Combustion and Flame最新文献

{"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}

{"title":"Effect of particle size distribution on the laminar flame speed of iron aerosols","authors":"Aravind Ravi,&nbsp;Philip de Goey,&nbsp;Jeroen van Oijen","doi":"10.1016/j.combustflame.2023.113053","DOIUrl":"10.1016/j.combustflame.2023.113053","url":null,"abstract":"<div><p>Iron particles in air burn in heterogeneous combustion mode and the flame speed is very sensitive to particle size. Previous numerical work on the propagation of flames in iron dust was based on average particle sizes. However, in practice, experiments are conducted with particle size distributions (PSD). This makes it challenging to compare different experiments as the samples used in those studies vary (the average particle size might be similar but not the particle size distribution). It is the aim of the current work to provide insight into the effect of particle size distribution on flame propagation. This involves identifying the minimum number of discrete averaged particle sizes (bins) required in the simulations to capture the burning characteristics of the PSD. Then, flame speed and flame structure for a narrow and broad distribution are investigated. It is shown that the equivalence ratio at which the maximum flame speed occurs for certain mean particle sizes varies with the width of the particle size distribution. The difference in the flame speed between the same average particle size but different standard deviation varies as a function of <span><math><mi>β</mi></math></span> (ratio between standard deviation and average particle size), not just the average particle size itself. For a constant <span><math><mi>β</mi></math></span> at a particular equivalence ratio, the difference in the flame speed between PSD and mono-dispersed aerosols is approximately the same irrespective of the particle size. The effects of the smaller and bigger particles in the PSD on the flame speed and flame structure are also systematically investigated. The findings in this study confirm that the particle width of the PSD plays a crucial role and that experiments and simulations can not be readily compared if different PSDs are used.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"257 ","pages":"Article 113053"},"PeriodicalIF":4.4,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0010218023004285/pdfft?md5=cd79cd30b97779bf0f6ebd6f264d5369&pid=1-s2.0-S0010218023004285-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44189851","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":"Adaptive phase shift control of thermoacoustic combustion instabilities using model-free reinforcement learning","authors":"Khalid Alhazmi,&nbsp;S. Mani Sarathy","doi":"10.1016/j.combustflame.2023.113040","DOIUrl":"10.1016/j.combustflame.2023.113040","url":null,"abstract":"<div><p>Combustion instability is a significant risk in the development of new engines when using novel zero-carbon fuels such as ammonia and hydrogen. These instabilities can be difficult to predict and control, making them a major barrier to the adoption of carbon-free gas turbine<span> technologies. In order to address this challenge, we propose the use of model-free reinforcement learning (RL) to adjust the parameters of a phase-shift controller in a time-varying combustion system. Our proposed algorithm was tested in a simulated time-varying combustion system, where it demonstrated excellent performance compared to other model-free and model-based methods, including extremum seeking controllers and self-tuning regulators. The ability of RL to effectively adjust the parameters of a phase-shift controller in a time-varying system, while also considering the safety implications of online system exploration, makes it a promising tool for mitigating combustion instabilities and enabling the development of safer, more efficient carbon-free gas turbine technologies.</span></p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"257 ","pages":"Article 113040"},"PeriodicalIF":4.4,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45231053","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":"Combustion synthesis mechanism of the Ni(NO3)2 + hexamethylenetetramine solutions to prepare nickel nanomaterials","authors":"Marieta K. Zakaryan ,&nbsp;Narine H. Amirkhanyan ,&nbsp;Khachik T. Nazaretyan ,&nbsp;Suren L. Kharatyan ,&nbsp;Khachatur V. Manukyan","doi":"10.1016/j.combustflame.2023.113049","DOIUrl":"10.1016/j.combustflame.2023.113049","url":null,"abstract":"<div><p><span>This work reports the combustion synthesis mechanism in a system with hexamethylenetetramine (C</span>₆H₁₂N₄) as the fuel and nickel nitrate (Ni(NO₃)₂<span><span>) as the oxidizer. Detailed investigations using combustion diagnostic methods, thermal analysis, and mass spectroscopy measurements allow us to propose that the process includes the </span>multistage decomposition of the oxidizer and sublimation of the fuel. The latter decomposes at the gas phase and releases nitrogen (N</span>₂), hydrazine (N₂H₄), and methane (CH₄<span>). The nitrogen oxides (NO, NO</span>₂, N₂O) emitted at the decomposition of Ni(NO₃)₂·2Ni(OH)₂·4H₂O intermediate, react with CH₄ and N₂H₄<span>. These highly exothermic reactions determine the maximum temperature of combustion. Comparative kinetic consideration allows us to attribute the Ni(NO</span>₃)₂·2Ni(OH)₂·4H₂<span>O decomposition producing nitrogen oxides and nickel oxide (NiO) as the rate-limiting stage of the process. Excessive amounts of N</span>₂H₄ and CH₄<span> in the fuel-rich system reduce NiO to nanoscale Ni. The synthesized Ni readily consolidates into samples with relative densities above 90%, even at 773 K during fast processing.</span></p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"257 ","pages":"Article 113049"},"PeriodicalIF":4.4,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43780567","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":"Revealing the role of limiting oxygen concentration test for a wick flame in characterizing the liquid fuel flammability","authors":"Feng Guo,&nbsp;Nozomu Hashimoto,&nbsp;Osamu Fujita","doi":"10.1016/j.combustflame.2023.113029","DOIUrl":"10.1016/j.combustflame.2023.113029","url":null,"abstract":"<div><p>A two-dimensional numerical model was established to simulate the wick combustion system for determining the limiting oxygen concentration (LOC) of organic solvents, called the wick-LOC method. The ethanol wick flame under forced flow with decreased oxygen concentrations in normal gravity was studied numerically. Three simplified reaction mechanisms, 1-step, 2-step, and quasi-global mechanisms of ethanol were employed in the simulations for comparison with experimental results. The responses of flame height and edge flame standoff distance to the oxygen decrease were analyzed for validation. As the oxygen concentration was reduced to the stability limit of the full flame, the blow-off of the edge flame can be observed. By comparing the simulated LOCs and near-limit stabilized flame structures, the 2-step mechanism can reproduce the wick-LOC well, while the quasi-global mechanism can provide a more detailed flame structure. Further investigation into flame blow-off processes revealed that the reaction rate in fuel-lean conditions is more important for determining the wick-LOC, and the local flow velocities at the flame kernel are almost constant until blow-off occurs. By combining the flame stabilization theory with simulations, the physical meaning of the wick-LOC value can be explained as the oxygen concentration where the local flow velocity can be balanced with critical edge flame speed (more fundamentally, the critical laminar burning velocity) in a certain fuel-lean equivalence ratio. Further applications of the wick-LOC method are expected to examine the simplified reaction mechanisms of other liquid fuels.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"257 ","pages":"Article 113029"},"PeriodicalIF":4.4,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42681409","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}