Combustion and Flame最新文献

{"title":"Effect of hydroxypropyl methylcellulose and ferric chloride on hypergolic ignition of solidified ethanol fuels","authors":"Jerin John ,&nbsp;Purushothaman Nandagopalan ,&nbsp;Ankur Miglani ,&nbsp;Pranay Mudaliar ,&nbsp;Seung Wook Baek","doi":"10.1016/j.combustflame.2025.114126","DOIUrl":"10.1016/j.combustflame.2025.114126","url":null,"abstract":"<div><div>This study investigates the hypergolic ignition of reaction-driven solidified ethanol (RDSE) fuels, focusing on the effects of varying concentrations of hydroxypropyl methylcellulose (HPMC) gellant and ferric chloride (FeCl₃) dopant. Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA) are employed to examine molecular interactions and thermal properties. FTIR results indicate that no new covalent bonds are formed upon adding FeCl₃, whereas interactions primarily governed by weak hydrogen and ionic bonds. The apparent activation energy (<span><math><msub><mi>E</mi><mi>a</mi></msub></math></span>) has been determined for the fuel samples using iso-conversional model-free kinetics approach and found that <span><math><msub><mi>E</mi><mi>a</mi></msub></math></span> decreased with HPMC and FeCl₃ concentrations. Hypergolic ignition delay tests were attempted with the droplet study rocket grade hydrogen peroxide (90 % RGHP; H₂O₂) as an oxidizer, demonstrated that increasing HPMC concentration by 3 wt.% reduced ignition delay by ∼20 %, while a 5 wt.% increase in FeCl₃ concentration led to a ∼25 % reduction. Higher fuel temperatures enhanced the wetting and spreading behavior of H₂O₂ droplets, improving oxidizer-fuel interaction and reducing ignition delay. Overall, solidification of ethanol using HPMC with FeCl₃ eliminates the catalyst as FeCl₃ acts as both catalyst and binding agent.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114126"},"PeriodicalIF":5.8,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental study and kinetic modeling of NH3/DME blends oxidation in a jet stirred reactor","authors":"Mingyu Yu,&nbsp;Guangqian Luo,&nbsp;Ruize Sun,&nbsp;Li Wang,&nbsp;Mengli Zhou,&nbsp;Lingxuan Chen,&nbsp;Xian Li,&nbsp;Hong Yao","doi":"10.1016/j.combustflame.2025.114125","DOIUrl":"10.1016/j.combustflame.2025.114125","url":null,"abstract":"<div><div>Since both can be obtained from renewable sources, ammonia and dimethyl ether (DME) emerge as one of the most promising fuel combination candidates. In this study, NH₃/DME oxidation experiments were conducted within a jet stirred reactor (JSR) across various operation conditions to reveal kinetics of NH₃/DME co-combustion. A detailed chemical mechanism was proposed to reasonably reproduce the measurements. The experimental results underscore the significant enhancement of DME on NH₃ oxidation, where a notable decline in the initial oxidation temperature of NH₃ was observed as the blending ratio of DME increased. At lean and stoichiometric conditions, NO concentration maintained a high level, exhibiting a consistent upward trend as the temperature progressively rose. The low NH₃/high DME blending conditions are more liable to lead to the conversion of NH₃ to NO. Whereas at rich conditions, the NO formation was inhibited. Moreover, the simulation results show that our proposed model could provide accurate predictions on the concentrations of NH₃, O₂, CO₂ and CO, but underestimate the rates of NO formation reactions. Overall, the present model has better prediction performances on NH₃/DME oxidation compared with the existing mechanism in the literatures. According to the sensitivity analysis, it is found that CH₃OCH₃(+M)=CH₃+CH₃O(+M) and H+O₂=O+OH are the major reactions that trigger production of OH and HO₂ active radicals, which promote the NH₃ oxidation reaction and the formation of NO further. While the chain termination reactions NH₂+NO=N₂+H₂O and CH₃+HO₂=CH₄+O₂ inhibit the reactivity. The HNO pathway dominates the formation of NO. With the escalation in the blending ratio of DME, the HNO pathway is strengthened, thereby causing a higher NO conversion. Above all, this research offers valuable insights into the oxidation mechanisms of NH₃/DME and provides reliable empirical data sources for model construction and optimization.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114125"},"PeriodicalIF":5.8,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684420","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":"Effects of obstacle hole shape, obstacle position and ammonia ratio on hydrogen-ammonia-air flame dynamics in a horizontal closed duct","authors":"Bo Liang ,&nbsp;Kai Zhang ,&nbsp;Wei Gao ,&nbsp;Jiaxing Zhang ,&nbsp;Yanchao Li","doi":"10.1016/j.combustflame.2025.114127","DOIUrl":"10.1016/j.combustflame.2025.114127","url":null,"abstract":"<div><div>As a carbon-free energy carrier, hydrogen-ammonia mixture has significant development potential in internal combustion engine applications. To clarify the coupling mechanisms between flame acceleration and explosion overpressure generation, the effects of obstacle hole shape, obstacle position, and ammonia ratio on flame evolution, flame tip speed, and pressure dynamics on hydrogen-ammonia-air flame in a horizontal closed duct were investigated. Specifically, the obstacle positions in this study were determined based on the three different stages of flame evolution: 1) the finger-shaped flame acceleration stage, 2) the flame skirt-wall contact deceleration stage, and 3) the tulip flame speed fluctuation stage. The objective is to investigate the influence mechanisms of obstacles at each stage. For flame evolution and flame tip speed, the obstacle installed at the tulip flame stage (#3) induces the strongest flame turbulence intensity, followed by the obstacle located at the flame skirt wall-contact stage (#2), with the lowest turbulence intensity observed for the obstacle installed in the early finger-shaped flame stage (#1). The enhancement effect of obstacle #2 on flame acceleration is the most significant, as the flame tip speed reaches its peak at the flame skirt wall-contact stage (#2). For pressure dynamics, the pressure fluctuation amplitude is greatest under obstacle #2 condition, while it is smallest under obstacle #3 condition due to the irregular flame front disrupting the reflection of pressure waves. For the explosion overpressure generation mechanism, the theoretical model exhibits good predictive performance, with the theoretical results effectively reproducing the experimental explosion overpressure. The acceleration factor can quantify the flame acceleration effects well and also reveal that the flame acceleration effect on flame tip speed is a key factor influencing explosion overpressure and pressure rise rate.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114127"},"PeriodicalIF":5.8,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684398","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":"Super adiabatic combustion of carbon-free and carbon-containing fuels","authors":"Jennifer L. Schurr ,&nbsp;Atmadeep Bhattacharya ,&nbsp;Alexander A. Konnov ,&nbsp;Ossi Kaario","doi":"10.1016/j.combustflame.2025.114106","DOIUrl":"10.1016/j.combustflame.2025.114106","url":null,"abstract":"<div><div>The present work provides a new perspective on super adiabatic combustion (SAC) of fuel/air mixtures involving methane, ethane, propane, butane, heptane, iso-octane, 1-hexene, toluene, ammonia, and hydrogen. The simulations cover the temperature range of 1200–2000 K, initial pressures of 1–50 atm, and equivalence ratios of 0.5–2.0. The detailed chemical kinetic mechanism C3MechV3.5 has been used for 0D simulations in a constant volume batch reactor with Cantera 2.5.0. It has been found that SAC can be observed in lean, stoichiometric, and rich mixtures. While all hydrocarbon fuels show a strong correlation with each other, hydrogen and ammonia produce a significantly different pattern of SAC compared to carbon-containing fuels. Two reasons for super adiabaticity have been identified: (1) the super-equilibrium of H₂O, NO, and/or CO₂ due to the time delay between their production and consumption, and (2) the energy intensive dissociation reactions of, e.g., N₂, H₂O, and CO₂. Furthermore, it has been found that a super-equilibrium of H₂O always indicates super adiabaticity. For paraffinic hydrocarbons, since SAC is primarily governed by C₀-C₁ and NO_x reactions, the low and intermediate temperature auto-ignition chemistry involving alkyl-peroxyl radical and the poly-aromatic hydrocarbon (PAH) reactions do not influence SAC.</div><div><strong>Novelty and Significance Statement</strong></div><div>As of now, super adiabatic combustion (SAC) has been shown mainly for rich premixed hydrocarbon/oxidizer mixtures. In the present work, SAC is reported for a wide range of equivalence ratios covering lean, stoichiometric, and rich mixtures of different classes of hydrocarbons in air. This work also presents a comprehensive analysis of SAC characteristics. Furthermore, the SAC of hydrocarbon fuels is compared with that of carbon-free fuels ammonia and hydrogen. For the first time in the literature, the following key facts about SAC are now reported: (a) there are different trends in SAC of hydrocarbon/air mixtures at different initial pressures and temperatures, (b) ammonia and hydrogen have significantly different trends, and (c) for linear and branched paraffins, SAC can be correlated with the number of carbon atoms in the fuel molecule. In this work, it has been pointed out that there is experimental data in the literature where the super-equilibrium of the water molecule has been observed during auto-ignition, but not linked to SAC. Therefore, the results presented in this work establishes SAC as an important topic in modern combustion chemistry research.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114106"},"PeriodicalIF":5.8,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684399","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical simulations of direct detonation initiation and propagation in methane/air mixtures containing coal particles","authors":"Shengnan Li ,&nbsp;Shangpeng Li ,&nbsp;Shumeng Xie ,&nbsp;Yong Xu ,&nbsp;Ke Gao ,&nbsp;Huangwei Zhang","doi":"10.1016/j.combustflame.2025.114120","DOIUrl":"10.1016/j.combustflame.2025.114120","url":null,"abstract":"<div><div>The mechanisms of direct detonation initiation (DDI) in methane/air mixtures containing coal particles are investigated through simulations conducted using the Eulerian-Lagrangian method in a two-dimensional configuration. Methane-air combustion is modelled with a detailed chemical mechanism involving 36 species and 219 reactions, while coal particle surface reactions are computed using a kinetic/diffusion-limited rate model. The findings indicate that shock waves generated from the hotspot can initiate detonation through heterogeneous and homogeneous reactions, with contributions from both methane and particle combustion. Coal particle surface reactions provide the dominant energy for detonation initiation, whereas gas-phase reactions enhance detonation stability during propagation. The difficulty of achieving detonation initiation exhibits a non-linear dependence on particle concentrations and gas equivalence ratios. An optimal particle concentration and gas equivalence ratio for successful DDI is identified. Smaller particles are found to facilitate detonation initiation more effectively. Key processes in DDI of two-phase mixtures are identified, including particle heating, methane combustion, and particle burning. Three DDI modes—critical, stable, and cell-free—are observed based on particle concentration. As particle concentration increases, the temperatures of both particles and gas become close, initially rising and then decreasing with further increases in particle concentration. Additionally, the introduction of coal particles gives rise to two distinct stages in gas-phase reactions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"275 ","pages":"Article 114120"},"PeriodicalIF":5.8,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143654575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chemical kinetics uncertainty quantification on the dynamic detonation parameters for hydrogen–air mixtures","authors":"Xiangrong Huang ,&nbsp;Zifeng Weng ,&nbsp;Rémy Mével ,&nbsp;Josué Melguizo-Gavilanes ,&nbsp;Karl P. Chatelain ,&nbsp;Joao Vargas ,&nbsp;Deanna A. Lacoste","doi":"10.1016/j.combustflame.2025.114107","DOIUrl":"10.1016/j.combustflame.2025.114107","url":null,"abstract":"&lt;div&gt;&lt;div&gt;This study aims at (i) presenting detail reaction kinetics and corresponding reduced model which include nitrogen species chemistry for conditions relevant to H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;-air detonations, (ii) based on the obtained kinetics, conducting the quantification of the uncertainty induced by the uncertainty of the rate constants on the dynamic detonation parameters (DDP) predicted using various semi-empirical and theoretical models, and (iii) investigating the impact of the induction length uncertainty on the 2-D detonation simulations. To achieve the first goal, a total of 72 detailed reaction models were compiled and quantitatively evaluated based on (a) shock tube ignition delay-time (&lt;span&gt;&lt;math&gt;&lt;mi&gt;τ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;) data under detonation-relevant conditions in H&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;-O&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;-diluent(-nitrogen oxide) mixtures, and (b) DDP data. The two evaluation approaches lead to the selection of two different reaction models. For both selected mechanisms, a Monte Carlo method was adopted to statistically identify the uncertainty on the dynamic detonation parameters induced by the uncertainty of rate constants. Reactions R1: H+O&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;=OH +O and R2: H+O&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;(+M)=HO&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;(+M) were shown to induce the largest uncertainty on the predicted DDP for initial conditions of 300 K and 101 kPa. Furthermore, the uncertainty bands of cell size for a range of equivalence ratios obtained by perturbing R1 and R2 were illustrated. The distribution type of the DDP induced by sampling the rate constant &lt;span&gt;&lt;math&gt;&lt;mi&gt;k&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; was investigated. To estimate the maximum possible uncertainty of cell size induced from rate constants, two extreme mechanisms were developed by perturbing the rate constants to their 3&lt;span&gt;&lt;math&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; limits. For a stoichiometric mixture, these extreme mechanisms present a variation of the induction zone length by a factor of 15, which results in a change in the predicted cell size by 10.7 times. The difference in cell size can be even larger for off-stoichiometric mixtures. Concerning the third goal of the current study, we varied the rate constant of H+O&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;=H+OH, the most sensitive reaction for the induction length, to its 3&lt;span&gt;&lt;math&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; limits to study the corresponding influence in 2-D unsteady simulations characteristics, i.e., soot foil, shock velocity profile, and temperature field, for a stoichiometric hydrogen–air mixture. A reduced mechanism was developed based on the selected kinetics to minimize the comput","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"275 ","pages":"Article 114107"},"PeriodicalIF":5.8,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143631995","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":"FGM-LES study of premixed H2/CH4/air flame flashback in a bluff-body swirl burner: The impact of preferential diffusion","authors":"Hao Xia ,&nbsp;Weijie Zhang ,&nbsp;Wang Han ,&nbsp;Jinhua Wang ,&nbsp;Zuohua Huang ,&nbsp;Jeroen van Oijen","doi":"10.1016/j.combustflame.2025.114059","DOIUrl":"10.1016/j.combustflame.2025.114059","url":null,"abstract":"<div><div>One of the major difficulties to adapt H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>-enriched fuels in industrial combustors is the high tendency of flashback. Given the challenge of transient flashback diagnostics in experiment, large eddy simulation (LES) becomes an effective approach to study it. In this study, the flamelet generated manifold (FGM) coupled with LES is applied to simulate the flashback of premixed CH<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>/air and (95% H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>/5% CH<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>)/air flames in a bluff-body swirl burner established by University of Texas. A revised tabulation method to include the preferential diffusion of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> was proposed, which is special to also efficiently cover the heat loss and stretch effects. Good agreement between experimental and numerical results is attained as to the flashback mode and speed. It is found that the preferential diffusion of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> significantly promotes the flashback, which causes increased H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> concentration near the flame front, and leads to higher flame temperature and lower tip–wall distance. The flame front area is also increased with preferential diffusion thus expected to promote the flashback speed.</div><div><strong>Novelty and Significance Statement</strong></div><div>A revised FGM method including preferential diffusion of hydrogen in the multi-dimension tabulation is proposed and applied to improve hydrogen-enriched flashback prediction. Especially, the varied mixture fraction in the FGM table is attained by varying the inlet mixture components instead of modifying the inlet equivalence ratio as traditionally conducted, which can capture the species and element variation better and cover the heat loss and stretch effects more efficiently. For both flames with or without hydrogen enrichment, the simulated flashback mode and flashback speed correspond well to the experimental results. The flashback behaviors were examined and major reasons for the improved flashback prediction due to the inclusion of hydrogen preferential diffusion were revealed.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"275 ","pages":"Article 114059"},"PeriodicalIF":5.8,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143629557","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":"Laminar burning velocity and unburnt temperature: Comparative analysis across a broad temperature range of atmospheric NH3+H2 flames","authors":"Xinlu Han ,&nbsp;Alexander A. Konnov","doi":"10.1016/j.combustflame.2025.114117","DOIUrl":"10.1016/j.combustflame.2025.114117","url":null,"abstract":"<div><div>Ammonia (NH₃) emerges as a promising carbon-free fuel, necessitating an understanding of its fundamental combustion properties, particularly the laminar burning velocity (<span><math><msub><mi>S</mi><mi>L</mi></msub></math></span>), at very high unburnt temperatures (<span><math><msub><mi>T</mi><mi>u</mi></msub></math></span>). Despite this need, a consensus on the relationship between <span><math><msub><mi>S</mi><mi>L</mi></msub></math></span> and <span><math><msub><mi>T</mi><mi>u</mi></msub></math></span> across a broad temperature range has not yet been established. This study investigated the <span><math><msub><mi>S</mi><mi>L</mi></msub></math></span> vs. <span><math><msub><mi>T</mi><mi>u</mi></msub></math></span> relationship from 298 K to above 800 K, analyzing both literature data and simulation results for 40%H₂+60%NH₃+air flames at 1 atm. Seven kinetic models were used in the simulations, among which the models from Shrestha, Stagni, Han, NUIG, and KAUST accurately reproduced the experimental data within uncertainty limits, making them suitable for investigating <span><math><msub><mi>S</mi><mi>L</mi></msub></math></span> vs. <span><math><msub><mi>T</mi><mi>u</mi></msub></math></span> relationship. The analysis revealed that no tested correlation perfectly captures the <span><math><msub><mi>S</mi><mi>L</mi></msub></math></span> vs. <span><math><msub><mi>T</mi><mi>u</mi></msub></math></span> relationship across the entire temperature range with their originally defined constants, because the overall activation energy of the global one-step reaction is indeed increasing rapidly with <span><math><msub><mi>T</mi><mi>u</mi></msub></math></span>. In addition, the much lower reaction sensitivities of the temperature dependence coefficient than <span><math><msub><mi>S</mi><mi>L</mi></msub></math></span>, along with the same effects of elevated temperature and oxygen enrichment on model validations, were found to be valid for temperatures up to 850 K in these simulations, consistent with those previously identified for <span><math><msub><mi>T</mi><mi>u</mi></msub></math></span> &lt; 500 K conditions. Reaction sensitivities were also calculated for the overall activation energy, which exhibits significantly stronger temperature dependence than <span><math><msub><mi>S</mi><mi>L</mi></msub></math></span>, thus more effective for identifying reactions requiring adjustment for improving predictions across wide unburnt temperature ranges. Based on these findings, a feasible strategy was proposed for future investigation of the laminar burning velocities with broad unburnt temperature range, helping with relevant applications.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"275 ","pages":"Article 114117"},"PeriodicalIF":5.8,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143619665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Investigation of combustion characterization of single-point and two-point laser ignition of LPG-air mixture in a constant volume combustion chamber","authors":"Prashant Mahadev Patane ,&nbsp;Shrimantini Shantaram Patil ,&nbsp;Milankumar Ramakant Nandgaonkar","doi":"10.1016/j.combustflame.2025.114111","DOIUrl":"10.1016/j.combustflame.2025.114111","url":null,"abstract":"<div><div>In this article, single and two-point laser-induced spark ignition (LISI) of liquified petroleum gas (LPG) - air mixture is investigated. The experiments were tested in a constant volume combustion chamber (CVCC) for an equivalence ratio (<em>ϕ</em>) of 0.6 to 1.2. The CVCC has four optical windows, which are used simultaneously for optical diagnostics and laser ignition. All experiments for both single and two-point laser ignition (LI) were tested at an initial chamber pressure of 6 bar and temperature of 298 K. Initially, the effect of distance between two plasms at focal points of 5 mm, 25 mm, and 45 mm apart on pressure time history was studied and observed a higher peak pressure and minimum combustion duration for 45 mm plasma spacing. It has been observed a peak pressure of 42.17 bar, 42.65 bar, and 43.92 bar for 5 mm, 25 mm, and 45 mm apart plasma spacing respectively for stoichiometric mixture, however, the combustion duration of 84.2 ms, 78.6 ms, and 73.2 ms were observed for 5 mm, 25 mm, and 45 mm apart plasma spacing respectively. The pressure-time (p-t) history for single and two-point LI was recorded, and a comparative study between the single and two-point LI of the LPG-air mixture analysis results in higher pressure with two-point LI of the LPG-air mixture compared to single-point LI for all equivalence ratios. The probability of laser ignition was investigated for single and two-point LI of LPG-air mixtures and observed a higher probability of ignition for two-point LI compared to single-point LI. With two-point LI the LPG-air mixture can be ignited up to an equivalence ratio of 0.52 however with single-point LI the mixture can be ignited up to an equivalence ratio of 0.56. Furthermore, the net heat release (NHR) was calculated for single and two-point LI and observed higher NHR for two-point LI compared to single-point LI. The NHR was observed to be 7872.75 J and 8111.88 J for single-point and two-point LI respectively at an equivalence ratio of 1.0. Lastly, the initial phases of the combustion progress for two-point LI were visualized using the Shadowgraphy technique with a high-speed camera. The growth of flame kernel for the LPG-air mixture of different <em>ϕ</em> (0.6, 0.8, 1.0, and 1.2) was visualized and analyzed and it has been observed the development of two flame kernels one on the upper side and another on the lower side of the chamber. Further, both flame kernel images show two toroidal rings with one front lobe propagating toward the incoming laser source. The flame kernel growth images obtained were used to measure the flame kernel propagation in different directions and it has been observed faster flame kernel propagation at an equivalence ratio of 1.0 in all directions.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"275 ","pages":"Article 114111"},"PeriodicalIF":5.8,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143619666","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 comparative study of hydrogen and methane enrichment on laminar flame propagation of ammonia","authors":"Lei Wang,&nbsp;Xingqian Mao,&nbsp;Jinguang Li,&nbsp;Haiqiao Wei,&nbsp;Gequn Shu,&nbsp;Jiaying Pan","doi":"10.1016/j.combustflame.2025.114119","DOIUrl":"10.1016/j.combustflame.2025.114119","url":null,"abstract":"<div><div>Active pre-chamber jet ignition technologies can mitigate the challenges of poor ignition and slow combustion in spark-ignition ammonia engines. The fuel injection in pre-chamber can largely affect mixture reactivity and thereby the jet ignition performance. However, the mechanisms for the impacts of active mixture preparation on flame propagation within the active pre-chamber remain not fully understood. In this work, we conducted a comparative study on the effect of hydrogen and methane enrichment on ammonia flame propagation in both planar and spherical configurations. A non-monotonic behavior in the laminar flame propagation of ammonia with hydrogen enrichment is identified. Specifically, as hydrogen enrichment is raised, the laminar flame speed and burning flux of ammonia initially increase and then decrease, peaking at <span><math><mrow><msub><mi>X</mi><mi>A</mi></msub><mo>=</mo></mrow></math></span> 40% and <span><math><mrow><msub><mi>X</mi><mi>A</mi></msub><mo>=</mo></mrow></math></span> 30%, respectively. In contrast, methane enrichment results in a continuous reduction in both flame speed and burning flux. Thermal and kinetic analysis indicates that the initial decrease in activation temperatures primarily enhances burning flux, but thermal effects start to dominate and suppress burning flux when hydrogen concentration <span><math><mrow><msub><mi>X</mi><mi>A</mi></msub><mo>&gt;</mo></mrow></math></span> 30%. Conversely, methane enrichment primarily reduces burning flux through thermal inhibition. Regarding stretched spherical laminar flames, two distinct stages are involved during ammonia combustion, i.e., ignition assisted flame kernel propagation and normal laminar flame propagation. The normal laminar flame propagation is dominantly controlled by stretching effects. Compared to methane, hydrogen tends to undergo a weakened stretching flame, manifesting pronounced flame stabilities. This work provides useful insights into the optimization and control of the active pre-chamber jet ignition in ammonia-hydrogen engines.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"275 ","pages":"Article 114119"},"PeriodicalIF":5.8,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143619512","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}