Combustion and Flame最新文献

{"title":"Experimental and numerical investigation on flashback of low-swirling hydrogen–air jet flames","authors":"Maho Kawai ,&nbsp;Takeshi Shoji ,&nbsp;Abhishek Lakshman Pillai ,&nbsp;Shigeru Tachibana ,&nbsp;Takeshi Yokomori ,&nbsp;Ryoichi Kurose","doi":"10.1016/j.combustflame.2026.114792","DOIUrl":"10.1016/j.combustflame.2026.114792","url":null,"abstract":"<div><div>Flashback of premixed hydrogen–air jet flames in a low-swirl burner (LSB) is investigated through experiments and Large-Eddy Simulations (LESs). The experiments include pressure measurements, high-speed chemiluminescence imaging of OH* radicals, and two-dimensional particle image velocimetry. The LESs are conducted on the same burner under various equivalence ratio conditions and are used to analyze local flame propagation dynamics. The experimental results show that core-flow flashback occurs after the lifted flame attaches to the burner exit periphery and then propagates upstream along the central region of the flow field, reflecting the characteristic velocity distribution in low-swirl burners. The LES results show that the regions on the flame surface where flashback is promoted are primarily governed by the local flow velocity, whereas the overall tendency for upstream flame propagation is influenced by the displacement speed. The analysis further shows that the relative contributions of reaction and diffusion to the displacement speed vary strongly across the flame thickness. Transient stagnations of upstream flame motion are also observed, together with a temporary reduction in the upstream-propagating flame surface area and a transition in the dominant pressure oscillation mode.</div><div><strong>Novelty and significance statement</strong></div><div>The present understanding of flashback in premixed low-swirl flames remains limited, particularly with respect to three-dimensional flame-structure dynamics. This study investigates flashback in low-swirling hydrogen–air jet flames using experiments and large-eddy simulations for the first time, to the best of the authors’ knowledge. This combined approach enables analysis of flame behavior as three-dimensional distributions that resolve variations across the flame thickness, rather than relying on representative or integral metrics. Local contributions from flow velocity, chemical reaction, and molecular diffusion to flame propagation are quantified, showing that their relative importance varies strongly across the flame thickness and along the flame surface. In addition, transient stagnation of upstream flame motion is associated with a temporary reduction of the flame area exhibiting upstream propagation and a transition of the dominant pressure-oscillation mode. These results link local flame structure, flow–flame interaction, and pressure dynamics in the flashback.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114792"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036409","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":"Tuning energy release in boron-based energetic composites via gradient thickness control of surface fluoride layer by in situ polymerization","authors":"Hongxia Zhang,&nbsp;Yaozhong Ran,&nbsp;Zhenyu Zhou,&nbsp;Jiawang Shuang,&nbsp;Jiaru Zhang,&nbsp;Fei Xiao,&nbsp;Chongwei An,&nbsp;Zhongliang Ma","doi":"10.1016/j.combustflame.2026.114784","DOIUrl":"10.1016/j.combustflame.2026.114784","url":null,"abstract":"<div><div>Boron powder exhibits exceptionally high gravimetric and volumetric calorific values, granting boron-rich propellants a significantly higher theoretical specific impulse compared to conventional hydrocarbon-based fuels. However, its practical application is severely limited by difficult ignition and incomplete combustion, resulting from the inherent oxide layer on the boron surface. Addressing these combustion inefficiencies is therefore critical. In this work, a series of modified B@FP composites with gradient fluoropolymer coating thicknesses were successfully synthesized through in situ polymerization of 1H,1H,2H,2H-perfluorooctyl acrylate (FOA) onto boron powder, where the coating mass was precisely tailored by varying the FOA monomer concentration. The surface morphology, elemental distribution, chemical composition, and hydrophobicity of the B@FP composites were comprehensively characterized. Their oxidation behavior, ignition performance, and combustion dynamics were further investigated. The results indicate that the fluoropolymer coating significantly reduces the ignition temperature of boron while increasing both the combustion heat and total exothermic enthalpy. Moreover, in combustion systems with ammonium perchlorate (AP) as oxidizer, the B@FP-1/AP mixture demonstrated higher combustion temperatures and a more vigorous reaction. Ultimately, the effect of the modified boron composites on the combustion performance of composite propellants was thoroughly evaluated, providing valuable insights for enhancing energy release efficiency in boron-containing propellant systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114784"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036472","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 of symmetry breaking in premixed flame propagation in narrow gaps","authors":"Cristian Mejía-Botero,&nbsp;Christophe Almarcha","doi":"10.1016/j.combustflame.2026.114837","DOIUrl":"10.1016/j.combustflame.2026.114837","url":null,"abstract":"&lt;div&gt;&lt;div&gt;This study presents an experimental analysis of the critical conditions governing symmetry breaking in premixed flame propagating within the gaps of narrow Hele-Shaw cells. Fluid dynamic analysis was performed using hydrogen/air mixtures with equivalence ratios &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;ϕ&lt;/mi&gt;&lt;mo&gt;∈&lt;/mo&gt;&lt;mrow&gt;&lt;mo&gt;[&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;5&lt;/mn&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;]&lt;/mo&gt;&lt;/mrow&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, focusing on gaps of thickness &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;h&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;, 2.6, and &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;7&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mi&gt;mm&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. The particle image velocimetry (PIV) technique was employed to measure the velocity field of the fresh gas. A glycerol/propylene glycol aerosol was used as a PIV tracer, and its influence on flame behavior was assessed. The study focuses on two key parameters: the dimensionless fresh gas velocity (&lt;span&gt;&lt;math&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;) and the gap-to-flame-thickness ratio (&lt;span&gt;&lt;math&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;). Results show that while &lt;span&gt;&lt;math&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; strongly influences both the flame propagation speed and its symmetry, it is not sufficient on its own to predict symmetry breaking. Instead, a critical boundary &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mi&gt;f&lt;/mi&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; is shown to accurately separate symmetric and asymmetric flame regimes across a wide range of experimental conditions. These findings demonstrate that the combined effect of &lt;span&gt;&lt;math&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; governs the transition between symmetric and asymmetric flame shapes, and establish a reliable experimental methodology for future studies of confined premixed flame behavior. Finally, to further analyze the physics underlying symmetry breaking, the roles of the Péclet (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) and Damköhler (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) numbers were examined. It is shown that flame symmetry is governed primarily by the combined effects of both parameters: low &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; promotes symmetric flames through strong diffusive smoothing regardless of &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, whereas high &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; leads to pronounced asymmetry. In the intermediate &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; range, symmetry is found to depend on &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, with advection-dominated conditions favoring symmetric structures provided that the flow is co-propagating with the flame.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This work experimentally demonstrates, for the first time, the effect of fresh gas velocity and channel size on flame symmetry in narrow channels. The results are val","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114837"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146184672","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":"Thermodiffusively-unstable lean premixed hydrogen–methane blends: Phenomenology and empirical modelling","authors":"E.F. Hunt,&nbsp;A. Moitro,&nbsp;A.J. Aspden","doi":"10.1016/j.combustflame.2026.114845","DOIUrl":"10.1016/j.combustflame.2026.114845","url":null,"abstract":"&lt;div&gt;&lt;div&gt;This paper considers direct numerical simulation of hydrogen–methane blends in three-dimensional freely-propagating and turbulent flames using the canonical flame-in-a-box configuration. Previous work has developed empirical models for mean local flame speed and thickness in two- and three-dimensional freely-propagating flames, as well as a Karlovitz-dependent modification to capture the exaggeration of thermodiffusive response by turbulence; more recently, a modification to the instability parameter was demonstrated for hydrogen–methane blends two-dimensional freely-propagating flames. The present paper first considers phenomenology of premixed flames of fuel blends where one component is thermodiffusively unstable, and shows that there are effectively two flames, correlated with local curvature. In regions of positive curvature (centre of curvature in the products), the usual thermodiffusive response is observed; diffusive focussing of hydrogen results in flames locally thinner and faster. For the fuel blend, the other component (in this case methane) is left behind, and burns more slowly in the negatively-curved regions (where extinction channels would be found in unblended hydrogen flames). The dual-flame nature of the burning means that the choice of progress variable becomes more important; the selected isosurfaces based on hydrogen and temperature did not correlate well with the negatively-curved heat release associated with methane consumption, and so a blend-based progress variable was required. Consequently, the blend-based flame surface area was up to 50% higher than the other surfaces, resulting in lower mean local flame speeds. Joint probability density functions of local flame speed and curvature highlight the dual-flame nature, with high flame speeds correlating positively with curvature and a second region of low level burning at negative curvatures. The empirical models are shown to work well in three dimensions; the modification to the instability parameter for blends is independent of dimension. An additional factor was required in the turbulent flame speed model to reduce the turbulent contribution to local flame speed as the hydrogen content goes to zero. The resulting empirical model is shown to work remarkably well, and provides a prediction of mean local flame speed for turbulent thermodiffusively-unstable lean premixed hydrogen–methane blends, which can be evaluated simply from one-dimensional flame simulations alone.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and Significance&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;The novelty of the paper is firstly in the phenomenological description of flames with fuel blends where one is thermodiffusively-unstable, specifically the dual-flame nature of the burning, correlated with flame surface curvature, and secondly in the extension of the empirical models for thermodiffusively-unstable blends in three-dimensional freely-propagating and turbulent flames. This is significant as it advances fundamental understa","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114845"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146184676","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":"The effects of friction and heat loss on two-dimensional H2–O2–Ar detonations in thin channels","authors":"Curran Schmitt ,&nbsp;Joshua Smith ,&nbsp;Brian Maxwell","doi":"10.1016/j.combustflame.2025.114760","DOIUrl":"10.1016/j.combustflame.2025.114760","url":null,"abstract":"<div><div>This current work extends a Zeldovich-type loss model for detonation waves in thin channels to account for both viscous friction and heat losses in a two-dimensional framework in order to better understand the impact of these losses on the detonation velocity, cellular structure, and ability to sustain detonation in the presence of losses. Two stoichiometric hydrogen–oxygen–argon mixtures below atmospheric pressure are considered, and the geometry under investigation is a thin, rectangular channel. This two-dimensional numerical model incorporated temperature-dependent thermodynamics, the San Diego detailed chemistry mechanism, and source terms to account for the losses due to the geometry in the third dimension, which are developed from the perspective of the entrance length problem from pipe flows. The individual contributions of the viscous and heat transfer effects to the velocity deficit were determined for mixtures both near and away from the quenching limit. It was found that away from the quenching limit, the velocity deficit is fairly insensitive to the amount of heat loss, but conversely, the onset of complete detonation failure is quite sensitive to heat loss. A nondimensional measure of the rate of energy loss was proposed, and was used to show that near failure, detonations are able to sustain losing up to 30% of the released chemical energy to the channel walls before the onset of failure.</div><div><strong>Novelty and Significance Statement</strong></div><div>This work introduces a novel numerical framework to investigate the effects of confinement on multidimensional hydrogen–oxygen–argon detonation wave dynamics. For likely the first time, a spatially-dependent skin-friction coefficient and Reynolds analogy-based heat loss model are integrated into a quasi-two-dimensional, transient simulation with detailed chemical kinetics and temperature-dependent thermodynamics. Source terms are used to account for three-dimensional loss mechanisms, with the primary innovation being the physics-informed treatment of skin-friction. The model is validated against experimental data through calibration of a heat loss parameter which enables the separation of frictional and heat loss contributions to the detonation velocity deficit, providing new insights into the sensitivity of detonation propagation to these losses.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114760"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976375","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":"Formation chemistry of quinoline, the smallest nitrogen-containing polycyclic aromatic hydrocarbon","authors":"Huajie Lyu ,&nbsp;Peng Liu ,&nbsp;Zhenrun Wu ,&nbsp;Hong Wang ,&nbsp;Zhandong Wang ,&nbsp;Xiang Gao ,&nbsp;Bingjie Chen","doi":"10.1016/j.combustflame.2026.114791","DOIUrl":"10.1016/j.combustflame.2026.114791","url":null,"abstract":"<div><div>Nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) are emerging pollutants originated from fuel-nitrogen in coal and nitrogen-rich biomass. They exhibit higher toxicity, carcinogenicity and mutagenicity to humans, animals, and plants in the nature than equivalent PAHs. However, the formation chemistry of even the smallest NPAH, quinoline, is still not well understood and needs further investigation. In this work, we investigated quinoline formation chemistry based on experimental measurements and quantum chemistry calculations. Pyrolysis experiments were performed in a laminar flow reactor with pyridine and acetylene as reactants at temperature range of 700–1100 K. Products were analyzed by <em>in-situ</em> time-of-flight molecular beam mass spectrometry using synchrotron vacuum ultraviolet radiation as photon ionization source. 33 chemical species were detected and measured, and 9 NPAHs, e.g., indole, quinoline, bi-pyridine, were identified by photon ionization energy curves and species ionization energies. Guided by the species distribution, quinoline formation pathways-two steps of acetylene addition to pyridine and cyclization-were proposed and investigated using high-level quantum chemistry calculations. The calculated yields, rate coefficients and kinetic modeling results examined the pathway competition and individual contribution to quinoline formation. The unraveled formation chemistry of quinoline may help explain how fuel-nitrogen is converted into quinoline and other NPAHs during biomass gasification, fast pyrolysis, and gas-phase combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114791"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969327","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":"Direct numerical simulation of a PMMA–GO2 slab burner: Experimental validation and extension to Marxman theory","authors":"Kenneth Budzinski,&nbsp;Kolos Retfalvi,&nbsp;Elektra Katz Ismael,&nbsp;Matthew McGurn,&nbsp;Paul E. DesJardin","doi":"10.1016/j.combustflame.2026.114821","DOIUrl":"10.1016/j.combustflame.2026.114821","url":null,"abstract":"<div><div>In this study, Polymethyl methacrylate slabs are burned in a pure oxygen environment and also modeled using direct numerical simulation (DNS) of the reacting Navier–Stokes equations. The DNS is validated against experiments using novel simultaneous non-intrusive temperature and velocity measurements. The experimental temperature profiles and 3D flame hulls are measured and reconstructed using two color pyrometry (TCP) from multiple high speed camera videos of different views. The stream-wise velocity fields above the slab burner are processed from the experimental images using a methodology similar to particle image velocimetry. The DNS data is processed in a similar manner using a novel virtual-TCP (VTCP) method for temperature and velocities condition on soot volume fraction. Comparison of time averaged DNS fuel regression rates, temperatures, and velocities agree reasonably well to the experiments indicating the DNS provides a faithful representation of the physics. The DNS data is then used to examine the assumptions made in Marxman’s 1960’s analysis of an ablating reacting boundary layer. The analysis reveals that Marxman’s assumed momentum profiles are not good approximations, due to the neglection of volumetric expansion from the reacting flame. Further investigation of the DNS also reveals the existence of self-similar solutions using a new set of conservative variables. A new similarity formulation is then derived by assuming that vertical and stream-wise mass flux, total enthalpy and mass fractions are functions of the normalized boundary layer height only. The chemical state solutions of the similarity problem are shown to agree reasonably to the DNS.</div><div><strong>Novelty and significance statement</strong></div><div>This study presents the DNS of a fuel slab burner experiment that, for the first time, allow for detailed examination of theories used in hybrid rocket propulsion. These theories originate from Marxman’s early work in the 1960s and are still widely used today. The DNS shows the limitations of Marxman’s theories and presents a new DNS guided similarity theory. In addition, this work presents a novel virtual two-color pyrometry (TCP) technique used in the DNS so direct comparisons to data may be conducted for model validation purposes. This approach avoids many of the pitfalls comparing DNS to non-intrusive TCP measurement techniques through temperature interpretation comparisons.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114821"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075183","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":"Effect of B4C addition on the combustion and energy release characteristics of boron-based slurry fuel droplets","authors":"Wentao Wan ,&nbsp;Zaizheng Li ,&nbsp;Yuanda Li ,&nbsp;Shengji Li ,&nbsp;Zhu Zhuo ,&nbsp;Xuefeng Huang ,&nbsp;Hang Zhang ,&nbsp;Jiangrong Xu","doi":"10.1016/j.combustflame.2026.114793","DOIUrl":"10.1016/j.combustflame.2026.114793","url":null,"abstract":"<div><div>To address the challenges of incomplete energy release and unstable combustion in boron-based slurry fuels, the incorporation of B₄C nanoparticles has emerged as a promising strategy to improve the fuel performance. This work investigated the combustion and energy release characteristics of high-solid-content (40.0 wt.%) boron-based slurry fuels with varying B₄C mass ratios. The combustion stage, droplet diameter evolution, micro-explosion intensity, two-dimensional flame temperature distribution, droplet lifetime, flame emission spectrum and morphology of residues were obtained and analyzed. Results showed that both the micro-explosion intensity and first combustion duration increased initially and then decreased with the rising of B₄C mass ratio, reaching optimal values at a B/B₄C mass ratio of 2:3. At this ratio, the fuel exhibited the highest average flame temperature (exceeding 2300 K) during the micro-explosion stage, along with more stable and sustained energy release, and the first combustion duration was prolonged by ∼30%. SEM observations revealed that B₄C addition suppressed dense shell formation by generating CO₂ during combustion, which improved the permeability and reduces pressure-induced fragmentation. Furthermore, two distinct micro-explosion pathways were identified: a frequent pathway associated with the flexible shell (The maximum temperature was around 1800 °C), and a rarer but more intense pathway caused by agglomerated impermeable shells (The maximum temperature exceeded 2500 °C). B₄C addition favored the former by reducing oxide barriers (B₂O₃) and suppressing particle agglomeration.</div></div><div><h3>Novelty and significance statement</h3><div>This study innovatively explores B₄C nanoparticles as additives in boron-based slurry fuels to enhance combustion efficiency and stability. By optimizing the B/B₄C mass ratio (2:3), it achieves superior micro-explosion intensity, prolonged combustion, and higher flame temperatures. The key innovation lies in B₄C's role in suppressing dense oxide shell formation via CO₂ generation, improving permeability and reducing fragmentation. Additionally, two micro-explosion pathways are identified, with B₄C favoring the more frequent, flexible shell route. These findings significantly advance slurry fuel design, offering a practical strategy for stable energy release and incomplete combustion mitigation in propulsion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114793"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075141","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":"Low-order modeling of thermoacoustic instability: Modal competition induced by fluid–structure interaction","authors":"Dario Passato ,&nbsp;Berksu Erkal ,&nbsp;Claire Bourquard ,&nbsp;Jim B.W. Kok ,&nbsp;Ines Lopez Arteaga","doi":"10.1016/j.combustflame.2026.114841","DOIUrl":"10.1016/j.combustflame.2026.114841","url":null,"abstract":"<div><div>This work presents an experimental and theoretical investigation into the influence of a passive, off-resonance flexible plate on a dual-mode thermoacoustic instability. Simultaneous measurements of acoustic pressure, heat release, and plate velocity (via Laser Doppler Vibrometry) are used to characterize the coupled fluid–structure dynamics. In the rigid-wall baseline, the combustor exhibits a limit cycle dominated by a single acoustic mode. Introducing the flexible plate fundamentally alters this behavior, inducing modal competition in which the dominance intermittently shifts between two closely spaced acoustic modes. A low-order model, consisting of two coupled delayed oscillators, is developed and calibrated against the experimental data to probe the underlying mechanism. The analysis shows that, although the plate acts as an energy sink, this additional damping alone cannot account for the emergence of the secondary mode. Instead, the model indicates that modal competition arises from an alteration of the thermoacoustic feedback loop, driven by an induced frequency shift and a modification of the effective flame driving strengths. This demonstrates that the compliant boundary does not merely introduce damping but reshapes the competitive stability balance between modes, revealing a non-intuitive mechanism with direct relevance for passive control strategies.</div><div><strong>Novelty and significance statement</strong> This work provides new insight into the complex dynamics of a multi-mode unstable thermoacoustic system interacting with a compliant boundary. The study combines simultaneous acoustic, heat release and vibrometry measurements to characterize such an interaction in-situ. We experimentally investigate a phenomenon of modal competition triggered by this passive, off-resonance structural element, which alters the dynamics of the thermoacoustic modes. The findings provide a valuable benchmark for the development and validation of descriptive low-order models.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114841"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075142","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":"Impact of thermal and differential-preferential diffusion on the dynamics and acoustics of hydrogen–air slit flames","authors":"Borja Pedro-Beltran ,&nbsp;Zin Shahin ,&nbsp;Matthias Meinke ,&nbsp;Sohel Herff ,&nbsp;Dominik Krug ,&nbsp;Wolfgang Schröder","doi":"10.1016/j.combustflame.2026.114810","DOIUrl":"10.1016/j.combustflame.2026.114810","url":null,"abstract":"<div><div>The influence of thermal and differential-preferential diffusion on the flame dynamics and acoustic emission of laminar hydrogen–air slit flames is investigated using two-dimensional direct numerical simulations (DNS) and modal decomposition techniques. Simulations span a range of equivalence ratios (<span><math><mrow><mi>ϕ</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>4</mn></mrow></math></span>–0.7) and diffusion models, including mixture-averaged diffusion with and without the Soret effect and a simplified Unity Lewis number approximation. Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) reveal that dominant hydrodynamic instabilities persist across models, particularly at richer conditions. However, the inclusion of Soret and differential-preferential diffusion modifies the spectral structure of the dominant modes, such that energy is redistributed across higher-order components and a shift in the acoustic peak frequency is induced. These effects occur across all equivalence ratios, but are most evident at intermediate values where competing instabilities increase sensitivity to diffusion-driven modal interactions. At lean conditions, diffusion drives the dominant instability, while at richer conditions it modulates the spectral features of hydrodynamic modes. Neglecting thermal and differential-preferential diffusion fails to capture this behavior, potentially leading to underestimated sound levels at key hydrodynamic frequencies. These findings highlight the importance of detailed diffusion modeling to accurately predict combustion generated noise in hydrogen systems.</div><div><strong>Novelty and significance statement</strong></div><div>The present study is the first to provide a detailed numerical analysis of the effects of differential-preferential and thermal diffusion on the dynamics and acoustic emissions of hydrogen–air slit flames. The novelty of this work lies in two main contributions. First, it demonstrates that diffusion model assumptions can substantially alter predicted instability growth rates and spatial organization in slit flames. Second, it establishes a clear link between these modeling-induced changes in instability behavior and measurable differences in the resulting acoustic field, essential for accurate prediction of flame dynamics and acoustic response.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"286 ","pages":"Article 114810"},"PeriodicalIF":6.2,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075144","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}