Combustion and Flame最新文献

{"title":"Ignition of micron amorphous boron particles in CO2 with shock tube","authors":"Shengyu Pang ,&nbsp;Kai Pang ,&nbsp;Long Miao ,&nbsp;Yugan Liao ,&nbsp;Xiao Hou ,&nbsp;Baolu Shi","doi":"10.1016/j.combustflame.2025.114311","DOIUrl":"10.1016/j.combustflame.2025.114311","url":null,"abstract":"<div><div>This study successfully ignited 11 μm amorphous boron (B) powder in a pure carbon dioxide (CO₂) atmosphere using a shock tube ignition platform, providing important insights for CO₂-B reaction which was generally neglected in propulsion system. The experiments were conducted at temperatures ranging from 2100 to 2900 K and 3.5 atm, focusing on the effects of temperature and CO₂ concentration on the ignition characteristics. The results show that the ignition delay time decreases with increasing temperature. And the critical ignition temperature of boron was found to beyond 2100 K. The effects of CO₂ concentration on the ignition delay time and critical ignition temperature were much complex. These findings provide new data on boron ignition characteristics in CO₂ environments, offering valuable reference information for CO₂ propulsion technologies in space exploration.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114311"},"PeriodicalIF":5.8,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144364923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A numerical method for the multidimensional hydrodynamic model of flames propagating in closed vessels","authors":"Gautham Krishnan ,&nbsp;Carlos Pantano ,&nbsp;Moshe Matalon","doi":"10.1016/j.combustflame.2025.114283","DOIUrl":"10.1016/j.combustflame.2025.114283","url":null,"abstract":"&lt;div&gt;&lt;div&gt;A numerical methodology has been developed to simulate the evolution of multidimensional premixed flames in closed vessels. The mathematical formulation is based on a hydrodynamic theory, wherein the flame is a surface of discontinuity that separates burned products from unburned gas. The flame front propagates into a mixture which is continuously compressed, causing a rise in pressure and temperature that affects the flow field and modifies the local burning rate. The latter depends on the voluminal stretch rate, which combines the effects of local variations in flame front curvature, flame thickness and hydrodynamic strain, and on the rate of the overall pressure rise. The burning rate is modulated by an effective pressure-dependent Markstein length, that exhibits a dependence on the extent of heat release and diffusion properties of the reactants, and decreases continuously as the pressure rises and the flame becomes thinner. A hybrid embedded-manifold/Navier–Stokes methodology is proposed to numerically solve this free-boundary hydrodynamic problem. It consists of two modules; the first involves solving the fluid dynamic equations and the second employs a level-set approach to advance the flame front in time. The two modules are coupled through a mass conservation constraint and a high-order geometrical closest point method used to evaluate fluid dynamical and geometrical quantities defined strictly on the flame surface. An immersed boundary method is utilized to implement boundary conditions at the walls of vessels of arbitrary shape. The numerical approach is validated against exact analytical solutions of planar and cylindrical flames, and is shown to describe highly corrugated flame conformations resulting from intrinsic combustion instabilities, in rectangular and circular domains. The methodology is adept at developing a comprehensive understanding of the effects of instabilities and low-intensity turbulence on the propagation of premixed flames in closed vessels.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This paper is based on a novel hydrodynamic theory that describes the propagation of premixed flames in closed vessels of arbitrary shapes, wherein the flame is treated as a surface of discontinuity. The nontrivial free-boundary problem is solved by an advanced numerical methodology that consists of two coupled modules: a variable-density Navier–Stokes solver for determining the flow field, and a level-set approach for tracking the evolution of the flame. It is the first such methodology that accounts for the continuous rise in pressure and temperature due to adiabatic compression, and for the dependence of the flame speed on a pressure-dependent Markstein length. The methodology is sufficiently robust and adept at handling multidimensional flames. It has been validated by comparing numerical results of planar and cylindrical flames against exact analytical solutions and has been shown to describ","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114283"},"PeriodicalIF":5.8,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144364924","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 and modeling of NOx formation in pulverized biomass flames under air and oxyfuel conditions","authors":"Pooria Farmand ,&nbsp;Christian Boehme ,&nbsp;Pascal Steffens ,&nbsp;Hendrik Nicolai ,&nbsp;Francesca Loffredo ,&nbsp;Paulo Debiagi ,&nbsp;Sanket Girhe ,&nbsp;Hongchao Chu ,&nbsp;Michael Gauding ,&nbsp;Christian Hasse ,&nbsp;Heinz Pitsch","doi":"10.1016/j.combustflame.2025.114284","DOIUrl":"10.1016/j.combustflame.2025.114284","url":null,"abstract":"&lt;div&gt;&lt;div&gt;In this study, NO&lt;sub&gt;x&lt;/sub&gt; formation pathways in biomass combustion in air and oxy-atmospheres are investigated by direct numerical simulations. Solid biomass fuels contain fuel-bound nitrogen, which contributes to NO&lt;sub&gt;x&lt;/sub&gt; formation and complicates NO&lt;sub&gt;x&lt;/sub&gt; predictions. The NO&lt;sub&gt;x&lt;/sub&gt; formation pathways and modeling of NO&lt;sub&gt;x&lt;/sub&gt; formation in biomass combustion are not fully understood, necessitating further investigation through detailed kinetic models. Reactive biomass simulations are performed in a drop tube configuration under laminar conditions, considering the detailed NO&lt;sub&gt;x&lt;/sub&gt; chemistry for both the solid fuel and the gas phase. To this end, the detailed CRECK-S kinetic scheme is employed for the solid phase. In addition, due to the lack of biomass-specific gas-phase kinetic models in the literature, particularly in terms of the released biomass volatiles and their impact on NO&lt;sub&gt;x&lt;/sub&gt; formation pathways, a special gas-phase kinetic model, including the NO&lt;sub&gt;x&lt;/sub&gt; formation pathways for biomass combustion, is designed and utilized in the simulations. NO&lt;sub&gt;x&lt;/sub&gt; formation in solid fuel flames can be affected by several parameters, such as solid fuel type and composition, particle injection rate, and ambient conditions. The current study assesses the sensitivity of NO&lt;sub&gt;x&lt;/sub&gt; formation to these parameters. In particular, a detailed pathway analysis is performed to identify the contributions of fuel-related and thermal pathways on the total NO&lt;sub&gt;x&lt;/sub&gt; formation. Finally, the released volatile composition effect on NO&lt;sub&gt;x&lt;/sub&gt; formation is evaluated using the fixed volatile composition assumption, which is required in flamelet-based reduced-order modeling of solid fuel combustion using simplified solid kinetic models, in comparison with the dynamically released volatiles predicted from detailed solid fuel kinetics. An improved approach for the fixed volatile composition formulation is proposed.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;In this work, NO&lt;sub&gt;x&lt;/sub&gt; formation pathways were numerically investigated during solid pulverized biomass combustion under different operating conditions using detailed chemical kinetic models for both solid and gas phases. Using the detailed numerical framework, the impact of fixed volatile composition on NO&lt;sub&gt;x&lt;/sub&gt; formation, which is the required assumption for reduced-order flamelet tabulated chemistry models, was evaluated. The novelty and significance of this work can be summarized in two points. First, the new chemical kinetic model containing the biomass-relevant chemistry based on the released volatile species from biomass enabled the detailed pathway analysis under different operating conditions. Second, the drawbacks of the FVC assumption in predicting NO&lt;sub&gt;x&lt;/sub&gt; were discovered, and a novel formulation was introduced for correctly capturing the NO&lt;sub&gt;x&lt;/sub&gt; pollutants. This is of critical import","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114284"},"PeriodicalIF":5.8,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144364925","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":"LES-FGM modelling of non-premixed auto-igniting turbulent hydrogen flames including preferential diffusion","authors":"A. Ballatore,&nbsp;D. Quan Reyes,&nbsp;H. Bao,&nbsp;J.A. van Oijen","doi":"10.1016/j.combustflame.2025.114270","DOIUrl":"10.1016/j.combustflame.2025.114270","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Tabulated chemistry methods are a well-known strategy to efficiently store the flow thermochemical properties. In particular, the Flamelet-Generated Manifold (FGM) is a widely used technique that generates the database with a small number of control variables. In order to build such a manifold, these coordinates must be monotonic in space and time. However, the high diffusivity of hydrogen can prevent such requisite. There have been many studies that successfully included non-unity Lewis effects in FGM, but mostly in the context of premixed flames. The problem of accounting for differential diffusion in purely non-premixed auto-igniting hydrogen flames still has to be investigated thoroughly. To avoid the non-monotonicity of control variables (the progress variable, in particular), one practical workaround is to perform the tabulation on zero-dimensional (0D) reactors rather than on one-dimensional (1D) flamelets. Various works already implemented and tested such 0D-based manifold, but mainly in the context of spray engines, where most of the composition is lean and information past the flammability limit is not relevant. The present work aims at investigating, for the first time, the applicability of a tabulation based on homogeneous reactors to study auto-igniting turbulent hydrogen jets.&lt;/div&gt;&lt;div&gt;Three different techniques to extrapolate the data beyond the flammability limit are evaluated in 1D simulations and assessed against detailed chemistry results. It is shown that a combined use of homogeneous reactors at the lean side and an extrapolation with 1D flamelets on the richer side is required to capture both chemistry and diffusive effects accurately in pure hydrogen flames. Then, this manifold is coupled to Large-Eddy Simulation (LES) of three-dimensional turbulent temporal evolving planar jets and evaluated against direct numerical simulation with detailed chemistry. Good agreement is found, in terms of both ignition delay and the following steady-state burning process. Further analyses are carried out on statistics and modelling. In particular, the sensitivity of the LES solution to filter width, turbulence-chemistry interaction and multidimensional flame effects is investigated to provide new relevant insights on modelling non-premixed auto-igniting turbulent hydrogen flames.&lt;/div&gt;&lt;div&gt;Novelty and Significance Statement&lt;/div&gt;&lt;div&gt;The novelty of this research is represented by a detailed and systematic numerical study on turbulent non-premixed auto-igniting hydrogen flames by means of tabulated chemistry, including preferential diffusion. There have been works that successfully accounted for non-unity Lewis effects in tabulated chemistry, but mainly in the context of premixed flames. As regards non-premixed flames, few works included preferential diffusion, but did not model any igniting phenomena at all. In order to conduct such work, we rely on a manifold based on homogeneous reactors (HR-FGM). This is the first time that su","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114270"},"PeriodicalIF":5.8,"publicationDate":"2025-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144330500","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":"One-dimensional flame subject to periodic and sinusoidal motion: frequency domain analysis and flame-motion contribution to combustion instability","authors":"Aurelien Genot ,&nbsp;Stéphane Boulal ,&nbsp;Jean-Michel Klein ,&nbsp;Axel Vincent-Randonnier ,&nbsp;Arnaud Mura","doi":"10.1016/j.combustflame.2025.114285","DOIUrl":"10.1016/j.combustflame.2025.114285","url":null,"abstract":"<div><div>Combustion instabilities are often an outcome of the interaction between fluctuations in the flame-induced heat release rate (HRR) and acoustic modes of the combustor. Thus, they are a direct consequence of the flame unsteady dynamics, which itself features multiple contributions. The present study is focused on one of them, namely that of the flame motion. Two distinct spatial distributions of the HRR subject to a periodic and sinusoidal motion (slower than the speed of sound) are analyzed in terms of its normalized motion amplitude. For these two distributions, a frequency domain analysis is conducted and the presence of peaks at the motion frequency, together with higher harmonics, are put into evidence. Thus, it is established that, even in (i) a simplified one-dimensional situation and (ii) with a slow periodic and sinusoidal motion featuring moderate amplitudes, flame motions can drive an energy transfer from the fundamental frequency to upper harmonics. This serves as a basis for the development of a simplified model, which is found able to retrieve the corresponding response in terms of its fundamental and harmonic frequencies. Flame-flow couplings are subsequently analyzed on the basis of stability criteria based on the Rayleigh index, the Chu index and a nonlinear index. This leads to the identification of a threshold value of the normalized motion amplitude with the flame motion contribution acting either as a source term below this value or as a damping term once it is exceeded.</div><div><strong>Novelty and significance</strong></div><div>This manuscript is focused on the flame motion contribution to flame dynamics and brings some new insights to the current state of the art: (i) for a periodic and sinusoidal motion, the flame response displays several harmonics that are triggered regardless of the motion amplitude and HRR distribution, (ii) a nonlinear and multi-harmonic model of the HRR fluctuations is presented for a boxcar HRR distribution moving periodically, and (iii) a threshold amplitude of the order of twenty times the flame thickness defines the flame motion contribution to combustion instabilities.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114285"},"PeriodicalIF":5.8,"publicationDate":"2025-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335878","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":"Quantitative measurement of aluminum atom number density around a burning micron-sized aluminum droplet using spatially resolved laser absorption spectroscopy","authors":"Can Ruan ,&nbsp;Zhiyong Wu ,&nbsp;Yue Qiu ,&nbsp;Edouard Berrocal ,&nbsp;Marcus Aldén ,&nbsp;Xue-Song Bai ,&nbsp;Zhongshan Li","doi":"10.1016/j.combustflame.2025.114297","DOIUrl":"10.1016/j.combustflame.2025.114297","url":null,"abstract":"<div><div>In this study, we demonstrate a successful application of laser absorption spectroscopy in an in-situ optical diagnostic system to map the radial distribution of the number density of vapor-phase aluminum (Al) atoms around a burning micron-sized Al droplet. This technique overcomes the challenges associated with the short optical path (at micron scale) and offers high sensitivity to Al atom concentration variations. Results indicate that the number density of Al atoms decreases sharply from ∼1.1 × 10²²/m³ within <em>r</em>/<em>r</em>₀ = 1.2∼1.4 (<em>r</em>₀ is the radius of the Al droplet and <em>r</em> is the distance from the center of the droplet) to ∼4.0 × 10²¹/m³ within <em>r</em>/<em>r</em>₀ = 1.4∼1.6, prior to the formation of the Al₂O₃ condensation layer (<em>r</em>/<em>r</em>₀ = 1.6∼1.9). This largest decline rate in the radial direction indicates the ‘flame front’ location. Additionally, a substantial number of Al atoms, i.e., at the scale of 10¹⁹∼10²¹/m³, are still present beyond the Al₂O₃ condensation layer, and their number densities continue to decrease further outwards gradually. This result agrees with the trend predicted by our detailed numerical simulation. Moreover, it is shown that the produced Al₂O₃ droplets are stable, as no detectable absorption signals from Al atoms can be found from the Al₂O₃ droplet dissociation even at ∼3500 K. In addition, as we used the radial temperature profiles obtained from simulations to correlate the number densities of Al atoms in different ground states, an uncertainty analysis was performed. It was shown that this might introduce a maximum uncertainty of 1.84 % in the total Al atom number density. To the awareness of the authors, this work represents the first quantitative in-situ measurement of the Al atom number density around a burning micron-sized Al droplet.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114297"},"PeriodicalIF":5.8,"publicationDate":"2025-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144330499","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":"Extinction behavior of a partially premixed flame and a nonpremixed flame in turbulent counterflow","authors":"Fernando M. Pereira ,&nbsp;Francesco Carbone ,&nbsp;Jonathan H. Frank ,&nbsp;Bruno Coriton ,&nbsp;Philip Wang ,&nbsp;Alessandro Gomez","doi":"10.1016/j.combustflame.2025.114268","DOIUrl":"10.1016/j.combustflame.2025.114268","url":null,"abstract":"<div><div>The present study experimentally investigates non-flamelet behavior leading to extinction in a NonPremixed Flame (NPF) and a Partially Premixed Flame (PPF) in a turbulent counterflow configuration. Both flames at Re_t∼ 900 are indistinguishable in terms of the turbulence properties that are imposed at the cold boundaries and persist up to the mixing layer. For each extinction event, the perturbation that leads to the first breach of the OH layer is tracked back in time in a Lagrangian manner using high-speed stereoscopic PIV and OH-PLIF imaging techniques, allowing the reconstruction of the time sequence of strain rate and vorticity that leads to flame extinction. The NPF is found to be more prone to extinction than the PPF, which is at odds with the computed laminar extinction strain rate, which is 23 % larger in the NPF than in the PPF, implying a greater resistance to strain for the NPF. Extinction appears to be caused by a combination of relatively intense strain rate and/or vorticity pockets interacting with the flame and causing a tear of the OH layer. The <em>maximum</em> strain rate norm exceeds the computed extinction limit in &gt;85 % of the cases for the PPF, whereas it does so in approximately 75 % of the cases for the NPF, revealing a more pronounced strain rate effect on the extinction process for the PPF. Vorticity plays multiple roles in extinction. It manifests itself as: i) a pair of counterrotating vortices approaching the flame from either or both sides, creating a region of high strain rate; ii) a single vortex interacting with the flame by diluting the reactants with inert, thereby, weakening the flame; and iii) a vortex penetrating the oxidizer layer, making it thicker and, possibly, disrupting the laminar flame structure. The last two scenarios may explain extinction without a history of remarkably high strain rates. A 35 % reduction in the overall strain rate of the flames resulted in nearly complete suppression of extinction events in both PPF and NPF.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114268"},"PeriodicalIF":5.8,"publicationDate":"2025-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A comparative analysis of plasma and hydrogen effects on premixed ammonia combustion","authors":"Mohammad Shahsavari ,&nbsp;Nilanjan Chakraborty ,&nbsp;Alexander A. Konnov ,&nbsp;Shenghui Zhong ,&nbsp;Agustin Valera-Medina ,&nbsp;Mehdi Jangi","doi":"10.1016/j.combustflame.2025.114300","DOIUrl":"10.1016/j.combustflame.2025.114300","url":null,"abstract":"<div><div>In this study, we use direct numerical simulations to investigate turbulent premixed ammonia flames assisted by non-equilibrium nanosecond plasma discharges and hydrogen addition. The results reveal the coupling effects of turbulence, the hydrogen concentration in the fuel blend, and plasma discharges on the microscopic structure of the flame and chemical pathways. It is found that the flame front assisted by plasma is more distributed, whilst 58 % less stretched when compared to the hydrogen-enriched un-assisted flame. Additionally, turbulence has more pronounced effects on the hydrogen-enriched flame, broadening the flame brush. A comparison of the reaction pathways contributing to the heat release indicates that turbulence shifts the key reactions producing heat from HNO+<em>H</em>⬄NO+H₂ and OH+H₂⬄<em>H</em> + H₂O to NH₂ dissociation reactions. Additionally, NOx emissions are more influenced by thermal effects in the hydrogen-enriched flame, with NO concentration being 35 % higher than in the plasma-assisted flame. The higher NOx emissions in the hydrogen-enriched flame are attributed to the higher concentration of H radicals, which react with HNO and produce NO.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114300"},"PeriodicalIF":5.8,"publicationDate":"2025-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144313739","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 laminar burning velocity of hybrid iron-methane-air flames","authors":"M.R. Hulsbos,&nbsp;R.T.E. Hermanns,&nbsp;R.J.M. Bastiaans,&nbsp;L.P.H. de Goey","doi":"10.1016/j.combustflame.2025.114274","DOIUrl":"10.1016/j.combustflame.2025.114274","url":null,"abstract":"<div><div>Iron combustion has gained a lot of traction in the last decade since it was proposed as a CO₂-emission-free energy carrier. To make this novel technology feasible, better understanding of iron combustion process is needed. The laminar burning velocity <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></math></span> of iron-particle-laden flames is an important parameter that can reveal a lot about the governing properties of the combustion process of these iron particles. However, the amount of experimental data on the burning velocity of iron flames is limited. Recently, (Hulsbos et al., 2024) proposed the Heat Flux Method (HFM) as a way to measure the burning velocity of hybrid-iron-methane-air flames with a stoichiometric methane-air equivalence ratio as base as a first step in producing experimental data of <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>L</mi></mrow></msub></math></span> in iron-laden flames. This work advances on the work from Hulsbos et al. and extends the measurements to hybrid iron-methane-air flames with a lean methane-air flame as base. By comparison with SiC particles and simulations, it is found that at low iron particle concentrations the iron acts as a heat sink and also interferes chemically with the methane-air flame, significantly reducing the burning velocity of the hybrid flame. For high iron particle concentrations within the flame the iron becomes the dominant fuel and an asymptotic burning velocity is reached. This asymptotic burning velocity is shown to be independent of both the iron or methane content in the flame.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this study is the extension of the recently presented burning velocities to hybrid flames by Hulsbos et al. (2024) to cases with a lean methane-air flame as a basis and a comparison with inert SiC particles. From this extensive range of experimental data, a hypothesis of iron-burning behaviour in a methane flame is produced. Two clear flame regimes are identified: One where the methane-air dominates the burning velocity, and one where the iron powder dominates the burning velocity. This work also shows at what conditions hybrid iron-methane-air flames transitions from one regime to the other, and elaborates on the consequences of this regime transition with respect to the burning velocity of the hybrid iron methane-air flames. The results from this can be used to validate models considering iron combustion and significantly increases the knowledge about the combustion behaviour of micron-sized iron particles.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114274"},"PeriodicalIF":5.8,"publicationDate":"2025-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322654","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":"Turbulence-chemistry interactions in piloted partially premixed cracked ammonia-air flames with high Reynolds numbers","authors":"Hao Tang ,&nbsp;Zeinab Al Hadi ,&nbsp;Robert Barlow ,&nbsp;Gaetano Magnotti","doi":"10.1016/j.combustflame.2025.114303","DOIUrl":"10.1016/j.combustflame.2025.114303","url":null,"abstract":"<div><div>This study investigates turbulence-chemistry interactions in piloted NH₃/H₂/N₂-air flames at Reynolds numbers of 24,000, 32,000, and 36,000, referred to as Flames D, E, and F, respectively. Raman/Rayleigh scattering and NH₂/OH-LIF measurements are used to analyze flame structure in mixture fraction and temperature space as well as physical space. Probability density functions (PDFs) provide insights on local extinction behavior, while conditional means of the NH₃/H₂ ratio yield insights on differential diffusion. With increasing Re, the flames exhibit stronger entrainment, leading to higher fluctuations in the outer shear layers between the piloted products and coflow air in the near-field (<em>Z/D</em> = <em>1-2</em>). At <em>Z/D &gt; 15,</em> enhanced turbulent mixing at higher Re results in lower NH₃, H₂, mixture fraction, OH, and NH₂ downstream. The local extinction probability increases with Re, with significant extinction observed in Flames E and F. Three distinct reaction zones are identified, corresponding to peak OH, peak temperature, and peak NH₂. Extinction initially occurs in the fuel-lean side, followed by the fuel-rich side. Reignition occurs earlier in Flame E (by <em>Z/D</em> = 10), whereas in Flame F, it is delayed until <em>Z/D</em> = <em>20</em>. The flame structure reveals a balance between differential diffusion effects and turbulent mixing in the fuel-rich regions for all three flames. Further downstream, differential diffusion effects are more pronounced in Flame D, resulting in a higher NH₃/H₂ ratio, while in Flames E and F, the influence of differential diffusion diminishes due to the higher Re. This series of flames (D, E, and F) provides a valuable dataset for validating ammonia combustion models, particularly in the context of differential diffusion, local extinction, and turbulence-chemistry interactions in high-Reynolds-number flows.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114303"},"PeriodicalIF":5.8,"publicationDate":"2025-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144313738","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}