Combustion and Flame最新文献

{"title":"Investigation of oscillatory behavior of high-energy solid propellants under various operational conditions in rocket motors","authors":"Kaixuan Chen ,&nbsp;Zhenwei Ye ,&nbsp;Xiaochun Xue ,&nbsp;Yonggang Yu","doi":"10.1016/j.combustflame.2025.113975","DOIUrl":"10.1016/j.combustflame.2025.113975","url":null,"abstract":"<div><div>Oscillations in the combustion chamber of solid rocket motors (SRMs) are quite common and can significantly impact the safe operation of SRMs, potentially leading to mission failure. Therefore, it is crucial to investigate the unsteady combustion mechanisms of solid propellants at the microscale. This paper focuses on Nitrate Ester Plasticized Polyether (NEPE) propellant and examines its unsteady combustion behavior under oscillatory pressure disturbances. The proposed numerical framework introduces a refined chemical kinetic model that accounts for condensed-phase pyrolysis and complex interactions in the gas phase. Compared to our previous work, this section's novelty lies in the updated condensed phase kinetic model and the revised combustion parameters for the primary flame and final diffusion flame. In the governing equations section, we solve the low-mach number incompressible ideal gas equations to address the complex laminar reactive flow in the gas phase, while the solid phase is simplified by only solving the heat conduction equation. To model the oscillation environment, a sine wave pressure oscillation is incorporated into the gas phase. In the results and discussion section, we analyze the combustion response of Al-based NEPE propellant under various amplitudes and frequencies. Additionally, we thoroughly investigate the effects of heterogeneity and pressure oscillations on transient burning rate oscillations.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113975"},"PeriodicalIF":5.8,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140180","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 study on the thermoacoustic instability and bifurcation phenomenon of ammonia-methane premixed swirl-stabilized combustor","authors":"Xianglan Fu ,&nbsp;Zhuming Rao ,&nbsp;Haifeng Hu ,&nbsp;Jianwen Yang ,&nbsp;Haocheng Wen ,&nbsp;Bing Wang","doi":"10.1016/j.combustflame.2025.113963","DOIUrl":"10.1016/j.combustflame.2025.113963","url":null,"abstract":"<div><div>The combustion characteristics of ammonia-methane composite fuel in a premixed swirl-stabilized combustor are experimentally investigated in the study. The combustion instability bifurcation phenomenon induced by the variation of ammonia-fuel ratio and equivalence ratio is observed and analyzed. It is found that, under fixed equivalence ratio (Φ) and inlet flow rate, when the ammonia-fuel ratio (<em>X</em>_NH3) is gradually increased, the flame heat release rate fluctuation is weakened, the phase difference between the pressure oscillation and heat release rate fluctuation is increased, and three distinct modes of limit are formed successively in the combustor. It is shown that when <em>X</em>_NH3 or the equivalence ratio is varied independently, subcritical bifurcation and supercritical bifurcation occur when the combustion mode is changed between limit-cycle oscillation and quasi-periodic oscillation. The equivalence ratio is an important parameter for determining the type of bifurcation in the stability of ammonia-methane swirl-stabilized combustor. Subcritical bifurcation occurs only under lean fuel conditions, and particularly, as <em>X</em>_NH3 is changed, its influence on the flame length and heat release fluctuations intensifies with increasing equivalence ratio, resulting in a progressive reduction in the hysteresis interval. When rich fuel conditions are reached, the hysteresis interval disappears and the combustor exhibits supercritical bifurcation.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113963"},"PeriodicalIF":5.8,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140182","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 numerical study of TiO2 nanoparticle evolution in a diffusion flame reactor","authors":"Song He,&nbsp;Cheng Shang,&nbsp;Hao Lu,&nbsp;Zuwei Xu,&nbsp;Haibo Zhao","doi":"10.1016/j.combustflame.2025.113965","DOIUrl":"10.1016/j.combustflame.2025.113965","url":null,"abstract":"<div><div>The spatiotemporally resolved formation and growth of TiO₂ nanoparticles synthesized in a pilot-scale diffusion flame reactor is investigated experimentally and numerically. More specifically, the detailed nanoparticle morphology, size and polydispersed size distribution information along the centerline of the flame are obtained using a custom-designed thermophoretic sampling device and a semi-automated TEM analysis software. Quantitative data on crucial parameters, particularly the spatial evolution of primary particle size distribution (PPSD) and aggregate (or agglomerate) size distribution (ASD) are reported simultaneously, providing the experimental data for developing or validating numerical models and methods. The characterization of the TiO₂ products synthesized at lab-scale (10 g/h) and pilot-scale (200 g/h) has also been performed. The results indicate that monodisperse spherical nanoparticles (∼ 1–3 nm) formed via multiple mechanisms are the primary characteristic of particle growth in the early stage near the burner. These single particles subsequently evolve into mature products in the end. Then, an advanced LES-bivariate sectional method (LES-BiSe) is used to simulate the spatiotemporally resolved formation and growth of TiO₂ nanoparticles in the diffusion flame. The employed model possesses the capability to simultaneously predict the size, morphology, as well as polydispersed PPSD and ASD of nanoparticles. Quantitative comparisons of spatially resolved PPSD, ASD, primary particle and aggregate diameters, as well as the average primary particle number per aggregate (or agglomerate) demonstrate satisfactory agreement with the experimental results. The differences between experiment and simulation are also thoroughly discussed. Owing to the pronounced inhomogeneous field information and the particle transport mixing in flame, the pilot-scale flame exhibits significantly broader size distributions compared to an ideal homogeneous system or a small-scale flame. Furthermore, once having access to the full information regarding the spatial evolution of particle morphology and polydisperse size distributions, a comprehensive spatial identification of various particle dynamic events is explored to discern their competitive influences on particle evolution.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113965"},"PeriodicalIF":5.8,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140224","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":"Microkinetic analysis of reactions between CO and CuO in chemical looping combustion","authors":"Chaohe Zheng,&nbsp;Mingze Su,&nbsp;Haibo Zhao","doi":"10.1016/j.combustflame.2025.113967","DOIUrl":"10.1016/j.combustflame.2025.113967","url":null,"abstract":"<div><div>Since the gas diffusion in the thermogravimetric analyzer crucible significantly limits the reactivity of samples, a down-top multi-scale kinetic model is proposed to predict the reduction rate in a diffusion-limited crucible, by considering the gas diffusion during the entire crucible domain. To improve the adaptability of kinetic parameter, the reaction kinetics are directly calculated by the first-principle method, rather than fitting the experimental data. The oxidation process of CO takes into account three-step reversible reaction (<em>i.e.</em>, adsorption, interface reaction, and desorption) on the surface and the diffusion of oxygen ions in the bulk. The impact factors, <em>i.e.</em>, particle polydispersity, gas diffusion, oxygen diffusion, and surface reaction, are all adequately considered, which can be easily extended to the different kinds of diffusion-limited crucibles of various commerce devices. Density functional theory calculations are used to analyze the mechanisms of CO oxidation on the surface of copper oxide, and the optimal adsorption site is the triple coordination copper top site. The corresponding kinetic parameters are then obtained via harmonic transition state theory. The multi-scale model can accurately predict the actual reduction rate of copper oxide in a commercial thermogravimetric analyzer under various operation conditions. Using the particle-resolved simulations, the effect of different physical properties is further studied to provide theoretical support for the design of copper-based oxygen carrier in fuel reactor. Results reveal that there is the optimal grain size for CuO reduction, and Cu-based oxygen carrier with the grain size of 30∼50 nm exhibits almost the same reaction performance.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113967"},"PeriodicalIF":5.8,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140181","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":"Carbon monoxide emissions from combustion of non-carbon-containing fuels","authors":"Renee Cole,&nbsp;Cristian D. Avila Jimenez,&nbsp;David Wu,&nbsp;Tim Lieuwen,&nbsp;Ben Emerson","doi":"10.1016/j.combustflame.2024.113913","DOIUrl":"10.1016/j.combustflame.2024.113913","url":null,"abstract":"<div><div>This short communication was motivated by measurements of non-negligible CO emissions from NH₃-air premixed flames. Given that NH₃ contains no carbon atoms, we initially thought this indicated some error or cross-sensitivity in the measurement system. However, as shown here, CO is indeed present in the exhaust emissions and originates from atmospheric CO₂ conversion to CO during combustion. We also show that CO levels of order 10-200 ppm are possible under rich burning conditions. Given that rich staged burning is a promising approach for NO_x control, particularly for NH₃ combustion, these results show that some level of C1 chemistry is inherently present when utilizing real air, that models must include CO₂ in air for capturing this CO production, and that practical combustors must consider CO burnout processes as well when utilizing rich-staged designs.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113913"},"PeriodicalIF":5.8,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143139817","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 comparative study of two methods for estimating aluminum agglomerate sizes: Cohen's pocket model and density-based clustering","authors":"L.Q. Xiao ,&nbsp;X.M. Shang ,&nbsp;Y. Zhao ,&nbsp;J.W. Li ,&nbsp;H.J. Curran ,&nbsp;P. Chen","doi":"10.1016/j.combustflame.2024.113957","DOIUrl":"10.1016/j.combustflame.2024.113957","url":null,"abstract":"<div><div>The effectiveness of two calculation methods—Cohen's pocket model and the cluster analysis method (specifically Density-Based Spatial Clustering of Applications with Noise, DBSCAN)—was compared in predicting aluminum agglomeration on the burning surfaces of solid propellants. The comparison focused on the effects of ammonium perchlorate (AP) particle size, AP size gradation, and the relative proportions of coarse and fine AP. Experimental investigations were also conducted on four hydroxyl-terminated polyether (HTPE) propellant samples and compared with the two methods. The results show that with larger AP particle sizes and higher coarse AP content, both methods predict an increase in average aluminum volume—whether in a pocket (according to Cohen's pocket model) or in localized aluminum-rich regions (as identified by DBSCAN)—which is consistent with experimental results on agglomerate diameter variations. Additionally, DBSCAN more accurately predicts the number mean (<em>D</em>_1,0) and number-volume mean (<em>D</em>_3,0) agglomerate diameters, while the pocket model provides results that are closer to the volume-moment mean diameters (<em>D</em>_4,3). For monomodal AP size distributions, the average aluminum volume calculated by DBSCAN correlates with the cubic power of AP size, which aligns with the results from the pocket model. However, for bimodal distributions, DBSCAN results deviate from the pocket model due to particle gradation effects. Using the Voronoi diagram, it was found that the spatial volumes partitioned by AP particles approximate a log-normal distribution. This finding explains the log-normal-like agglomerate size distributions predicted by DBSCAN and suggests that the pocket volumes should also follow a log-normal distribution when AP particles are graded and randomly distributed.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113957"},"PeriodicalIF":5.8,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143139583","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":"Analysis of the origin of NOx emissions in non premixed dual swirl hydrogen flames","authors":"M. Vilespy ,&nbsp;A. Aniello ,&nbsp;D. Laera ,&nbsp;T. Poinsot ,&nbsp;T. Schuller ,&nbsp;L. Selle","doi":"10.1016/j.combustflame.2024.113925","DOIUrl":"10.1016/j.combustflame.2024.113925","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The mechanisms of NO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; formation in swirled hydrogen-air flames are investigated with Large Eddy Simulations (LES). Two operating conditions, A (3 kW) and L (9 kW), are considered. Flame A is M-shaped with a first diffusion-controlled front attached to the hydrogen injector rim and a second flame front burning hydrogen and vitiated recirculating air. Flame L, instead, is lifted and stabilized as a V-flame at the bottom of the central recirculation zone. Flame L also features a diffusion reaction layer in the central recirculation zone with partially premixed wings that develop along the inner shear layer above the injector. It is shown that the central diffusion front is common to both operating points and plays an essential role in the global NO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; emissions of the burner for both operating conditions. A comparison between flamelets extracted from 3D simulations and results obtained with one-dimensional strained flames shows that strain plays an essential role in the production rate of NO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; for all zones. In both flames, nitrous oxides are mainly produced in the central diffusion front. The high temperature in this front favor NO formation through the thermal NO pathway, which is strongly dominant over the other ones. Nevertheless, the central diffusion front of the lifted flame (L) is submitted to a higher strain rate than the attached flame (A), which leads to lower temperature and consequently to a smaller NO production. Interestingly, it is demonstrated that these differences can be predicted using one-dimensional strained diffusion flames. These simulations emphasize the key role of strain rate to control NO emissions in hydrogen non-premixed flames, and show that NO emissions are not necessarily increased by diffusion hydrogen flames attached to the injector lips.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;NO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; emissions are a key factor in designing future hydrogen gas turbines. While it is commonly assumed that diffusion-dominated flames produce high NO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; levels, this paper shows that hydrogen swirled burners can achieve low NO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; emissions even in a diffusion regime. Strained laminar diffusion hydrogen flames are known to limit NO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; production, and this study extends that understanding to turbulent swirled flames. The main source of NO is not the typical diffusion ‘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 (Flame I) near the injector, but rather a second","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113925"},"PeriodicalIF":5.8,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140223","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":"Ignition by concentrated heat sources: Minimum energy required and flame propagation over long distances in mixtures below the flammability limit","authors":"Vadim N. Kurdyumov,&nbsp;Carmen Jiménez","doi":"10.1016/j.combustflame.2024.113959","DOIUrl":"10.1016/j.combustflame.2024.113959","url":null,"abstract":"<div><div>Numerical analysis based on a chain-branching chemistry model reveals the possibility of successful ignition and flame propagation over long distances at a sufficiently high localized concentrated energy in mixtures below the flammability limit at low Lewis numbers.</div><div><strong>Novelty and significance statement</strong></div><div>This work demonstrates for the first time that the application of a concentrated energy source of sufficient intensity can cause not only ignition but also flame propagation over long distances in mixtures with low Lewis numbers below the flammability limit. This can result in safety issues.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113959"},"PeriodicalIF":5.8,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143139818","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 numerical analysis of the effects of fire size on the sooting radiative structure of medium-scale heptane pool fires","authors":"Fatiha Nmira ,&nbsp;Sébastien Thion ,&nbsp;Jean-Louis Consalvi","doi":"10.1016/j.combustflame.2024.113946","DOIUrl":"10.1016/j.combustflame.2024.113946","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The principle aim of this article is to perform a detailed analysis of the impact of the fire size on the radiative structure of lab-scale heptane pool fires. The article first reports the comparison of a new exhaustive set of measurements for a 30 cm diameter (&lt;span&gt;&lt;math&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;) heptane pool fire with a heat release rate (HRR) of &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mover&gt;&lt;mrow&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;̇&lt;/mo&gt;&lt;/mrow&gt;&lt;/mover&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;45&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;.82 kW with numerical predictions obtained from a Large Eddy Simulation (LES)-based model. The modeling strategy combines the RCFSK as a gas/soot radiative property model, a two-equation acetylene/benzene soot model and flamelet/presumed filtered density function approaches to model the interactions between turbulence, chemistry, soot and radiation. The model accurately reproduces all the experimental data, including temperature statistics, mean soot volume fraction (SVF), radiative loss to the surroundings and heat feedback to the pool surface. Second, these results are combined with previously-published experimental data and LES relative to a 15 cm diameter heptane pool with a five times lower HRR of &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mover&gt;&lt;mrow&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;̇&lt;/mo&gt;&lt;/mrow&gt;&lt;/mover&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;.89 kW. The experimental and numerical results reveal for the first time that, at normalized locations &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;r&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;⋆&lt;/mo&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mi&gt;r&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;z&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;⋆&lt;/mo&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mi&gt;z&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mover&gt;&lt;mrow&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;̇&lt;/mo&gt;&lt;/mrow&gt;&lt;/mover&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mn&gt;5&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; with &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, temperature statistics are virtually independent of the HRR whereas the SVF and the soot radiative emission term depend very little on it, both scaling with &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mover&gt;&lt;mrow&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;̇&lt;/mo&gt;&lt;/mrow&gt;&lt;/mover&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;. A consequence is that the evolution of the radiant fraction while increasing the fire size is driven by a competition between a weak increase in the radiative emission fraction as &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mover&gt;&lt;mrow&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;̇&lt;/mo&gt;&lt;/mrow&gt;&lt;/mover&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; and a reduction in flame transparency. These two processes are found to be balanced, explaining why the radiant fraction of the two pool fires remains almost constant. Eventually, it is found that for both 15 and 30 cm heptane pools, neglecting the radiative contribution of the heptane fuel vapor leads to a non-negligible overprediction of the radiative heat feedback, this overprediction increasing with the pool diameter.&lt;/div&gt;&lt;di","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113946"},"PeriodicalIF":5.8,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140183","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 and experimental investigation of flame dynamics in opposed-flow solid fuel burner","authors":"Ryan DeBoskey ,&nbsp;Clayton Geipel ,&nbsp;David Kessler ,&nbsp;Brian Bojko ,&nbsp;Brian Fisher ,&nbsp;Ryan F. Johnson ,&nbsp;Venkat Narayanaswamy","doi":"10.1016/j.combustflame.2024.113960","DOIUrl":"10.1016/j.combustflame.2024.113960","url":null,"abstract":"<div><div>Understanding the complex coupled physics of phase change and turbulent gas-phase combustion in solid fuel combustors is critical to the design of advanced propulsion systems. This study considers the combustion of hydroxyl-terminated polybutadiene (HTPB) in an opposed-flow burner (OFB) configuration. High-speed shadowgraph imaging on the OFB is conducted to capture the unsteady flame dynamics surrounding the burner. Unsteady two-dimensional axisymmetric simulations, performed using a high-fidelity 20-species, 109-reaction pressure comprehensive skeletal kinetics mechanism, show improved agreement in the prediction of flame thickness in comparison to previous quasi-one-dimensional modeling, attributed to the significant deviation from self-similarity in the OFB configuration. Experimental and numerical data are compared showing strong trend-wise agreement and providing novel insight into the hitherto unexplored complex dynamics of the OFB configuration. Power spectral density (PSD) profiles of the flame oscillations demonstrate strong agreement in the broad peak frequency between simulations and experiments. PSD of flame thickness, regression rate, and azimuthal vorticity from the computed flame dynamics show strong coupling between the instantaneous regression rate and flame thickness, which is largely driven by the low-frequency vortex shedding from the OFB nozzle lip. Snapshots of the flowfield show a secondary diffusion flame with the majority of <span><math><mi>CO</mi></math></span> to CO₂ oxidation downstream of the fuel grain edge. Variations in the species composition along the fuel surface highlight the complex balance between convective and diffusive forces arising from the proximity of the stagnation plane adjacent to the fuel surface.</div><div><strong>Novelty and Significance Statement</strong></div><div>This work utilizes large-eddy simulation (LES) to improve the prediction of flame thickness by 1000+% in an opposed flow solid fuel burner (OFB). Demonstration of significant deviation from self-similarity profiles highlight the limitations of current state-of-the art quasi one-dimensional modeling techniques and provides a viable strategy for predictive modeling of solid fuel combustion systems. Accurate prediction of heterogeneous combustion is a critical challenge limiting propellant and fuel discovery. Alongside validating experimental data, high-fidelity numerical simulations of heterogeneous combustion systems are of topical importance to advancing community understanding. High-fidelity modeling and experimental imaging gives unprecedented insight into the coupling between solid fuel combustion, unsteady flame dynamics, and unsteady fluid dynamics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"273 ","pages":"Article 113960"},"PeriodicalIF":5.8,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143139545","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}