ceiling are found to be insensitive to the tunnel slope, whereas in the longitudinal direction, the flame extension length is increased in the upward direction while decreased in the downward direction due to thermal buoyancy. Based on dimensionless analysis, a new correlation was developed incorporating the effects of HRRs, opening sizes and tunnel slopes for the longitudinal flame extension in upward and downward directions, which is found to be in good agreement with the present data and also available data in the literature. The experimental data and the correlation developed are important in understanding the extension behavior of the ejected fire from a carriage in an inclined tunnel, which are essential to assess the thermal hazard and risk of fire spreading to adjacent vehicles.
{"title":"Experimental study on the ceiling jet characteristics caused by carriage fire in an inclined tunnel: Temperature distribution and flame extension","authors":"Tong Xu, Fei Tang, Jianping Zhang","doi":"10.1016/j.proci.2024.105274","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105274","url":null,"abstract":"This work was aimed at investigating the temperature profile and flame extension characteristics of the ceiling jet, which was induced by the fire ejected from a carriage in an inclined tunnel. A series of experiments were conducted in a 1 : 6 reduced-scale model, including a compartment with a window in an inclined tunnel (from 0 to 10 %). Tests were conducted with various heat release rates (HRRs) and opening dimensions. Results showed that with the decreasing ventilation factor, the mixing degree of the air and fuel gases is weakened inside the compartment and the average temperature at the continuous flames ejecting stage is also reduced. For a given opening size, the tunnel slope is shown to affect the temperature distribution inside the enclosure only before reaching the steady burning stage, after which the temperature inside the compartment becomes almost uniform independent of the tunnel slope. In the transverse direction, both the temperature profile and flame extension length under the tunnel ceiling are found to be insensitive to the tunnel slope, whereas in the longitudinal direction, the flame extension length is increased in the upward direction while decreased in the downward direction due to thermal buoyancy. Based on dimensionless analysis, a new correlation was developed incorporating the effects of HRRs, opening sizes and tunnel slopes for the longitudinal flame extension in upward and downward directions, which is found to be in good agreement with the present data and also available data in the literature. The experimental data and the correlation developed are important in understanding the extension behavior of the ejected fire from a carriage in an inclined tunnel, which are essential to assess the thermal hazard and risk of fire spreading to adjacent vehicles.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-03DOI: 10.1016/j.proci.2024.105358
Hans-Christoph Ries, Christian Eigenbrod, Florian Meyer
The flame spread of thin PMMA sheets has been studied both in opposed configuration under microgravity (9.3 s drop tower) and in downward configuration under normal gravity conditions. The position of the flame front has been determined with the help of an infrared camera. Propagation rates have been measured over a range of 30–200 mm/s forced opposed flow (only microgravity), 60–101.3 kPa ambient pressure, and oxygen concentrations of 21–35.4 vol. %, which corresponds to real environmental conditions on spacecraft. In addition to variations along the normoxic curve with constant oxygen partial pressure, the parameters oxygen and pressure were examined independently of each other in order to be able to determine their respective effects. The variation of the flow velocity was carried out at 60 kPa and 35.4 vol. % oxygen. The results for both microgravity and normal gravity are discussed separately on the basis of the respective atmospheric effect. Along the normoxic curve, a significant increase in the flame spread rate was found with increasing oxygen concentration and correspondingly decreasing pressure. This results in a significant increase in the risk of fire with regard to future exploration missions. The effect of the flow velocity cannot be neglected in the investigated velocity range and was linked to the influencing parameters in a correlation. Based on this parameterization, a linear function is given that reflects both the downward and the opposed results well. This function can be used to predict the flame spread in the given parameter space. Under normal gravity, the tested samples show a slightly increased propagation rate in most cases. This can essentially be attributed to the difference in velocity between the buoyant flow and the forced flow in µg.
{"title":"Effect of oxygen concentration, pressure, and opposed flow velocity on the flame spread along thin PMMA sheets","authors":"Hans-Christoph Ries, Christian Eigenbrod, Florian Meyer","doi":"10.1016/j.proci.2024.105358","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105358","url":null,"abstract":"The flame spread of thin PMMA sheets has been studied both in opposed configuration under microgravity (9.3 s drop tower) and in downward configuration under normal gravity conditions. The position of the flame front has been determined with the help of an infrared camera. Propagation rates have been measured over a range of 30–200 mm/s forced opposed flow (only microgravity), 60–101.3 kPa ambient pressure, and oxygen concentrations of 21–35.4 vol. %, which corresponds to real environmental conditions on spacecraft. In addition to variations along the normoxic curve with constant oxygen partial pressure, the parameters oxygen and pressure were examined independently of each other in order to be able to determine their respective effects. The variation of the flow velocity was carried out at 60 kPa and 35.4 vol. % oxygen. The results for both microgravity and normal gravity are discussed separately on the basis of the respective atmospheric effect. Along the normoxic curve, a significant increase in the flame spread rate was found with increasing oxygen concentration and correspondingly decreasing pressure. This results in a significant increase in the risk of fire with regard to future exploration missions. The effect of the flow velocity cannot be neglected in the investigated velocity range and was linked to the influencing parameters in a correlation. Based on this parameterization, a linear function is given that reflects both the downward and the opposed results well. This function can be used to predict the flame spread in the given parameter space. Under normal gravity, the tested samples show a slightly increased propagation rate in most cases. This can essentially be attributed to the difference in velocity between the buoyant flow and the forced flow in µg.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-02DOI: 10.1016/j.proci.2024.105220
Linlin Yang, Yiqing Wang, Peng Dai, Zheng Chen
Knocking is one of the main constrains in improving the thermal efficiency of spark ignition engines. It is generally accepted that normal knock and super-knock are respectively caused by autoignition and detonation development in end-gas. In this study, the effect of temperature disturbance on end-gas autoignition and detonation development in a closed circular domain is examined through 2D simulations considering detailed chemistry. In simulations we find typical end-gas combustion modes including triple-detonation, double-detonation and double-tongue structures, which were also observed in previous rapid compression machine (RCM) experiments. It is shown that the detonation development in end-gas is very sensitive to the temperature disturbance, Δ. As Δ increases, the first autoignition in end-gas induced by temperature disturbance occurs earlier while the corresponding pressure wave is weaker, which subsequently results in different combustion modes in end-gas. Specifically, for small Δ, a supersonic autoignition is initiated and then it triggers a triple-detonation structure consisting of a radial detonation induced by shock-flame coupling and two circumferential detonations that are caused by the near-wall shock compression induced detonation (NWSCD) mechanism. For moderate Δ, the radial detonation is suppressed due to the earlier first autoignition and weaker pressure waves, and thereby the double-detonation structure consisting of two circumferential detonations appears. These two detonations are formed through near wall autoignition induced detonation (NWAID) mechanism. For relatively large Δ, there is no detonation development since the end-gas is quickly consumed by autoignition, which results in a double autoignition front structure, referred to as the double-tongue structure. In this study, the formation of complicated autoignition and detonation structures is interpreted. The results provide insight in understanding the development of normal knock and super-knock in spark ignition engines.
{"title":"Effect of temperature disturbance on end-gas autoignition and detonation development","authors":"Linlin Yang, Yiqing Wang, Peng Dai, Zheng Chen","doi":"10.1016/j.proci.2024.105220","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105220","url":null,"abstract":"Knocking is one of the main constrains in improving the thermal efficiency of spark ignition engines. It is generally accepted that normal knock and super-knock are respectively caused by autoignition and detonation development in end-gas. In this study, the effect of temperature disturbance on end-gas autoignition and detonation development in a closed circular domain is examined through 2D simulations considering detailed chemistry. In simulations we find typical end-gas combustion modes including triple-detonation, double-detonation and double-tongue structures, which were also observed in previous rapid compression machine (RCM) experiments. It is shown that the detonation development in end-gas is very sensitive to the temperature disturbance, Δ. As Δ increases, the first autoignition in end-gas induced by temperature disturbance occurs earlier while the corresponding pressure wave is weaker, which subsequently results in different combustion modes in end-gas. Specifically, for small Δ, a supersonic autoignition is initiated and then it triggers a triple-detonation structure consisting of a radial detonation induced by shock-flame coupling and two circumferential detonations that are caused by the near-wall shock compression induced detonation (NWSCD) mechanism. For moderate Δ, the radial detonation is suppressed due to the earlier first autoignition and weaker pressure waves, and thereby the double-detonation structure consisting of two circumferential detonations appears. These two detonations are formed through near wall autoignition induced detonation (NWAID) mechanism. For relatively large Δ, there is no detonation development since the end-gas is quickly consumed by autoignition, which results in a double autoignition front structure, referred to as the double-tongue structure. In this study, the formation of complicated autoignition and detonation structures is interpreted. The results provide insight in understanding the development of normal knock and super-knock in spark ignition engines.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551155","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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