Combustion and Flame最新文献

{"title":"An experimental and kinetic modeling study on 4-methylheptane pyrolysis at atmospheric pressure","authors":"Haikun Lang ,&nbsp;Fangping Bin ,&nbsp;Shuyao Chen ,&nbsp;Xiaoli Zhang ,&nbsp;Jiuzheng Yin ,&nbsp;Jinzeng Pan ,&nbsp;Zhandong Wang ,&nbsp;Lixia Wei","doi":"10.1016/j.combustflame.2024.113790","DOIUrl":"10.1016/j.combustflame.2024.113790","url":null,"abstract":"<div><div>Fischer–Tropsch synthesis is an important route for the productions of cleaner fuels from non-petroleum materials. Monomethylated alkanes are present in large quantities in Fischer–Tropsch synthetic fuels. However, side-chain position may make a difference in the combustion of the fuels. In this work, the 4-methylheptane (MH4) pyrolysis was investigated experimentally by using a jet-stirred reactor at 800–1125 K and at 760 Torr. Major pyrolysis products, including small molecules and aromatic products, were identified and measured by using the synchrotron ultra-violet photoionization method. Several species were detected and measured, including CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₄, C₃H₆, C₃H₈, C₄H₆, IC₄H₈, C₅H₆, C₅H₈1-3, C₅H₁₀-2, benzene, naphthalene, indene and C₆H₅C₂H, etc. A detailed kinetic model of MH4 pyrolysis was developed and validated against the experimental results in this work. Rate of production analysis of MH4 indicates that the most significant consumption pathways are H-abstractions. The unimolecular decomposition reactions by the breakages of C<img>C bonds are also important pathways in MH4 consumption. The pyrolysis product distributions of 4-methylheptane, 3-methylheptane and 2-methylheptane were compared to demonstrate the effect of the methyl side chain position on the pyrolysis of those fuels. It is noted that the mole fraction distributions of the smaller species, including CH₄, C₂H₂ and C₂H₆, are not sensitive to the position of the methyl side-chain, while those of C3-C5 products, including PC₃H₄, C₃H₆, C₄H₆, IC₄H₈, C₅H₈1-3 and C₅H₁₀-2, are strongly affected.</div></div><div><h3>Novelty and significance statement</h3><div>The products of 4-methylheptane pyrolysis were identified and measured by using the synchrotron ultra-violet photoionization method. A detailed kinetic model of 4-methylheptane pyrolysis at atmospheric was constructed for the first time. The consumption pathways of 4-methylheptane pyrolysis were clarified. The effect of methyl side chain position on fuel pyrolysis was analysed. 4-Methylheptane is one of the important branched alkanes in Fischer–Tropsch synthetic diesel fuel. The present work extends the understanding of pyrolysis of long branched alkanes. The results of the study provide guidance in exploring ideal compositions for diesel alternative fuels.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113790"},"PeriodicalIF":5.8,"publicationDate":"2024-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423808","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":"Size-resolved ignition temperatures of isolated iron microparticles","authors":"Daoguan Ning,&nbsp;Yuhang Li,&nbsp;Tao Li,&nbsp;Benjamin Böhm,&nbsp;Andreas Dreizler","doi":"10.1016/j.combustflame.2024.113779","DOIUrl":"10.1016/j.combustflame.2024.113779","url":null,"abstract":"<div><div>Ignition temperatures of metal particles play an essential role in not only the fundamental theories of non-volatile dust flames but also the robust operation of practical metal fuel burners. The present paper introduces a novel approach to accurately measure the ignition temperature of an isolated particle. Micron-sized single particles are injected downwards into a quartz tube heated externally by a premixed flame near the bottom end. During free fall, a particle, if sufficiently small, closely follows the gas-phase temperature that increases gradually from top to bottom. By measuring the ignition position of the particles, the ignition temperature is determined from the gas-phase temperature profile that is quantified <em>a priori</em>. Applying the approach together with high-speed imagining and diffuse backlight-illumination techniques, the ignition temperature of approximately 30–60 <span><math><mi>μ</mi></math></span>m iron particles in O₂/N₂ mixtures are comprehensively measured at oxygen mole fractions of 10%–50%. The experimental results reveal that the measured ignition temperatures is in the range of 1030–1130<!--> <!-->K that are independent of the oxygen mole fraction and the particle size. In contrast, the particle size significantly influences the ignition probability. Smaller particles have lower probabilities to ignite. At the oxygen mole fraction of 10%, ignition is only observed for iron particles larger than approximately 45 <span><math><mi>μ</mi></math></span>m. For all other cases, ignition is detected for all particle diameters. Possible mechanisms underlying the experimental observations are discussed.</div><div><strong>Novelty and significance statement</strong></div><div>A novel approach to measure the ignition temperature of an isolated, micron-sized particle is developed. Compared to existing methods, the new approach provides a convenient way to determine the ignition temperature accurately and examine the size dependence of the ignition characteristics. For the first time, size-resolved ignition temperatures of isolated iron particles are reported. For a fixed particle diameter, the existence of an ignition probability is revealed. The quantitative experimental results have a high potential to be widely used to validate models of iron particle ignition.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113779"},"PeriodicalIF":5.8,"publicationDate":"2024-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423854","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":"The improved performance of plasma assisted combustion (PAC) simulations using the fully analytical Jacobian","authors":"Yangyang Ban ,&nbsp;Fan Zhang ,&nbsp;Naiyuan Zhang ,&nbsp;Shenghui Zhong ,&nbsp;Jiajian Zhu ,&nbsp;Yiqiang Pei","doi":"10.1016/j.combustflame.2024.113788","DOIUrl":"10.1016/j.combustflame.2024.113788","url":null,"abstract":"<div><div>The open-source package ZDPlasKin is integrated into OpenFOAM to develop the ZDP-OF platform, facilitating simultaneous computations of plasma discharge and chemical reactions for plasma assisted combustion (PAC) simulations. To address the computational challenges arising from the disparity between plasma and chemical kinetics, a chemical model program providing a novel fully analytic molar concentration-based Jacobian, CKJac, is introduced, which incorporates computation cost minimization (CCM) strategies and a revised third-body reactions treatment to enhance the efficiency of solving Ordinary Differential Equations (ODE). Then, the efficiency, accuracy, and applicability of CKJac in handling stiff reactions are evaluated by comparing it with other chemistry models, such as pyJac and Standard (a native chemical model in OpenFOAM). The KLU sparse linear algebra library and LAPACK dense linear algebra library are integrated into CVODE and seulex. The effectiveness and robustness of CKJac with stiff ODE solvers, CVODE, and seulex are rigorously validated and demonstrated on four academic configurations: the zero-dimensional (0D) autoignition and PAC under adiabatic homogeneous constant-pressure systems, a two-dimensional (2D) turbulent reacting shear layer case, the three-dimensional (3D) Sandia Flame D, and 2D plasma assisted flame propagation configuration. It is found that CVODE exhibits a requirement for tighter tolerances to achieve high accuracy, and when using the internally generated numerical Jacobian, CVODE demonstrates high robustness. Seulex consistently presents high efficiency and comparable accuracy to CVODE. The low efficiency of CVODE is ascribed to the inefficient linear algebraic equation solving brought by the inherent reinitialization problem in CVODE. CKJac+seulex showcases a notable up to twofold speedup, delivering high accuracy under loose tolerances compared to Standard+seulex. Moreover, CKJac exhibits superior performance compared to pyJac in diverse combustion scenarios due to its low time costs associated with omega and Jacobian formulation evaluations. When combing with linear algebra libraries, pyJac+seulex_LAPACK shows high robustness and CKJac+seulex_KLU shows orders of magnitude speedup for large mechanisms tested in this work.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113788"},"PeriodicalIF":5.8,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423855","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 Thickened Flame Model adaptation to weakly stretched flames for non-unity Lewis number mixtures","authors":"S. Poncet,&nbsp;C. Mehl,&nbsp;K. Truffin,&nbsp;O. Colin","doi":"10.1016/j.combustflame.2024.113758","DOIUrl":"10.1016/j.combustflame.2024.113758","url":null,"abstract":"&lt;div&gt;&lt;div&gt;For the study and design of industrial scale combustion systems, the Thickened Flame Model (TFM) is a widely used turbulent combustion model. It allows for the direct resolution of the flame front on Large Eddy Simulation (LES) meshes by artificially thickening the flame front by a factor &lt;span&gt;&lt;math&gt;&lt;mi&gt;F&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, i.e. &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;δ&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mi&gt;F&lt;/mi&gt;&lt;msubsup&gt;&lt;mrow&gt;&lt;mi&gt;δ&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, while the unstretched adiabatic flame speed &lt;span&gt;&lt;math&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;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;/math&gt;&lt;/span&gt; is preserved. However, when considering differential diffusion effects, the modification of flame reactivity induced by strain rate and curvature is enhanced by the flame thickening process. Especially, at low stretch rates, the derivative of the flame speed with stretch, i.e. the Markstein length &lt;span&gt;&lt;math&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, is multiplied by &lt;span&gt;&lt;math&gt;&lt;mi&gt;F&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;. This induces large errors on the stretched flame speed estimation for mixtures with Lewis numbers &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; far from unity, such as for lean hydrogen/air combustion. The present work proposes a methodology to recover the exact Markstein length of thickened flames, called &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;-TFM. This easy-to-implement method relies on a 2-parameters evaluation, which monitors &lt;span&gt;&lt;math&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&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;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;/math&gt;&lt;/span&gt;. Various Markstein length definitions from literature are considered and estimated using two laminar stretched flame configurations: (i) reactants-to-products counter-flow and (ii) spherical flames. &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;-TFM is evaluated for (i) 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;/air (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) and (ii) stoichiometric C&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;8&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;H&lt;sub&gt;18&lt;/sub&gt;/air (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mo&gt;&gt;&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) mixtures at ambient conditions. &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;-TFM accurately recovers the targeted Markstein lengths for both mixtures, enabling precise estimation of either consumption or displacement flame speed at low stretch rates. &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;-TFM remains fairly accurate even at large strain rates for the &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mo&gt;&gt;&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; flame, while on the contrary for the &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; flame, the consumption","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113758"},"PeriodicalIF":5.8,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423987","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":"Kinetic investigations on the β-scission reactions of hydroperoxy methyl-ester radicals and the concerted HO2 elimination reactions of methyl-ester peroxy radicals: Implication for low-temperature combustion modeling of methyl esters","authors":"Tao Li ,&nbsp;Siyu Chen ,&nbsp;Juanqin Li ,&nbsp;Quan Zhu ,&nbsp;Zerong Li","doi":"10.1016/j.combustflame.2024.113787","DOIUrl":"10.1016/j.combustflame.2024.113787","url":null,"abstract":"<div><div>The β-scission reactions of hydroperoxy methyl-ester radicals (•QOOH radicals in methyl esters) and the concerted HO₂• elimination reactions of methyl-ester peroxy radicals (ROO• in methyl esters) are two reaction classes that play a crucial role in terminating the chain reaction during the low-temperature combustion of methyl esters. These reactions are also key contributors to the negative temperature coefficient behavior and ignition inhibition observed in biodiesel. Although limited rate constants for these classes in small methyl esters have been calculated, those in larger methyl ester models are frequently approximated based on analogous alkyl reactions in alkanes. In this study, the isodesmic reaction method is utilized to correct the energy barriers and high-pressure-limit rate constants calculated at the low-level B3LYP method. The objective is to approximate the results obtained with the high-level G4 method. The β-scission class is further categorized into 6 subclasses based on the position of the newly formed C<img>C bond in the olefin ester product and the location of the radical on the reactant and the concerted elimination class is divided into 4 subclasses based on the position of the newly formed C<img>C bond in the olefin ester product and the carbon sites where the -OOH group and the eliminated H atom are situated. High-pressure-limit and pressure-dependent rate rules for subclasses are established by averaging rate constants within each subclass. Notably, substantial disparities are observed between our rate constants and those reported in models for large methyl esters, where rate constants are approximated from analogous alkyl reactions in alkanes. This underscores the significant uncertainty associated with the direct application of alkyl reaction rate constants in biodiesel models. Consequently, a low-temperature oxidation model of methyl octanoate/ethanol is developed through the incorporation of the rate rules derived in this study, resulting in a model that effectively reproduces experimental data within the conditions of a jet-stirred reactor.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113787"},"PeriodicalIF":5.8,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423806","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":"Shock tube experiments and numerical study on ignition delay times of ammonia/oxymethylene ether-2 (OME2) mixtures","authors":"Lingfeng Dai,&nbsp;Jiacheng Liu,&nbsp;Chun Zou,&nbsp;Qianjin Lin,&nbsp;Tong Jiang,&nbsp;Chao Peng","doi":"10.1016/j.combustflame.2024.113783","DOIUrl":"10.1016/j.combustflame.2024.113783","url":null,"abstract":"<div><div>Recently, ammonia (NH₃) becomes an attractive alternative fuel to reduce CO₂ emissions. The combustion of NH₃ mixed with reactive fuels is a feasible solution to the issue of low reactivity. In the present study, the ignition delay times (IDTs) of NH₃/OME₂ were measured in a shock tube at an equivalence ratio of 0.5, two pressures of 1.75 and 10 bar, and a temperature range of 1245–1797 K with OME₂ mole fractions of 0.05, 0.1, and 0.2. The OME₂<img>NH₃ model was proposed including the OME₂ model updated in this work, the NH₃ model optimized in our previous work, and some cross-reactions between nitrogen-containing species and C₁<img>C₄ species. The OME₂<img>NH₃ model well predicts the IDTs and species profiles of NH₃/OME₂ and IDTs and laminar flame speeds of NH₃/OME₁, as well as the IDTs, laminar flame speeds, and species profiles of OME₁ and OME₂. The cross-reactions considered in this work significantly improve the model prediction. The effects of cross-reactions on the high and low-temperature reactivity of NH₃/OME₂ were analyzed in detail. The comparison between the OME₂<img>NH₃ model and the Li-Shrestha model illustrated that the OME₂ model updated in this work significantly improves the model prediction. This research provides archival experimental data for the NH₃/OME₂ ignition and provides insights into the interactions between OME₂ and NH₃ by the detailed numerical simulations.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113783"},"PeriodicalIF":5.8,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423809","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 analysis of the flame piston-model for acceleration runaway in thin tubes","authors":"Raúl Hernández-Sánchez ,&nbsp;Bruno Denet","doi":"10.1016/j.combustflame.2024.113775","DOIUrl":"10.1016/j.combustflame.2024.113775","url":null,"abstract":"<div><div>A one-dimensional model is developed and studied to explore the flame acceleration runaway mechanism for deflagration-to-detonation transition in thin tubes. This mechanism relies solely on the thermal feedback between the compression waves ahead of the flame and the temperature-sensitive laminar velocity of the flame. Within this model, the primary driver of the flame acceleration and compressive heating enhancement is the gas flow caused by the increased flame surface area. Results from the numerical integration of the reactive Navier–Stokes equations for perfect gases with a single-step chemical-kinetics model are compared with the solutions obtained when considering the flame as a steady-state discontinuity. The numerical results illustrate the flame acceleration runaway in finite time caused by a double feedback loop established in this model. The evolution of the flame acceleration towards a finite-time singularity eventually leads to the formation of a shock wave within the flame structure, triggering the onset of a detonation.</div><div><strong>Novelty and significance statement</strong></div><div>This paper presents numerical results obtained using an approach recently proposed to study the effect of flame acceleration on the one-dimensional internal structure of the flame. Unlike previous studies on flame acceleration leading to DDT based on one-dimensional models in which the flame acceleration due to the increase of its surface area is modeled by accelerating chemical kinetics, the present approach consists in the introduction of a backflow of burned gases pushing the flame tip from behind as a piston. The numerical analysis performed in this work allows considering finite reaction rates in this model obtaining results that compare favorably with those obtained when the flame is considered as a discontinuity. The results of this numerical study support previous analytical studies on the flame acceleration runaway mechanism for DDT and illustrate the acceleration process of a flame propagating over a gas flow with a markedly subsonic velocity which leads to the onset of a detonation.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113775"},"PeriodicalIF":5.8,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423807","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":"Investigating combustion efficiency and NOx emission reduction in fluidized bed ammonia-coal co-firing","authors":"Tianxin Li ,&nbsp;Lin Li ,&nbsp;Chong Liu ,&nbsp;Heng Liu ,&nbsp;Guang Sun ,&nbsp;Ning Ding ,&nbsp;Dennis Lu ,&nbsp;Lunbo Duan","doi":"10.1016/j.combustflame.2024.113735","DOIUrl":"10.1016/j.combustflame.2024.113735","url":null,"abstract":"<div><div>Ammonia, a carbon-free fuel, can significantly reduce CO₂ emissions when co-fired with coal in power plants. Fluidized bed combustion, known for its excellent gas-solid mixing and low NO_x emissions, is a promising method for ammonia-coal co-firing. However, challenges remain in optimizing ammonia injection and controlling nitrogen oxide emissions. This study investigates these aspects using a lab-scale fluidized bed reactor with flexible ammonia injection points. Key variables, such as ammonia co-firing ratios, injection location, temperature, and outlet oxygen concentration, are examined. The results show that with ammonia injection ratios up to 70 %, NO and N₂O emissions slightly increase, while ammonia escape is maintained below 5 ppm. Air staging effectively controls NO_x emissions, and higher temperatures promote N₂O decomposition, but increase NO_x levels. Ammonia injection does not raise unburned carbon content. Rate of production and sensitivity analyses highlight the role of OH radicals in ammonia conversion and identify the critical reactions affecting NO generation. This study highlights the feasibility of fluidized bed ammonia-coal co-firing technology.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113735"},"PeriodicalIF":5.8,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423810","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":"Strong and weak interactions of a V-shaped premixed swirling flame with outer vortex rings","authors":"Yongzhi Ren,&nbsp;Qiuxiao Wang,&nbsp;Yuqian Peng,&nbsp;Liangliang Xu,&nbsp;Xi Xia,&nbsp;Fei Qi","doi":"10.1016/j.combustflame.2024.113760","DOIUrl":"10.1016/j.combustflame.2024.113760","url":null,"abstract":"<div><div>This paper reports two distinct vortex-flame interaction mechanisms existing in a self-excited V-shaped premixed flame. Time-resolved simultaneous measurements of particle image velocimetry (PIV) and OH* chemiluminescence are employed to capture the mean and coherent flow and flame structures. The qualitative study demonstrates the importance of the outer vortex rings (OVR) in governing the flame front dynamics of two representative lean and near-stoichiometric cases. The interaction of the flame with the OVRs is further analyzed quantitatively during one OVR's entire lifespan. Results suggest that the vortex-flame interaction in the lean case is a weak one as the response of the flame's HRR to OVR's growth is interrupted by the tip extinction. This can be understood as a response to the flow perturbation excited in the Helmholtz mode of the plenum. However, the near-stoichiometric case yields a strong interaction that the peak HRR is synchronized with the OVR's peak circulation, which could contribute to a stronger thermoacoustic coupling that leads to the stronger pressure oscillation and frequency drift away from the Helmholtz mode.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113760"},"PeriodicalIF":5.8,"publicationDate":"2024-10-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423853","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":"Three-dimensional simulations of NEPE propellant combustion under depressurization effects","authors":"Kaixuan Chen ,&nbsp;Zhenwei Ye ,&nbsp;Yizhe Yu ,&nbsp;Xiaochun Xue ,&nbsp;Yonggang Yu","doi":"10.1016/j.combustflame.2024.113785","DOIUrl":"10.1016/j.combustflame.2024.113785","url":null,"abstract":"<div><div>This study aims to analyze the characteristics of micro-combustion and unsteady flame development in nitrate ester-plasticized polyether (NEPE) propellant when exposed to rapid pressure decay. A three-dimensional NEPE propellant combustion model is firstly established to achieve this goal. The framework consists of two parts. Firstly, we used sequential algorithms to generate a 3D numerical pack satisfying industrial requirements. In the numerically generated propellant pack, Ammonium perchlorate (AP) particles, and Cyclotetramethylene tetranitramine (HMX) particles are assumed as spheres, whereas the void space is Nitroglycerin/1,2,4-Butane triol trinitrate (NG/BTTN) binder. Secondly, a new kinetic model considering the pyrolysis of condensed phase and complicated interaction of gas species in the gas phase is proposed, which has been not reported until now. The accuracy of this framework is verified via comparing with experimental results. Upon simulating the depressurization combustion of NEPE propellant, it is observed that the non-planar surface stimulates the growth of Leading-Edge Flames, leading to intensified burning during the initial stage of depressurization combustion. After 5.2 ms of depressurization combustion, a remarkable increase in bulk heat release in the gas phase is discovered, attributed to the involvement of coarse AP particles, thereby providing a conducive oxidizing burning environment. Examination of the propellant surface temperature reveals that the oxidizer/binder interface exhibits higher temperatures (∼950 K) at 3.4 MPa, while the particle core typically remains cooler (∼850 K) at pressures ranging from 1.0 to 3.5 MPa. The dynamic temperature fluctuations are a result of the heterogeneity of the propellant microstructure, which also serves as the primary cause of oscillations in several globally averaged parameters. The flickering flame behavior during transient combustion, along with the corresponding combustion characteristics, offers theoretical insights for the study of combustion instability in solid rocket motors, warranting further validation through experimental cases.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"270 ","pages":"Article 113785"},"PeriodicalIF":5.8,"publicationDate":"2024-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142423852","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}