Combustion and Flame最新文献

{"title":"Three-dimensional dynamics of unstable lean premixed hydrogen-air flames: Intrinsic instabilities and morphological characteristics","authors":"Yu Xie,&nbsp;Junfeng Yang,&nbsp;Pervez Ahmed,&nbsp;Benjamin John Alexander Thorne,&nbsp;Xiaojun Gu","doi":"10.1016/j.combustflame.2024.113800","DOIUrl":"10.1016/j.combustflame.2024.113800","url":null,"abstract":"<div><div>The 3D swinging laser sheet technique was employed to study the development and morphological characteristics of premixed hydrogen-air unstable flames in a spherical explosion vessel. Pressure dependencies for laminar flame propagation were sought to exploit the role of the Darrieus-Landau (DL) and Thermal-diffusive (TD) instabilities in the unstable self-accelerating flame regime. A sufficiently low Markstein number, as a consequence of the increased pressure, leads to more cracking and smaller cells over the flame surface. The degree of wrinkling on the flame surface is proportional to the increase in flame burning velocity, a relationship that holds true for low pressures but is not applicable under high pressures. External turbulence can significantly alter the extent of flame surface wrinkling even at low root mean square velocities, producing a more wrinkled flame surface compared to intrinsic cellularity, and distinctly affecting flame dynamics. The increased wrinkling and flame speed due to external turbulence can be attributed to the synergistic effects between thermo-diffusive instabilities and turbulence, resulting in higher fuel consumption rates per flame surface area and the formation of finger-like structures that enhance flame displacement speed in curved segments. The parameters, <span><math><mi>ϵ</mi></math></span>, deviation of the Lewis number from a critical value, and <span><math><msub><mi>ω</mi><mn>2</mn></msub></math></span>, obtained through classical linear stability analysis, display a clear linear relationship with the ratio of the wrinkled surface area observed in planar flames. This study enhances the understanding of hydrogen flame instabilities, which is crucial for preventing explosions in hydrogen storage and utilization, and provides valuable insights into flame dynamics, supporting the design of safer and more efficient hydrogen-fueled engines and turbines.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113800"},"PeriodicalIF":5.8,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528496","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Data-driven model-based instability prediction in an annular combustor relying on a flame response mapping of the operating domain","authors":"Véranika Latour,&nbsp;Daniel Durox,&nbsp;Antoine Renaud,&nbsp;Sébastien Candel","doi":"10.1016/j.combustflame.2024.113782","DOIUrl":"10.1016/j.combustflame.2024.113782","url":null,"abstract":"<div><div>At a stage where new architectures and alternative fuels are being proposed to tackle the environmental challenges, it is important to be able to deal with combustion dynamics issues that may arise in these new developments. Reduced order models are generally considered for that purpose but their capacity to predict combustion instabilities is still not fully demonstrated. One advantage of these models is that they mainly rely on flame transfer or describing functions (FTFs or FDFs) representing the flames’ response to incoming disturbances. Recent measurements indicate that FDFs exhibit gain and phase variations with fuels, fuel blends, injector characteristics, but also with operating conditions. However, FTFs and FDFs are generally documented only for a few operating points and do not cover the entire domain of operation, limiting the scope of the analysis. The logical step taken in the present investigation is to collect FDFs for a large number of flow conditions of the laboratory-scale annular combustor MICCA-Spray. This is achieved using a single-injector system, SICCA-Spray, representing one sector of MICCA-Spray and that allows external flame modulation. The collected FDF data correspond to injectors of two types, characterized by different combustion dynamics in MICCA-Spray. This FDF database, in combination with an analytical framework derived from acoustic energy balance equations, serves to determine growth rates and define a theoretical instability domain. A comparison with the stability maps obtained in the annular combustor indicates that the general layout of these maps can be retrieved for the two injector types, validating the relevance of this data-driven model-based analysis of thermo-acoustic instabilities.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this work lies in the reported flame describing function (FDF) database, measured in the single-injector setup SICCA-Spray, for a wide range of operating conditions corresponding to the operation domain of the MICCA-Spray annular combustor, and for two types of injectors leading to different flame dynamics (stable and unstable). An analytical framework is then used to determine growth rates of oscillation based on the FDF data, enabling to perform a stability analysis and interpret the observations in MICCA-Spray: the differences in flame dynamics observed between the two injectors are successfully retrieved, and for the unstable injector, stable and unstable regions of the operating domain can also be distinguished.</div><div>This work is significant because it provides an analytical framework of interest from a theoretical standpoint and for practical applications that is validated against a broad experimental dataset.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113782"},"PeriodicalIF":5.8,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534775","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}

{"title":"Measuring acoustic transfer matrices of high-pressure hydrogen/air flames for aircraft propulsion","authors":"Abel Faure-Beaulieu ,&nbsp;Bayu Dharmaputra ,&nbsp;Bruno Schuermans ,&nbsp;Guoqing Wang ,&nbsp;Stephan Caruso ,&nbsp;Maximilian Zahn ,&nbsp;Nicolas Noiray","doi":"10.1016/j.combustflame.2024.113776","DOIUrl":"10.1016/j.combustflame.2024.113776","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Destructive thermoacoustic instabilities may potentially slow down significantly the ongoing development of hydrogen combustors for decarbonizing aviation. Their early prediction requires the knowledge of the heat release rate response of individual flames to acoustic perturbations. Obtaining this response at engine conditions is very challenging as it requires the development of sophisticated acoustic actuation and sensing techniques for harsh temperature and pressure environment. To date, experimental measurements of the response of single-flames to upstream and downstream acoustic excitation have been limited to academic burners operated at atmospheric condition. Moreover, to the authors knowledge, the response of turbulent non-premixed H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/air flames has not been experimentally investigated yet, not even at atmospheric pressure. Our experiments address this challenge by determining the acoustic transfer matrix of rich-quench-lean H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; flames anchored on an industrial prototype burner at engine-relevant conditions, including high-altitude flight. The response of the flame is measured up to 2 kHz by using the multi microphone method (MMM). It is shown that the MMM becomes more sensitive to temperature estimations at high frequency and we outline a strategy to improve the method. It is found that the acoustic response of these H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/air non-premixed flames exhibit large gains with non-monotonic trends over a wide frequency range. Different fuel-to-air ratios and flow velocities are considered up to nearly 7 bar. We show that the equivalence ratio and operating pressure do not alter significantly the acoustic flame response, while the flow velocity does, although the flame shape is nearly unchanged when the latter parameter is varied. Furthermore, we extend the classic model of low-Mach-number flame transfer matrices to the relevant case of RQL combustors.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and Significance&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;The ability to accurately measure, at relevant mean pressure, the transfer matrix linking acoustic pressure and velocity across a single burner and its turbulent H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;/air flame is key for the development of H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; powered medium-range civil aircrafts. This is because such measurement enables predictions of potential thermoacoustic instabilities in the full annular combustor featuring a large number of burners and flames, and therefore it offers possibilities for burner prototype selection and optimization before full engine tests. The present study is the first demonstration of such challenging measurement, revealing the peculiar acoustic response of non-premixed H&lt;span&gt;&lt;m","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113776"},"PeriodicalIF":5.8,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534776","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unraveling combustion chemistry of dimethyldiethoxysilane. I. A comprehensive pyrolysis investigation with insight into ethanol formation mechanism in combustion of ethoxysilane flame synthesis precursors","authors":"Qilong Fang ,&nbsp;Jun Fang ,&nbsp;Wei Li ,&nbsp;Tianyou Lian ,&nbsp;Long Zhao ,&nbsp;Wang Li ,&nbsp;Lili Ye ,&nbsp;Yuyang Li","doi":"10.1016/j.combustflame.2024.113794","DOIUrl":"10.1016/j.combustflame.2024.113794","url":null,"abstract":"<div><div>Ethoxysilanes are a family of precursors widely used in flame synthesis of silica nanoparticles. The existence of a silicon atom greatly amplifies the complexity of ethoxysilane combustion reactions, especially the detection of silicon-containing products and exploration of the specific reaction pathways, which hinders the unambiguous understanding of the combustion chemistry of ethoxysilanes. As the first part of a serial work on the combustion of dimethyldiethoxysilane (DMDEOS), a representative ethoxysilane precursor, reports a theoretical, experimental, and kinetic modeling investigation on its pyrolysis. The potential energy surface and rate constants show that the four-membered ethylene elimination dominates the decomposition of DMDEOS. Pyrolysis products in the micro-flow reactor pyrolysis of DMDEOS are detected using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), including six silicon-containing products and an abundant of hydrocarbon molecules and radicals. Novel insight is provided into the unclear ethanol formation mechanism in previous pyrolysis investigations of ethoxysilanes. Previously proposed one-step mechanisms are found to be less efficient based on theoretical exploration and experimental evidence. A new multi-step mechanism initiated from the ethanol elimination of HOSi(CH₃)₂OC₂H₅ is concluded to be energy-favorable, which is supported by the identification of relevant products in the micro-flow reactor pyrolysis experiment. Based on the product information detected by SVUV-PIMS and the exploration of ethanol formation mechanism, a kinetic model of DMDEOS pyrolysis is constructed and validated against the new data that flow reactor pyrolysis of DMDEOS at 1.05 atm and 849–1113 K using gas chromatography. The model can effectively reproduce the formation of observed products and successfully address the substantial underprediction of ethanol caused by previously proposed one-step mechanisms. Modeling analyses, including rate of production analysis and sensitivity analysis, are performed to provide insight into the key pathways of DMDEOS decomposition and product formation.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113794"},"PeriodicalIF":5.8,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142445588","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}

{"title":"Experimental and kinetic model studies of 2,3-dimethylhexane pyrolysis at atmospheric pressure","authors":"Jinzeng Pan ,&nbsp;Jinyu Tan ,&nbsp;Shiling Wei ,&nbsp;Shuyao Chen ,&nbsp;Haikun Lang ,&nbsp;Fangping Bin ,&nbsp;Zhandong Wang ,&nbsp;Lixia Wei","doi":"10.1016/j.combustflame.2024.113781","DOIUrl":"10.1016/j.combustflame.2024.113781","url":null,"abstract":"<div><div>Isomers of alkanes have a significant effect on their combustion performance. In order to better understand the effect of the number of methyl side chains on fuel performance, the pyrolysis experiments of 2,3-dimethylhexane (C₈H₁₈–23) were carried out by using a jet-stirred reactor and the synchrotron vacuum ultraviolet photoionization mass spectrometry at 770 - 1130 K and at atmospheric pressure. Key pyrolysis products, such as acetylene, ethylene, propene, 1,3-butadiene, 2-butene, 1-pentene, 2-methyl-2-butene, 2-methyl-2-hexene, 3-methyl-2-hexene, as well as benzene, styrene and naphthalene, etc., were identified and measured. A detailed kinetic model of C₈H₁₈–23 pyrolysis, including 1756 species and 6023 reactions, was constructed and validated against the experimental results in the present work. Rate of production and sensitivity analysis of C₈H₁₈–23 showed that the major consumption pathways are H-abstractions and unimolecular dissociation reactions, with the highest contributions from those at/between C(2) and C(3) atoms. Theoretical comparison of the pyrolysis of the three isomers of C₈H₁₈ hydrocarbon, i.e., C₈H₁₈–23, 2-methylheptane and <em>n-</em>octane, shows that with increasing of the number of methyl side chains, C₈H₁₈ will be more reactive in pyrolysis and be more effective in producing soot precursors.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113781"},"PeriodicalIF":5.8,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142445586","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}

{"title":"Unraveling combustion chemistry of dimethyldiethoxysilane. II. A comprehensive study on the laminar flame propagation of ethoxysilane flame synthesis precursors","authors":"Qilong Fang ,&nbsp;Jun Fang ,&nbsp;Yi Zhang ,&nbsp;Tianyou Lian ,&nbsp;Wei Li ,&nbsp;Lili Ye ,&nbsp;Yuyang Li","doi":"10.1016/j.combustflame.2024.113795","DOIUrl":"10.1016/j.combustflame.2024.113795","url":null,"abstract":"<div><div>The ethoxysilane family is a popular precursor family for SiO₂ nanoparticle flame synthesis, understanding their combustion characteristics and reaction mechanisms are essential to control the synthesis performance. However, there is a scarcity of fundamental combustion studies on ethoxysilane precursors, particularly regarding fuel decomposition and oxidation under flame circumstances. This work, as the second part of a serial work on the combustion of dimethyldiethoxysilane (DMDEOS) which is a representative ethoxysilane precursor, reports an experimental, theoretical, and kinetic modeling investigation on its laminar flames. Laminar burning velocities of the DMDEOS/air mixtures are obtained using the spherically propagating flame method at the initial pressure of 1 atm and initial temperature of 423 K, and equivalence ratios from 0.7 to 1.5. The H-abstraction reactions of DMDEOS by H, CH₃, and OH, followed by the subsequent isomerization and β-scission reactions of fuel radicals, are theoretically investigated using <em>ab initio</em> quantum chemical calculations and rate constant calculations. A kinetic model of DMDEOS combustion incorporated with the present theoretical results is developed and validated against the new data. The rate of production analysis and sensitivity analysis indicate that the CH₃SiOOH plays an important role in the laminar flame propagation of DMDEOS/air mixtures, and the relevant reactions exhibit significant sensitivity for the laminar flame propagation of DMDEOS. Additionally, the consumption of CH₃SiOOH is the main source of key species that are essential for molecular growth. The modified fictitious diluent gas method is adopted to provide insights into the fuel molecular structure effects from the comparison with diethoxymethane (DEM), which has the same molecular skeleton length as DMDEOS. The thermal effect plays a dominantly positive role in the slower laminar flame propagation of DMDEOS than DEM under stoichiometric and rich conditions, while the chemical effect exhibits a negative effect.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113795"},"PeriodicalIF":5.8,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142445587","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}

{"title":"Laser-induced plasma analysis of ammonia-oxygen and ammonia-oxygen-enriched-air flames at elevated pressures","authors":"Bilge Kaan Gokcecik,&nbsp;Nagaraju Guthikonda,&nbsp;Aleksander Clark,&nbsp;Peng Zhao,&nbsp;Zhili Zhang","doi":"10.1016/j.combustflame.2024.113803","DOIUrl":"10.1016/j.combustflame.2024.113803","url":null,"abstract":"<div><div>This study employed Laser-induced breakdown spectroscopy (LIBS) to measure the fuel-oxidizer ratio (FOR) of ammonia combustion with oxygen-enriched air and pure oxygen flames at elevated pressures (100 - 300 kPa). The correlations between the spectral line intensity ratios of nitrogen (N), hydrogen (H), oxygen (O), and equivalence ratio were used to quantify the FOR of flames at various pressures. The effect of pressure on the stability and precision of the calibration profiles for the elemental intensity ratios in flames was investigated. It was observed that the H/O correlation decreases with pressure increase for both ammonia flames. N/O correlations decrease with elevated pressure for the ammonia-oxygen flame. Furthermore, the nitrogen (N_II) spectral emission lines at 568 nm and 595 nm were used to estimate the plasma temperature, while the hydrogen (H_α) line at 656 nm was used for electron number density measurements.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113803"},"PeriodicalIF":5.8,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446722","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}

{"title":"Parameter estimation of distributed activation energy models via chemical reaction neural network","authors":"Chunjie Zhai ,&nbsp;Xinmeng Wang ,&nbsp;Siyu Zhang ,&nbsp;Zhaolou Cao","doi":"10.1016/j.combustflame.2024.113798","DOIUrl":"10.1016/j.combustflame.2024.113798","url":null,"abstract":"<div><div>Kinetic parameter estimation is of fundamental importance in modeling the biomass pyrolysis process for biofuel production. In this work, a neural network architecture, named chemical reaction neural network (CRNN), was utilized to learn kinetic parameters (pre-exponential factor and distribution) in distributed activation energy models from the measurement of conversion rate without prior knowledge of the reaction. The Arrhenius equation is reformulated as the activation function of a neuron in the hidden layer of a three-layer neural network. The gradients of loss with respect to kinetic parameters can then be derived analytically, with which a gradient-based training algorithm is employed to optimize the kinetic parameters. The CRNN performance was evaluated based upon systematical numerical investigation of reactions with a double-Gaussian distribution function. The results show that by transforming the optimization problem into neural network training, the CRNN can accurately and efficiently recover the distribution and pre-exponential factor due to the embedded chemical knowledge. The applicability of CRNN in the pyrolysis of rice straw under different heating rates is examined by experimental measurements. It is shown that with the estimation provided the Kissinger method as the starting point, the CRNN is capable of reconstructing the conversion rate curve. We anticipate, as a feasible, efficient, and accurate model, the CRNN will benefit in enhancing the practice of biomass pyrolysis analysis.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113798"},"PeriodicalIF":5.8,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142440926","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}

{"title":"Experimental and modeling study of the oxidation of NH3/C2H4 mixtures in a shock tube","authors":"Shubao Song,&nbsp;Wanting Jia,&nbsp;Jiachen Sun,&nbsp;Cheng Wang,&nbsp;Jiankun Shao","doi":"10.1016/j.combustflame.2024.113777","DOIUrl":"10.1016/j.combustflame.2024.113777","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Ammonia is a promising zero-carbon fuel, offering new possibilities for sustainable energy system development. In this study, ignition delay times (IDTs) of NH&lt;sub&gt;3&lt;/sub&gt;/C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; mixtures with C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; contents of 0 %, 5 %, 10 %, and 25 % were measured using a shock tube at temperatures ranging from 1176 to 1904 K, pressures of 1.0–8.5 atm, and equivalence ratios of 0.5, 1.0 and 2.0. A laser absorption diagnostic system was developed to track the temporal evolution of NH&lt;sub&gt;3&lt;/sub&gt; concentration during the oxidation process behind the reflected shock waves. The experimental results indicate that the IDTs of the mixtures exhibit non-linear decrease with the addition of ethylene. Specifically, compared to pure ammonia, the addition of 5 %, 10 % and 25 % ethylene significantly increases the reactivity of the mixture, leading to a 36.7 %, 75.9 % and 90.2 % reduction in IDT at a temperature of 1563 K and a pressure of 1.0 atm, respectively. Moreover, the mixture exhibits similar reactivity under fuel-lean and stoichiometric conditions, which remains higher than the reactivity observed under fuel-rich conditions. Overall, the IDTs and the time required for complete consumption of the mixture decreases as temperature, pressure, and ethylene blending ratio increase. In order to simulate and analyze the reaction process of NH&lt;sub&gt;3&lt;/sub&gt;/C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; mixtures, a detailed kinetic model was constructed based on previous studies by updating the interaction reaction between C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; and NH&lt;sub&gt;2&lt;/sub&gt; radical and validated against the current experimental results. Rate of production (ROP) and sensitivity analysis were performed to identify the primary consumption pathways of NH&lt;sub&gt;3&lt;/sub&gt;/C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; and the significant impact of C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; on the reactivity. Additionally, due to the addition of C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt;, a substantial amount of NH&lt;sub&gt;2&lt;/sub&gt; radical participates in the H-abstraction reaction (C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; + NH&lt;sub&gt;2&lt;/sub&gt;&lt;=&gt;C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt; + NH&lt;sub&gt;3&lt;/sub&gt;). This results in a reduced involvement of NH&lt;sub&gt;2&lt;/sub&gt; in the DeNO&lt;sub&gt;x&lt;/sub&gt; process and, consequently, the NH&lt;sub&gt;3&lt;/sub&gt;/C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; mixture exhibits a higher tendency to produce NO&lt;sub&gt;x&lt;/sub&gt; compared to pure ammonia.&lt;/div&gt;&lt;/div&gt;&lt;div&gt;&lt;h3&gt;Novelty and significance statement&lt;/h3&gt;&lt;div&gt;Ammonia offers new possibilities for sustainable energy systems but faces challenges like low combustion rate and mixing with reactive fuels can effectively enhance the ignition characteristics of NH&lt;sub&gt;3&lt;/sub&gt;. The ignition delay times and speciation NH&lt;sub&gt;3&lt;/sub&gt;/C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; mixtures are systemically measured by using shock tube and laser absorption spectroscopy. A newly detailed kinetic NH&lt;sub&gt;3&lt;/sub&gt;-C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt; model is also developed based on previous studies by updating the interaction reaction between C&lt;sub","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142441558","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}

{"title":"Resident mechanism of a holder-stabilized ultra-lean hydrogen enriched residual flame","authors":"Wenquan Yang,&nbsp;Jianlong Wan","doi":"10.1016/j.combustflame.2024.113797","DOIUrl":"10.1016/j.combustflame.2024.113797","url":null,"abstract":"<div><div>The lean premixed combustion near the flammability limit is a promising technology to achieve cleaner and higher efficiency combustion of gaseous fuels. The residual flame usually occurs in the vicinity of the flammability limit. The deep insight into this flame behavior is crucial to further improve the lean premixed combustion performance. In the present study, the ultra-lean 40%H₂–60%CH₄-air premixed residual flame stabilized on the heat-conducting holder in a preheated micro burner is observed experimentally and numerically, and its resident mechanism is analyzed quantitatively in terms of the effects of the stretch, preferential transport, and conjugate heat transfer. The stretch and heat-loss effects do harm to the anchoring performance of the residual flame root. By contrast, the preferential transport effect contributes to maintaining it via generating the local fuel-richer region. This is why the flame root can still maintain although it suffers a higher stretch rate compared to the corresponding extinction strain rate of a planar flame. The small stretch and heat-loss effects as well as the noticeable preferential transport effect contribute to maintaining the residual flame tip. More critically, the preferential transport effect increases and heat-loss effect decreases when the equivalence ratio reduces, which ensures that the residual flame tip still can maintain at the ultra-low equivalence ratio. To the best of our knowledge, such a detailed main factors visualization of the stable residual flame has not been reported yet. The present study helps us to further understand the ultra-lean residual flame dynamics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113797"},"PeriodicalIF":5.8,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142440856","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}