Combustion and Flame最新文献

{"title":"Surface morphology effects on ignition temperature of single micron-sized Iron particles","authors":"Liulin Cen,&nbsp;Yong Qian,&nbsp;Xingcai Lu","doi":"10.1016/j.combustflame.2025.114216","DOIUrl":"10.1016/j.combustflame.2025.114216","url":null,"abstract":"<div><div>Micron-sized iron particles are promising energy storage carriers for combustion-based power systems, underscoring the critical importance of understanding their combustion performance and reaction kinetics. In this study, sponge iron particles with diameters ranging from 20 to 65 μm, and specific surface areas 4 to 6 times greater than those of spherical iron particles of equivalent mass, were injected into uniform high temperature environments at varying temperatures. High-speed microscopic imaging was employed to capture ignition frequencies with particle size resolution. Experimental results indicate that a small fraction of sponge iron particles can ignite at an ambient temperature of 880 K. When the ambient temperature increases to 1000 K, over 90% of the particles undergo ignition. Within the temperature range of 900–1000 K, the ignition frequency of iron particles increases with particle diameter and is independent of oxygen concentration. A numerical model based on the parabolic law on the growth of the oxide layer shows good agreement with the experimental results. Theoretical analysis reveals that increasing the specific surface area of iron particles can effectively lower their ignition temperature. Notably, iron particles produced through the hydrogen direct reduction of combusted iron oxide particles in iron fuel cycle, which possess significantly higher specific surface areas, are predicted to achieve ignition temperatures as low as 630 K, making them highly advantageous for combustion applications in power systems.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114216"},"PeriodicalIF":5.8,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143918438","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":"Experimental and modeling study of the autoignition behavior of a saturated heterocycle: Pyrrolidine","authors":"S. Scott Goldsborough ,&nbsp;Mads C. Jespersen ,&nbsp;Jeffrey S. Santner ,&nbsp;Raghu Sivaramakrishnan ,&nbsp;Hong-Quan Do ,&nbsp;Benoîte Lefort ,&nbsp;Zeynep Serinyel ,&nbsp;Guillaume Dayma ,&nbsp;Luna Pratali Maffei ,&nbsp;Marco Mehl ,&nbsp;Matteo Pelucchi ,&nbsp;William J. Pitz","doi":"10.1016/j.combustflame.2025.114134","DOIUrl":"10.1016/j.combustflame.2025.114134","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Experiments are conducted in both rapid compression machine (RCM) and shock tube (ST) to better quantify autoignition behavior (e.g., ignition delay, heat release) and understand heteroatomic effects in heterocyclic compounds, which are important reference components for the combustion of biomass-derived liquid fuels. These tests focus on the nitrogen-containing, five-membered saturated ring, pyrrolidine, at diluted conditions covering pressures of 20 and 50 bar, temperatures of 720–1450 K and a range of stoichiometries (ϕ = 0.5–2). A chemical kinetic model is developed and coupled to an existing combustion kinetics framework describing key nitrogen containing intermediates (e.g. pyrrole, ammonia and NOx). H-abstraction reactions by OH, H, CH&lt;sub&gt;3&lt;/sub&gt; and HO&lt;sub&gt;2&lt;/sub&gt;, are determined using ab-initio transition state theory methods, while analogies to cyclopentane are adopted for many other reactions, such as ring-opening. The autoignition measurements reveal the lack of negative temperature coefficient (NTC) behavior and low-temperature chemistry for pyrrolidine, as opposed to its saturated hydrocarbon analogue, cyclopentane. Interestingly, at the lowest temperatures (&lt;em&gt;T&lt;/em&gt; &lt; 750 K), the reactivity of cyclopentane is greater than pyrrolidine, while at higher temperatures, pyrrolidine becomes more reactive. Agreement between the experimental measurements and the model is good, and it is found that H-abstraction reactions by HO&lt;sub&gt;2&lt;/sub&gt; and ensuing chemistry play key roles in controlling the reactivity of this cyclic amine. Most of the fluxes, i.e., &gt;70 %, are predicted to move through 1- or 2-pyrroline (C&lt;sub&gt;4&lt;/sub&gt;H&lt;sub&gt;7&lt;/sub&gt;N) and then the cyclic C&lt;sub&gt;4&lt;/sub&gt;H&lt;sub&gt;6&lt;/sub&gt;N radical, at both lower and higher temperatures, to form either CH&lt;sub&gt;2&lt;/sub&gt;CHCHCHNH via ring-opening or pyrrole via β-scission. It appears that the ring opens more easily at lower temperature whereas the C–H β-scission dominates at higher temperature and lower pressure, such that the reaction of the fuel radical intermediate carrying an unpaired electron on the nitrogen atom with HO&lt;sub&gt;2&lt;/sub&gt; is the next most notable in promoting oxidation.&lt;/div&gt;&lt;div&gt;When comparing pyrrolidine and cyclopentane, which exhibits distinct pathways in different temperature regimes, the pyrrolidine pathways and sensitivity analysis align more closely to the high temperature case of cyclopentane where the important role of HO&lt;sub&gt;2&lt;/sub&gt; radicals is seen to provide chain branching through HO&lt;sub&gt;2&lt;/sub&gt; reaction with the fuel, accompanied by H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation and decomposition to OH. The formation of 5-membered diene rings and ring opening reactions are also found to be highly relevant. Of particular note, it is found that there is little influence of small molecule nitrogen-chemistry, e.g., NH&lt;sub&gt;2&lt;/sub&gt;, HCN, NO/NO&lt;sub&gt;2&lt;/sub&gt; on the reactivity of the pyrrolidine mixtures investigated here where no recirculated combustion gases are included.&lt;","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114134"},"PeriodicalIF":5.8,"publicationDate":"2025-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143903747","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A focus on the first-stage ignition of n-pentane","authors":"Pengzhi Wang ,&nbsp;Jesus Caravaca-Vilchez ,&nbsp;Tibor Nagy ,&nbsp;Shijun Dong ,&nbsp;Xiaobei Cheng ,&nbsp;Karl Alexander Heufer ,&nbsp;Henry J. Curran","doi":"10.1016/j.combustflame.2025.114207","DOIUrl":"10.1016/j.combustflame.2025.114207","url":null,"abstract":"<div><div>It is important to investigate the first-stage ignition of alkane fuels as it is responsible for the cool flame heat release in combustors, particularly engines. In the present study, a new set of ignition delay time (IDT) data of <em>n</em>-pentane is measured in a rapid compression machine (RCM) at <em>φ</em> = 1.0, <em>p</em> = 30 atm, and <em>T</em> = 685–994 K. Moreover, the species concentration profiles of major intermediate species, including alkenes, cyclic ethers, and aldehydes are measured in an RCM at a two-stage ignition condition (<em>T</em> = 730 K) using an updated 2 × fast-acting-valves sampling system. A new kinetic model has been developed to simulate this data. Both the core chemistry and thermochemistry of the low-temperature species associated with <em>n</em>-pentane have been systematically updated. It is found that updating the HȮ₂ + HȮ₂ reaction, which leadstwo ȮH radicals and O₂_, has no obvious influence on the 1st-stage ignition but significantly affects the prediction of the total IDT. This is because ȮH radicals are mainly produced from the formation and consumption of carbonyl-hydroperoxide species before the 1st-stage ignition; HȮ₂ radical recombination and the reaction H₂O₂ (<em>+</em>M) ↔ ȮH + ȮH (<em>+</em>M) become the main source of ȮH radical production only at/after the 1st-stage ignition. The updated thermochemistry data inhibit both the 1st-stage and total IDTs due to the shift towards reactant in the equilibrium of the RȮ₂ ⇌ <span><math><mover><mi>Q</mi><mi>˙</mi></mover></math></span>OOH reaction. The key reactions involved in the low-temperature chemistry are optimized using the Optima++ code within the uncertainty limits of reviewed rate constants in the literature. The present model can predict the experimentally measured data well and shows an improvement compared to previous models.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114207"},"PeriodicalIF":5.8,"publicationDate":"2025-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143902056","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":"Similarity in laminar burning velocity and scaling of turbulent flame speed of real fuel/air expanding flames: RP-3 kerosene with complex compositions","authors":"Linyuan Huang ,&nbsp;Sheng Huang ,&nbsp;Xinke Wang ,&nbsp;Xiaomeng Zhao ,&nbsp;Hui Li ,&nbsp;Quan Zhu","doi":"10.1016/j.combustflame.2025.114209","DOIUrl":"10.1016/j.combustflame.2025.114209","url":null,"abstract":"<div><div>In this study, we analyzed the similarity in the laminar burning velocity of RP-3 kerosene with different components and proposed the scaling of the turbulent flame speed for RP-3 kerosene/air premixed expanding flames. The laminar/turbulent flame propagation characteristics of the RP-3 kerosene/air mixture were measured using a constant volume combustion bomb. The results revealed that despite significant differences in the chemical composition of six RP-3 kerosene samples, their laminar burning velocities exhibited minimal variation under the same conditions. This was attributed to the inherent complexity of real fuels, which makes them less sensitive to the properties of any of their single components. Also, it was also confirmed that this low sensitivity became more pronounced when there were eight or more components in the fuel mixture. Moreover, it was found that the average molecular weights of the small pyrolysis fragments decomposed in the preheating zone were comparable between RP-3 kerosene and some hydrocarbon fuels with large molecular weights (e.g. C4-C8 n-alkanes, iso-octane, iso-cetane, n-decane and decalin). Consequently, they exhibited analogous thermal-diffusional effects. Based on this, it was also found that these fuels had similar normalized turbulent flame speeds under the scaling of the correlation of <span><math><mrow><mrow><mo>(</mo><mrow><mi>d</mi><mo>〈</mo><mi>r</mi><mo>〉</mo><mo>/</mo><mi>d</mi><mi>t</mi></mrow><mo>)</mo></mrow><mo>/</mo><mrow><mo>(</mo><mrow><mi>σ</mi><msub><mi>S</mi><mi>L</mi></msub></mrow><mo>)</mo></mrow><mo>=</mo><mi>A</mi><mi>R</mi><msubsup><mi>e</mi><mrow><mi>T</mi><mo>,</mo><mi>f</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msubsup></mrow></math></span>, and the coefficient (<span><math><mi>A</mi></math></span>) had a pronounced nonlinear relationship with the Markstein number (<span><math><mrow><mi>M</mi><mi>a</mi></mrow></math></span>). Finally, a unified correlation for turbulent flame speed considering the thermal-diffusional effect (<span><math><mrow><mrow><mo>(</mo><mrow><mi>d</mi><mo>〈</mo><mi>r</mi><mo>〉</mo><mo>/</mo><mi>d</mi><mi>t</mi></mrow><mo>)</mo></mrow><mo>/</mo><mrow><mo>(</mo><mrow><mi>σ</mi><msub><mi>S</mi><mi>L</mi></msub></mrow><mo>)</mo></mrow><mo>=</mo><mrow><mo>(</mo><mrow><mn>0.0664</mn><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo><mi>M</mi><mi>a</mi><mo>/</mo><mn>2</mn></mrow></msup><mo>+</mo><mn>0.0803</mn></mrow><mo>)</mo></mrow><mi>R</mi><msubsup><mi>e</mi><mrow><mi>T</mi><mo>,</mo><mi>f</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msubsup></mrow></math></span>) based on the Markstein number was proposed, which could describe not only the present experimental data, but also turbulent flame speeds from literature for other fuels under wide conditions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114209"},"PeriodicalIF":5.8,"publicationDate":"2025-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899441","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":"Co-pyrolysis of 1-naphthylmethyl radical with allene and propyne: Radical-molecule (C3H4) vs. radical-radical (C3H3) reaction pathways","authors":"Zhongkai Liu ,&nbsp;Mengqi Wu ,&nbsp;Zhaohan Chu ,&nbsp;Xiaoqing Wu ,&nbsp;Jiabin Huang ,&nbsp;Jiuzhong Yang ,&nbsp;Bin Yang ,&nbsp;Feng Zhang","doi":"10.1016/j.combustflame.2025.114206","DOIUrl":"10.1016/j.combustflame.2025.114206","url":null,"abstract":"<div><div>In this work, we conducted a combined experimental and theoretical investigation into the reactivity of naphthylmethyl radical (1-A2CH₂, C₁₁H₉) with allene (aC₃H₄) and propyne (pC₃H₄). Co-pyrolysis experiments of 1-(chloromethyl)naphthalene (1-A2CH₂Cl) with aC₃H₄ or pC₃H₄ were studied using a flash pyrolysis microreactor coupled with synchrotron vacuum ultraviolet photoionization mass spectrometry. Significant signals at <em>m/z</em> = 39 (C₃H₃), attributed to the rapid H-abstraction and/or pyrolysis of C₃H₄ molecules, were detected in both experiments, indicating concurrent radical-radical (1-A2CH₂ + C₃H₃) and radical-molecule (1-A2CH₂ + aC₃H₄/pC₃H₄) reactions. Theoretical calculations reveal that the radical-radical reaction is kinetically favored under experimental conditions compared to the radical-molecule reaction, dominantly forming two C₁₄H₁₂ adducts, 1-(1,2-butadiene-4-yl)naphthalene (1-W1) and 1-(but‑yn-3-yl)naphthalene (1-W2), along with minor amounts of other C₁₄H₁₂ isomers and C₁₄H₁₁ + H products. The computed rate coefficients and branching ratios of various reaction channels expand the analysis to broader temperature and pressure ranges. The radical-radical products (1-W1 and 1-W2) dominate at atmospheric-to-high pressures (&gt;1 atm) or relatively lower temperatures (&lt;1500 K). At higher temperatures and low pressures, competition arises between radical-radical and radical-molecule pathways. Furthermore, the structures of bimolecular products differ significantly between the 1-A2CH₂ + aC₃H₄ and 1-A2CH₂ + pC₃H₄ reaction systems, with implications for the formation of larger polycyclic aromatic hydrocarbons.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114206"},"PeriodicalIF":5.8,"publicationDate":"2025-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A physics-informed machine learning approach for predicting dynamic behavior of reacting flows with application to hydrogen jet flames","authors":"Pushan Sharma ,&nbsp;Wai Tong Chung ,&nbsp;Matthias Ihme","doi":"10.1016/j.combustflame.2025.114190","DOIUrl":"10.1016/j.combustflame.2025.114190","url":null,"abstract":"<div><div>Traditional data-driven modeling approaches suffer from large error accumulation over time, divergence from expected physical behavior, and poor generalizability for out-of-distribution samples. To address this, we present Physics-informed hybrid Multiscale and Partitioned Network (PiMAPNet), a physics-informed machine learning (ML) strategy for generating multi-scale and multi-physics predictions by integrating low-resolution physics-based models with neural networks. Motivated by prior work on hybrid methods that combine coarse-grain simulations with ML, PiMAPNet employs state-space decomposition on the hydrodynamic (velocity and pressure) and thermochemical (temperature and species mass fractions) quantities for improved predictions of multiphysical processes. In addition, the ML model utilizes a mixture-of-experts (MoE) architecture that partitions the thermochemical state-space and employs a separate ML model to represent a specific region within this partition. We demonstrate this ML framework on a reacting hydrogen/air jet flame configuration. Results demonstrate that both the purely data-driven ML model and a traditional PIML approach could not represent the entire state-space, which resulted in unphysical behavior in long-term predictions. In contrast, the MoE-based PiMAPNet achieves higher accuracy and demonstrates improved robustness over extended time windows and out-of-distribution scenarios. Through our analysis, we show that PiMAPNet offers faster inference speed than a numerical simulation with comparable accuracies in multiple physical quantities.</div><div><strong>Novelty and Significance Statement</strong></div><div>This study introduces a novel physics-informed machine learning framework that enhances the predictive accuracy for chemically reacting flows by integrating low-resolution physics-based models with neural networks. The novelty of the framework lies in its specialized treatments for hydrodynamic and thermochemical variables. Additionally, the thermochemical state-space is partitioned to effectively capture the evolution of different regions within the state-space. The significance of our work is its ability to deliver highly accurate and robust predictions over extended time periods and for out-of-distribution scenarios. Furthermore, the separate treatment of different physical processes enables this framework to be extendable to other multi-physics systems, such as plasma physics or multiphase flows, making it a valuable tool for researchers across various domains in computational physics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114190"},"PeriodicalIF":5.8,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143894762","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":"Active control of thermoacoustic instability in a lean-premixed hydrogen-enriched combustor via open-loop acoustic forcing","authors":"Yu Liao ,&nbsp;Yongseok Choi ,&nbsp;Peijin Liu ,&nbsp;Kyu Tae Kim ,&nbsp;Yu Guan","doi":"10.1016/j.combustflame.2025.114175","DOIUrl":"10.1016/j.combustflame.2025.114175","url":null,"abstract":"<div><div>Open-loop control is proven effective in mitigating self-excited oscillations in conventional hydrocarbon-fueled combustors, but its effectiveness in hydrogen-fueled combustors remains unknown. This study experimentally investigates the effectiveness of open-loop acoustic forcing in mitigating self-excited periodic thermoacoustic oscillations in a lean-premixed, hydrogen-enriched turbulent combustor. We conducted experiments across a range of hydrogen volume fractions (20% to 50%), varying both the frequencies and amplitudes of the acoustic forcing introduced via three loudspeakers positioned upstream of the combustor. For the first time, we have demonstrated the effectiveness of open-loop acoustic forcing in mitigating self-excited periodic thermoacoustic oscillations in a hydrogen-enriched combustor, with suppression effects becoming more pronounced as the hydrogen content increases. We achieve up to a 90% reduction in pressure amplitude with minimal energy input—less than 1% of the combustor’s thermal power. At lower hydrogen fractions, the acoustic forcing fails to effectively decouple the flame dynamics from the acoustic field, resulting in significant oscillation amplification, with natural mode amplitudes increasing by over 2000%. A critical transition from global amplification to suppression occurs at a hydrogen volume fraction of 40%, where successful decoupling between the flame dynamics from the acoustic field is observed. These findings highlight the potential of open-loop control for mitigating thermoacoustic oscillations in hydrogen-enriched combustion systems, offering a promising approach to aid the decarbonization of gas turbines.</div><div><strong>Novelty and significance statement</strong></div><div>This study provides the first experimental evidence that open-loop acoustic forcing can effectively suppress thermoacoustic oscillations in hydrogen-enriched turbulent combustors. We show that increasing hydrogen volume fraction (20% to 50%) in the reactant mixtures enhances oscillation suppression, achieving up to a 90% reduction in pressure oscillation amplitude with minimal energy input (less than 1% of thermal power). A critical transition from oscillation amplification to suppression occurs at a hydrogen volume fraction of 40%, highlighting a threshold where decoupling between flame dynamics and the acoustic field becomes effective. These findings demonstrate the potential of open-loop control for stable operation in future hydrogen-enriched gas turbines.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114175"},"PeriodicalIF":5.8,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143888100","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":"Reactive nitrogen emissions and combustion dynamics in an axially staged rich-premixed ammonia combustion system","authors":"Jun Lee ,&nbsp;Ukhwa Jin ,&nbsp;Kyu Tae Kim","doi":"10.1016/j.combustflame.2025.114133","DOIUrl":"10.1016/j.combustflame.2025.114133","url":null,"abstract":"<div><div>The key technical problems associated with ammonia-fueled gas turbine combustion are well established in terms of flame-stabilization mechanisms for the less reactive ammonia and the overwhelming tendency to produce excessive nitrogen oxides through the fuel-NOx pathways. Recent studies suggest that these problems can be alleviated by chemical-kinetics-controlled fuel/air injection strategies, particularly those involving spatially separated reaction zones. The mechanistic role of axially staged secondary air and lean-premixed fuel/air jets injected into a high-temperature vitiated crossflow is, however, relatively underexplored; our knowledge of the effectiveness and relative importance of these strategies with regard to exhaust gas emissions and combustion dynamics is limited. Here, we undertake reduced-order kinetic modeling and comprehensive measurements of reactive nitrogen compounds (NOx, N₂O, NH₃) and unreacted hydrogen concentrations using an axial-staging-enhanced fuel-flexible test facility. We show that an increase in the primary equivalence ratio to 1.25 under non-staged rich-premixed conditions causes the total NOx emissions to be reduced substantially from 3030 to 57 ppmvd while producing unreacted ammonia and hydrogen emissions. When the rich-premixed ammonia condition is kept unchanged for the primary reaction zone, the second-stage reaction volume sequentially created by transverse air or lean-premixed H₂/air injection is revealed to mitigate unburned ammonia and hydrogen emissions effectively by reinitiating related elementary reactions. The existence of a second-stage reaction region, however, tends to augment NH-related NO production and thermal NO reactions, potentially nullifying or strongly reducing the effective gains. This apparent drawback is found to be much less pronounced in the H₂/air axial staging situations, as the production of the ammonia-derived fuel NO through <em>N</em> + OH → NO + <em>H</em> is relatively reduced, in close connection with the enhanced OH depletion reaction, H₂ + OH → H + H₂O. As well as achieving the minimum NOx concentration of about 367 ppmvd with no unreacted ammonia and nitrous oxide emissions, we demonstrate that high-amplitude low-frequency pressure fluctuations are largely suppressed under the investigated H₂/air-staged conditions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114133"},"PeriodicalIF":5.8,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143890911","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":"Rayleigh–Taylor instability-induced turbulence in lean hydrogen/air premixed flames","authors":"Jian Zheng ,&nbsp;Haiou Wang ,&nbsp;Evatt R. Hawkes ,&nbsp;Kun Luo ,&nbsp;Jianren Fan","doi":"10.1016/j.combustflame.2025.114183","DOIUrl":"10.1016/j.combustflame.2025.114183","url":null,"abstract":"&lt;div&gt;&lt;div&gt;In the present work, direct numerical simulations (DNS) are employed to investigate Rayleigh–Taylor (RT) instability-induced turbulence in planar hydrogen/air premixed flames. Four cases with different values of body force are considered, where the body force in cases G0-L30, G10-L30, G30-L30 and G50-L30 is 0, 10, 30 and 50 times the normal gravity &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;g&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, respectively. The effect of RT instability on flame morphology and flame speed was examined. It was found that the morphology of the flame front differs noticeably among the four cases. In case G0-L30, thermo-diffusive instability is evident, leading to small-scale cellular structures. In case G10-L30, RT instability becomes significant and finger structures of the flame develops. In cases G30-L30 and G50-L30, RT instability becomes dominant, resulting in the formation of bubble structures, while cellular structures due to thermo-diffusive instability are suppressed. The flame speed increases with increasing body force, primarily due to the increase in flame surface area, while the local reactivity remains largely unchanged. The characteristics of RT instability-induced turbulence in hydrogen/air flames are investigated. In cases G0-L30 and G10-L30, the weak turbulence first tends to be three-dimensional isotropic and subsequently evolves into one-component rod-like turbulence in the downstream region. In contrast, for cases G30-L30 and G50-L30 where RT instability has a dominant role, the RT instability-induced turbulence behind the flame is significant and predominantly rod-like, which then approximates three-dimensional isotropic in the downstream region. The analyses of turbulent kinetic energy spectra indicate that RT instability-induced turbulence follows the &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;k&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;5&lt;/mn&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; power-law scaling of isotropic turbulence to some extent for all cases. It was shown that the vorticity magnitude is several times larger in cases G30-L30 and G50-L30 compared with that in cases G0-L30 and G10-L30. The budget of enstrophy transport equation is examined to understand the mechanism of vorticity generation. The dissipation term was found to be the primary sink, while the baroclinic term was the main source term in the region immediately behind the flame. Moreover, it was found that the baroclinic term is mainly determined by the magnitudes of the pressure gradient. For cases G30-L30 and G50-L30, the increase in vorticity magnitude causes a rise in the vortex-stretching term in the downstream region, which becomes the primary source of enstrophy. The effect of domain size on flame structures and RT instability-induced turbulence was investigated, revealing that the domain length in the transverse direction affects the flame morphology. The flame speed is correlated with the product of the normalized body force magnitude","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114183"},"PeriodicalIF":5.8,"publicationDate":"2025-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143879259","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":"Ammonium dinitramide (ADN)-based hydroxyl-terminated polybutadiene (HTPB) propellant prepared by dimeryl diisocyanate (DDI)","authors":"Kai Xin,&nbsp;Yuanlu Cui,&nbsp;Zheng Huo,&nbsp;Ju Li,&nbsp;Kairui Yang,&nbsp;Chong Teng,&nbsp;Jianmin Li,&nbsp;Jinxian Zhai,&nbsp;Rongjie Yang","doi":"10.1016/j.combustflame.2025.114178","DOIUrl":"10.1016/j.combustflame.2025.114178","url":null,"abstract":"<div><div>Toluene diisocyanate (TDI) reacts with ammonium dinitramide (ADN), and isophorone diisocyanate (IPDI) adversely affects the thermal stability of ADN, which limits the application of ADN in hydroxyl‑terminated polybutadiene (HTPB) propellant. Due to the low toxicity and good physicochemical properties, dimeryl diisocyanate (DDI) is a good alternative for HTPB propellant. It was found that DDI is compatible with ADN, and HTPB/ammonium perchlorate (AP)/ADN/Al propellant cured by DDI was successfully prepared. Compared with HTPB/AP/Al and HTPB/AP/cyclotrimethylene trinitramine (RDX)/Al propellants, HTPB/AP/ADN/Al propellant has the lowest density, but the highest heat of combustion and theoretical specific impulse, which is related to the low density, high oxygen balance, high gas production and high energy of ADN. The addition of ADN promotes the low-temperature decomposition of AP in propellant, shortens the ignition delay time, and improves the burning rate and burning rate-pressure exponent. RDX and ADN have lower melting point and decomposition temperature, and release a lot of heat during decomposition, so it is easier to form a molten layer on the combustion surface, which promotes the Al agglomeration. However, the high gas production of ADN inhibits the Al agglomeration to some extent. The proportion of agglomerates in condensed combustion products of HTPB/AP/ADN/Al propellant is 5.11 % lower than that of HTPB/AP/RDX/Al propellant, and its size is also smaller. The Al content of condensed combustion products of HTPB/AP/ADN/Al propellant is nearly 1/3 lower than that of HTPB/AP/RDX/Al propellant. DDI is a curing agent suitable for ADN-based HTPB propellant, and compared with nitroamine explosives with negative oxygen balance such as RDX, ADN has many advantages in HTPB system.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"277 ","pages":"Article 114178"},"PeriodicalIF":5.8,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143873174","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}