Combustion and Flame最新文献

{"title":"A fundamental study on ignition dynamics and combustion characteristics of Al–Mg alloys with varied magnesium content","authors":"Huanhuan Gao ,&nbsp;Tuanwei Xu ,&nbsp;Bozhi Hu ,&nbsp;Jianzhong Liu ,&nbsp;Haiou Wang ,&nbsp;Jianren Fan","doi":"10.1016/j.combustflame.2025.114429","DOIUrl":"10.1016/j.combustflame.2025.114429","url":null,"abstract":"<div><div>Due to their exceptional combustion properties, highly reactive Al–Mg alloys exhibit significant technological applicability in military and aerospace fields. This study systematically investigates the mechanisms of thermal oxidation, ignition, and combustion in Al–Mg alloys with Mg contents ranging from 0 % to 50 %, employing thermogravimetric analysis and laser ignition tests. Furthermore, based on temperature-dependent thermophysical parameters and an oxidizer diffusion model, a kinetic model for Al–Mg alloy ignition was established, elucidating the effects of Mg content on ignition delay time and oxide formation. Simulation outcomes exhibited a 1.25∼7.46 % deviation relative to experimentally determined ignition delay times, confirming the model's accuracy. The comprehensive results demonstrate that, compared to raw Al, Mg significantly enhances the overall chemical reaction heat of the alloy through its surface reaction heat and gas-phase reaction heat, thereby accelerating oxidation kinetics and enhancing energy release efficiency. Moreover, Mg effectively disrupts the dense oxide shell and utilizes jetting and boiling phenomena driven by the significant boiling point disparity between Mg and Al, consequently improving combustion efficiency. Increasing Mg content also accelerates alloy heating and melting rates, facilitating heterogeneous chemical reactions and thermal release, which reduces the ignition threshold and extends the reaction scope. These insights establish a theoretical foundation for applying Al–Mg alloys in high-performance fuels and energy-regulating materials.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114429"},"PeriodicalIF":6.2,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144866178","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 characteristics of methanol-rich renewable gasoline","authors":"Khalid Aljohani ,&nbsp;Aamir Farooq","doi":"10.1016/j.combustflame.2025.114416","DOIUrl":"10.1016/j.combustflame.2025.114416","url":null,"abstract":"<div><div>In the pursuit of renewable fuels, few options are as promising as methanol. Methanol’s unique properties, such as the absence of C–C bonds, high oxygen content, and elevated octane numbers, offer a compelling avenue as an additive for conventional and renewable gasoline fuels. Notably, methanol and e-gasoline (e.g., methanol-to-gasoline, MTG) can be sustainably derived from renewable sources, reinforcing their role in cleaner energy systems. Within the MTG framework, methanol acts as a primary feedstock, subsequently transformed into high-quality e-gasoline, demonstrating its dual functionality as both a precursor and an effective octane booster. This dual functionality positions methanol as a crucial facilitator in the transition towards more sustainable and efficient fuel alternatives. In this work, we studied the impact of methanol additions (20–40 %, by vol.) on the octane and autoignition characteristics of an MTG having Research Octane Number (RON) of 82.1. The octane ratings of methanol-rich MTG were measured using a Cooperative Fuel Research (CFR) engine, while autoignition studies were conducted using a high-pressure shock tube (HPST) and a rapid compression machine (RCM). Autoignition experiments covered a broad spectrum of temperatures (680–1370 K), pressures (10, 20, 30, and 40 bar), and varied fuel composition (<em>φ</em> = 0.5, 1). Results indicate that ignition delay times of MTG are significantly perturbated with methanol additions. At intermediate and low temperature (≈ &lt; 920 K), methanol-rich MTGs exhibit a strong reactivity-inhibiting effect, with ignition delays prolonged as methanol content rises. This trend agrees well with the RON values of MTG and MTG blended with methanol. Conversely, at higher temperatures (&gt; 920 K), methanol blending promotes reactivity, shortening the ignition delays. This reactivity-promoting effect increases with increasing methanol content. A recently developed gasoline kinetic model by the authors was employed to evaluate the influence of methanol blending on MTG reactivity. Ignition delay predictions were validated using both quaternary and multicomponent (MC) methanol-containing surrogates, with the MC surrogate providing the most accurate predictions. Lastly, temperature-based sensitivity analyses were performed to identify key reactions responsible for the reactivity- promoting and inhibiting effects of methanol blending on MTG combustion characteristics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114416"},"PeriodicalIF":6.2,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144866203","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":"Flame dynamics of nonpremixed coflow DME jets in momentum-driven and buoyancy-momentum-driven regimes","authors":"Dong Jun Kim ,&nbsp;Jeong Park ,&nbsp;Suk Ho Chung ,&nbsp;Chun Sang Yoo","doi":"10.1016/j.combustflame.2025.114396","DOIUrl":"10.1016/j.combustflame.2025.114396","url":null,"abstract":"&lt;div&gt;&lt;div&gt;This study experimentally investigates the behavior of laminar nonpremixed flames of 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;-diluted Dimethyl ether (DME) in a coflow jet under varying fuel mole fractions (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;X&lt;/mi&gt;&lt;mi&gt;F&lt;/mi&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;), jet velocities (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;U&lt;/mi&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;), and temperatures (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; = 300, 400, and 500 K). A wide range of lifted flame behaviors is observed as &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;U&lt;/mi&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; increases, including three distinct trends in liftoff height (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;H&lt;/mi&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;): Monotonically increasing (M.I.), Monotonically decreasing (M.D.), and U-shaped &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;H&lt;/mi&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. In addition, two flame extinction modes (i.e., flame blowoff and blowout) are identified depending on the jet developing length (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;Z&lt;/mi&gt;&lt;mi&gt;f&lt;/mi&gt;&lt;mi&gt;r&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;). The observed flame behaviors are classified into three different regimes based on the Richardson number (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;i&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;): Momentum-driven (MD), Buoyancy-momentum-driven (BMD), and Buoyancy-driven (BD) regimes. The monotonically decreasing &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;H&lt;/mi&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; behavior appears exclusively in the buoyancy-momentum-driven regime, where buoyancy effects remain significant. In contrast, the monotonically increasing &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;H&lt;/mi&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; behavior is confined to the momentum-driven regime, where jet momentum dominates. The U-shaped &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;H&lt;/mi&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; behavior emerges during the transition between the buoyancy-momentum-driven and momentum-driven regimes. To elucidate the underlying stabilization mechanisms, time-resolved flame edge measurements are conducted using laser ignition downstream of the nozzle, from which flame stabilization and blowout mechanisms are identified for each regime. In the buoyancy-momentum-driven regime, flame liftoff is influenced by a combination of buoyancy, jet momentum, and heat loss to the nozzle rim. In the momentum-driven regime, jet momentum is the dominant factor. Correlations for &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;H&lt;/mi&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; are developed in terms of the laminar flame speed (&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;), &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;U&lt;/mi&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;X&lt;/mi&gt;&lt;mi&gt;F&lt;/mi&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, and &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;i&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, reflecting the regime-dependent influence of buoyancy and momentum. Finally, the flame blowoff and liftoff limits of attached flames are characterize","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114396"},"PeriodicalIF":6.2,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144880074","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":"An experimental and kinetic modeling study of ethyl tert-butyl ether. Part I: High-temperature pyrolysis and oxidation chemistry","authors":"Jiaxin Liu ,&nbsp;Jin-Tao Chen ,&nbsp;Maryam Khan-Ghauri ,&nbsp;Joseph E. Jacobs ,&nbsp;Claire M. Grégoire ,&nbsp;Olivier Mathieu ,&nbsp;Eric L. Petersen ,&nbsp;Peter K. Senecal ,&nbsp;Chong-Wen Zhou ,&nbsp;Henry J. Curran","doi":"10.1016/j.combustflame.2025.114394","DOIUrl":"10.1016/j.combustflame.2025.114394","url":null,"abstract":"<div><div>A comprehensive experimental and kinetic modeling study of the combustion of ethyl <em>tert</em>-butyl ether (ETBE) is conducted over a wide range of engine-relevant conditions. Part I focuses exclusively on the high-temperature chemistry including relevant experimental pyrolysis and high-temperature oxidative validation targets. Part II focuses on the low- to intermediate temperature chemistry of ETBE and uses ignition delay times to validate the mechanism. CO time-history profiles from highly-diluted ETBE pyrolysis are measured behind reflected shock waves with a spectroscopic laser diagnostic in the 1235–1528 K temperature range near atmospheric pressure. Laminar flame speed (LFS) measurements of ETBE oxidation in air are conducted at 1 and 3 atm in the equivalence ratio range of 0.7–1.6. Reaction classes involving unimolecular decomposition, hydrogen atom abstraction, fuel radical <em>β</em>-scission and isomerization reactions are included to describe the high-temperature chemistry using the GalwayMech1.0 core C₀–C₄ chemistry. Sensitivity analyses reveal that the rate constant of the elimination reaction ETBE ⇌ IC₄H₈ + C₂H₅OH is very important to species profile predictions, followed by the two C–O bond breaking channels. Hence, pressure- and temperature-dependent rate constants for the two alcohol elimination channels: (a) ETBE ⇌ IC₄H₈ + C₂H₅OH and (b) ETBE ⇌ TC₄H₉OH + C₂H₄ were calculated using quantum chemistry. Similarly, the C–O bond <em>β</em>-scission reaction of ETBE radical, ETBE-S ⇌ TĊ₄H₉ + CH₃CHO was also calculated in this study. The LFS predictions are dominated by the C₀–C₂ core chemistry with the fuel chemistry not appearing to be sensitive.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114394"},"PeriodicalIF":6.2,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144866177","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":"Unraveling the low-temperature chemistry of nitrogenous compounds by informatively kinetic modeling of N,N-dimethylformamide","authors":"Du Wang ,&nbsp;Zhi-Hao Zheng ,&nbsp;Zhi-Min Wang ,&nbsp;Xu-Peng Yu ,&nbsp;Kai-Ru Jin ,&nbsp;Wang Li ,&nbsp;Chang-Yang Wang ,&nbsp;Ling-Nan Wu ,&nbsp;Long Zhao ,&nbsp;Jiu-Zhong Yang ,&nbsp;Zhen-Yu Tian","doi":"10.1016/j.combustflame.2025.114390","DOIUrl":"10.1016/j.combustflame.2025.114390","url":null,"abstract":"&lt;div&gt;&lt;div&gt;N,N-Dimethylformamide (DMF) is a volatile organic pollutant prevalent in many modern industrial processes and an intermediate formed in nitrogenous compound low-temperature oxidation. The low-temperature oxidation of DMF was performed between 450 and 900 K under fuel-lean conditions (Φ = 0.5) in a jet-stirred reactor coupled with synchrotron vacuum ultraviolet photoionization molecular beam mass spectrometry. Weak negative temperature coefficient (NTC) behavior was observed within 520 - 650 K. A comprehensive kinetic model was developed based on the previous pyrolysis model. Key reaction parameters, including hydrogen atom abstraction, first O&lt;sub&gt;2&lt;/sub&gt; addition to fuel radicals, and intermediate radical decomposition pathways, were determined through &lt;em&gt;ab initio&lt;/em&gt; - transition state theory - RRKM/ME calculation. The model successfully predicts DMF consumption and major product formation, though discrepancies persist for certain intermediates due to remaining uncertainties in nitrogen chemistry. Kinetic analysis reveals that at NTC temperatures, DMF oxidation is predominantly controlled by carbonyl-site oxygen addition followed by rapid QOOH radical decomposition, generating CH&lt;sub&gt;3&lt;/sub&gt;NCH&lt;sub&gt;2&lt;/sub&gt;, CO&lt;sub&gt;2&lt;/sub&gt;, and OH through Waddington-type reactions and inhibiting second O&lt;sub&gt;2&lt;/sub&gt; addition. In contrast, methyl-site O&lt;sub&gt;2&lt;/sub&gt; addition exhibits higher reaction barriers for QOOH decomposition, enabling second oxygen addition and subsequent low-temperature chain-branching reaction pathways critical for NTC behavior. Based on recent advances in nitrogen compound oxidation kinetics, the generalized behavior of different types of nitrogen-containing compounds was further discussed. Compounds with primary and secondary nitrogen atoms rarely exhibit NTC behavior due to preferential HO&lt;sub&gt;2&lt;/sub&gt; elimination from α-site ROO radicals via adjacent N&lt;img&gt;H sites, effectively suppressing low-temperature reactivity. Conversely, tertiary nitrogen compounds lacking N&lt;img&gt;H bonds can undergo efficient auto-oxidation through rapid intramolecular hydrogen migration. It generates highly oxygenated intermediates along with OH radicals and, therefore, is very likely to exhibit NTC behavior, though its magnitude depends on the competition between fuel-specific rates of oxygen addition and QOOH decomposition.&lt;/div&gt;&lt;/div&gt;&lt;div&gt;&lt;h3&gt;Novelty and significance statement&lt;/h3&gt;&lt;div&gt;The negative temperature coefficient (NTC) behavior of nitrogenous compounds was first experimentally reported during the low-temperature oxidation of N,N-dimethylformamide. Leveraging advanced diagnostic techniques and comprehensive high-level ab initio calculations, we developed an informative kinetic model that successfully reproduces the observed oxidation behavior. Through detailed model analysis and integration with recent advances in nitrogenous compound low-temperature chemistry, we have formulated general principles governing NTC behavior in nitrogen-contai","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114390"},"PeriodicalIF":6.2,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144860933","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":"Direct numerical simulation of nonpremixed ignition under gasoline compression-ignition engine conditions","authors":"Zisen Li ,&nbsp;Evatt R. Hawkes ,&nbsp;Armin Wehrfritz ,&nbsp;Bruno Savard","doi":"10.1016/j.combustflame.2025.114393","DOIUrl":"10.1016/j.combustflame.2025.114393","url":null,"abstract":"&lt;div&gt;&lt;div&gt;We present an analysis of the ignition process in thermochemical conditions relevant to gasoline compression-ignition (GCI) engines using direct numerical simulation (DNS). Two-dimensional DNS modelling the interaction of turbulence with an igniting double mixing layer are carried out. Three different primary reference fuel (PRF) blends, PRF0, PRF70, and PRF90, to span a range of different possible compression ignition scenarios are investigated. The fuel chemistry is shown to significantly affect the ignition process and the transition to a fully burning high-temperature flame. All three cases exhibit a diffusively supported cool flame which propagates towards richer mixtures faster than expected from homogeneous ignition delays. High-temperature combustion (HTC) initiates in rich mixtures in the PRF0 case, in both rich and lean mixtures in the PRF70 case, and in lean mixtures in the PRF90 case, which is consistent with expectations from homogeneous ignition delays. Budget analysis shows that HTC flames are diffusively supported in all cases, and as a result progress more rapidly from the ignition location to surrounding mixtures than homogeneous ignitions suggest. A quantitative model is proposed for the premixed flame propagation speed in the stratified and autoignitive mixtures. By considering the effects of normalised residence time of reactant at the flame surface, the conditional mean turbulent flame speed, conditioned upon mixture fraction, can be related to 1D referenced laminar flame speeds. The mechanism of consumption of the stoichiometric surface is examined by considering both displacement speed statistics and by tracking each single edge flame front. In the PRF0 case the results show the stoichiometric surface is consumed mostly by propagating HTC fronts that are almost parallel to it, which is referred to parallel consumption mode, while results in the PRF70 and PRF90 cases show signatures of edge-flame propagation as a secondary mechanism. For edge-flame mode the contribution of tangential-to &lt;span&gt;&lt;math&gt;&lt;mi&gt;Z&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; diffusion to the displacement speed prevails over that of normal-to-&lt;span&gt;&lt;math&gt;&lt;mi&gt;Z&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; diffusion. Overall the results demonstrate significant fuel-chemistry effects on the evolution of the ignitions, which will probably translate into significant differences in flame structure in a practical GCI engine.&lt;/div&gt;&lt;div&gt;&lt;strong&gt;Novelty and significance statement&lt;/strong&gt;&lt;/div&gt;&lt;div&gt;This work presents the first DNS of turbulent, nonpremixed autoignition targeting fuel chemistry effects in gasoline compression ignition (GCI) engines. The novelty further arises from two aspects. First, it is the first study to quantitatively model flame displacement speed in autoignitive, stratified mixing layers using the residence time concept. Second, the evolution of edge flame fronts is tracked in complex turbulent flows to enable temporal characterisation of edge flame dynamics and reveal how tangen","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114393"},"PeriodicalIF":6.2,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144866740","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":"Hysteresis phenomenon in oblique detonation wave/boundary layer interactions","authors":"Xin Han,&nbsp;Ruofan Qiu,&nbsp;Yancheng You","doi":"10.1016/j.combustflame.2025.114399","DOIUrl":"10.1016/j.combustflame.2025.114399","url":null,"abstract":"<div><div>This paper investigates the hysteresis phenomenon in the interaction between the oblique detonation wave (ODW) and the turbulent boundary layer within the oblique detonation engine (ODE) combustor. The oblique detonation wave within the combustor reflects downstream of the expansion corner on the upper wall, causing boundary layer separation. Hysteresis phenomenon has been observed in the flow field as the upper wall expansion angle varies along a loop. The hysteresis is categorized into three types: 1) hysteresis of boundary layer separation, 2) hysteresis of the reflection pattern formed by the incident ODW and separation shock wave, and 3) hysteresis in thrust performance. The first type of hysteresis arises from the irreversibility of boundary layer separation. Hysteresis in the reflection pattern is dominated by inviscid mechanisms. That is, under the inflow conditions considered in this paper, a dual-solution domain exists for the inviscid reflections of the asymmetric shock wave and detonation wave. Polar analysis provides an angular interval where the transition from regular to Mach reflection occurs. However, it does not identify the dual-solution domain, which shows the limitations of polar analysis in shock and detonation wave reflections. The physical dissipation in the viscous simulation enables the regular reflection to persist even when the intensity of the separation shock slightly exceeds the inviscid transition angle. The hysteresis in thrust performance is a result of the reflection pattern hysteresis, with the presence of the Mach stem leading to a loss in thrust performance. An in-depth understanding of hysteresis is essential for the engineering applications of ODEs, particularly for their active control.</div></div><div><h3>Novelty and significance statement</h3><div>The novelty of this work lies in the first identification of hysteresis induced by looped variations in wall configuration within a space-confined viscous ODE combustor. This paper presents a detailed investigation of the asymmetric reflection of shock waves and oblique detonation waves, providing angular intervals for the transition from regular to Mach reflections based on polar analysis. Furthermore, the dual-solution domain, which cannot be accurately captured by conventional polar analysis, is revealed through inviscid numerical simulations.</div><div>The significance of this research is twofold: it reveals the hysteresis phenomenon within an ODE combustor, enhancing the understanding of detonation wave dynamics, and it offers critical insights into the active control of ODE flow fields.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114399"},"PeriodicalIF":6.2,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144866179","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 threshold and emission characteristics of self-sustaining smoldering combustion","authors":"Yuying Chen ,&nbsp;Shaorun Lin ,&nbsp;Yichao Zhang ,&nbsp;Yunzhu Qin ,&nbsp;Yuxin Zhou ,&nbsp;Wei Wei ,&nbsp;Xinyan Huang","doi":"10.1016/j.combustflame.2025.114411","DOIUrl":"10.1016/j.combustflame.2025.114411","url":null,"abstract":"<div><div>Smoldering, as a flameless combustion of porous fuels, is slow, low-temperature, and persistent, so its ignition criteria are fundamentally different from igniting a flame. This work designs a 1D smoldering reactor to investigate the minimum smoldering ignition requirements of biomass fuel (150 kg/m³) and applies a porous plate ignitor to control the heating intensity and duration. For initiating smoldering towards self-sustaining, we found the minimum ignition heat flux approaching 0.5 kW/m² under a long heating duration and the minimum ignition energy (MIE) of 0.06 MJ/m² under short and intensive heating. At a low ignition intensity, a large Darcy airflow through the fuel bed will cool the heating zone and delay the ignition. With a strong ignition source, the cooling effect of Darcy airflow becomes negligible, so the increasing airflow enhances the oxygen supply and accelerates smoldering ignition. Reducing fuel moisture content or improving oxygen supply can further lower the required MIE. During smoldering ignition, CO₂ exhibits a much earlier increase than CO and CH₄, so it could be an optimal indicator for the early detection of smoldering fires. This work helps understand the governing mechanisms of smoldering ignition and is of practical significance in mitigating fire hazards in urban and wildland.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114411"},"PeriodicalIF":6.2,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144860931","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":"Publication / Copyright Information","authors":"","doi":"10.1016/S0010-2180(25)00409-2","DOIUrl":"10.1016/S0010-2180(25)00409-2","url":null,"abstract":"","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"279 ","pages":"Article 114372"},"PeriodicalIF":6.2,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144860904","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":"Measurements and modeling of laminar burning velocities and chemical kinetics analysis of CH3OH blended with NH3 and H2, with and without CO2 addition","authors":"Xiangyu Meng ,&nbsp;Xianrong Wu ,&nbsp;Mingkun Zhang ,&nbsp;Wenchao Zhu ,&nbsp;Zechuan Cui ,&nbsp;Jianlin Cao ,&nbsp;Mingshu Bi","doi":"10.1016/j.combustflame.2025.114414","DOIUrl":"10.1016/j.combustflame.2025.114414","url":null,"abstract":"<div><div>Methanol (CH₃OH), a carbon-neutral fuel, blended with ammonia (NH₃) cracked gas, has significant potential for efficient combustion. Additionally, the use of CO₂-enriched exhaust gas recirculation (EGR) systems can effectively reduce NO_x emissions. However, experimental data on the laminar burning velocity (LBV) of CH₃OH blended with NH₃ cracked gas under CO₂ dilution conditions are scarce. In this study, the LBV of low-carbon ternary fuels with different fuel blending ratios and CO₂ dilution ratios was measured at elevated temperatures and pressures. The previously developed CH₃OH/NH₃/H₂ combustion mechanism was optimized and then used to analyze the combustion characteristics of a mixture with high-proportion NH₃ cracked gas combined with CH₃OH. The results showed that the optimized mechanism accurately predicted the LBV and NO emissions of the CH₃OH/NH₃/H₂/CO₂ blends. With increasing NH₃ cracking ratios, the co-combustion of CH₃OH with cracking NH₃ significantly enhanced the LBV and reduced NO emissions. The reduction in NO emissions followed a nonlinear relationship with the NH₃ cracking ratio, with more significant reductions observed at cracking ratios of 90–99%, compared to the 50–90% range. At NH₃ cracking ratios of 90–99%, most NH₃ in the mixture is cracked, leading to sharp reductions in NH and HNO concentrations. Meanwhile, the cracking of NH₃ produces substantial amounts of H₂, which accelerates combustion and shortens the duration of NO formation. Additionally, a significant correlation was observed between LBV and NO. Using the NO and LBV of pure NH₃ at an equivalence ratio of 1 as a baseline, four distinct regions were delineated. It was found that X70CR99 (30% CH₃OH/70% NH₃ with 99% cracking ratio), X70CR98, and X30CR99 were located in the high LBV and low NO region.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"281 ","pages":"Article 114414"},"PeriodicalIF":6.2,"publicationDate":"2025-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144851873","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}