Combustion and Flame最新文献

{"title":"Investigating the combustion-flow coupling effects in a cavity-based scramjet combustor","authors":"Ming Yan ,&nbsp;Ye Tian ,&nbsp;Jialing Le ,&nbsp;Ji Li ,&nbsp;Changchun Yan ,&nbsp;Wenyan Song","doi":"10.1016/j.combustflame.2025.114485","DOIUrl":"10.1016/j.combustflame.2025.114485","url":null,"abstract":"<div><div>This study investigates combustion-flow interactions within a scramjet combustor, examining how varying fuel equivalence ratios influence flow characteristics and combustion performance. By employing numerical simulations and experimental validations, we explore the dynamic interplay between combustion flames, shock waves, and localized flow fields, aiming to elucidate the evolution laws governing flow dynamics and flame propagation. The findings reveal that the recirculation zone within the cavity undergoes continuous disassembly and merging, inducing periodic oscillations in the flow field with a cycle duration of 3.6 ± 0.2 ms. Hydrogen injection stabilizes the flow field by balancing upstream and downstream pressures, thereby creating a structured mixing flow field. Furthermore, under reacting flow conditions, a pre-combustion shock train forms due to the combined effects of heat release from combustion and compression caused by fuel injection. Notably, at a fuel equivalence ratio of 0.398, reducing hydrogen supply causes a shift in the combustion regime, accompanied by decreased heat release and weakened shock train intensity. The specific impulse reaches its maximum at a ratio of 0.453, while flow uniformity at the combustor exit is optimized at 0.496. This study contributes to the understanding of complex combustion-flow interactions in scramjet engines, offering valuable insights into optimizing engine performance.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114485"},"PeriodicalIF":6.2,"publicationDate":"2025-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107454","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the influence of the small-scale flow on cycle-to-cycle variations in charge diluted spark-ignition engines","authors":"Linus Engelmann ,&nbsp;Jongkwon Lee ,&nbsp;Bok Jik Lee ,&nbsp;Benjamin Böhm","doi":"10.1016/j.combustflame.2025.114470","DOIUrl":"10.1016/j.combustflame.2025.114470","url":null,"abstract":"<div><div>Charge dilution via exhaust gas recirculation (EGR) enhances efficiency and reduces nitrogen oxide emissions in spark-ignition engines but intensifies cycle-to-cycle variation (CCV), compromising stability. This study experimentally assesses flow-induced CCV drivers under charge dilution using homogeneous mixtures and artificially prepared EGR in an optically accessible spark-ignition engine, eliminating inhomogeneity effects. Residual gas effects are excluded by using a skip-firing scheme. High-speed particle image velocimetry (PIV) and flame imaging are used to capture the flow evolution and flame propagation. This work examines turbulence–flame interactions, identifying distinct flow conditions for fast and slow flame development during compression and ignition, with and without EGR. The flame size is analyzed in relation to cycle outcomes, while global and local flow properties – including kinetic energy, turbulent kinetic energy, and strain – are systematically evaluated. In mixtures with EGR, small differences in the kinetic and turbulent kinetic energy are found to be sufficient to cause differences in the flame propagation. Principal component analysis of the strain tensor highlights different behaviors for cycles of fast and slow flame propagation. Local flow conditions at the spark plug emerge as a decisive factor in both cases, with the orientation of the velocity vector at the spark gap and the turbulent kinetic energy exhibiting a notable influence on CCV.</div><div><strong>Novelty and Significance</strong></div><div>This work investigates cycle-to-cycle variations (CCV) in an optical spark-ignition engine with exhaust gas recirculation (EGR). A key novelty of this study is the systematic analysis and comparison of bulk and fluctuating flow structures with and without EGR, achieved by using artificially prepared exhaust gas and skip-firing to eliminate mixture-induced CCV and isolate the effects of fluctuating turbulent flow structures. While previous work has focused on the bulk flow neglecting the fluctuating components, this work employs conditioned statistics and empirical mode decomposition are applied to separate coherent structures and turbulent fluctuations from the bulk flow. A significant finding is that the importance of the local and global distribution of these structures changes depending on the presence of EGR.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114470"},"PeriodicalIF":6.2,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107452","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":"Thermal and chemical effects of nanosecond repetitively pulsed glow discharges applied to an ammonia–hydrogen–air flame","authors":"Ammar M. Alkhalifa,&nbsp;Deanna A. Lacoste","doi":"10.1016/j.combustflame.2025.114473","DOIUrl":"10.1016/j.combustflame.2025.114473","url":null,"abstract":"&lt;div&gt;&lt;div&gt;This work investigates the thermal and kinetic effects of non-equilibrium plasma produced by nanosecond repetitively pulsed (NRP) glow discharges applied across an ammonia–hydrogen–air flame. The examined flame is stationary, laminar, and axis-symmetric. The discharges are applied across the symmetry axis of the flame crossing the fresh reactants, flame front, and burned products, resulting in a stable flame with reproducible discharges allowing for phase-locked averaged diagnostics. The thermal effects of the plasma are investigated by temporally resolved thermometry, based on optical emission spectroscopy of the second positive system of nitrogen. Kinetic effects are investigated by spatially and temporally resolved measurements of the imidogen radical (NH), amidogen radical (NH&lt;sub&gt;2&lt;/sub&gt;), and ammonia (NH&lt;sub&gt;3&lt;/sub&gt;) with planer laser-induced fluorescence. The temperature measurements reveal the presence of ultra-fast heating by up to 380&lt;!--&gt; &lt;!--&gt;K within 14&lt;!--&gt; &lt;!--&gt;ns during a discharge but only near the anode and not detectable in other locations of the inter-electrode gap. Although reactants are injected at 293&lt;!--&gt; &lt;!--&gt;K, their temperature near the anode is stable at 480 ± 50&lt;!--&gt; &lt;!--&gt;K. This slow heating was not caused by proximity to the flame front, but rather by the discharges themselves. An enhancement of the flame propagation speed by the plasma is shown by a 1.60-mm shift of the position of the flame closer to the nozzle, i.e., a shift of the NH, NH&lt;sub&gt;2&lt;/sub&gt;, and NH&lt;sub&gt;3&lt;/sub&gt; fluorescence signals. Each discharge dissociates less than 10% of NH&lt;sub&gt;3&lt;/sub&gt; upstream of the flame and produces less than &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;85&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; &lt;!--&gt; &lt;!--&gt;ppm of NH and NH&lt;sub&gt;2&lt;/sub&gt;. NH and NH&lt;sub&gt;2&lt;/sub&gt; upstream of the flame are initially produced during the discharges, then their intensity increases and peaks 400-800&lt;!--&gt; &lt;!--&gt;ns after each discharge, revealing post-discharge chemistry induced by the plasma. Although the ammonia in the reactants is subjected to around 60 pulses before it reaches the flame front, its consumption by the plasma is minimal compared to the consumption of ammonia in the preheat zone of the flame. These results illustrate that NRP glow discharges induce various thermal and kinetic effects while enhancing ammonia flames.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance&lt;/strong&gt; This work presents the first temperature and important chemical species measurements for NRP discharges in the glow regime applied to an ammonia–hydrogen–air flame at atmospheric conditions highlighting different thermal and kinetic interactions induced by the plasma such as ultra-fast/slow heating, and prolonged post-discharge chemistry. In addition, this work demonstrates the ability of imaging imidogen radical (NH), amidogen radical (NH&lt;sub&gt;2&lt;/sub&gt;), and ammonia (NH&lt;sub&gt;3&lt;/sub&gt;) in plasma assisted ammonia c","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114473"},"PeriodicalIF":6.2,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107453","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":"Vortex-driven subharmonic bifurcation in a multi-flame Rijke tube","authors":"Yue Weng,&nbsp;Yihong Zhu,&nbsp;Abhishek Saha","doi":"10.1016/j.combustflame.2025.114447","DOIUrl":"10.1016/j.combustflame.2025.114447","url":null,"abstract":"<div><div>The Rijke tube is widely used in the literature to study combustion dynamics, offering a simple, self-excited setup for laboratory-scale experiments. While many studies utilize laminar multi-flame burners, most analyses focus on changes in pressure and global heat release rate, often overlooking interactions between individual flames. This study experimentally investigates the role of individual flame dynamics and their influence on neighboring flames in shaping overall pressure fluctuations. By varying the hydrogen percentage in premixed hydrogen/propane/air flames, we demonstrate how the system transitions from periodic oscillations to quasi-periodic oscillations and, ultimately, to half-integer subharmonic oscillations. Through high-speed imaging of individual flames in a seven-flame burner, we further reveal the emergence of an alternating oscillation pattern from interactions between flames and vortex shedding. This effect intensifies with increasing hydrogen content. Additionally, we compare the fundamental modes of the air column in the Rijke tube and the harmonics of flame oscillations to illustrate how energy within the pressure dynamics is redistributed among different frequencies.</div><div><strong>Novelty and Significance Statement</strong></div><div>Previous studies with Rijke tube often used these multi-flame configurations to create complex combustion dynamics, yet the genesis of this complexity remained unexplored. This research explores such flames from different perspectives. The novelty in our approach is that we visualized and analyzed the dynamics of individual flames, while previous studies focused only on collective dynamics. This paved the way for investigating local interactions, which unveiled that the interactions between vortices shed by neighboring flames lead to subharmonic bifurcations, a critical transition process for combustion dynamics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114447"},"PeriodicalIF":6.2,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107451","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":"Acoustic parametric instability of non-planar premixed flames: Extension of wavenumber-based Markstein numbers via N₂ dilution","authors":"Jerric R. Delfin ,&nbsp;Nozomu Hashimoto ,&nbsp;Osamu Fujita","doi":"10.1016/j.combustflame.2025.114483","DOIUrl":"10.1016/j.combustflame.2025.114483","url":null,"abstract":"<div><div>Self-excited thermoacoustic parametric instabilities in downward-propagating laminar premixed flames are studied experimentally and analytically. Propane-air flames were propagated in an open-closed combustion tube to capture the spatiotemporal flame evolution in transition to acoustic parametric instabilities. The wavenumber response of the vibrating flame, initially planar, from parametric resonance is measured to derive the Markstein number. The Markstein number is determined by employing a thin laminar flame model under acoustic flow-field excitation governed by one-step, high-activation-energy Arrhenius kinetics whose analytical functions are reduced into a Mathieu equation. To promote flame planarization, N₂ dilution is introduced for stoichiometric and rich propane-air flames which exhibit complete instability across the range of acoustic intensities tested in the experiments. Experimental results show that the wavelength of cellular flames at the onset of parametric instability is primarily influenced by stoichiometry rather than N₂ dilution. However, the Markstein number decreases with increasing N₂ dilution due to the corresponding reduction in flame temperature. For completely unstable flames, Markstein numbers are extrapolated based on the gas expansion coefficient. This work highlights the relative importance of temperature-dependent diffusivities, gas expansion coefficient and effective Lewis number on the derived value of the Markstein number; however, the Markstein number alone is not sufficient to characterize flame stability. The values obtained in this study are compared with Markstein numbers relative to fresh gases from various experimental methods reported in the literature.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114483"},"PeriodicalIF":6.2,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107501","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":"Shock tube experiment on ignition delay times and kinetic modeling study of MMH/O2/N2 mixtures","authors":"Xuan Ren ,&nbsp;Ruining He ,&nbsp;Yilin Zhao ,&nbsp;Pengzhi Wang ,&nbsp;Xin bai ,&nbsp;Yang Li","doi":"10.1016/j.combustflame.2025.114478","DOIUrl":"10.1016/j.combustflame.2025.114478","url":null,"abstract":"<div><div>Monomethylhydrazine (CH₃NHNH₂ MMH) has been widely used as a propellant for spacecraft and rockets. In this study, the shock tube experiment on ignition delay times (IDTs) and the kinetic modeling study of MMH/O₂/N₂ mixtures are undertaken to improve the understanding of the oxidation and combustion properties of MMH. Ignition delay times are measured in shock tube at pressures of 4, 8, 18 bar in the temperature range of 1250–1500 K, for two equivalence ratios of 1.0 and 2.0 for MMH/O₂/N₂ mixtures. The OH signal indicates that secondary ignition occurs during the ignition of MMH/O₂/N₂ mixtures at lower temperatures. As the ignition temperature rises, the two ignition events gradually evolve into one ignition. The energy of the first ignition is increased due to the high O₂ concentration under the same conditions.</div><div>A detailed kinetic model consisting of 1333 reactions and 188 species was developed for the combustion of MMH/O₂/N₂ mixtures. This model, which also includes the MMH decomposition model (Diévart_2020), nitrogen chemistry (Glarborg_2018) and C_0<img>C₂ (C3Mech 4.0_2025) introduced as the core mechanisms. H-atom abstraction, unimolecular decomposition and reactions were also considered as two important classes affecting combustion. Good agreement between measured and simulated IDTs was obtained for MMH/O₂/N₂ mixtures at high temperatures (&gt; 1250 K). Sensitivity and flux analyses were conducted to highlight the key reactions in MMH/O₂/N₂ combustion. MMH is mainly consumed by H-atom abstraction reactions and less by bond dissociation reactions at early ignition stages. cCH₃NHNH and CH₂NHNH₂ radicals also play a crucial role in the ignition of MMH/O₂/N₂, which has been overlooked in the previous model in literature.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114478"},"PeriodicalIF":6.2,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107500","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":"Large-eddy simulation of a turbulent bluff-body stabilized flame using the Bernstein Decomposition Conditional Source-Term Estimation model","authors":"Peyman Haghighi Tajvar,&nbsp;M. Mahdi Salehi","doi":"10.1016/j.combustflame.2025.114449","DOIUrl":"10.1016/j.combustflame.2025.114449","url":null,"abstract":"<div><div>Originating from the Conditional Moment Closure (CMC), the Conditional Source-Term Estimation (CSE) is a model for predicting the interaction between turbulence and chemistry. Compared to CMC, CSE offers reduced computational cost and implementation complexities by solving an integral equation to obtain the conditional scalars. This paper applies a modified version of CSE, termed Bernstein Decomposition Conditional Source-Term Estimation (BDCSE), which results in additional savings in terms of numerical effort compared to the traditional CSE method. The BDCSE approach also provides a more robust regularization of the ill-posed integral equation. In this work, the BDCSE model is integrated into a Large Eddy Simulation (LES) framework and employed to simulate an experimental-scale combustor with a bluff-body burner operating in a lean premixed regime. Two flames with inlet turbulence intensities of 2% and 22% are simulated. Results demonstrate that BDCSE effectively predicts temperature and velocity fields, as well as minor and major species concentrations, highlighting its strong potential for turbulent combustion modeling.</div><div><strong>Novelty and Significance</strong></div><div>This work contributes to turbulent combustion modeling by advancing the Bernstein Decomposition Conditional Source-Term Estimation (BDCSE) model in two important ways. First, BDCSE, a modified variant of the Conditional Source-Term Estimation (CSE) approach, is extended from Reynolds-Averaged Navier–Stokes (RANS) framework to Large Eddy Simulation (LES). Second, unlike previous studies, BDCSE is applied to a realistic combustion environment—a confined, premixed combustion chamber. The model’s ability to accurately predict temperature, velocity and species distributions under both low and high turbulence intensities demonstrates its robustness and applicability to real-life industrial applications. These developments support the use of BDCSE in predictive tools for designing combustion systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114449"},"PeriodicalIF":6.2,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107505","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":"Uncertainty quantification for oxidative kinetic parameters in smoldering model with oxygen nonequilibrium concept","authors":"Zeyang Song,&nbsp;Boyuan Dang,&nbsp;Renkun Dai","doi":"10.1016/j.combustflame.2025.114480","DOIUrl":"10.1016/j.combustflame.2025.114480","url":null,"abstract":"<div><div>Uncertainty quantification is very crucial for combustion models. Smoldering models have been questioned by large uncertainties resulting from the underlying multiphase and multiscale physics. The confidence for most of smoldering models has been unknown because their uncertainties have been rarely quantified. This work attempts to quantify the uncertainties of oxidative kinetic parameters in a newly developed smoldering model with oxygen nonequilibrium concept that has been demonstrated to successfully predict smoldering under a variety of conditions covering from propagation to extinction as well as from buoyancy-driven fires to applied smoldering engineering. The uncertainty quantification is comprehensively investigated by 135 models in total, which involves 15 sets of oxidative kinetic parameters with the <em>aleatory uncertainty</em> (Φ_oxid) of TG-scale experiments ranging between 0.04 and 0.6 and three physic variables, i.e. Darcy flux (2.7 cm s^-1 – 21.2 cm s^-1), fuel type (PSFs including bituminous coal and anthracite and CFIPM i.e., food waste in sand), and spread mode (forced reverse, forced forward and buoyancy-driven forward). Results show that the confidence for smoldering model with oxygen nonequilibrium concept is rather good with the model bias less than 0.25 if the <em>aleatory uncertainty</em> is smaller than 0.15. Particularly, the confidence is extremely good for forced reverse smoldering of bituminous coal since the model bias is always less than 0.25 even though the oxidative kinetic parameters’ uncertainty reaches as high as 0.57. Besides, the model confidence for CFIPM is better than PSFs as the fuel loads become less. With the oxygen nonequilibrium concept, the <em>apparent</em> kinetic parameters with Φ_oxid &lt; 0.15 could achieve a rather low and acceptable bias of model prediction, which is beneficial to save enormous time and efforts by avoiding to seek the <em>intrinsic</em> kinetic parameters from a large high-dimensional space. Nevertheless, the model confidence decreases for large Darcy flux &gt; 20 cm s^-1, forward spread, and buoyant effect. It is for the first time that the uncertainty quantification for input oxidative kinetic parameters optimized from TG-scale experiments is comprehensively investigated for smoldering models. This work elucidates the confidence of smoldering models with oxygen nonequilibrium concept and improves our understanding how the <em>aleatory uncertainty</em> induced by kinetic parameters’ optimization propagate in multiscale modelling for smoldering combustion.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114480"},"PeriodicalIF":6.2,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107504","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":"Deep reinforcement learning for adaptive control of thermoacoustic instabilities in a lean-premixed methane/hydrogen/air combustor","authors":"Bassem Akoush ,&nbsp;Guillaume Vignat ,&nbsp;Ryan Finley ,&nbsp;Wai Tong Chung ,&nbsp;Matthias Ihme","doi":"10.1016/j.combustflame.2025.114406","DOIUrl":"10.1016/j.combustflame.2025.114406","url":null,"abstract":"<div><div>Thermoacoustic instabilities are a challenge in the design and operation of combustion systems. Addressing this challenge is becoming even more critical with the development of fuel-flexible combustors capable of operating with hydrogen and other sustainable fuel sources. While active control is a well-known method for damping combustion instabilities, identifying appropriate control parameters becomes increasingly complex in the presence of changing fuel composition and operating conditions. In this work, we present a model-free deep reinforcement learning (RL) technique to adaptively tune an active control system. We demonstrate that the RL-based active control system is able to adaptively suppress thermoacoustic instabilities over an extended range of operating conditions with minimal training. The demonstration is performed on a laboratory-scale bluff-body-stabilized premixed methane/hydrogen/air flame, at equivalence ratios ranging from 0.5 to stoichiometric, and with up to 80%_vol hydrogen in the fuel. After training the RL system on a single operating condition, combustion instabilities can be mitigated over the entire operating range of the burner. Extending the training to three additional operating conditions allows the RL control system to fine-tune its policy and further reduce thermoacoustic instabilities, achieving a sixfold reduction in the acoustic source term over most of the operating range. We observe a reduction of up to 40 dB in acoustic pressure over 50% of the operating range. The proposed approach offers a promising path towards more efficient, adaptive control systems for thermoacoustic instabilities, demonstrating the potential of RL to address the operational challenges of fuel-flexible combustion systems.</div><div><strong>Novelty and Significance Statement</strong></div><div>We show the first experimental demonstration of a reinforcement learning-based control method for thermoacoustic instabilities. The experiments are performed on a laboratory-scale premixed methane/hydrogen/air bluff-body burner, which exhibits strong combustion instabilities over a wide range of operating conditions. Building upon a conventional control system, which utilizes a pressure sensor, an acoustic driver, and a gain- and phase-shift controller, the reinforcement learning-based controller is able to dampen instabilities over the entire operating range. This is achieved while training the controller on a single operating condition. Extending training to a total of four distinct operating conditions further fine-tunes the control policy and yields an additional reduction in the acoustic pressure amplitude. This research illustrates the potential of reinforcement learning for robust control in combustion systems - capable of addressing the challenges of complex combustion physics, adapting to unseen conditions, and merging information from heterogeneous sensors.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114406"},"PeriodicalIF":6.2,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107449","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 role of reaction directions for thermochemistry impacts on chemical kinetic model predictions","authors":"Yuxi Zhao ,&nbsp;Florian vom Lehn ,&nbsp;Heinz Pitsch ,&nbsp;Liming Cai","doi":"10.1016/j.combustflame.2025.114476","DOIUrl":"10.1016/j.combustflame.2025.114476","url":null,"abstract":"<div><div>Thermochemical species properties can have a significant effect on kinetic model predictions due to their impacts on the chemical equilibria of elementary reactions, as demonstrated in several recent studies by means of sensitivity analysis and uncertainty quantification methods. Since the reverse rate coefficients are commonly obtained from the forward rate coefficients and the equilibrium constants (which depend on the thermochemistry data of the involved species), the sensitivities of quantities of interest on the thermochemical properties are expected to depend significantly upon the directions for which the forward rate coefficients are provided in a model. Nevertheless, this dependence has not yet been well quantified in the literature. Deeper insight is thus of high interest. The present work systematically assesses the extent to which the sensitivities on thermochemical properties as well as the resulting uncertainties in model predictions depend upon the choice of forward reaction directions. The mechanisms of two exemplary fuel components, i.e., diethyl ether and <span><math><mi>n</mi></math></span>-heptane, are assessed for ignition conditions. When all reactions are defined in their respective main directions of net reaction flux at the conditions of interest, the impacts of thermochemistry data on model predictions are shown to become relatively low. In particular, only the thermochemistry data of reactants and products of the low-temperature isomerization reactions are found to be moderately sensitive at intermediate temperatures in that case. Conversely, the prediction uncertainties due to thermochemistry data can be more than an order of magnitude higher when all reactions are defined contrary to their main directions of net reaction flux. These results highlight the relevance of the selection of forward reaction directions in terms of minimization of model prediction uncertainties caused by the thermochemistry data, especially if relatively accurate kinetic rate data are available. Further practical implications are finally discussed.</div><div><strong>Novelty and significance statement</strong> This work evaluates quantitatively the impacts of the choice of forward reaction directions on the sensitivities of prediction targets on thermochemical properties and the resulting uncertainties in model predictions for the first time. It is found that the model prediction uncertainties can be minimized, if all reactions are defined in their respective directions of net reaction flux. The results of this work highlight the importance of the selection of reaction directions in the model development for the minimization of model prediction uncertainties caused by the thermochemistry data.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114476"},"PeriodicalIF":6.2,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107450","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}