Combustion and Flame最新文献

{"title":"Effects of the inflow total temperature on the non-premixed rotating detonation engine performances","authors":"Zhenyi Chen ,&nbsp;Sihang Rao ,&nbsp;Jian Peng ,&nbsp;Xu Xu","doi":"10.1016/j.combustflame.2024.113726","DOIUrl":"10.1016/j.combustflame.2024.113726","url":null,"abstract":"<div><div>As a promising propulsion system, air-breathing rotating detonation engines (RDEs) are investigated with significant interest recently. However, simulations of air-breathing RDE with real flight condition are limited, and performance of RDEs with high inflow total temperature, as well as the influence of inflow total temperature on RDEs, needs further exploration. In this paper, simulations with four inflow total temperatures (300 K, 500 K, 700 K and 900 K) were conducted to analyze the propagation features of rotating detonation waves (RDWs) and operation modes in the RDE at low and high inflow total temperatures. Additionally, injection and mixing, as well as combustion characteristics and propulsion performance of the RDE were researched. It is found that with low inflow total temperature, single wave propagates in the combustor, which degenerates into shock wave at the outer wall due to insufficient mixing. When inflow total temperature is high, the RDE is in multi-wave operation mode and detonative combustion only occurs around the outer wall. With increase of inflow total temperature, mixability of reactants initially improves but then deteriorates slightly. Moreover, RDW propagation velocity and specific impulse of the RDE decrease. Though fuel utilization rate improves, detonation fraction drops dramatically and parasitic combustion fraction rises significantly, resulting from intensification of pre-combustion. Particularly, the detonation fraction is only 16.7 % and parasitic combustion fraction reaches up to 56.35 % at inflow total temperature of 900 K. Furthermore, regardless of the variation of inflow total temperature, detonative combustion is prominent in the premixed combustion mode, and the peak fraction of detonation appears at the off-stoichiometric ratio.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113726"},"PeriodicalIF":5.8,"publicationDate":"2024-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653980","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":"Coupling regimes of premixed laminar flames with thermal radiation absorption in fresh gases. Application to H2O-/CO2-diluted mixtures","authors":"J. Ben Zenou,&nbsp;R. Vicquelin","doi":"10.1016/j.combustflame.2024.113830","DOIUrl":"10.1016/j.combustflame.2024.113830","url":null,"abstract":"&lt;div&gt;&lt;div&gt;In the context of decarbonizing industry and transportation, the combustion of hydrogen and oxycombustion of methane play a pivotal role. Hydrogen combustion can use steam (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;O) to mitigate pollutant emissions, while methane’s oxycombustion involves recirculating burnt gases (EGR or Exhaust Gas Recirculation process), particularly CO&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;. This paper investigates the complex role of thermal radiation in premixed laminar flames, in particular in such 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; &lt;img&gt;Air&lt;img&gt;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;O and CH&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; &lt;img&gt;O&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; &lt;img&gt;CO&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; mixtures. It highlights how radiation assumes a significant role in flames diluted with radiative participating gases, through both emission and reabsorption. The main objective is to achieve a comprehensive physical understanding of the coupling between thermal radiation and combustion, examining its effects on flame structure and burning velocity and how it varies with different parameters (equivalence ratio, dilution level, pressure, and domain size). The study employs detailed 1D premixed laminar flame simulations by coupling a fluid and a radiative solver. Both a grey gas approximation for preliminary understanding and realistic radiative gas properties (CK model) are considered. Coupling numbers derived from characteristic time ratios for convection, chemistry, and radiation, are presented. These metrics facilitate the classification of radiation-combustion coupling into three distinct regimes that represent distinct qualitative physical phenomena. The regimes are defined as follows: &lt;em&gt;WeakAbs&lt;/em&gt;, where the effects of thermal radiation absorption are minor; &lt;em&gt;RadConv&lt;/em&gt;, where thermal radiation competes with convection in the fresh and burnt gases but does not interact directly with chemistry within the flame front; and &lt;em&gt;RadChem&lt;/em&gt;, where thermal radiation also competes with chemistry within the flame front. For the investigated conditions in both 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; and CH&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; flames, thermal radiation also quantitatively alters the flame speed, with an acceleration that can be significant. Furthermore, the paper presents an iterative two-layer model to efficiently estimate the impact of thermal radiation on flames, which shows high accuracy except in the &lt;em&gt;RadChem&lt;/em&gt; regime. Lastly, it introduces a predictive model that quickly determines a flame’s coupling regime using only an adiabatic simul","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113830"},"PeriodicalIF":5.8,"publicationDate":"2024-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653190","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":"Real-fluid effects on laminar premixed hydrogen flames under cryogenic and high-pressure conditions","authors":"Ziting Lv ,&nbsp;Hanzhang Cao ,&nbsp;Wang Han ,&nbsp;Lijun Yang","doi":"10.1016/j.combustflame.2024.113837","DOIUrl":"10.1016/j.combustflame.2024.113837","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The combustion of hydrogen (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;) under cryogenic and high-pressure conditions has the potential to increase the volume-based energy density 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; and combustion efficiency. Predictive modeling of cryogenic 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; premixed flames at high pressures requires a clear understanding of real-fluid effects. While substantial effort has been made to study the real-fluid effects in nonpremixed flames, comparatively fewer investigations have been performed to explore real-fluid effects on premixed flames, especially at cryogenic and high-pressure conditions. This work aims to fill a part of this gap by conducting a series of laminar 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; flame simulations at cryogenic and high-pressure conditions (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;u&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;50&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;–350&lt;!--&gt; &lt;!--&gt;K and &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;p&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mn&gt;20&lt;/mn&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mn&gt;40&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; &lt;!--&gt; &lt;!--&gt;MPa). Four cases are considered to examine the role of corrections of the equation of state (EOS), thermodynamic properties, and transport properties in predicting flame structure and properties. It is found that the real-fluid effects mainly occur in the fresh/preheat regions and that the correction of EOS plays a critical role in the prediction of flame structure and the laminar flame speed (&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;), while the correction of transport properties is critical for predicting flame thickness. Each correction could contribute to the predictions of the mass burning rate and the flame thickness but hardly affect the flame temperature (less than 1% relative difference). A scaling law of &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msubsup&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;Real&lt;/mi&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;msubsup&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;Ideal&lt;/mi&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;Z&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;u&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; (&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;Z&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;u&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; is the compressibility factor of the unburned mixture) is proposed, which can be used to readily predict &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; of real fluid from the speed evaluated by the ideal gas model. In addition, the Monte Carlo sampling method is used to perform uncertainty quantification of S&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; due to the uncertainty of the real-fluid model parameters. The results show that the critical properties of H&lt;span&gt;&lt;","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113837"},"PeriodicalIF":5.8,"publicationDate":"2024-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653975","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":"A framework for obtaining frequency-dependent stability maps to mitigate thermoacoustic instabilities","authors":"Hamed F. Ganji ,&nbsp;Viktor Kornilov ,&nbsp;Ines Lopez Arteaga ,&nbsp;Philip de Goey ,&nbsp;Jeroen van Oijen","doi":"10.1016/j.combustflame.2024.113836","DOIUrl":"10.1016/j.combustflame.2024.113836","url":null,"abstract":"<div><div>This paper utilizes Cauchy’s argument principle in the frequency domain to develop novel stability maps, providing guidelines for measures which can be taken to mitigate thermoacoustic instabilities in combustion appliances. The existing approaches mainly concentrate on identifying the onset of thermoacoustic instabilities by calculating unstable frequencies and growth rates. However, they provide limited practical guidance for modifying system characteristics, especially those dependent on frequency, to achieve flame stabilization. In the present contribution, several thermoacoustic stability criteria are introduced that leverage the Cauchy’s argument principle and direct evaluation of the dispersion relation’s argument. These criteria offer deeper insights and facilitate a systematic flame stabilization process by enabling modifications to both the (passive) acoustic subsystems and/or the (active) subsystem containing the combustion processes. This approach allows for a construction and comprehensive understanding of the stability map for a given thermoacoustic system, leading to more effective guidelines to elaborate and implement the combustion system stabilization strategies. To demonstrate the practical application of this framework, two illustrative thermoacoustic systems are discussed.</div><div><strong>Novelty and significance statement</strong> This study introduces a novel framework for assessing thermoacoustic stability. <ul><li><span>•</span><span><div>It provides a method for detecting the onset of thermoacoustic instability and offers valuable insights into critical frequency ranges. This approach facilitates the identification of necessary modifications in flame and acoustic subsystems across different frequencies to achieve system stabilization.</div></span></li><li><span>•</span><span><div>This framework allows for the selection of the most suitable stability criterion based on the available combustion system’s characteristics. For example, by knowing acoustic properties in both upstream and downstream components, either the DDS or DCS criterion can generate a comprehensive, frequency-dependent stability map for flame transfer function values. This approach eliminates the need for iterative integration, differential equations, or direct solutions to dispersion relations.</div></span></li></ul></div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113836"},"PeriodicalIF":5.8,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653974","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":"Flame structure of single aluminum droplets burning in hot steam-dominated flows","authors":"Zhiyong Wu ,&nbsp;Can Ruan ,&nbsp;Yue Qiu ,&nbsp;Mehdi Stiti ,&nbsp;Shijie Xu ,&nbsp;Niklas Jüngst ,&nbsp;Edouard Berrocal ,&nbsp;Marcus Aldén ,&nbsp;Xue-Song Bai ,&nbsp;Zhongshan Li","doi":"10.1016/j.combustflame.2024.113838","DOIUrl":"10.1016/j.combustflame.2024.113838","url":null,"abstract":"<div><div>In this work, a specially designed experimental setup is employed to study the ignition and combustion of single aluminum droplets in hot steam-dominated flows. The transient burning behaviors of Al droplets of different sizes are characterized by simultaneously visualizing the flame incandescence and droplet shadowgraphs with two high-speed cameras at high magnification. The combustion process can be described in three stages: Al ignition and droplet generation, droplet evaporation and flame development, and steady combustion. During the steady combustion stage, a bright flame sheet, characterized by a narrow layer of dense nano-micron-sized alumina droplets, encapsulates the Al droplet core. The flame sheet composed of alumina droplets is located on a stagnation plane where the radial velocities relative to the droplet core are close to zero. The standoff ratio is around two, and it slightly decreases with the droplet size and increases with the oxygen content in the ambient gas. The thickness of the flame sheet (the alumina particle layer) is analyzed using Abel inversion of the projected profile of the flame incandescence and optical depth, revealing a thickness of about 50 μm for a burning droplet of a 550 μm diameter. Based on the shadowgraph images, the evaporation rate of the Al droplets is determined from the shrinking rate of the droplet projected area. Size-dependent evaporation rates are found to be related to different slip velocities, and the addition of oxygen to the oxidizer can significantly increase the evaporation rate. Finally, a conceptual model of a burning Al droplet in the steady combustion stage is proposed based on the experimental findings. The presented results provide novel datasets that contribute to model development and deepen the understanding of the physical and chemical processes involved in aluminum droplet combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113838"},"PeriodicalIF":5.8,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653238","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":"Computational investigation on the formation of liquid-fueled oblique detonation waves","authors":"Wenhao Wang ,&nbsp;Zongmin Hu ,&nbsp;Peng Zhang","doi":"10.1016/j.combustflame.2024.113839","DOIUrl":"10.1016/j.combustflame.2024.113839","url":null,"abstract":"<div><div>Utilizing a two-phase supersonic chemically reacting flow solver with the Eulerian-Lagrangian method implemented in OpenFOAM, this study computationally investigates the formation of liquid-fueled oblique detonation waves (ODWs) within a pre-injection oblique detonation wave engine operating at an altitude of 30 km and a velocity of Mach 9. The inflow undergoes two-stage 12.5° compression, followed by uniform mixing with randomly distributed n-heptane droplets before entering the combustor. The study examines the effects of droplet breakup models, gas-liquid ratios, and on-wedge strips on the ODW formation. Results indicate that under the pure-droplet condition, the ODW fails to form within the combustor, irrespective of the breakup models used. However, increasing the proportion of n-heptane vapor in the fuel/air mixture facilitates the ODW formation, because the n-heptane vapor rapidly participates in the gaseous reactions, producing heat and accelerating the transition from low- to intermediate-temperature chemistry. Additionally, the presence of on-wedge strips enhances ODW formation by inducing a bow shock wave within the combustor, which significantly increases the temperature, directly triggering intermediate-temperature chemistry and subsequent heat-release reactions, thereby facilitating the formation of ODW.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113839"},"PeriodicalIF":5.8,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653240","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":"Features of lean premixed flame stabilized on a bluff-body with different temperature magnitude","authors":"Siqi Cai ,&nbsp;Wenquan Yang ,&nbsp;Lang Li,&nbsp;Jianlong Wan","doi":"10.1016/j.combustflame.2024.113840","DOIUrl":"10.1016/j.combustflame.2024.113840","url":null,"abstract":"<div><div>The bluff-body is widely employed to improve the performance of the lean premixed combustion LPC which has advantages of high efficiency and low pollutant emissions. To further improve the LPC performance stabilized on the bluff-body, the effect of the bluff-body temperature on the lean premixed flame LPF feature near the flammability limit is studied here. The bluff-body temperature is controlled by the electrically heated rod or cooling water, and its values are set as ∼300 K (CB), naturally heat-conducting condition (NHB), 600 K (HB-600), and 900 K (HB-900), respectively. The experimental results show that the flammability limits and LPF behaviors in the case of CB and NHB are nearly the same because of the insignificant difference in the bluff-body temperature magnitude between them. The flammability limit can be significantly extended when the bluff-body temperature is heated to 900 K. Unexpectedly, the stable residual flame appears at the near-limit condition in the case of HB-900. It is the first time to observe the stable residual flame in the case of the fuel of Lewis number Le≈1.0. Then, the flame structures in the case of NHB, HB-600, and HB-900 are revealed numerically. It is found that the fresh reactant arrives at the flame primarily via diffusion rather than convection. The pre-heating effect on the fresh reactants and heat-loss effect to the bluff-body are also evaluated quantitatively. In the case of NHB, the flame can be classified to the adiabatic zone and mixed zone. By contrast, in the case of HB-600 and HB-900, the flame can be classified to the adiabatic zone, excess reaction zone, and weak reaction zone. This study expands our understanding on improving the LPC performance via controlling the bluff-body temperature.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113840"},"PeriodicalIF":5.8,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653239","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":"A hydrogen deflagration-jet flame coupled behavior in a ventilated confined space: Effects of ventilation area and leakage duration","authors":"Hongsheng Ma ,&nbsp;Changjian Wang ,&nbsp;Yang Li ,&nbsp;Tao Du ,&nbsp;Quan Li","doi":"10.1016/j.combustflame.2024.113842","DOIUrl":"10.1016/j.combustflame.2024.113842","url":null,"abstract":"<div><div>Non-uniform hydrogen deflagrations were experimentally conducted in a ceiling ventilated chamber considering the effects of ventilation area <em>A_v</em> and leakage duration <em>t_ig</em>. Two new coupled flame behaviors are observed. The first type of coupled flame structure involves the non-growing conical flame bubbles and jet flames, while the second type involves the growing ellipsoid flame bubbles and jet flames. A decrease in <em>A_v</em> or an increase in <em>t_ig</em> promotes the evolution of first type of coupled flame behavior into the second type. The horizontal propagation of deflagration flames can be divided into three typical stages and the horizontal flame front undergoes a gradual decrease in speed and then a slight acceleration. The overpressure transient exhibits a double peak structure in under-ventilated cases. The overpressure peak P₁ is induced by the coupled upward propagation of jet flames and initial flame bubbles. The overpressure peak P₂ is related to the coupled flame behavior involving jet flame combustion and flame bubble expansion. The maximum overpressure and maximum pressure rise rate show a sharp upward trend as the first type of coupled flame structure evolves into the second type.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113842"},"PeriodicalIF":5.8,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653187","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":"Numerical sensitivity analysis of HTPB counterflow combustion using neural networks","authors":"Brian T. Bojko ,&nbsp;Clayton M. Geipel ,&nbsp;Brian T. Fisher ,&nbsp;David A. Kessler","doi":"10.1016/j.combustflame.2024.113829","DOIUrl":"10.1016/j.combustflame.2024.113829","url":null,"abstract":"<div><div>Solid fuel combustion requires pyrolysis gases to burn near its surface to provide enough heat feedback to decompose the solid and continue to provide the volatile gases required to sustain combustion. This coupled process defines the difficulty in sustaining solid fuel combustion in a variety of propulsion environments and necessitates a fundamental understanding of the physical processes in order to drive system design. This study explores the combustion of hydroxyl-terminated polybutadiene (HTPB) in a counterflow diffusion flame burner with 50% and 100% oxygen content and compares the regression rate and flame standoff to experimental data. A sensitivity analysis is pursued to identify the model parameters that need improvement and to help guide the next campaign of experiments. Neural networks are developed in a compact way as a means of providing quantitative results on the sensitivity of input parameters. Then a fully connected, deeper neural network is trained on the input parameters – oxidizer mole fraction, solid fuel heat of formation, pre-exponential factor of pyrolysis Arrhenius rate, molecular weight of pyrolysis species, oxidizer mass flux, separation distance, and the oxidizer temperature, – and shown to predict output variables – regression rate and flame standoff – within 90% and 95% accuracy respectively. This network is then used to create millions of data points with an overlapping parameter space for further statistical analysis and improvement of model parameters. In all, the data analysis presented using a neural network approach will help drive the design of experiments and is shown to increase the accuracy of the model in comparison to experimental measurements.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113829"},"PeriodicalIF":5.8,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653188","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":"A numerical study of internal transport in oxidizing liquid core–shell iron particles","authors":"Leon C. Thijs ,&nbsp;Marie-Aline Van Ende ,&nbsp;Jeroen A. van Oijen ,&nbsp;Philip de Goey ,&nbsp;XiaoCheng Mi","doi":"10.1016/j.combustflame.2024.113826","DOIUrl":"10.1016/j.combustflame.2024.113826","url":null,"abstract":"<div><div>In an effort to improve the understanding of the rate-limiting mechanisms in liquid iron particle combustion, this study investigates the impact of internal transport within a core–shell structure. The two-dimensional axisymmetric transient continuum model as presented in previous publication (Thijs et al., 2023) is extended, such that the boundary layer between the particle and the gas, surface processes at the particle–gas interface, as well as the internal oxide layer within the particle, considering the transport of reactive O and Fe ions, are resolved. Information from the equilibrium phase diagram, which is included as supplementary data, is used to determine oxidation rate of the particle. The study reveals that finite-rate internal transport significantly alters the temperature evolution compared to models assuming infinitely fast transport. At elevated oxygen concentrations, internal transport becomes rate-limiting, restricting the maximum particle temperature. The core–shell assumption leads to a higher local oxidation degree at the particle–gas interface than the average in the particle, reducing the overall oxygen consumption rate. The maximum particle temperature is reached when heat loss exceeds heat release. Although internal transport limits the maximum temperature, the initial heating rate remains overestimated, suggesting that the initial phase is not solely limited by external oxygen diffusion, and the L2-gas surface is not at thermodynamic equilibrium. The model does not account for the particle size effect on maximum temperature as observed in some experiments. A hypothetical explanation is that internal convection, more pronounced in larger particles, may reduce the internal transport limitation, leading to higher maximum temperatures in larger particles.</div><div><strong>Novelty and significance</strong></div><div>This study advances the understanding of oxidation rate-limiting mechanisms in liquid iron particle combustion by numerically investigating the impact of internal transport within a core–shell structure. By using a two-dimensional axisymmetric transient continuum model, the research reveals that finite-rate internal transport significantly affects temperature evolution of an oxidizing micron-sized iron particle, particularly at elevated oxygen concentrations where it becomes rate-limiting. The findings demonstrate that a finite-rate internal transport leads to a higher local oxidation degree at the particle–gas interface, reducing the oxygen consumption rates. The study highlights that finite-rate internal transport limits the maximum particle temperature at elevated oxygen concentrations, a trend observed in isolated iron particle combustion experiments. Furthermore, this study provides a hypothetical explanation for the experimentally observed particle size effects on the maximum particle temperature, emphasizing the role of internal convection in larger particles</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"271 ","pages":"Article 113826"},"PeriodicalIF":5.8,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653189","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}