Pub Date : 2024-11-30DOI: 10.1016/j.combustflame.2024.113855
E.F. Hunt, A.J. Aspden
<div><div>This paper presents direct numerical simulations (DNS) of thermodiffusively-unstable lean premixed hydrogen flames in the canonical turbulent flame-in-a-box configuration. A range of reactant (pressure, temperature, and equivalence ratio) and turbulent (Karlovitz and Damköhler number) conditions are used to explore the effects of the small and large turbulent scales on local and global flame response. Turbulence-flame interactions are confirmed to be independent from integral length scale (or equivalently, from Damköhler number) for a fixed Karlovitz number. Furthermore, a recent model that predicts mean local flame speed as a function of an instability parameter and Karlovitz number is also demonstrated to be independent from integral length scale. This model thereby reduces turbulent flame speed modelling for thermodiffusively-unstable cases to predicting surface area enhancement. Flame surface area wrinkling is found to have good agreement with Damköhler’s small-scale limit. There is some scatter in the data, although this is comparable with similar experimental data, and the freely-propagating flame properties have a greater impact on the turbulent flame speed than the flame surface area. It is demonstrated that domain size can have an effect on flame surface area even if the integral length scale remains unchanged; the larger volume into which flame surface area can develop results in a higher turbulent flame speed. This is not accounted for in conventional algebraic models for turbulent flame speed. To investigate the influence of the fuel Lewis number <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span>, an additional study is presented where <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span> (alone) is artificially modified to span a range from 0.35 to 2. The results demonstrate that more flame surface area is generated for smaller <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span>, but the difference for <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span> <!--> <span><math><mo>≲</mo></math></span> <!--> <!-->1 is much smaller than that observed for <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span> <!--> <span><math><mo>></mo></math></span> <!--> <!-->1. A volume-filling-surface concept is used to argue that there is a limit to how much flame surface can develop in a given volume, and so there is only so much more flame surface can be induced by the thermodiffusive response; whereas the thermodiffusive response at high <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span> is to reduce flame surface area. The agreement of the present data (and previous work) with Damköhler’s small-scale limit (even for low-to-moderate Karlovitz numbers) suggests that a distinction should be made betwe
本文对典型湍流箱内火焰结构下热扩散不稳定稀薄预混氢火焰进行了直接数值模拟。使用一系列反应物（压力、温度和等效比）和湍流（Karlovitz和Damköhler数）条件来探索小尺度和大尺度湍流对局部和全局火焰响应的影响。对于固定的Karlovitz数，证实湍流-火焰相互作用与积分长度尺度（或等价于Damköhler数）无关。此外，最近的模型预测平均局部火焰速度作为不稳定参数和Karlovitz数的函数，也证明了与积分长度尺度无关。因此，该模型减少了热扩散不稳定情况下的湍流火焰速度建模，以预测表面积增强。发现火焰表面起皱与Damköhler的小尺度极限符合得很好。虽然这与类似的实验数据相当，但数据中存在一定的分散，并且自由传播的火焰特性对湍流火焰速度的影响大于火焰表面积。结果表明，在整体长度尺度不变的情况下，区域尺寸对火焰表面积也有影响；火焰表面积发展的体积越大，湍流火焰速度越快。这在紊流火焰速度的传统代数模型中没有考虑到。为了研究燃料刘易斯数Lef的影响，提出了一项额外的研究，其中将Lef（单独）人为地修改为跨越0.35至2的范围。结果表明：较小的Lef产生的火焰表面积更大，但Lef > 1时的差异远小于Lef >时的差异；1. 用体积填充表面的概念来论证在给定体积内可以发展多少火焰表面是有限制的，因此热扩散响应所能引起的火焰表面只有这么多；而在高左侧的热扩散响应是减少火焰表面积。目前的数据（和以前的工作）与Damköhler的小尺度极限（即使是低到中等的Karlovitz数）的一致表明，应该区分小尺度极限和分布式燃烧状态。此外，有人认为，应根据Damköhler数字来区分大限额和小限额。因此，小火焰、稀薄反应和分布状态（如通常）应该用Karlovitz数来区分，但后两种状态都有单独的大型和小型状态。最后，讨论了紊流预混状态图的意义，并提出了一种修正的状态图。本文证实了湍流-火焰在火焰尺度上的相互作用与积分长度尺度（固定Karlovitz数）无关，热扩散不稳定火焰的局部火焰速度模型也是如此（Howarth et al., 2023）；演示了湍流火焰模型中未考虑的潜在域尺寸效应；在低Damköhler数下，薄反应区热扩散不稳定火焰的火焰表面起皱符合Damköhler的小尺度极限；低燃料刘易斯数时火焰表面起皱略有增加，高燃料刘易斯数时火焰表面起皱明显减少。对紊流预混状态图有重要的影响：区分Damköhler的小尺度极限和分布燃烧状态；以Damköhler数量限制小、大规模分离；λ-火焰概念在薄反应区的应用并专门使用Karlovitz数和Damköhler数进行制度分类和图表轴。
{"title":"Thermodiffusively-unstable lean premixed hydrogen flames: Length scale effects and turbulent burning regimes","authors":"E.F. Hunt, A.J. Aspden","doi":"10.1016/j.combustflame.2024.113855","DOIUrl":"10.1016/j.combustflame.2024.113855","url":null,"abstract":"<div><div>This paper presents direct numerical simulations (DNS) of thermodiffusively-unstable lean premixed hydrogen flames in the canonical turbulent flame-in-a-box configuration. A range of reactant (pressure, temperature, and equivalence ratio) and turbulent (Karlovitz and Damköhler number) conditions are used to explore the effects of the small and large turbulent scales on local and global flame response. Turbulence-flame interactions are confirmed to be independent from integral length scale (or equivalently, from Damköhler number) for a fixed Karlovitz number. Furthermore, a recent model that predicts mean local flame speed as a function of an instability parameter and Karlovitz number is also demonstrated to be independent from integral length scale. This model thereby reduces turbulent flame speed modelling for thermodiffusively-unstable cases to predicting surface area enhancement. Flame surface area wrinkling is found to have good agreement with Damköhler’s small-scale limit. There is some scatter in the data, although this is comparable with similar experimental data, and the freely-propagating flame properties have a greater impact on the turbulent flame speed than the flame surface area. It is demonstrated that domain size can have an effect on flame surface area even if the integral length scale remains unchanged; the larger volume into which flame surface area can develop results in a higher turbulent flame speed. This is not accounted for in conventional algebraic models for turbulent flame speed. To investigate the influence of the fuel Lewis number <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span>, an additional study is presented where <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span> (alone) is artificially modified to span a range from 0.35 to 2. The results demonstrate that more flame surface area is generated for smaller <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span>, but the difference for <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span> <!--> <span><math><mo>≲</mo></math></span> <!--> <!-->1 is much smaller than that observed for <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span> <!--> <span><math><mo>></mo></math></span> <!--> <!-->1. A volume-filling-surface concept is used to argue that there is a limit to how much flame surface can develop in a given volume, and so there is only so much more flame surface can be induced by the thermodiffusive response; whereas the thermodiffusive response at high <span><math><msub><mrow><mi>Le</mi></mrow><mrow><mtext>f</mtext></mrow></msub></math></span> is to reduce flame surface area. The agreement of the present data (and previous work) with Damköhler’s small-scale limit (even for low-to-moderate Karlovitz numbers) suggests that a distinction should be made betwe","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113855"},"PeriodicalIF":5.8,"publicationDate":"2024-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142744377","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}
Pub Date : 2024-11-29DOI: 10.1016/j.combustflame.2024.113859
Yan Ding , Xinyang Wang , Grayson Bellamy , Mark McKinnon , Yu Wang
This work details a hierarchical methodology to develop a pyrolysis model for ultra porous energy-efficient polyurethane-based aerogel (PU-aerogel). This methodology relied on simultaneous measurements of sample mass, back surface temperature (Tback), as well as sample shape profiles collected from controlled atmosphere pyrolysis apparatus (CAPA II) experiments. Based on the measured radiation-optical properties and the developed reaction mechanism, the thermal transport properties were determined based on the inverse modeling of these measurements. The resulting pyrolysis model was able to reproduce the sample shape profiles and Tback with an average accuracy of 10.5 % and 6.2 %, respectively. The model also predicted the burning rates of PU-aerogel at both radiative heat fluxes. An additional sensitivity analysis was conducted to systematically investigate the impact of input parameters on the burning behavior of PU-aerogel. The average MLR (avgMLR) and time to Tback = 533K () of the CAPA II experiment under 60 kW m−2 were defined as the model outputs. The density of the virgin material showed the most significant impact on changing avgMLR (-27.4 %) and (108.7 %), followed by the density and thermal conductivity of intermediate components. The variations in material properties yielded a negligible effect on the time to peak MLR because the peak MLR of this specific material occurred very rapidly upon exposure. The findings of this work enabled the prediction of burning behavior of PU-aerogel and the design of a more flame-resistant PU-aerogel.
{"title":"Characterization of the burning behavior of Ultra porous polyurethane-based aerogel: Impact of material properties on burning behavior","authors":"Yan Ding , Xinyang Wang , Grayson Bellamy , Mark McKinnon , Yu Wang","doi":"10.1016/j.combustflame.2024.113859","DOIUrl":"10.1016/j.combustflame.2024.113859","url":null,"abstract":"<div><div>This work details a hierarchical methodology to develop a pyrolysis model for ultra porous energy-efficient polyurethane-based aerogel (PU-aerogel). This methodology relied on simultaneous measurements of sample mass, back surface temperature (<em>T<sub>back</sub></em>), as well as sample shape profiles collected from controlled atmosphere pyrolysis apparatus (CAPA II) experiments. Based on the measured radiation-optical properties and the developed reaction mechanism, the thermal transport properties were determined based on the inverse modeling of these measurements. The resulting pyrolysis model was able to reproduce the sample shape profiles and <em>T<sub>back</sub></em> with an average accuracy of 10.5 % and 6.2 %, respectively. The model also predicted the burning rates of PU-aerogel at both radiative heat fluxes. An additional sensitivity analysis was conducted to systematically investigate the impact of input parameters on the burning behavior of PU-aerogel. The average MLR (<em>avgMLR</em>) and time to <em>T<sub>back</sub> = 533K</em> (<span><math><msub><mi>t</mi><mrow><mn>533</mn><mi>K</mi></mrow></msub></math></span>) of the CAPA II experiment under 60 kW m<sup>−2</sup> were defined as the model outputs. The density of the virgin material showed the most significant impact on changing <em>avgMLR</em> (-27.4 %) and <span><math><msub><mi>t</mi><mrow><mn>533</mn><mi>K</mi></mrow></msub></math></span> (108.7 %)<em>,</em> followed by the density and thermal conductivity of intermediate components. The variations in material properties yielded a negligible effect on the time to peak MLR because the peak MLR of this specific material occurred very rapidly upon exposure. The findings of this work enabled the prediction of burning behavior of PU-aerogel and the design of a more flame-resistant PU-aerogel.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113859"},"PeriodicalIF":5.8,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142744373","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}
Pub Date : 2024-11-29DOI: 10.1016/j.combustflame.2024.113862
João G.S. Monteiro , Arthur C.P.G. Ventura , Eric B. Lindgren , Felipe P. Fleming , Anderson R. dos Santos , André G.H. Barbosa
Cyclopentene, a prototype for studying the combustion chemistry of cyclic olefins, appears in the oxidation of cyclic hydrocarbons and can provide key information in the understanding of the formation of polycyclic aromatic hydrocarbons. The addition to the double-bond is one of the main steps in low-temperature oxidation mechanisms of unsaturated organic compounds. In the case of cyclopentene, addition of yields a hydroxycyclopentyl radical, that can further react with O2. In this work, we studied the potential energy surface and reaction rates for the subsequent reactions of O2 with the hydroxycyclopentyl radical. The temperature and pressure dependence of the rate constants were determined using master equation simulations, with microcanonical rate coefficients calculated by RRKM theory. The potential energy surface was extracted from high-level electronic structure theory, based on geometries and frequencies obtained using density functional theory. Our results indicate that a Waddington-type mechanism, which produces glutaraldehyde and regenerates , is the dominant reaction pathway. However, at low-temperatures, a secondary pathway leading to the formation of epoxycyclopentanol and becomes equally significant. The thermochemistry of all radicals involved were also evaluated. The kinetic and thermodynamic data were incorporated into a comprehensive mechanism of cyclopentene autoignition, in order to simulate the associated ignition delays. The updated reaction mechanism resulted in shorter ignition delays compared to the non-updated mechanism. Sensitivity analysis was performed to identify the primary contributors.
Novelty and Significance Statement
Cyclopentene is an important intermediate in the oxidation of cyclic olefins and serves as a precursor in the formation of polycyclic aromatic hydrocarbons. Kinetic modeling studies require detailed information on elementary reactions, much of which is typically unavailable from experiments. The novelty and significance of this study lie in the theoretical calculations of rate constants for key reactions in the oxidation of cyclopentene and their evaluation within the comprehensive mechanism proposed by Lokachari et al. The results demonstrate that the studied reactions significantly influence the ignition delays of cyclopentene at low temperatures. Furthermore, the data presented here can be applied in future studies focusing on the oxidation of cyclic olefins.
{"title":"A detailed analysis of the key steps of the cyclopentene autoignition mechanism from calculated RRKM rate constants associated with ignition delay time simulations","authors":"João G.S. Monteiro , Arthur C.P.G. Ventura , Eric B. Lindgren , Felipe P. Fleming , Anderson R. dos Santos , André G.H. Barbosa","doi":"10.1016/j.combustflame.2024.113862","DOIUrl":"10.1016/j.combustflame.2024.113862","url":null,"abstract":"<div><div>Cyclopentene, a prototype for studying the combustion chemistry of cyclic olefins, appears in the oxidation of cyclic hydrocarbons and can provide key information in the understanding of the formation of polycyclic aromatic hydrocarbons. The <figure><img></figure> addition to the double-bond is one of the main steps in low-temperature oxidation mechanisms of unsaturated organic compounds. In the case of cyclopentene, addition of <figure><img></figure> yields a hydroxycyclopentyl radical, that can further react with O<sub>2</sub>. In this work, we studied the potential energy surface and reaction rates for the subsequent reactions of O<sub>2</sub> with the hydroxycyclopentyl radical. The temperature and pressure dependence of the rate constants were determined using master equation simulations, with microcanonical rate coefficients calculated by RRKM theory. The potential energy surface was extracted from high-level electronic structure theory, based on geometries and frequencies obtained using density functional theory. Our results indicate that a Waddington-type mechanism, which produces glutaraldehyde and regenerates <figure><img></figure> , is the dominant reaction pathway. However, at low-temperatures, a secondary pathway leading to the formation of epoxycyclopentanol and <figure><img></figure> becomes equally significant. The thermochemistry of all <figure><img></figure> radicals involved were also evaluated. The kinetic and thermodynamic data were incorporated into a comprehensive mechanism of cyclopentene autoignition, in order to simulate the associated ignition delays. The updated reaction mechanism resulted in shorter ignition delays compared to the non-updated mechanism. Sensitivity analysis was performed to identify the primary contributors.</div><div><strong>Novelty and Significance Statement</strong></div><div>Cyclopentene is an important intermediate in the oxidation of cyclic olefins and serves as a precursor in the formation of polycyclic aromatic hydrocarbons. Kinetic modeling studies require detailed information on elementary reactions, much of which is typically unavailable from experiments. The novelty and significance of this study lie in the theoretical calculations of rate constants for key reactions in the oxidation of cyclopentene and their evaluation within the comprehensive mechanism proposed by Lokachari et al. The results demonstrate that the studied reactions significantly influence the ignition delays of cyclopentene at low temperatures. Furthermore, the data presented here can be applied in future studies focusing on the oxidation of cyclic olefins.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113862"},"PeriodicalIF":5.8,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142744376","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}
Pub Date : 2024-11-29DOI: 10.1016/j.combustflame.2024.113865
Boris I. Loukhovitski, Alexander S. Sharipov
<div><div>Here, we propose a new physically consistent modeling scheme, <span><math><mrow><msub><mrow><mtext>JIHT-OHex(C</mtext></mrow><mrow><mi>x</mi></mrow></msub><msub><mrow><mtext>H</mtext></mrow><mrow><mi>y</mi></mrow></msub><mtext>)</mtext></mrow></math></span>, that accurately predicts the formation and consumption of electronically excited chemiluminescent OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> molecules in hydrocarbon flames over a wide range of temperatures, pressures, and mixture compositions. It incorporates (unchanged) our recent well-founded <span><math><mrow><msub><mrow><mtext>JIHT-OHex(H</mtext></mrow><mrow><mn>2</mn></mrow></msub><mtext>)</mtext></mrow></math></span> reaction submodel (Sharipov et al., 2024, <em>Combust. Flame</em>, <strong>263</strong>, 113417), aimed at describing the OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> evolution in hydrogen oxidation, and contains a necessary set of elementary processes involving OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> and carbon-containing species with the rate constants that are based either on a critical review of known, sometimes conflicting literature data on the elementary reaction kinetics of OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> or, where necessary and appropriate, on semiempirical estimates. To improve the <span><math><mrow><msub><mrow><mtext>JIHT-OHex(C</mtext></mrow><mrow><mi>x</mi></mrow></msub><msub><mrow><mtext>H</mtext></mrow><mrow><mi>y</mi></mrow></msub><mtext>)</mtext></mrow></math></span> performance against a representative data set for the observed OH(<span><math><mrow><msup><mrow><mi>A</mi></mrow><mrow><mn>2</mn></mrow></msup><msup><mrow><mi>Σ</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><msup><mrow><mi>X</mi></mrow><mrow><mn>2</mn></mrow></msup><mi>Π</mi></mrow></math></span>) chemiluminescent emission (near 309 nm) accompanying high-temperature oxidation of various (from C<span><math><msub><mrow></mrow><mrow><mn>1</mn></mrow></msub></math></span> to C<sub>10</sub>) hydrocarbon-based mixtures that we aggregated at the preparatory stage of the work, the rate coefficients of reaction and quenching processes that the overall OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> kinetics is most sensitive to (or for which there is a particular scatter in the available kinetic data, if any) were jointly optimized within their theoretical expectations and experimental uncertainties. It is shown that our universal detailed OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> submechanism, which includes a much larger pool of elementary processes (32 reactions and 36 quenching partners) than previous essentially global models (consisting of only a few processes and tailored to specific mixtures and combustion conditions), clearly outperforms the competitors in terms of
{"title":"A detailed kinetic submechanism for OH* chemiluminescence in hydrocarbon combustion","authors":"Boris I. Loukhovitski, Alexander S. Sharipov","doi":"10.1016/j.combustflame.2024.113865","DOIUrl":"10.1016/j.combustflame.2024.113865","url":null,"abstract":"<div><div>Here, we propose a new physically consistent modeling scheme, <span><math><mrow><msub><mrow><mtext>JIHT-OHex(C</mtext></mrow><mrow><mi>x</mi></mrow></msub><msub><mrow><mtext>H</mtext></mrow><mrow><mi>y</mi></mrow></msub><mtext>)</mtext></mrow></math></span>, that accurately predicts the formation and consumption of electronically excited chemiluminescent OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> molecules in hydrocarbon flames over a wide range of temperatures, pressures, and mixture compositions. It incorporates (unchanged) our recent well-founded <span><math><mrow><msub><mrow><mtext>JIHT-OHex(H</mtext></mrow><mrow><mn>2</mn></mrow></msub><mtext>)</mtext></mrow></math></span> reaction submodel (Sharipov et al., 2024, <em>Combust. Flame</em>, <strong>263</strong>, 113417), aimed at describing the OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> evolution in hydrogen oxidation, and contains a necessary set of elementary processes involving OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> and carbon-containing species with the rate constants that are based either on a critical review of known, sometimes conflicting literature data on the elementary reaction kinetics of OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> or, where necessary and appropriate, on semiempirical estimates. To improve the <span><math><mrow><msub><mrow><mtext>JIHT-OHex(C</mtext></mrow><mrow><mi>x</mi></mrow></msub><msub><mrow><mtext>H</mtext></mrow><mrow><mi>y</mi></mrow></msub><mtext>)</mtext></mrow></math></span> performance against a representative data set for the observed OH(<span><math><mrow><msup><mrow><mi>A</mi></mrow><mrow><mn>2</mn></mrow></msup><msup><mrow><mi>Σ</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><msup><mrow><mi>X</mi></mrow><mrow><mn>2</mn></mrow></msup><mi>Π</mi></mrow></math></span>) chemiluminescent emission (near 309 nm) accompanying high-temperature oxidation of various (from C<span><math><msub><mrow></mrow><mrow><mn>1</mn></mrow></msub></math></span> to C<sub>10</sub>) hydrocarbon-based mixtures that we aggregated at the preparatory stage of the work, the rate coefficients of reaction and quenching processes that the overall OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> kinetics is most sensitive to (or for which there is a particular scatter in the available kinetic data, if any) were jointly optimized within their theoretical expectations and experimental uncertainties. It is shown that our universal detailed OH<span><math><msup><mrow></mrow><mrow><mo>∗</mo></mrow></msup></math></span> submechanism, which includes a much larger pool of elementary processes (32 reactions and 36 quenching partners) than previous essentially global models (consisting of only a few processes and tailored to specific mixtures and combustion conditions), clearly outperforms the competitors in terms of","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113865"},"PeriodicalIF":5.8,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142744378","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}
<div><div>This paper presents a high-efficiency and high-fidelity approach to model supersonic combustion using the extended flamelet-generated manifold (FGM) and the Eulerian transported probability density function (PDF), also known as the Eulerian stochastic fields (ESF) method. The efficiency benefits from the FGM, where the compressibility effects induced by shock waves are considered using two extra control variables, i.e., the pressure (<span><math><mi>p</mi></math></span>) and the absolute internal energy of the oxidizer (<span><math><msub><mrow><mi>E</mi></mrow><mrow><mi>o</mi><mi>x</mi></mrow></msub></math></span>), in addition to the mixture fraction (<span><math><mi>Z</mi></math></span>) and progress variable (<span><math><msub><mrow><mi>Y</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span>) in traditional flamelet tables. The joint PDF for these control variables is modeled using transported PDF based on the ESF method. The ESF method enhances accuracy in the prediction of turbulence-chemistry interactions, avoiding complexity induced by the presumed PDF in the flamelet table and ad-hoc presumed and independent joint PDF assumptions, e.g., the typical presumed <span><math><mi>β</mi></math></span>-PDF for <span><math><mi>Z</mi></math></span> and <span><math><mi>δ</mi></math></span>-PDF for <span><math><msub><mrow><mi>Y</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span>. This FGM-ESF method is tested in large eddy simulations of two canonical hydrogen supersonic flames: a strut-stabilized hydrogen supersonic flame (DLR case) and a transverse hydrogen jet flame in a high-enthalpy incoming flow (Stanford case). For both cases, results show that including the compressibility effects in the FGM table is essential for properly describing the flame behaviors near shock waves. The sub-grid PDF of control variables significantly influences near-wall and shear-layer combustion, and the ESF method demonstrates superior performance in predicting the near-wall reaction zone and the shear-layer reaction zone compared to the perfectly micro-mixed sub-grid model (<span><math><mi>δ</mi></math></span>-PDF) for the Stanford case. This study marks the first application of the FGM-ESF approach with a <span><math><mi>Z</mi></math></span>-<span><math><msub><mrow><mi>Y</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span>-<span><math><msub><mrow><mi>E</mi></mrow><mrow><mi>o</mi><mi>x</mi></mrow></msub></math></span>-<span><math><mi>p</mi></math></span> FGM table to simulate supersonic flames, offering a novel perspective for future modeling efforts in this domain.</div><div><strong>Novelty and Significance Statement</strong></div><div>The novelty of this research lies in the development and application of an efficient computational approach that for the first time couples the extended flamelet-generated manifold (FGM) method with the Eulerian stochastic fields (ESF) to simulate supersonic flames. This combined FGM-ESF method incorporates pressure
{"title":"A flamelet-based Eulerian transported PDF method for the modeling and simulation of supersonic combustion","authors":"Shenghui Zhong , Shijie Xu , Wubin Weng , Weiwei Cai , Longfei Chen","doi":"10.1016/j.combustflame.2024.113864","DOIUrl":"10.1016/j.combustflame.2024.113864","url":null,"abstract":"<div><div>This paper presents a high-efficiency and high-fidelity approach to model supersonic combustion using the extended flamelet-generated manifold (FGM) and the Eulerian transported probability density function (PDF), also known as the Eulerian stochastic fields (ESF) method. The efficiency benefits from the FGM, where the compressibility effects induced by shock waves are considered using two extra control variables, i.e., the pressure (<span><math><mi>p</mi></math></span>) and the absolute internal energy of the oxidizer (<span><math><msub><mrow><mi>E</mi></mrow><mrow><mi>o</mi><mi>x</mi></mrow></msub></math></span>), in addition to the mixture fraction (<span><math><mi>Z</mi></math></span>) and progress variable (<span><math><msub><mrow><mi>Y</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span>) in traditional flamelet tables. The joint PDF for these control variables is modeled using transported PDF based on the ESF method. The ESF method enhances accuracy in the prediction of turbulence-chemistry interactions, avoiding complexity induced by the presumed PDF in the flamelet table and ad-hoc presumed and independent joint PDF assumptions, e.g., the typical presumed <span><math><mi>β</mi></math></span>-PDF for <span><math><mi>Z</mi></math></span> and <span><math><mi>δ</mi></math></span>-PDF for <span><math><msub><mrow><mi>Y</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span>. This FGM-ESF method is tested in large eddy simulations of two canonical hydrogen supersonic flames: a strut-stabilized hydrogen supersonic flame (DLR case) and a transverse hydrogen jet flame in a high-enthalpy incoming flow (Stanford case). For both cases, results show that including the compressibility effects in the FGM table is essential for properly describing the flame behaviors near shock waves. The sub-grid PDF of control variables significantly influences near-wall and shear-layer combustion, and the ESF method demonstrates superior performance in predicting the near-wall reaction zone and the shear-layer reaction zone compared to the perfectly micro-mixed sub-grid model (<span><math><mi>δ</mi></math></span>-PDF) for the Stanford case. This study marks the first application of the FGM-ESF approach with a <span><math><mi>Z</mi></math></span>-<span><math><msub><mrow><mi>Y</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span>-<span><math><msub><mrow><mi>E</mi></mrow><mrow><mi>o</mi><mi>x</mi></mrow></msub></math></span>-<span><math><mi>p</mi></math></span> FGM table to simulate supersonic flames, offering a novel perspective for future modeling efforts in this domain.</div><div><strong>Novelty and Significance Statement</strong></div><div>The novelty of this research lies in the development and application of an efficient computational approach that for the first time couples the extended flamelet-generated manifold (FGM) method with the Eulerian stochastic fields (ESF) to simulate supersonic flames. This combined FGM-ESF method incorporates pressure ","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113864"},"PeriodicalIF":5.8,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142744375","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}
Pub Date : 2024-11-28DOI: 10.1016/j.combustflame.2024.113881
Zhiyao Zhang , Lili Ye , Hanfeng Jin , Mengmeng Li , Yubo Bi
Biphenyl is a crucial precursor to polycyclic aromatic hydrocarbons (PAHs), and phenylacetylene is an abundant product in aromatic hydrocarbons combustion. By exploring the reaction kinetics of phenylacetylene with biphenyl radicals, we further explore the novel hydrogen-abstraction phenylacetylene-addition (HAPaA) mechanism which is recently proposed to account for alternative mass growth pathways of PAHs. A combination of M06–2X/6–311+G(d,p) and PWPB95-D3/def2-QZVPP calculations were performed to construct the potential energy surfaces, and the rate coefficients were determined via solution of transition state theory based master equations. We demonstrate the capability of biphenyl species to grow with the assistance of phenylacetylene by unraveling the ring growth process of biphenyl radicals, establishing the main evolution routes of key intermediates, and quantifying the competition relationship between various channels. Energetic analysis and kinetic calculations demonstrate that the initial orientations of the reacting moieties do have a remarkable impact on the detailed kinetics of the entrance channels. However, the two adducts formed from initial additions achieve a rapid equilibrium because of the largest rate constants of the interconversion reactions between them, which counteracts the orientation effect on the overall kinetics. Further reaction pathways and corresponding products are related to the aryl radical position. Specifically, the aromatics of 4-phenylphenanthrene or phenanthrene, formed through cyclization reactions followed by hydrogen or phenyl eliminations, are preferred for the “armchair” type 2-biphenyl radical. In contrast, products featuring a triple bond generated through CH β-scission reactions are favored for the “free” type 3-biphenyl and 4-biphenyl radicals. The present research can serve as a good basis for further experimental and modeling studies of PAHs and soot formation.
{"title":"Kinetic study of the growth of PAHs from biphenyl with the assistance of phenylacetylene","authors":"Zhiyao Zhang , Lili Ye , Hanfeng Jin , Mengmeng Li , Yubo Bi","doi":"10.1016/j.combustflame.2024.113881","DOIUrl":"10.1016/j.combustflame.2024.113881","url":null,"abstract":"<div><div>Biphenyl is a crucial precursor to polycyclic aromatic hydrocarbons (PAHs), and phenylacetylene is an abundant product in aromatic hydrocarbons combustion. By exploring the reaction kinetics of phenylacetylene with biphenyl radicals, we further explore the novel hydrogen-abstraction phenylacetylene-addition (HAPaA) mechanism which is recently proposed to account for alternative mass growth pathways of PAHs. A combination of M06–2X/6–311+<em>G</em>(d,p) and PWPB95-D3/def2-QZVPP calculations were performed to construct the potential energy surfaces, and the rate coefficients were determined via solution of transition state theory based master equations. We demonstrate the capability of biphenyl species to grow with the assistance of phenylacetylene by unraveling the ring growth process of biphenyl radicals, establishing the main evolution routes of key intermediates, and quantifying the competition relationship between various channels. Energetic analysis and kinetic calculations demonstrate that the initial orientations of the reacting moieties do have a remarkable impact on the detailed kinetics of the entrance channels. However, the two adducts formed from initial additions achieve a rapid equilibrium because of the largest rate constants of the interconversion reactions between them, which counteracts the orientation effect on the overall kinetics. Further reaction pathways and corresponding products are related to the aryl radical position. Specifically, the aromatics of 4-phenylphenanthrene or phenanthrene, formed through cyclization reactions followed by hydrogen or phenyl eliminations, are preferred for the “armchair” type 2-biphenyl radical. In contrast, products featuring a triple bond generated through C<img>H β-scission reactions are favored for the “free” type 3-biphenyl and 4-biphenyl radicals. The present research can serve as a good basis for further experimental and modeling studies of PAHs and soot formation.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113881"},"PeriodicalIF":5.8,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142744374","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}
Pub Date : 2024-11-26DOI: 10.1016/j.combustflame.2024.113848
W.J. S. Ramaekers , T. Hazenberg , L.C. Thijs , D.J.E.M. Roekaerts , J.A. van Oijen , L.P.H. de Goey
It is demonstrated that in the (near) zero-gravity experiments conducted by Tang et al. (Combust. Flame; 2009, 2011) iron powder aerosols created using the finest powders are optically thick, implying that radiative heat transfer between particles should not be neglected. To test this concept, an iron particle oxidation model has been implemented in OpenFOAM, including a coupling with the P1-model for radiative heat transfer.
For flame simulations in which radiation is not included, obtained flame propagation velocities deviate less than 8% with results obtained using Chem1D-Fe and also show a good correspondance with algebraic models for optically thin aerosols. No significant difference in predicted flame propagation velocity is observed between 1D and 3D simulations: contrary to what is seen in gaseous flames, including the curvature of the flame does not increase predicted flame speeds substantially. However, measured flame propagation velocity values exceed numerically obtained predictions excluding thermal radiation by a factor of three to four. To the authors’ knowledge, this discrepancy is exemplary for the difference between experimentally obtained values for flame propagation velocities, and predictions made using numerical simulation tools neglecting radiative heat transfer.
Accounting for radiation increases predicted flame propagation velocities, in the absence of confining boundaries, by approximately a factor of 10 which is in line with algebraic models for optically thick aerosols. In 3D simulations for the two finest iron powders in the experiments, including radiation and accounting for the presence of the confining tube wall results in an error of 11% and 35% with respect to measured flame propagation velocities, significantly smaller than predictions obtained excluding thermal radiation. Although these flames are not purely radiation-driven, inclusion of particle-to-particle radiative heat transfer enhances flame propagation velocities in simulations to values that correspond much better with experimental values than if radiation would not be taken into account.
{"title":"The influence of radiative heat transfer on flame propagation in dense iron-air aerosols","authors":"W.J. S. Ramaekers , T. Hazenberg , L.C. Thijs , D.J.E.M. Roekaerts , J.A. van Oijen , L.P.H. de Goey","doi":"10.1016/j.combustflame.2024.113848","DOIUrl":"10.1016/j.combustflame.2024.113848","url":null,"abstract":"<div><div>It is demonstrated that in the (near) zero-gravity experiments conducted by Tang et al. (Combust. Flame; 2009, 2011) iron powder aerosols created using the finest powders are optically thick, implying that radiative heat transfer between particles should not be neglected. To test this concept, an iron particle oxidation model has been implemented in OpenFOAM, including a coupling with the P1-model for radiative heat transfer.</div><div>For flame simulations in which radiation is not included, obtained flame propagation velocities deviate less than 8% with results obtained using Chem1D-Fe and also show a good correspondance with algebraic models for optically thin aerosols. No significant difference in predicted flame propagation velocity is observed between 1D and 3D simulations: contrary to what is seen in gaseous flames, including the curvature of the flame does not increase predicted flame speeds substantially. However, measured flame propagation velocity values exceed numerically obtained predictions excluding thermal radiation by a factor of three to four. To the authors’ knowledge, this discrepancy is exemplary for the difference between experimentally obtained values for flame propagation velocities, and predictions made using numerical simulation tools neglecting radiative heat transfer.</div><div>Accounting for radiation increases predicted flame propagation velocities, in the absence of confining boundaries, by approximately a factor of 10 which is in line with algebraic models for optically thick aerosols. In 3D simulations for the two finest iron powders in the experiments, including radiation and accounting for the presence of the confining tube wall results in an error of 11% and 35% with respect to measured flame propagation velocities, significantly smaller than predictions obtained excluding thermal radiation. Although these flames are not purely radiation-driven, inclusion of particle-to-particle radiative heat transfer enhances flame propagation velocities in simulations to values that correspond much better with experimental values than if radiation would not be taken into account.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113848"},"PeriodicalIF":5.8,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142704180","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}
Pub Date : 2024-11-25DOI: 10.1016/j.combustflame.2024.113880
Robin Neupane, Ya- Ting Liao
Ambient pressure and gravity are important parameters in buoyant flow that governs upward flame spread process. Based on the concept of pressure modelling, this experimental study investigates extinction and upward flame spread process of a thermally-thin solid fuel in different pressure and oxygen conditions. Experiments are performed in a combustion chamber in air at different pressures (ranging from 10 kPa to 100 kPa) and different oxygen molar fraction environment (9–21 %). As pressure increases, different burning behaviors are observed: no ignition, partial flame spread, steady flame spread, and accelerating flame spread. Similar trend is observed as the ambient oxygen molar fraction increases. In partial pressure conditions (e.g., 25–50 kPa), flames exhibit characteristics that are typically observed in micro- and partial gravity environments: blue and dim. Flame spread rate and sample burnt length are deduced and compared between different pressure and oxygen levels. Overall, the burning intensity and the flame spread rate decrease with the decrease in ambient pressure and oxygen. The decrease in flame spread rate at reduced pressure is attributed to increase in flame standoff distance and decrease in convective heat transfer to the solid, whereas the decrease in flame spread rate in reduced oxygen molar fraction environment is attributed to decrease in flame temperature. Lastly, current and previous studies performed at different ambient environments are correlated using the concept of flame standoff distance (, which is estimated using the theoretical viscous boundary layer thickness (. It was found that approximating for forced flow and for natural flow can predict the flame spread rate reasonably well for data obtained in micro-, partial, and normal gravities, for a wide range of environmental conditions away from extinction limits.
{"title":"Correlating concurrent-flow flame spread rates in different pressure and oxygen conditions: Ground experiments and comparisons with previous micro-, partial, and normal gravities experiments","authors":"Robin Neupane, Ya- Ting Liao","doi":"10.1016/j.combustflame.2024.113880","DOIUrl":"10.1016/j.combustflame.2024.113880","url":null,"abstract":"<div><div>Ambient pressure and gravity are important parameters in buoyant flow that governs upward flame spread process. Based on the concept of pressure modelling, this experimental study investigates extinction and upward flame spread process of a thermally-thin solid fuel in different pressure and oxygen conditions. Experiments are performed in a combustion chamber in air at different pressures (ranging from 10 kPa to 100 kPa) and different oxygen molar fraction environment (9–21 %). As pressure increases, different burning behaviors are observed: no ignition, partial flame spread, steady flame spread, and accelerating flame spread. Similar trend is observed as the ambient oxygen molar fraction increases. In partial pressure conditions (e.g., 25–50 kPa), flames exhibit characteristics that are typically observed in micro- and partial gravity environments: blue and dim. Flame spread rate and sample burnt length are deduced and compared between different pressure and oxygen levels. Overall, the burning intensity and the flame spread rate decrease with the decrease in ambient pressure and oxygen. The decrease in flame spread rate at reduced pressure is attributed to increase in flame standoff distance and decrease in convective heat transfer to the solid, whereas the decrease in flame spread rate in reduced oxygen molar fraction environment is attributed to decrease in flame temperature. Lastly, current and previous studies performed at different ambient environments are correlated using the concept of flame standoff distance (<span><math><mrow><msub><mi>δ</mi><mi>f</mi></msub><mrow><mo>)</mo></mrow></mrow></math></span>, which is estimated using the theoretical viscous boundary layer thickness (<span><math><mrow><msub><mi>δ</mi><mi>v</mi></msub><mrow><mo>)</mo></mrow></mrow></math></span>. It was found that approximating <span><math><mrow><msub><mi>δ</mi><mi>f</mi></msub><mo>∼</mo><msub><mi>δ</mi><mi>v</mi></msub><mspace></mspace></mrow></math></span>for forced flow and <span><math><mrow><msub><mi>δ</mi><mi>f</mi></msub><mo>∼</mo><mn>1</mn><mo>/</mo><mn>3</mn><mspace></mspace><msub><mi>δ</mi><mi>v</mi></msub></mrow></math></span> for natural flow can predict the flame spread rate reasonably well for data obtained in micro-, partial, and normal gravities, for a wide range of environmental conditions away from extinction limits.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"272 ","pages":"Article 113880"},"PeriodicalIF":5.8,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142704179","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}
Pub Date : 2024-11-25DOI: 10.1016/j.combustflame.2024.113846
Neha Vishnoi , Richard Steinert , Aditya Saurabh , Christian Oliver Paschereit , Lipika Kabiraj
<div><div>In this work, we experimentally investigate the noise-induced dynamics of a lean premixed combustion system operating on natural gas–air mixtures that exhibit thermoacoustic instability via a subcritical Hopf bifurcation. The investigation is done before the bistable region with equivalence ratio (<span><math><mi>ϕ</mi></math></span>) as the control parameter. We analyze the acoustic pressure oscillations (<span><math><msup><mrow><mi>p</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>) in the combustor and fluctuations in the heat release rate (<span><math><msup><mrow><mi>q</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>) from the laminar quasi-flat flame at increasing levels of white noise. We show the effects of noise intensity on the reliability of various types of early warning indicators (EWIs) to predict the onset of the impending thermoacoustic oscillations. We investigate the indicators based on statistical measures (variance, skewness, and kurtosis), autocorrelation and spectral properties (coherence factor), system identification (growth/decay rates of <span><math><msup><mrow><mi>p</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>), multi-fractality (Hurst exponent), and time series complexity (permutation entropy and Jensen–Shannon complexity). The coherence factor, variance, and decay rates of <span><math><msup><mrow><mi>p</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span> always increases as the system approaches thermoacoustic instability, indicating their robustness as an EWI under most noise levels. An increase in kurtosis cannot be employed as an EWI. Implementing autocorrelation, skewness, Hurst exponent, permutation entropy and Jensen–Shannon complexity as effective EWIs has limitations: they can be estimated accurately only from pressure oscillations (<span><math><msup><mrow><mi>p</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>) data and work only above a particular threshold value of noise intensity. Our results have direct implication on early prediction and control of thermoacoustic instability in practical gas turbine combustors.</div><div><strong>Novelty and significance statement</strong></div><div>Developing effective early warning indicators (EWIs) to anticipate the onset of thermoacoustic instability is crucial for preventing potential damage and ensuring the reliable operation of lean premixed gas turbine combustion systems. In such systems, inherent noise dynamics undergo variations with changing operating conditions and combustor designs. Specifically, noise intensity increases as the system becomes more turbulent. In this study, we demonstrate that the inherent noise dynamics in a lean premixed combustion system play a crucial role in influencing the trends observed in early warning indicators of thermoacoustic instability. We address several key questions, including (a) whether comparative reliability assessments of different classes of EWIs exist, (b) the effect of vari
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