Combustion and Flame最新文献

{"title":"Cellular stability of hydrogen–oxygen detonation","authors":"Jonathan Timo Lipkowicz ,&nbsp;Jackson Crane ,&nbsp;Xian Shi ,&nbsp;Irenaeus Wlokas ,&nbsp;Hai Wang ,&nbsp;Andreas Markus Kempf","doi":"10.1016/j.combustflame.2025.114417","DOIUrl":"10.1016/j.combustflame.2025.114417","url":null,"abstract":"<div><div>A detonation cellular stability mechanism based on the dynamics of reactive decaying blasts is examined through detailed analyses of two-dimensional (2D) numerical simulations of hydrogen-oxygen detonations. Different from previous blast-based examinations, we resolve the transient process of decoupling between shock and reaction fronts in decaying blasts, and correlate the size of unburnt gas mixtures behind decaying shocks to that of the subsequent blast kernels. The impact on the stability mechanism of (1) chemical kinetics, (2) diffusive processes, and (3) boundary conditions are examined through a series of simulations. At a dopant level, ozone is known to reduce ignition delay without altering thermodynamic properties of the mixture, enabling investigation of the impact of ignition kinetics on the cellular stability. The addition of ozone leads to a stronger coupling between shock and reaction fronts and stabilizes the blast kernel to a smaller size. The resulting global cell size reduction in the ozonated detonation is well described by the stability analysis and in agreement with experimental cell measurements reported in Crane <em>et al.</em>, <em>Combust. Flame</em> 200 (2019) 44–52. The inclusion of diffusive physics marginally affects the detonation cellular structure, but causes a global propagation speed deficit. Results from two channel heights show that cell size increases in the smaller channel due to mode-locking. A detailed grid convergence study is performed, which examines both kinetic and macroscopic structural features as a function of grid resolution. The results of the stability analysis is independent of numerical grid resolution.</div><div><strong>Novelty and Significance Statement</strong></div><div>This work develops a novel theory for detonation cellular stability, enabling the prediction of detonation cell size and instabilities. Theory validation leverages the statistical analysis of blast propagation and decoupling, which is an entirely new way of post-processing detonation simulation. This work also presents the first time, to our knowledge, the link between molecular viscosity and cellular structure has been isolated, accomplished through a set of simulations using both Navier-Stokes and Euler equations, and several boundary conditions. This work is impactful because it enables and validates the modeling of detonation propagation behavior using a blast-based construct. This blast-based construct is many orders of magnitude less expensive as compared to conventional CFD.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114417"},"PeriodicalIF":6.2,"publicationDate":"2025-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145010141","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":"Consumable embedded microwave Antenna in AP/HTPB propellant to focus energy at the reaction front","authors":"Keren Shi,&nbsp;Erik Hagen,&nbsp;Yujie Wang,&nbsp;Michael R. Zachariah","doi":"10.1016/j.combustflame.2025.114304","DOIUrl":"10.1016/j.combustflame.2025.114304","url":null,"abstract":"<div><div>This study demonstrates a novel method to modulate the burn rate of AP/HTPB propellants by embedding a <em>consumable</em> microwave (MW) antenna, which can be directly coupled to a MW source. The tip of the antenna, which is being consumed, is thus always at the burning surface of the propellant and radiates MW energy to weakly absorbing HTPB. We found a significant increase in burn rate (up to ∼2X), with increasing MW power, despite the fact that the flame temperatures were unaffected. These results indicated that the function of the antenna was restricted to delivering power to the condensed phase. Electric field simulation indicates that the MW energy focused at the burning surface and along the axial direction along the MW antenna. This study shows that focusing on MW energy on the burning surface can be used to modulate burn rate of propellants by embedding a consumable MW antenna.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114304"},"PeriodicalIF":6.2,"publicationDate":"2025-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145004360","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":"On the segregation of NH3 and H2 within the flame front in premixed turbulent combustion of NH3/H2/N2 blends","authors":"Nilanjan Chakraborty ,&nbsp;Ruslan Khamedov ,&nbsp;Hamid Kavari ,&nbsp;Francisco E. Hernández-Pérez ,&nbsp;Hong G. Im","doi":"10.1016/j.combustflame.2025.114455","DOIUrl":"10.1016/j.combustflame.2025.114455","url":null,"abstract":"<div><div>The study analyses the segregation of NH₃ and H₂ in globally lean premixed turbulent flames of NH₃/H₂ fuel blends using direct numerical simulation (DNS) data of statistically planar turbulent flames. Turbulent premixed flames for two fuel blends, 60%NH₃/25%H₂/15%N₂ and 40%NH₃/45%H₂/15%N₂, with an equivalence ratio of 0.81, were examined in the thin reaction zones regime. Differences in chemical reactivity and differential diffusion between NH₃ and H₂ lead to local variations in equivalence ratio within the flame, significantly affecting species distribution compared to one-dimensional (1D) laminar premixed flames. The equivalence ratio variation within the flame causes locally either stoichiometric or fuel-rich pockets despite the globally lean condition in the cases considered here. This also enables localised diffusion mode burning, which is stronger for H₂ in the 60%NH₃/25%H₂/15%N₂ blend, whereas it is stronger for NH₃ in the case of 40%NH₃/45%/15%N₂ H₂ blend. The transition from lean premixed to non-premixed combustion at the rear end of the flame leads to the misalignment of the normal vectors of NH₃, H₂, and temperature isosurfaces, impacting reaction-diffusion balance. The displacement speeds of H₂ isosurfaces exceed those of NH₃, leading to differences in effective normal strain rates, which along with local equivalence ratio variation, influence the behaviour of the scalar gradient magnitude. These findings suggest that the modelling of premixed combustion of NH₃/H₂ blends must account for variable equivalence ratio combustion and non-premixed burning mode, even for globally lean mixtures.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114455"},"PeriodicalIF":6.2,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145004358","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 oxidation-chemistry of iso-propanol and tetrahydrofuran blends using a jet-stirred reactor","authors":"Meenu Sharma,&nbsp;Mengdi Li,&nbsp;Solmaz Nadiri,&nbsp;Ajoy Ramalingam,&nbsp;Bo Shu,&nbsp;Ravi Fernandes,&nbsp;Kai Moshammer-Ruwe","doi":"10.1016/j.combustflame.2025.114365","DOIUrl":"10.1016/j.combustflame.2025.114365","url":null,"abstract":"<div><div>Decarbonizing the aviation sector is crucial for meeting global climate goals, with a strong emphasis on reducing emissions from long-range flights where liquid fuels are indispensable. Synthetic fuels or e-fuels have emerged as a promising solution for sustainable aviation. This study explores the oxidation chemistry of fuel blends consisting of <em>iso</em>-propanol and tetrahydrofuran (THF), two liquid e-fuels that show potential for use in energy-efficient aviation. By utilizing a jet-stirred reactor (JSR) coupled with a Time-of-Flight Mass Spectrometer (TOF-MS), the study examines the oxidation behavior of these fuels, both individually and in blends, under controlled temperature and pressure conditions. Experiments were conducted over a temperature range of 500 to 1200 K, at a pressure of 1 bar, and with lean fuel-air mixtures (<em>ϕ</em> = 0.5). These conditions are typical for lean premixed pre-vaporized (LPP) combustion systems, commonly used in gas turbines to lower NO_x and soot emissions. The results highlight a critical reactivity threshold for THF at low temperatures, below which its oxidation ceased, particularly at mole fractions &lt;0.0035. The presence of <em>iso</em>-propanol in the blends further influenced the oxidation behavior: at low temperatures, <em>iso</em>-propanol suppressed THF’s reactivity by forming stable acetone. In contrast, at higher temperatures, <em>iso</em>-propanol enhanced overall reactivity by promoting radical formation, converting acetone to ketene, and facilitating significant propene production through primary isopropyl radical channels. This study reveals the intricate chemical interactions between <em>iso</em>-propanol and THF, offering critical insights into their oxidation mechanisms, with a particular focus on the low-temperature reactivity pathways of <em>iso</em>-propanol.</div><div><strong><em>Novelty and significance statement:</em></strong> This study explores the testing of novel fuels for Lean Premixed Pre-vaporized (LPP) combustion, focusing on the oxidation chemistry of <em>iso</em>-propanol and tetrahydrofuran (THF) as alternative fuels. The research examines the low-temperature reactivity of <em>iso</em>-propanol and THF, both individually and in blends, using a Jet-Stirred Reactor (JSR). Notably, it provides the first detailed low temperature analysis of <em>iso</em>-propanol’s reactivity without the addition of oxidizers like O₃. The study reveals unique suppression mechanisms and temperature-dependent shifts in reaction pathways when the fuels are blended. Through experimental testing and kinetic modeling, the research refines predictive existing models, advancing the understanding of these fuels for cleaner and more efficient combustion applications.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114365"},"PeriodicalIF":6.2,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144989055","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":"Microscale impact response characteristics of ε-CL-20: A multiscale simulation study with coupled force fields","authors":"Shu Ren ,&nbsp;Wei Yang ,&nbsp;Qiang Gan ,&nbsp;Min Xia ,&nbsp;Yajun Wang ,&nbsp;Gen Li ,&nbsp;Chengjie Tong ,&nbsp;Lin Liang ,&nbsp;Wenbo Zhang","doi":"10.1016/j.combustflame.2025.114441","DOIUrl":"10.1016/j.combustflame.2025.114441","url":null,"abstract":"<div><div>Exploring the microscopic mechanism of critical initiation conditions is a challenging task in shock research on energetic materials. Herein, a multiscale impact simulation of hexanitrohexaazaisowurtzitane (<em>ε</em>-CL-20) was conducted within a velocity range of 8.0∼10.0 km/s by coupling the NNP-SHOCK force field with the ReaxFF-lg force field. Using peak pressure as a stage division indicator, the impact initiation process was quantitatively divided into two stages: impact compression and intense reaction. Among the large variety of <em>ε</em>-CL-20 decomposition products, CO₂ content was identified as a key metric to reflect the initial reaction process of <em>ε</em>-CL-20, rather than the initial product NO₂. The correlation between the change in CO₂ quantity and the change in unit cell pressure is particularly high when the shock wave velocity is below the critical shock initiation velocity (9.1 km/s) of CL-20. Correspondingly, the calculated critical decomposition rate of CL-20 reaches 9.451 ps^-1 when subjected to a critical detonation velocity. In addition, reaction network diagrams of <em>ε</em>-CL-20 and its typical final products (CO₂, H₂O, and N₂) were drawn to clarify the initial transformation pathways of <em>ε</em>-CL-20 and to determine the intrinsic relationships among the chemical reactions of CO₂, H₂O, and N₂.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114441"},"PeriodicalIF":6.2,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144996530","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 investigation of a detonation-assisted fuel injection system in supersonic crossflow","authors":"Moeno Miyashita ,&nbsp;Akiko Matsuo ,&nbsp;Eiji Shima ,&nbsp;Noboru Itouyama ,&nbsp;Akira Kawasaki ,&nbsp;Ken Matsuoka ,&nbsp;Jiro Kasahara","doi":"10.1016/j.combustflame.2025.114442","DOIUrl":"10.1016/j.combustflame.2025.114442","url":null,"abstract":"<div><div>A novel detonation-assisted fuel injection system was developed in this study to achieve highly efficient supersonic combustion in scramjet engines. In this configuration, a Rotating Detonation Combustor (RDC) with an annular shape was coaxially employed around the main fuel injector, where hydrogen was injected perpendicular to the supersonic airflow. The computational domain consisted of a three-dimensional rectangular region, into which a Mach 2.4 supersonic flow was introduced to simulate flight conditions corresponding to Mach 8.0 at an altitude of 30 km. The main fuel injector and the RDC were coaxially connected to the isothermal lower wall of the scramjet engine. In the RDC, a stoichiometric premixed H₂–O₂ mixture was supplied from the bottom to generate a detonation wave. The compressible Navier–Stokes equations were solved under unsteady conditions. As a result, a detonation wave propagated continuously within the RDC, even when connected to the combustor section exposed to the supersonic main stream. The detonation products, accelerated to supersonic speeds, were discharged together with the main fuel into the scramjet combustor. This configuration generated large-scale vortex structures in the main stream, leading to a combustion efficiency up to 1.9 times higher and a 56% reduction in combustor length. This enhancement was primarily attributed to the high-enthalpy detonation products containing reactive radicals, which assisted main fuel penetration, increasing the penetration height by approximately 85%. Furthermore, high-frequency pressure disturbances with helically distributed spatial patterns were observed on the lower wall of the scramjet combustor, which were considered to contribute to combustion enhancement. These results demonstrate the effectiveness of detonation-assisted injection and highlight its potential as a solution to the long-standing challenges of stable and efficient combustion in supersonic propulsion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114442"},"PeriodicalIF":6.2,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144989056","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":"Preferential vaporization effects on multicomponent n-dodecane/iso-octane non-premixed spray cool flames","authors":"Wenbin Xu ,&nbsp;Bowen Mei ,&nbsp;Ziyu Wang ,&nbsp;Martin A. Erinin ,&nbsp;Andy Thawko ,&nbsp;Luc Deike ,&nbsp;Yiguang Ju","doi":"10.1016/j.combustflame.2025.114453","DOIUrl":"10.1016/j.combustflame.2025.114453","url":null,"abstract":"<div><div>Experimental and numerical studies are performed on the non-premixed <em>n</em>-dodecane/<em>iso-</em>octane spray flames to investigate the effects of preferential vaporization on cool flame extinction and the repetitive autoignition-extinction instability. A well-defined counterflow burner is employed for cool flame studies. Inline holography is used to measure the spray size distribution and the mean droplet diameter, where d₃₂ is 167 <em>μm</em>. Gas chromatography is used to measure the vaporized fuel concentrations. The preferential vaporization is demonstrated by the increased <em>n</em>-dodecane to <em>iso</em>-octane ratio along the centerline from the spray nozzle. The extinction limits of cool flames are examined with three <em>n-</em>dodecane/<em>iso</em>-octane blending ratios at two temperatures respectively below and above the fuel boiling points. It is shown that at the lower temperature of 450 K, the increased preferential vaporization of <em>iso</em>-octane weakens more the low-temperature reactivity of the <em>n</em>-dodecane vapor mixture and leads to a greater decrease in the extinction limits with the increase of the blending ratio compared to pre-vaporized gas cool flames. The repetitive autoignition-extinction instability is examined by measuring the frequency distribution of spray cool flame stabilization time at a near-limit strain rate of 100 s^-1 for the pure <em>n</em>-dodecane and the blended fuel. The temperature rise on the fuel side promotes the preferential vaporization, causing more <em>iso</em>-octane released in the early gasification, which amplifies the instability at higher temperature. One-dimensional monodisperse spray cool flame simulations are performed across a wide range of spray sizes under the measured boundary conditions. With preferential vaporization, most <em>iso</em>-octane vaporizes outside the flame region and the subsequently released <em>n</em>-dodecane vapor is concentrated in the reaction zone for the droplets below 100 <em>μm.</em> For large droplets over 150 <em>μm</em>, more <em>iso-</em>octane is introduced to the reaction zone and the <em>n</em>-dodecane vapor is more dispersed along the droplet trajectory. The present results demonstrate the significant impacts of preferential vaporization on the low-temperature combustion of multicomponent spray. These results will contribute to the advancement of low-temperature combustion technologies with practical liquid fuels.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114453"},"PeriodicalIF":6.2,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144989054","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":"Advancing 3D understanding of aluminum agglomerates in propellant environment using reconstruction techniques","authors":"Lu Liu ,&nbsp;Geng Xu ,&nbsp;Yao Shu ,&nbsp;Guoqiang He ,&nbsp;Peijin Liu ,&nbsp;Wen Ao","doi":"10.1016/j.combustflame.2025.114448","DOIUrl":"10.1016/j.combustflame.2025.114448","url":null,"abstract":"<div><div>Aluminum is commonly used in solid propellants to enhance energy density, but it tends to form large agglomerations during combustion, leading to incomplete combustion and reduced propulsion efficiency. To better understand the agglomeration and combustion behavior of aluminum particles, we developed a dual-perspective high-speed microscopic imaging system that captures the evolution of agglomerations from two aligned viewpoints. A two-step unsupervised segmentation algorithm based on K-means clustering and a Neural Radiance Field (NeRF)-based reconstruction framework were employed to resolve the 3D distribution of molten aluminum droplets and oxide caps. The results revealed a linear increase in the oxide-to-metal ratio over time. A combustion model was further developed to describe the burning process of aluminum particles in multi-component oxidizing atmospheres, incorporating O₂, CO₂, and H₂O as oxidants. The model assumes diffusion-limited combustion with oxide deposition, and was validated against literature and experimental data, showing good agreement in predicting particle size evolution and burning time. Sensitivity studies showed that oxidizer concentration has a significantly greater impact on combustion rate than temperature. The proposed imaging and modeling approach improves the understanding of aluminum agglomerate evolution in realistic propellant environments, and provides valuable guidance for optimizing propellant formulations to reduce incomplete combustion and improve solid rocket motor performance.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114448"},"PeriodicalIF":6.2,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144932736","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 aluminum, iron, and zirconia additives on the combustion of boron","authors":"Mysha Momtaz,&nbsp;Jonathan L. McNanna,&nbsp;Purvam Gandhi,&nbsp;Mirko Schoenitz,&nbsp;Edward L. Dreizin","doi":"10.1016/j.combustflame.2025.114446","DOIUrl":"10.1016/j.combustflame.2025.114446","url":null,"abstract":"<div><div>Spherical composite powders with particle sizes around 10 µm, combining boron and aluminum, were prepared by emulsion-assisted milling. Powders milled using the steel and zirconia milling media were contaminated by iron and zirconia, respectively. Some powders used small amounts of Fluorel® as a binder. The oxidation of the prepared powders heated in an Ar/O₂ gas flow was studied using thermal analysis. The ignition temperature in air was determined using an electrically heated filament. Prepared powders were blended with KNO₃ as an oxidizer and ignited using a CO₂ laser beam. The powders were also injected into a closed vessel and burned as an aerosol. The results show no effect of Fluorel® or zirconia contamination on the powder reactivity. The added iron causes a reduction in the oxidation onset temperature, whereas added aluminum increases that temperature. Both added iron and aluminum cause a reduction in the flame temperature and suppress the formation of the vapor-phase intermediate BO₂. A reduced flame temperature delays the aerosol flame propagation rate. The powder morphology achieved by emulsion-assisted milling enhances the powder reactivity, as is evidenced by reduced ignition temperatures and accelerated rate of flame propagation for the milled powders containing no iron or aluminum.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114446"},"PeriodicalIF":6.2,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144926321","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":"Propagation of ultra-lean hydrogen/air flames in a Hele-Shaw cell","authors":"Linlin Yang ,&nbsp;Yan Wang ,&nbsp;Tianhan Zhang ,&nbsp;Xiaolong Gou ,&nbsp;Wenjun Kong ,&nbsp;Zheng Chen","doi":"10.1016/j.combustflame.2025.114444","DOIUrl":"10.1016/j.combustflame.2025.114444","url":null,"abstract":"<div><div>Ultra-lean hydrogen flame is closely related to hydrogen safety. Recently, different types of hydrogen flame have been observed in experiments under ultra-lean conditions. However, the evolution and propagation of ultra-lean hydrogen flames are still not well understood. In this study, 3D simulations considering detailed chemistry and transport models are conducted for ultra-lean premixed hydrogen/air flames propagating in an open Hele-Shaw cell with isothermal walls. It is found that ultra-lean hydrogen flames are very sensitive to equivalence ratio, <em>ϕ</em>. As <em>ϕ</em> decreases from 0.225 to 0.21, different cellular flame regimes, including two-headed branching, two-headed finger and one-headed finger (ball-like flame) are sequentially observed. The cell size shows a decreasing tendency. Isolated ball-like flames and two-headed finger are stable in the ultra-lean mixture. During the flame cell propagation, both heat loss and heat release exhibit oscillatory characteristics since they are correlated with each other. The oscillation frequency is found to increase with <em>ϕ</em>. In order to balance the conductive heat loss to walls, two-headed flames split while isolated ball-like flames shrink, resulting in periodic changes in flame surface area and heat release rate. Moreover, ultra-lean flames are found to be characterized by high local equivalence ratio caused by strong differential diffusion of hydrogen over other species, highlighting the effect of diffusional-thermal instability (DTI) on sustaining the ultra-lean flame. Furthermore, stable ball-like flames and two-headed finger can exist simultaneously. Interestingly, flame instabilities play a stabilizing role in the ultra-lean flames. Darrieus-Landau instability (DLI) contributes to the stabilization of two-headed finger flames with strong mutual interaction between adjacent cells, whereas ball-like flames dominated by DTI tend to move away from each other to gain deficient fuel and drift in a zigzag manner. The present 3D simulations help to understand flame cell propagation and stabilization in ultra-lean hydrogen/air mixture within an open Hele-Shaw cell.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114444"},"PeriodicalIF":6.2,"publicationDate":"2025-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144922926","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}