Proceedings of the Combustion Institute最新文献

{"title":"A dynamic adaptive table look-up approach for FGM modeling of axially staged ammonia flames","authors":"Liqing Lu, Meng Zhang, Weijie Zhang, Ziqi Wang, Jinhua Wang, Zuohua Huang","doi":"10.1016/j.proci.2026.106129","DOIUrl":"10.1016/j.proci.2026.106129","url":null,"abstract":"<div><div>Staged ammonia combustion in gas turbine combustors is a key strategy for achieving low-NOx operation while maintaining high efficiency. However, the substantial difference between the primary and secondary zone thermochemical states challenges conventional flamelet-based models, as a single manifold cannot accurately capture both regimes, leading to critical errors in intermediate species and NOx predictions. To overcome this, a dynamic adaptive table look-up Flamelet-Generated Manifold (DA-FGM) model is developed. This model employs two distinct flamelet manifolds: a primary reaction manifold (Manifold <span><math><msub><mrow><mi>P</mi></mrow><mrow><mi>1</mi></mrow></msub></math></span>) and a secondary manifold (Manifold <span><math><msub><mrow><mi>P</mi></mrow><mrow><mi>2</mi></mrow></msub></math></span>) constructed by counterflowing primary burnt products against secondary air, thereby ensuring the accurate representation of secondary-zone mixing and oxidation chemistry. A physically based switching criterion, coupled with an adaptive blending region, guarantees smooth and continuous transitions between the two flamelet regimes, effectively preventing non-physical artifacts like spurious fuel formation. Validation against quasi-Direct Numerical Simulation (DNS) for laminar flames demonstrates excellent agreement in species profiles and temperature fields. Furthermore, the DA-FGM accurately reproduces experimental NOx emissions in turbulent swirl combustors simulated using Large Eddy Simulation (LES). The framework is robustly extended and validated for staged flames with a partially premixed primary zone, utilizing a multi-dimensional manifold formulation (Manifold <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>1</mi></mrow></msub></math></span>/<span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>2</mi></mrow></msub></math></span>). By reducing computational cost to approximately 1/27 of quasi-DNS while preserving predictive accuracy, the DA-FGM provides a physically grounded, highly efficient, and versatile tool essential for the design and optimization of advanced low-NOx ammonia gas turbines.</div><div><em>Novelty and significance statement:</em> Conventional single-manifold FGM fails in staged ammonia combustion because the secondary mixing trajectories are often thermodynamically orthogonal to the primary flame, leading to non-physical fuel reformation and erroneous NOx predictions. This study introduces a dynamic adaptive FGM (DA-FGM) that resolves this by explicitly generating a secondary manifold from primary products, thereby preserving the inherited reaction history. The novelty lies in the physics-based segregation of combustion regimes through dynamic manifold switching and adaptive transition, as well as its robust extension to flow stratification via a multi-dimensional (<span><math><mi>Z</mi></math></span>-<span><math><msub><mrow><mi>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>-<span><math><mi>y</mi>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106129"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582476","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":"Manifold modeling of flame–flame interactions in turbulent premixed combustion","authors":"Michael D. Walker, Katie VanderKam, Michael E. Mueller","doi":"10.1016/j.proci.2026.106064","DOIUrl":"10.1016/j.proci.2026.106064","url":null,"abstract":"<div><div>Whether premixed flame annihilation interactions can be captured by a manifold model for premixed combustion is an open question since flame–flame interactions give rise to local extrema in progress variable dissipation rate (<span><math><mrow><msub><mrow><mi>χ</mi></mrow><mrow><mi>ΛΛ</mi></mrow></msub><mo>⇾</mo><mn>0</mn></mrow></math></span>) at non-zero/-unity progress variable. This work demonstrates the ability to replicate the local thermochemical state at flame–flame interaction critical points (where <span><math><mrow><mo>∇</mo><mi>Λ</mi><mo>⇾</mo><mn>0</mn></mrow></math></span>) using a manifold model in progress variable <span><math><mi>Λ</mi></math></span> by comparing the conditional statistics of Direct Numerical Simulations (DNS) to predictions from the manifold model. A DNS database of turbulent premixed statistically planar hydrogen–air flames in moderate turbulence was generated with conditions that exist firmly in the thin reaction zone regime. Extracting local progress variable dissipation rate profiles at the critical points as a function of progress variable <span><math><mrow><msub><mrow><mi>χ</mi></mrow><mrow><mi>ΛΛ</mi></mrow></msub><mrow><mo>(</mo><mi>Λ</mi><mo>)</mo></mrow></mrow></math></span>, these profiles are used to close the dissipation rate term in the premixed manifold equations. Furthermore, owing to the influence of differential diffusion, the progress variable curvature <span><math><mi>κ</mi></math></span> was extracted from the DNS and closed in the same manner <span><math><mrow><mi>κ</mi><mrow><mo>(</mo><mi>Λ</mi><mo>)</mo></mrow></mrow></math></span>. Good agreement between the manifold model and the DNS for important thermochemical scalars can be achieved but only if the exact progress variable dissipation rate and curvature are enforced in the manifold model, demonstrating that the manifold model is an appropriate framework for modeling flame–flame interactions. A brief perspective is provided for closure of these quantities.</div><div><strong>Novelty and significance statement:</strong> This work demonstrates, for the first time, that a reduced-order, one-dimensional manifold model for premixed combustion can accurately capture the local thermochemical state of turbulent premixed flame–flame interactions. This addresses an “open question” in combustion modeling: annihilation events are a principal mechanism of local extinction but have lacked explicit representation in manifold-based paradigms. The primary scientific advance shows that closing the manifold equations with DNS-extracted profiles for progress variable dissipation rate and curvature yields very close agreement with DNS data. By showing that computationally efficient manifold models can replicate these complex thermochemical states when progress variable dissipation rate and curvature are accurately represented, this study establishes a vital foundation for developing general closure models to enable predictive, low-cost simulations","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106064"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Toward a rational interpretation of quantum-dot behavior of flame-formed carbon nanoparticles: Electronic excitation energies of different PAH families","authors":"Luna Pratali Maffei, Andrea Nobili, Nikolaos Kateris, Amitesh S. Jayaraman, Patrizia Crepaldi, Matteo Tommasini, Tiziano Faravelli, Hai Wang","doi":"10.1016/j.proci.2026.106160","DOIUrl":"10.1016/j.proci.2026.106160","url":null,"abstract":"<div><div>Accurate prediction of the electronic and optical properties of polycyclic aromatic hydrocarbons (PAHs) is critical to understanding the gas-phase formation of nano-carbon materials, including soot and graphene. Here, CASPT2 and RASPT2 calculations are reported for excitation energies (<span><math><msub><mrow><mi>E</mi></mrow><mrow><mn>0</mn><mi>n</mi></mrow></msub></math></span>) and corresponding oscillator strengths (<span><math><msub><mrow><mi>f</mi></mrow><mrow><mn>0</mn><mi>n</mi></mrow></msub></math></span>) describing the transitions from the ground state (0) to low-lying excited state (<span><math><mrow><mi>n</mi><mo>=</mo><mn>1</mn><mtext>–</mtext><mn>3</mn></mrow></math></span>) for neutral (molecules and <span><math><mi>π</mi></math></span>-radicals) and cationic PAHs up to 20 rings. Calculated <span><math><msub><mrow><mi>E</mi></mrow><mrow><mn>0</mn><mi>n</mi></mrow></msub></math></span> values show good agreement with available absorption and photoionization measurements. Larger uncertainty is estimated for <span><math><msub><mrow><mi>E</mi></mrow><mrow><mn>0</mn><mi>n</mi></mrow></msub></math></span> of <span><math><mi>π</mi></math></span>-radicals with strong electron delocalization due to the sensitivity of the values to the theory adopted. TD-DFT calculations, also performed for comparison, quantitatively reproduce the evolution of <span><math><msub><mrow><mi>E</mi></mrow><mrow><mn>0</mn><mi>n</mi></mrow></msub></math></span> with size observed in multireference calculations for the different PAH families studied. HOMO–LUMO gaps obtained from DFT calculations agree with the CASPT2 excitation energies for molecules, but overestimate by up to 1.5 eV those of open-shell PAHs, while still generally reproducing the trends of <span><math><msub><mrow><mi>E</mi></mrow><mrow><mn>02</mn></mrow></msub></math></span> in PAH <span><math><mi>π</mi></math></span>-radicals and cation radicals.</div><div><em>Novelty and significance statement:</em> Understanding and deriving optical properties of carbon nanoparticles (CNPs) is crucial to unravel their formation mechanisms and to synthesize CNPs with tailored characteristics.</div><div>This work paves the way to bridge this gap by accurate calculations of excited state energies of different polycyclic aromatic hydrocarbons (PAHs) families identified as potential CNP precursors, including resonance-stabilized radicals with up to 20 aromatic rings. To the best of our knowledge, this is the first systematic application of high-level multireference methods to such large PAH systems. In particular, we demonstrate that the traditionally adopted DFT HOMO–LUMO gaps not necessarily provide a quantitative the optical band gaps for open-shell aromatic species.</div><div>These results can be used directly to improve lower-level estimates of PAHs optical properties currently adopted in e.g., two-dimensional quantum dot models for CNP band gaps. Combining the present results with complementary works ","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106160"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148582706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Extreme flame acceleration and field–flame coupling mechanism under DC electric fields","authors":"Siyeong Yu, Suhyeon Kim, Dae Geun Park, Seung-Gon Kim, Sung Hwan Yoon","doi":"10.1016/j.proci.2026.106114","DOIUrl":"10.1016/j.proci.2026.106114","url":null,"abstract":"<div><div>Electric-field-assisted combustion under sub-breakdown conditions has traditionally been interpreted in terms of ionic-wind-induced flow modification, yet the origin of large flame-speed enhancement remains unresolved. Here, we report an extreme flame-acceleration regime in premixed flames propagating through a cylindrical dielectric-tube burner under DC electric fields. The configuration allows the imposed field to bias the early ignition-kernel stage, while the post-ignition propagation stage proceeds under an electrically conditioned flame front coupled with charge redistribution, dielectric surface charging, and intrinsic flame instability. Across nine mixtures with Lewis numbers <span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span>=0.76–1.88, a clear <span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span>-dependent polarity reversal was observed: low-<span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span> flames were most strongly accelerated under negative polarity, whereas high-<span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span> flames responded more favorably to positive polarity. For <span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span>=0.76, the flame displacement velocity reached ∼107 cm/s at −10 kV, approximately 10.7 times the baseline value. PIV-based flow decomposition further showed that the excess acceleration of low-<span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span> flames cannot be attributed to ionic-wind-driven flow modification alone, but arises primarily from transport-mediated enhancement of flame propagation coupled with flame-front instability. A phenomenological scaling using <span><math><mrow><mstyle><mi>Ψ</mi></mstyle><mo>·</mo><mi>ω</mi></mrow></math></span> further organizes the polarity- and <span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span>-dependent response, indicating that the applied electric bias modulates the intrinsic instability landscape rather than acting solely as a direct external forcing.</div></div><div><h3>Novelty and significance statement</h3><div><strong>:</strong> This study identifies an extreme sub-breakdown flame-acceleration regime that cannot be explained by the conventional ionic-wind paradigm alone. By separating the early electrically biased ignition-kernel stage from the subsequent post-ignition propagation stage, the work establishes a time-dependent field–flame coupling framework in which charge redistribution, dielectric surface charging, and intrinsic flame instability jointly determine flame acceleration. The observation of a clear <span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span>-dependent polarity reversal, together with PIV-based separation of flow and flame-propagation contributions, demonstrates that low-<span><math><mrow><mi>L</mi><mi>e</mi></mrow></math></span> flames undergo transport-mediated propagation enhancement far beyond ordinary flow modification. These findings provide a new basis for controlling pre","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106114"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567304","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":"Kinetic insight into plasma-assisted oxidation of ethanol based on SVUV-MBMS diagnostic","authors":"Zhaoying Li,&nbsp;Haodong Chen,&nbsp;Chengcheng Liu,&nbsp;Chengyin Tu,&nbsp;Long Zhao,&nbsp;Minggao Xu,&nbsp;Bin Yang","doi":"10.1016/j.proci.2026.106074","DOIUrl":"10.1016/j.proci.2026.106074","url":null,"abstract":"<div><div>The low-temperature oxidation kinetics of ethanol were investigated in an argon-diluted atmosphere using a nanosecond-pulsed dielectric barrier discharge (DBD) in a plasma flow reactor at 340 K and 20 Torr. Species were identified and quantified using photoionization molecular beam mass spectrometry (PI-MBMS). This diagnostic technique effectively minimizes post-sampling reactions and preserves reactive species, enabling the detection of both stable molecules and radicals. Intermediates identified in the experiments include methane (CH₄), water (H₂O), acetylene (C₂H₂), carbon monoxide (CO), ethylene (C₂H₄), formaldehyde (CH₂O), methanol (CH₃OH), ketene (CH₂CO), carbon dioxide (CO₂), acetaldehyde (CH₃CHO), methyl hydroperoxide (CH₄O₂), acetic acid (CH₃COOH), and methyl acetate (CH₃COOCH₃). Furthermore, a kinetic mechanism for plasma-assisted low-temperature ethanol oxidation was developed and validated against the experimental results. Rate-of-production (ROP) analysis revealed that the plasma-induced reaction e/Ar* + C₂H₅OH → e/Ar + C₂H₅O + H serves as an important pathway for ethanol decomposition. The generated alkoxy radicals subsequently undergo the reaction C₂H₅O → CH₃ + CH₂O, which promotes direct oxygen addition CH₃ + O₂ (+M) → CH₃O₂ (+M), leading to peroxide formation. These results demonstrate that DBD plasma effectively activates ethanol oxidation at low temperature of 340 K.</div></div><div><h3>Novelty and significance statement</h3><div>This study employs synchrotron vacuum ultraviolet photoionization molecular beam mass spectrometry (SVUV-MBMS) to diagnose species in the plasma-assisted oxidation of ethanol, enabling the detection of a wide range of intermediates, including both radicals and stable molecules. The present study notably detected peroxides and esters that had not been previously reported in plasma-driven ethanol oxidation. Based on the experimental data, a kinetic mechanism was developed, and the reaction pathways for ethanol consumption, as well as the formation of products and intermediates, were revealed. Given that the kinetics of plasma-assisted alcohol oxidation remain poorly understood and detailed species diagnostics are scarce, this study provides unique species-resolved information essential for elucidating the reaction kinetics in such systems. The results offer critical experimental evidence and kinetic insights into the plasma-assisted oxidation pathways of ethanol, supplying valuable data for mechanism development and modeling.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106074"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567310","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":"Dynamics of flame spread over filter papers in microgravity aboard the ISS","authors":"Yoshinari Kobayashi,&nbsp;Shuhei Takahashi,&nbsp;Hiroyuki Torikai,&nbsp;Masao Kikuchi,&nbsp;Osamu Fujita","doi":"10.1016/j.proci.2026.106032","DOIUrl":"10.1016/j.proci.2026.106032","url":null,"abstract":"<div><div>Flame spread over solid fuels in microgravity is a fundamental phenomenon relevant to fire safety in spacecraft and space habitats. However, experimental data obtained under sustained microgravity conditions are still very limited because access to orbital research platforms is restricted. In the present study, flame spread over filter paper was experimentally investigated through orbital combustion experiments conducted aboard the International Space Station (ISS) using the Solid Combustion Experiment Module (SCEM) installed in the Japanese Experiment Module “Kibo.” Experiments were performed under various combinations of opposed-flow velocity and oxygen concentration to clarify flame spread characteristics in low-flow microgravity environments. Two distinct flame spread modes were observed: conventional two-dimensional (2D) flame spread and a unique spread mode referred to as <em>flamelet spread</em>. The flamelet spread was characterized by a small flame spreading in a zigzag manner along the sample surface and was mainly observed under extremely low-flow conditions near the flammability limit. Notably, flame spread was observed even below the limiting oxygen concentration predicted by a conventional two-dimensional flame spread model, suggesting that the conventional LOC concept may underestimate flammability limits under microgravity conditions. The measured flame spread rates for the 2D flame spread were typically 1.0–1.5 mm/s in the thermal regime, whereas the flamelet spread exhibited significantly lower spread rates. The preheating length decreased with increasing opposed-flow velocity, and the observed trends were reasonably reproduced by theoretical scaling relations. These findings provide new experimental insights into flame spread behavior over thin cellulosic fuels in microgravity and contribute to improving the understanding of solid fuel combustion relevant to fire safety in future space habitats.</div></div><div><h3>Novelty and significance statement</h3><div>This study reports orbital combustion experiments on flame spread over thermally thin filter paper conducted aboard the International Space Station. The results reveal a distinct flame spread mode, termed <em>flamelet spread</em>, which occurs under extremely low-flow conditions near the flammability limit and differs fundamentally from conventional two-dimensional flame spread. The observation that flame spread can occur even below the limiting oxygen concentration predicted by conventional models suggests that existing flammability criteria may underestimate material flammability in microgravity. These findings provide new insights into solid-fuel combustion in low-flow microgravity environments.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106032"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567401","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Radiative heat feedback to the fuel surface in heptane/toluene pool fires","authors":"Jean-Louis Consalvi,&nbsp;Fatiha Nmira,&nbsp;Hussain Najmi","doi":"10.1016/j.proci.2026.106057","DOIUrl":"10.1016/j.proci.2026.106057","url":null,"abstract":"&lt;div&gt;&lt;div&gt;This article provides a detailed analysis of how enhancing the fuel sooting propensity affects the heat feedback to the fuel surface in 30 cm diameter (&lt;span&gt;&lt;math&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;) pool fires. It combines specific experiments involving pure heptane (Hept100) and heptane/toluene blends with 5 (Hept95) and 10% (Hept90) toluene in volume and large eddy simulation (LES) based on state-of-the-art turbulent combustion, soot formation, and radiation models. The experiments were designed to isolate the effects of the fuel sooting propensity on the radiative feedback. This was achieved by controlling the addition of toluene to significantly enhance the fuel sooting propensity while preserving the flame structure and the local temperature statistics. In addition, the filtered narrow-band correlated-&lt;span&gt;&lt;math&gt;&lt;mi&gt;k&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; radiative transfer equation is solved during the LES along vertical lines of sight from remote locations within the fire plume towards the fuel surface to provide a detailed spectral representation of the radiative feedback process. The simulations reproduce with fidelity the flame structure as well as the heat feedback towards the flame surface. The experimental and numerical results reveal a very limited impact of the enhancement in fuel sooting propensity on both total and radiative heat feedback. This counterintuitive behavior is explained by analyzing the filtered NB radiative intensity: as the fuel sooting propensity increases, the increasing soot radiative emission for &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;z&lt;/mi&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;mi&gt;D&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; is counterbalanced by the increase in absorption by relatively cold soot in the fuel rich core of the flame. The results also show that the fuel rich core of flame is mainly dominated by the absorption of soot and radiating gases which attenuates the radiative feedback.&lt;/div&gt;&lt;div&gt;&lt;em&gt;Novelty and significance statement:&lt;/em&gt; Although it is known that heat feedback to the fuel surface is dominated by radiation (Hamins et al., 1994; Kim et al., 2019) the effect of increasing fuel sootiness on this process is not fully understood. This article aims to fill this gap through a combined experimental and numerical study of 30 cm diameter heptane/toluene pool fires. The experiments reported here are designed to isolate the effects of the fuel sooting propensity on the radiative feedback while the proposed models allow a deep analysis of the underlying physics. The results highlight the competitive mechanisms that drive this radiative feedback as the fuel’s sooting propensity increases: the enhancement in soot emission is counterbalanced by an increase in absorption by cold soot in the fuel dome. Additionally, the results reveal that the fuel-rich core of these pool fires is mainly dominated by radiative absorption. These findings could represent a significant step towards developing reduced-order models for predicting radiative feedback.&lt;/div&gt;&lt;/d","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106057"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567402","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":"Prediction of limit cycle amplitudes over an operating domain and direct comparison with thermoacoustic instability experiments","authors":"Pierre-Alexandre Barré,&nbsp;Sébastien Candel,&nbsp;Daniel Durox,&nbsp;Antoine Renaud","doi":"10.1016/j.proci.2026.106002","DOIUrl":"10.1016/j.proci.2026.106002","url":null,"abstract":"&lt;div&gt;&lt;div&gt;One central challenge in combustion instability analysis is to reconcile experimental data and model predictions. In most cases, experimental observations are carried out at the limit cycle, i.e. when the regime of oscillation is established, while modeling generally provides growth rates which are used to infer whether the system is stable or unstable. A considerable effort has been made to develop models that describe linear and nonlinear features of the unstable process. However, there are not many contributions that are trying to obtain the layout of the unstable domain as a function of operating parameters. This article is aimed at showing that it is possible to calculate amplitudes at the limit cycle over a wide domain of operation with a reduced-order model, thus distinguishing stable and unstable regions and compare the calculated levels of oscillations to the amplitudes determined experimentally in a laboratory scale annular combustor (the MICCA facility). Calculations are carried out by projecting the wave equation onto acoustic modes to derive coupled evolution equations, which are then solved using slow-flow variables and time averaging. This model enables the determination at low computational cost of both limit-cycle amplitudes and effective growth rates, relying on velocity-based Flame Describing Function (FDF) data measured in a single-sector combustor equipped with the same injection unit, converted to pressure-based FDF and extended to actual oscillation conditions. The flame response (gain and phase of the FDF) is updated during integration to match with the observed frequency drift which is continuously monitored. The model successfully reproduces the experimental instability domain layout, as well as a frequency drift, highlighting its predictive capability for nonlinear dynamics in realistic annular combustor geometries.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This work extends a reduced-order model for thermoacoustic instability prediction in a multi-burner annular combustor &lt;span&gt;&lt;span&gt;[1]&lt;/span&gt;&lt;/span&gt; to a wide operating domain. The model includes several novel elements: an extension to annular conditions of velocity-based Flame Describing Functions using single-sector measurements; a frequency monitoring scheme based on dynamical equations to ensure consistent flame response; and a method to constrain admissible frequency shift using experimental knowledge and an extended Rayleigh criterion accounting for damping effects. This approach demonstrates, for the first time, that single-sector flame response data can be used to predict nonlinear instability behavior and limit-cycle amplitudes in multi-injector annular geometries across a broad operating range. The model captures experimental trends and stability boundaries with low computational cost and provides a practical framework for stability analysis and design optimization in future low-emission engines, offering a simple yet ","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106002"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567571","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":"Interplay of strain and thermodiffusive instabilities in lean premixed hydrogen flames","authors":"V. Schuh,&nbsp;M. Glushko,&nbsp;C. Hasse,&nbsp;H. Nicolai","doi":"10.1016/j.proci.2026.106092","DOIUrl":"10.1016/j.proci.2026.106092","url":null,"abstract":"<div><div>Lean premixed hydrogen combustion is a promising route toward low-NOx carbon-free energy systems, but its high sensitivity to thermodiffusive instabilities (TDI) and flow-induced strain presents major design challenges. While both effects enhance burning rates, their mutual interaction and formation remain insufficiently understood. This study investigates the interplay between strain and TDI in a well-defined 2D Tsuji burner configuration through detailed chemistry simulations spanning a range of global strain rates and operating conditions, while independently varying the Markstein number <span><math><mi>M</mi></math></span> and the mixture’s instability factor <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>. The flames consistently transition from strain-dominated to TDI-dominated regimes, with increasing global strain pushing the onset of instability further downstream from the high-strain zone. A detailed local stretch analysis shows that TDI formation is triggered only once the local strain rate falls below a small, nearly constant critical value — significantly lower than the globally imposed strain — highlighting a consistent onset condition across all cases. A budget analysis of differential transport elucidates this mechanism: strain-induced tangential fuel transport stabilizes the flame by suppressing local mixture-leaning; once this transport weakens, differential diffusion promotes the emergence of TDI cells. Comparisons across operating points with identical instability susceptibility demonstrate a pronounced sensitivity to the Markstein number, establishing a clear link between mixture-dependent strain response and the suppression of TDI formation.</div><div><strong>Novelty and significance statement</strong></div><div>Understanding the interplay of strain and thermodiffusive instabilities in lean hydrogen flames is crucial since both effects have been shown to dominate flame propagation and stabilization under various conditions. This study examines the interplay between flow strain and thermodiffusive instabilities in the non-linear regime in a well-defined steady-state configuration where regions governed by strain and by thermodiffusive instabilities coexist. In particular, the study reveals how strain suppresses the formation of thermodiffusive instability (TDI) structures, a key mechanism that has not been fully understood so far, and subsequently characterizes the transition between strain-dominated and TDI-dominated regions. The findings advance the community’s understanding of flame physics and provide essential insight for model development by identifying the conditions under which TDI can emerge in strained flame configurations, while linking these results to well-established quantities such as the Markstein number and the instability factor.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106092"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148567576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Combined effects of heat losses and curvature in hydrogen–air flame propagation below the lean flammability limit","authors":"Rubén Palomeque-Santiago,&nbsp;Anne Dejoan,&nbsp;Daniel Fernández-Galisteo,&nbsp;Mariano Rubio-Rubio,&nbsp;Mario Sánchez-Sanz","doi":"10.1016/j.proci.2026.106100","DOIUrl":"10.1016/j.proci.2026.106100","url":null,"abstract":"<div><div>Recent experiments have shown that, below the flammability limit, ultra-lean hydrogen flame fronts can fragment into isolated flame cells when propagating within narrow channels. To further elucidate the underlying mechanisms of this behavior, three-dimensional (3D) numerical simulations are performed, systematically varying the heat losses through the confining walls. Under adiabatic conditions, a continuous flame front embedded with small cellular structures is sustained. When heat losses are introduced, this front fragments, forming isolated flame cells. The characteristic size of these cells is found to be comparable to the dominant wavelength of the corrugated front obtained under adiabatic conditions. The results indicate that heat losses have a pronounced impact on the flame curvature between the wall plates, which transitions from a highly asymmetric configuration to a nearly circular shape as the heat losses increase, while the curvature in the mid-channel plane is barely affected. The size and propagation velocity of the isolated flame cells exhibit a moderate dependence on the magnitude of the heat losses. Sufficiently large heat losses induce a bifurcation of the isolated fronts from a circular to a double-cell flame shape</div><div><em>Novelty and significance statement</em></div><div>This work presents fully three-dimensional numerical simulations to investigate the mechanisms governing the fragmentation of ultra-lean hydrogen–air flame fronts in narrow channels under the influence of varying wall heat losses. The main novelty is the quantification of the heat-loss effect on flame curvature, both across and along the confining plates. A direct correspondence is established between the characteristic size of the isolated cells and the dominant wavelength of flame corrugation under adiabatic conditions, revealing how increasing heat losses promote the transition from a non-symmetric flame to stable, symmetric isolated flame cells below the lean flammability limit of the adiabatic planar deflagration. This study explains that heat losses, typically associated with quenching, can instead stabilize discrete flame cells by reshaping the flame’s three-dimensional curvature and propagation dynamics. These findings clarify the mechanisms behind stable ultra-lean hydrogen combustion, with direct implications for hydrogen safety and the design of efficient, low-emission micro-combustion systems.</div></div>","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"42 ","pages":"Article 106100"},"PeriodicalIF":4.6,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148587491","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}