Combustion and Flame最新文献

{"title":"FGM modeling of thermo-diffusive unstable lean premixed hydrogen–air flames","authors":"Stijn N.J. Schepers,&nbsp;Jeroen A. van Oijen","doi":"10.1016/j.combustflame.2025.114332","DOIUrl":"10.1016/j.combustflame.2025.114332","url":null,"abstract":"<div><div>Ultra-lean premixed hydrogen combustion is a possible solution to decarbonize industry, while limiting flame temperatures and thus nitrous oxide emissions. These lean hydrogen/air flames experience strong preferential diffusion effects, which result in thermo-diffusive (TD) instabilities. To efficiently and accurately model lean premixed hydrogen flames, it is crucial to incorporate these preferential diffusion effects into flamelet tabulated chemistry frameworks, such as the Flamelet-Generated Manifold (FGM) method. This is challenging because the preferential diffusion terms in the control variable transport equations contain diffusion fluxes of all species in the mechanism. In this work, a new implementation is presented; the full term is reduced by only considering the most contributing species. When carefully selecting this set of major species, preferential diffusion fluxes along the flame front, i.e., cross-diffusion, can be captured. This is particularly important for manifolds that include heat loss effects, where enthalpy is one of the control variables. The diffusion of the H-radical has a significant contribution to the enthalpy transport equation, and cross-diffusion of the H-radical is non-negligible. Two manifolds, without and with heat loss effects, and the set of major species are analyzed in an <em>a-priori</em> and <em>a-posteriori</em> manner. Simulations of TD unstable hydrogen–air flames with detailed chemistry and several FGM models show that accurately capturing cross-diffusion of enthalpy is important for correctly predicting the flame shape and dynamics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114332"},"PeriodicalIF":6.2,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144810176","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":"Destabilization mechanism of oblique detonation induced by the recirculation zone in a channel flow","authors":"Wenqiang Du ,&nbsp;Shuzhen Niu ,&nbsp;Pengfei Yang ,&nbsp;Honghui Teng","doi":"10.1016/j.combustflame.2025.114401","DOIUrl":"10.1016/j.combustflame.2025.114401","url":null,"abstract":"<div><div>The stability of flow structures is crucial for the combustion efficiency of oblique detonation waves (ODWs). Prior studies have predominantly attributed the destabilization of ODWs to the merging of subsonic regions behind detonation Mach stem. However, the flow structures of ODWs in channels are complex, probably leading to a variety of destabilization mechanisms. This study numerically investigates the ODWs under the influence of viscosity using a detailed chemical reaction model. Results show that the recirculation zone on the lower channel wall plays an important role in the stability of the detonation wave system, which has been ignored in most studies. Specifically, when the secondary reflected shock generated by the lower recirculation zone interacts with the recirculation zone on the upper wall, it triggers the continuous growth of the upper recirculation zone and the formation of an aerodynamic throat. This ultimately leads to flow choking and destabilization of the detonation waves. Based on the above findings, we further evaluate the effectiveness of a moving wedge in regulating the unstable ODWs. It is found that promptly moving the wedge downstream can suppress the upstream movement of the lower recirculation zone, preventing secondary reflected shocks from disrupting the upper recirculation zone. As a result, the unstable detonation wave system is successfully re-stabilized.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114401"},"PeriodicalIF":6.2,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144810240","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":"Role of the argon and helium bath gases on the structure of H2/O2 detonations","authors":"Farzane Zangene,&nbsp;Matei I. Radulescu","doi":"10.1016/j.combustflame.2025.114381","DOIUrl":"10.1016/j.combustflame.2025.114381","url":null,"abstract":"<div><div>This study investigates the role of two inert mono-atomic diluents, argon and helium, on the detonation structure in order to assess the importance of vibrational non-equilibrium and wall losses. When relaxation effects and wall losses are neglected, the detonation waves in mixtures diluted with either of these gases have the same kinetics, Mach number, and specific heat ratio and hence are expected to lead to the same cellular dynamics. Differences in transport properties and species relaxation rates thus permit to establish the importance of these effects. The experiments were conducted in <span><math><mrow><mn>2</mn><msub><mrow><mtext>H</mtext></mrow><mrow><mn>2</mn></mrow></msub><mo>+</mo><msub><mrow><mtext>O</mtext></mrow><mrow><mn>2</mn></mrow></msub><mo>+</mo><mn>7</mn><mtext>Ar</mtext></mrow></math></span> and <span><math><mrow><mn>2</mn><msub><mrow><mtext>H</mtext></mrow><mrow><mn>2</mn></mrow></msub><mo>+</mo><msub><mrow><mtext>O</mtext></mrow><mrow><mn>2</mn></mrow></msub><mo>+</mo><mn>7</mn><mtext>He</mtext></mrow></math></span> mixtures in a narrow channel, where boundary layer losses can be controlled by the proximity of the detonations to their propagation limits. The initial pressure was adjusted in such a way that the induction zone length calculated from the ideal ZND model remained constant. This is expected to also constrain the cell size. The experiments revealed differences in velocity deficits and cell sizes despite maintaining a constant induction zone length across the mixtures. These differences were minimal in sensitive mixtures but became more pronounced as velocity deficits increased and cell sizes approached the channel dimensions. Near the detonation limits, the disparity in cell sizes between the two mixtures nearly doubled. We incorporated the boundary layer flow divergence in a perturbation analysis based on the square-wave detonation assumption. This permitted to establish the controlling loss parameter as the product of the induction to channel size and the inverse of the square root of the Reynolds number. The very good collapse of the experimental results with the loss parameter, and further comparison with two-dimensional numerical simulations with account for flow divergence to the third dimension, confirmed the viscous loss mechanism to be dominating. Calculations suggest that the slower relaxation of <span><math><msub><mrow><mtext>H</mtext></mrow><mrow><mn>2</mn></mrow></msub></math></span> becomes comparable with the ignition delay anticipated from the ZND model and is slower by 70% in the argon diluted system. Differences possibly highlighting the role of non-equilibrium were not observed. This suggests the vibrational non-equilibrium effect may be less apparent in cellular detonations in the system studied in this work due to the lengthening of the ignition delays owing to the non-steady detonation structure. This study establishes that the large differences between the enlarged cells observe","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114381"},"PeriodicalIF":6.2,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144827485","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":"Two-dimensional burn velocity and analysis of burn products of nitromethane at high pressure","authors":"Christopher Perreault,&nbsp;Jason Baker,&nbsp;Jonathan Crowhurst","doi":"10.1016/j.combustflame.2025.114348","DOIUrl":"10.1016/j.combustflame.2025.114348","url":null,"abstract":"<div><div>We have studied the laser-initiated deflagration of nitromethane (CH₃NO₂) under high static pressure in the diamond anvil cell. Time-resolved images of the deflagrations have been obtained using intensified CCDs (ICCD). In contrast with previous work, we rely on spontaneous emission from the reaction, rather than changes in the speckle pattern produced by artificial illumination of the sample. Furthermore, as opposed to the 1D records obtained previously with streak cameras, ICCDs permit imaging of the burn in two dimensions providing the ability to directly observe anisotropic deflagration behavior. We report several examples of this behavior and discuss its possible origins. We have also investigated the products of the reaction using Raman spectroscopy. At pressures below 25 GPa, the burn product is observed to be opaque and has a Raman spectrum consistent with a carbonaceous soot. At pressures above 25 GPa, the burn product is observed to be transparent (consistent with earlier reports) and its Raman spectrum reveals the presence of molecular N₂ and a nitrogen-carbonate species. The latter species can be recovered to ambient pressure and has a Raman spectrum consistent with ammonium carbonate or ammonium bicarbonate. To aid interpretation of the Raman spectra, measurements have also been made on the isotopologues CH₃¹⁵NO₂ and ¹³CH₃NO₂. This work establishes the importance of advanced time-resolved imaging to reveal the details of deflagration under high pressure and further advances our understanding of the corresponding chemistry.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114348"},"PeriodicalIF":6.2,"publicationDate":"2025-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144780036","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":"UnblindMix: An unsupervised reference-free framework for multi-species detection in high-temperature combustion diagnostics","authors":"Mohamed Sy,&nbsp;Emad Al Ibrahim,&nbsp;Aamir Farooq","doi":"10.1016/j.combustflame.2025.114383","DOIUrl":"10.1016/j.combustflame.2025.114383","url":null,"abstract":"<div><div>High-temperature combustion processes are characterized by the rapid formation and consumption of numerous reactive species, presenting substantial challenges for accurate diagnostic measurements. Traditional approaches often require labor-intensive collection of high-temperature absorption cross-section spectra, which limits scalability and efficiency. To address these challenges, we present UnblindMix, an unsupervised, reference-free diagnostic framework that leverages blind source separation (BSS) to simultaneously infer species concentrations and reconstruct high-temperature reference spectra directly from composite mixture spectra. This study demonstrates the capability of UnblindMix in pyrolysis experiments of n-butane and iso-butane at 923 K and 1 atm, as well as in non-reactive mixtures of <span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>−</mo><msub><mrow><mi>C</mi></mrow><mrow><mn>3</mn></mrow></msub></mrow></math></span> hydrocarbons in a high-temperature static cell. Using an interband cascade laser (ICL) operating over 2984.5–2989.5 cm⁻¹ range, the model accurately predicts time-resolved species profiles and reconstructs high-temperature reference spectra with minimal reliance on pre-existing spectral databases. Validation against AramcoMech 3.0 simulations and experimental data revealed good agreement. UnblindMix represents a significant advancement absorption diagnostics, reducing the dependency on extensive spectral databases and offering a scalable, efficient solution for multi-species detection in laboratory and industrial applications.</div><div><strong>Novelty and significance</strong></div><div>The novelty of this research lies in the introduction of UnblindMix, an autoencoder-based blind source separation model capable of inferring species concentrations and reconstructing high-temperature reference spectra solely from mixture spectra. It is significant because it eliminates the reliance on labor-intensive high-temperature absorption cross-section datasets, providing a scalable and robust framework for multi-species detection in combustion diagnostics. The model’s application to real-time pyrolysis of n-butane and iso-butane demonstrates its potential to revolutionize high-temperature spectroscopic analysis for both research and industrial applications.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114383"},"PeriodicalIF":6.2,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144772048","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":"Ignition, combustion modes and NO/N2O emissions in ammonia/n-heptane combustion under RCCI engine conditions","authors":"Yuchen Zhou,&nbsp;Shijie Xu,&nbsp;Leilei Xu,&nbsp;Xue-Song Bai","doi":"10.1016/j.combustflame.2025.114352","DOIUrl":"10.1016/j.combustflame.2025.114352","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Ammonia has been considered a promising carbon-free fuel for marine engines. However, its low flame speed and high nitrogen oxides (NO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;) and nitrous oxide (N&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O) emissions present significant challenges. To address these issues, novel combustion concepts, such as ammonia/diesel dual-fuel Reactivity-Controlled Compression Ignition (RCCI) engines, have been proposed. This paper presents a detailed investigation of ammonia/n-heptane combustion under RCCI engine conditions using direct numerical simulation (DNS) to gain insights into ignition, combustion modes, and emission formation mechanisms. A temporally evolving jet configuration is considered in the DNS, with the computational domain comprising two regions: a fuel-lean premixed ammonia/air mixture and a fuel-rich n-heptane jet/ammonia/air mixing region. The pressure and temperature in these regions are representative of typical marine engine operating conditions. The DNS results reveal multiple reaction layers, including the fuel-lean premixed flame (LPF), fuel-rich premixed flame (RPF), diffusion flame (DF), and rich ammonia oxidation layer (RAOL). The LPF propagates into the ambient ammonia/air mixture, significantly influencing combustion efficiency and NO formation, while the RPF propagates into the fuel-rich n-heptane/ammonia/air mixture due to low-temperature ignition. The DF oxidizes combustion intermediates and NO, while the RAOL facilitates ammonia oxidation, forming intermediate species such as hydrogen (H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;), amino radicals (NH&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;), and nitrene radicals (NH), which eventually participate in the reactions in the DF and RPF. The back-supported propagation of the LPF is influenced by n-heptane mixing, heat, and radical transfer from the DF, and jet-induced vortices and turbulence. Increasing n-heptane jet speed enhances this effect, improving ammonia combustion efficiency. NO primarily forms in the LPF and is consumed in the DF, while N&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O is generated in the LPF (continuously) and RPF (during the ignition stage), while being consumed in the RAOL. Higher n-heptane jet velocity accelerates NO consumption but increases N&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;O formation due to enhanced mixing and ammonia entrainment. Understanding these mechanisms provides valuable insights into optimizing RCCI combustion for reduced emissions and improved efficiency in ammonia-fueled marine engines.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;• This research investigates ammonia-fueled RCCI engines using high-fidelity direct numerical simulations, examining the effects of t","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114352"},"PeriodicalIF":6.2,"publicationDate":"2025-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144767199","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":"Broadened mechanism of the flammability limit of lean premixed mixture via increasing bluff-body temperature","authors":"Siqi Cai,&nbsp;Jianlong Wan","doi":"10.1016/j.combustflame.2025.114388","DOIUrl":"10.1016/j.combustflame.2025.114388","url":null,"abstract":"&lt;div&gt;&lt;div&gt;To provide the guideline for enlarging the flammability limit by the means of increasing the bluff-body temperature, the present study investigates the effect of the bluff-body temperature on the flammability limit of lean methane-air premixed mixture in a wide temperature range. It is interesting to experimentally observe that the flammability limit of lean methane-air premixed mixture can be significantly enlarged by the high-temperature bluff-body. At first, the flame behavior and structure features at various bluff-body temperatures are revealed. The bilateral flame fronts get away from each other and split into two parts at the flame base gradually with the increased bluff-body temperature. In the case of the high-temperature bluff-body, the heat release rate HRR value sharply increases first and then decreases to a specific value gradually. The diffusion and convection fluxes of the fresh methane which arrives at the flame front increase when the bluff-body temperature increases. Subsequently, the broadened mechanism of the flammability limit in the case of the high-temperature bluff-body is revealed quantitatively in terms of the effects of flow recirculation, stretch, preferential transport, and conjugate heat transfer. The analysis indicates that the effects of flow recirculation and preferential transport do not contribute to improving the flame anchoring performance in the case of the high-temperature bluff-body. The negative stretch rate near the flame base in the case of the high-temperature bluff-body is beneficial to anchoring the flame. In addition, when the bluff-body temperature increases, the preheating effect on the fresh mixture significantly increases and the heat-loss effect decreases, which greatly contributes to improving the flame anchoring performance. The stretch and conjugate heat transfer effects are the main factors that broaden the flammability limit. This study provides a new strategy for extending the operating range of lean premixed flame by controlling the bluff-body temperature and expands our understanding of the lean premixed flame dynamics stabilized by the bluff-body.&lt;/div&gt;&lt;/div&gt;&lt;div&gt;&lt;h3&gt;Novelty and Significance Statement&lt;/h3&gt;&lt;div&gt;Lean premixed combustion is regarded as a promising technology to achieve cleaner and higher efficiency combustion of fossil fuels. To provide the guideline for enlarging its flammability limit via controlling the bluff-body temperature, the effect of the bluff-body temperature on the flammability limit of lean methane-air premixed mixture is studied. It is observed that the flammability limit can be significantly enlarged by the high-temperature bluff-body, and the corresponding broadened mechanism is revealed quantitatively in terms of the flow recirculation, stretch, preferential transport, and conjugate heat transfer effects. Such detailed visualization of the main factors that enlarge the flammability limit in the case of the high-temperature bluff-body is provided","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114388"},"PeriodicalIF":6.2,"publicationDate":"2025-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144767198","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":"Modeling self-ignition of high-pressure hydrogen leaks in confined space","authors":"Marc Le Boursicaud ,&nbsp;Song Zhao ,&nbsp;Jean-Louis Consalvi ,&nbsp;Pierre Boivin","doi":"10.1016/j.combustflame.2025.114386","DOIUrl":"10.1016/j.combustflame.2025.114386","url":null,"abstract":"<div><div>The numerical study of ignition risk in the event of high-pressure hydrogen leakage presents numerous challenges. The first is to properly simulate the complex multi-dimensional flow, characterized by a hemispherical expanding shock and a contact discontinuity. The second is to accurately resolve the diffusion/reaction interface, which exhibits a very small length scale compared to the jet radius. These challenges were addressed in our previous work (Le Boursicaud <em>et al.</em>, Combust. Flame 274, 2025), leading to the development of a reduced-order model capable of efficiently predicting the risk of self-ignition in the case of high-pressure hydrogen storage leakage for various geometries. The present work focuses on extending the previously developed model to account for the effects of leakage in confined spaces. These modifications include a simple adjustment of the pseudo-1D model to account for shock reflection, as well as the consideration of entropy jumps occurring during the interaction between the reflected shock wave and the diffusion layer. This work is motivated by the potential increase in ignition risk when leaks occur in confined environments, as opposed to the open environments previously considered (Smygalina and Kiverin, Int. J. Hydrog. Energy 47, 2022).</div><div><strong>Novelty and Significance Statement</strong>: This work extends a reduced-order model for shock-induced ignition of high-pressure hydrogen leaks from open to confined environments, capturing key effects such as shock reflection and shock–contact interaction. It enables efficient assessment of ignition risk in scenarios where full-resolution simulations are computationally prohibitive.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114386"},"PeriodicalIF":6.2,"publicationDate":"2025-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144756746","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":"Non-linear evolution and acceleration of unstable fuel-lean hydrogen/air flame at ambient and cryogenic temperatures","authors":"Linlin Yang ,&nbsp;Tianhan Zhang ,&nbsp;Yiqing Wang ,&nbsp;Xiaohang Fang ,&nbsp;Felix Leach ,&nbsp;Zheng Chen","doi":"10.1016/j.combustflame.2025.114346","DOIUrl":"10.1016/j.combustflame.2025.114346","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Hydrogen storage at cryogenic temperatures is crucial for industrial applications, yet these conditions can significantly affect flame behavior. Both Darrieus–Landau instability (DLI) and diffusional-thermal instability (DTI) can intensify at cryogenic temperature, leading to unique flame dynamics relevant to safe hydrogen usage. In this study, two-dimensional simulations are performed to assess the effects of cryogenic temperature on the non-linear evolution and acceleration of fuel-lean hydrogen/air flames. By changing the initial temperature and equivalence ratio of the unburned gas as well as the channel width, distinct flame evolution regimes driven by the interplay of DLI and DTI are identified. Specifically, for fuel-lean hydrogen/air flames, the growth rate of DLI and DTI in the linear stage increases at cryogenic temperatures. In the non-linear stage, DTI leads to the chaotic evolution of the cellular flame, which is further destabilized at cryogenic temperatures. It is found that the long-term dynamics, characterized by cell splitting, merging, and lateral movement, result from complex interactions among flow, flame stretch, and chemical reactions. Moreover, flame structure analysis shows that, compared to ambient temperatures, cryogenic temperatures significantly increase the local reaction rate. The propagation speed of fuel-lean hydrogen/air flames is further accelerated at cryogenic temperature, which is associated with the combined effects of enhanced local reaction rate and increased flame surface area, with the primary contribution from enhanced DTI and the secondary contribution from enhanced DLI. In contrast, stoichiometric and fuel-rich flames propagate in a stable single-cusp shape, with their acceleration primarily driven by DLI and flame surface area increase. The width of the channel also affects cellular flame evolution. Rather than altering reaction rates, channel geometry influences flame acceleration mainly through constraining the surface area during flame propagation. These insights contribute to our understanding of cryogenic hydrogen flame dynamics and have important implications for hydrogen safety management.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance Statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;The novelty of this study lies in assessing and interpreting the effects of cryogenic temperatures on fuel-lean hydrogen/air flames subjected to both Darrieus–Landau instability (DLI) and diffusional-thermal instability (DTI) for the first time. Through detailed numerical simulations, we reveal mechanisms driving the chaotic evolution and cellular structure of flame fronts under cryogenic conditions. Our quantitative analysis demonstrates the relative contributions of DLI and DTI. The research fills a critical knowledge gap by examining the role of DLI and DTI at cryogenic conditions for highly unstable fuel-lean hydrogen/air flame. The results are especially valuable for predicting and managing potential flame acceleration haz","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114346"},"PeriodicalIF":6.2,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144749288","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":"Amplification of thermoacoustic flame response to investigate high frequency combustion instabilities with LES","authors":"Jonas Eigemann ,&nbsp;Philip Bonnaire ,&nbsp;Lukasz Panek ,&nbsp;Christian Beck ,&nbsp;Wolfgang Polifke ,&nbsp;Andreas Kempf","doi":"10.1016/j.combustflame.2025.114317","DOIUrl":"10.1016/j.combustflame.2025.114317","url":null,"abstract":"<div><div>We present a novel technique to enhance the thermoacoustic coupling in large-eddy simulations (LES) of self-excited oscillations, aiming to (a) recover high frequency thermoacoustic oscillations lost to the effect of LES-filtering, and to (b) establish a measure for a flame‘s proximity to the thermoacoustic stability limit. To this end, the naturally occurring link between isentropic pressure fluctuations and heat release rate is amplified. This thermoacoustic flame response amplification (TAFRA) is demonstrated in a compressible reactive LES of a single-jet case with experimentally confirmed high frequency thermoacoustic instability. TAFRA was found to not alter (non-acoustic) flame-properties and to selectively target thermoacoustic modes only, without amplifying the hydrodynamic instability modes. TAFRA has the potential of reducing the computational cost for the LES of high-frequency thermoacoustics, where acoustic resolution is the limiting factor, enabling more affordable simulations and design variations.</div><div><strong>Novelty and Significance</strong></div><div>In this paper, we present a novel method and a prototype implementation to artificially amplify the response of a flame to acoustic waves by increasing sensitivity to isentropic pressure fluctuations. The method contributes to the investigation of high-frequency thermoacoustic instabilities with large-eddy simulations (LES). The method amplifies the energy transferred from the flame to the acoustic field, which enables the prediction of high-frequency thermoacoustic instabilities with an LES grid that is sufficient for the flame, but not much finer, and therefore significantly lowers computational cost. At the same time, the paper demonstrates the important effect of pressure fluctuations on flame speed and thus on thermoacoustics. The new method may, eventually, also enable the quantification of thermoacoustic stability, i.e. the proximity to stability or instability.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"280 ","pages":"Article 114317"},"PeriodicalIF":6.2,"publicationDate":"2025-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144749287","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}