Pub Date : 2023-09-20DOI: 10.1080/13647830.2023.2254734
Joel Daou, Prabakaran Rajamanickam
The stability of a thick planar premixed flame, propagating steadily in a direction transverse to that of unidirectional shear flow, is studied. A linear stability analysis is carried out in the asymptotic limit of infinitely large activation energy, yielding a dispersion relation. The relation characterises the coupling between Taylor dispersion (or shear-enhanced diffusion) and the flame thermo-diffusive instabilities, in terms of two main parameters, namely, the reactant Lewis number Le and the flow Peclet number Pe. The implications of the dispersion relation are discussed and various flame instabilities are identified and classified in the Le-Pe plane. An important original finding is the demonstration that for values of the Peclet number exceeding a critical value, the classical cellular instability, commonly found for Le<1, exists now for Le>1 but is absent when Le<1. In fact, the cellular instability identified for Le>1 is shown to occur either through a finite-wavelength stationary bifurcation (also known as type-Is) or through a longwave stationary bifurcation (also known as type-IIs). The latter type-IIs bifurcation leads in the weakly nonlinear regime to a Kuramoto-Sivashinsky equation, which is determined. As for the oscillatory instability, usually encountered in the absence of Taylor dispersion in Le>1 mixtures, it is found to be absent if the Peclet number is large enough. The stability findings, which follow from the dispersion relation derived analytically, are complemented and examined numerically for a finite value of the Zeldovich number. The numerical study involves both computations of the eigenvalues of a linear stability boundary-value problem and numerical simulations of the time-dependent governing partial differential equations. The computations are found to be in good qualitative agreement with the analytical predictions.
{"title":"Diffusive-thermal instabilities of a planar premixed flame aligned with a shear flow","authors":"Joel Daou, Prabakaran Rajamanickam","doi":"10.1080/13647830.2023.2254734","DOIUrl":"https://doi.org/10.1080/13647830.2023.2254734","url":null,"abstract":"The stability of a thick planar premixed flame, propagating steadily in a direction transverse to that of unidirectional shear flow, is studied. A linear stability analysis is carried out in the asymptotic limit of infinitely large activation energy, yielding a dispersion relation. The relation characterises the coupling between Taylor dispersion (or shear-enhanced diffusion) and the flame thermo-diffusive instabilities, in terms of two main parameters, namely, the reactant Lewis number Le and the flow Peclet number Pe. The implications of the dispersion relation are discussed and various flame instabilities are identified and classified in the Le-Pe plane. An important original finding is the demonstration that for values of the Peclet number exceeding a critical value, the classical cellular instability, commonly found for Le<1, exists now for Le>1 but is absent when Le<1. In fact, the cellular instability identified for Le>1 is shown to occur either through a finite-wavelength stationary bifurcation (also known as type-Is) or through a longwave stationary bifurcation (also known as type-IIs). The latter type-IIs bifurcation leads in the weakly nonlinear regime to a Kuramoto-Sivashinsky equation, which is determined. As for the oscillatory instability, usually encountered in the absence of Taylor dispersion in Le>1 mixtures, it is found to be absent if the Peclet number is large enough. The stability findings, which follow from the dispersion relation derived analytically, are complemented and examined numerically for a finite value of the Zeldovich number. The numerical study involves both computations of the eigenvalues of a linear stability boundary-value problem and numerical simulations of the time-dependent governing partial differential equations. The computations are found to be in good qualitative agreement with the analytical predictions.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136309158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-08-23DOI: 10.1080/13647830.2023.2248960
Weijie Zhang, De-Xu Li, Guangya Hu, Jinhua Wang
{"title":"LES of premixed jet flames subjected to extreme turbulence using flamelet-generated manifolds: a comparison of unstrained and strained flamelets","authors":"Weijie Zhang, De-Xu Li, Guangya Hu, Jinhua Wang","doi":"10.1080/13647830.2023.2248960","DOIUrl":"https://doi.org/10.1080/13647830.2023.2248960","url":null,"abstract":"","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45221677","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-08-21DOI: 10.1080/13647830.2023.2248954
M. Mosbah, Z. Boutera, Y. Rezgui, M. Guemini, A. Tighezza
Based on models resulting from the merging of validated kinetic schemes, four reaction mechanisms were developed to describe the combustion of biodiesel-surrogate/ethanol blends in an HCCI engine. The proposed models were then compared to experimental data issued from a modified cooperative fuel research (CFR) engine which can be considered as an HCCI engine. The kinetic scheme displaying the best predictive capabilities, in conjunction with the single-zone HCCI code from the chemkin library, was used to investigate effects of ethanol enrichment and the variation of some important parameters, such as inlet temperature, relative air/fuel ratio and compression ratio, on the combustion and performance characteristics of the investigated HCCI engine. The blended fuels were formed by incrementally adding 10% of ethanol to the neat biodiesel mixture. The inlet temperature ranged from 320 to 420 K with a step of 20 K, whereas air/fuel and compression ratios were varied from 2 to 5 with a step of 0.5, and from 9 to 14 with a step equal to 1, respectively. The obtained data indicated that ethanol effects on the starting of combustion, combustion duration and indicated mean effective pressure were dependent on intake temperature, air/fuel and compression ratios.
{"title":"Effect of ethanol enrichment and engine parameters on the performance of an HCCI engine fuelled with biodiesel/ethanol mixtures","authors":"M. Mosbah, Z. Boutera, Y. Rezgui, M. Guemini, A. Tighezza","doi":"10.1080/13647830.2023.2248954","DOIUrl":"https://doi.org/10.1080/13647830.2023.2248954","url":null,"abstract":"Based on models resulting from the merging of validated kinetic schemes, four reaction mechanisms were developed to describe the combustion of biodiesel-surrogate/ethanol blends in an HCCI engine. The proposed models were then compared to experimental data issued from a modified cooperative fuel research (CFR) engine which can be considered as an HCCI engine. The kinetic scheme displaying the best predictive capabilities, in conjunction with the single-zone HCCI code from the chemkin library, was used to investigate effects of ethanol enrichment and the variation of some important parameters, such as inlet temperature, relative air/fuel ratio and compression ratio, on the combustion and performance characteristics of the investigated HCCI engine. The blended fuels were formed by incrementally adding 10% of ethanol to the neat biodiesel mixture. The inlet temperature ranged from 320 to 420 K with a step of 20 K, whereas air/fuel and compression ratios were varied from 2 to 5 with a step of 0.5, and from 9 to 14 with a step equal to 1, respectively. The obtained data indicated that ethanol effects on the starting of combustion, combustion duration and indicated mean effective pressure were dependent on intake temperature, air/fuel and compression ratios.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47037794","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-08-10DOI: 10.1080/13647830.2023.2245380
A. Moroshkina, Alina A. Ponomareva, V. Mislavskii, E. Sereshchenko, V. Gubernov, V. Bykov, S. Minaev
In this work, the determination of the apparent activation energy of a global chemical reaction mechanism of the methane–air flames is revisited. The one-step formulation allows to derive the theoretical background for the method to measure the activation energy within the burner stabilised flame setup. The validity of this approach is demonstrated by using the numerical simulations with the detailed reaction model and direct thin filament pyrometry measurements of the temperature distribution in flame. The combination of numerical and experimental approaches allows us to find the activation energy for various mixture compositions. The prediction of numerical simulations and measured values of the activation energy is found to be in good agreement with each other and the data known from the literature. It is demonstrated that two critical phenomena need to be taken into account to obtain a reliable estimate of the activation energy: the flame blow-off and the onset of the diffusive-thermal instabilities. The effect of these critical events on the accuracy of the measurements is discussed as well as prospects of further investigation.
{"title":"Determining the global activation energy of methane–air premixed flames","authors":"A. Moroshkina, Alina A. Ponomareva, V. Mislavskii, E. Sereshchenko, V. Gubernov, V. Bykov, S. Minaev","doi":"10.1080/13647830.2023.2245380","DOIUrl":"https://doi.org/10.1080/13647830.2023.2245380","url":null,"abstract":"In this work, the determination of the apparent activation energy of a global chemical reaction mechanism of the methane–air flames is revisited. The one-step formulation allows to derive the theoretical background for the method to measure the activation energy within the burner stabilised flame setup. The validity of this approach is demonstrated by using the numerical simulations with the detailed reaction model and direct thin filament pyrometry measurements of the temperature distribution in flame. The combination of numerical and experimental approaches allows us to find the activation energy for various mixture compositions. The prediction of numerical simulations and measured values of the activation energy is found to be in good agreement with each other and the data known from the literature. It is demonstrated that two critical phenomena need to be taken into account to obtain a reliable estimate of the activation energy: the flame blow-off and the onset of the diffusive-thermal instabilities. The effect of these critical events on the accuracy of the measurements is discussed as well as prospects of further investigation.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48675913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-08-02DOI: 10.1080/13647830.2023.2241421
A. Knyazeva, N. Bukrina
In the present work, we propose a new variant of the model of the composite synthesis under surface heating. We believe that the formation of the composition occurs at the level of reaction cell. The diffusion-controlled process of reduction of one material by another from an oxide is described in the framework of the problem with moving boundaries. It is assumed that the formation of the matrix composition is carried out by the diffusion mechanism. From the position of interfaces, we find the relative volume fractions of oxide phases and the fraction of volume occupied by the matrix. The averaging method of the analysis results at the reaction cell level makes it possible to use these data at the macroscopic level. Volume fractions of phases and average matrix composition (obtained by averaging over the area occupied by the matrix) provide values reflecting the composition of the composite at the macro level. The problem is solved numerically in dimensionless formulation. Dimensionless complexes of physical quantities are distinguished. The estimation of these parameters is performed. The conditions of correctness of the proposed approach are established from comparison of temporal and spatial scales of thermal and diffusion phenomena. A numerical algorithm for the joint solution of macro- and mesolevel problems has been developed. The proposed algorithm makes possible the investigation of the dynamics of composition changes at all points. The model is supplemented by the calculation of stresses and strains from the data on composition and temperature changes in reaction cells. Averaged values of stresses are transferred to macro level.
{"title":"Simulation of reaction initiation in powder compacting from the surface with composite formation in equivalent reaction cell","authors":"A. Knyazeva, N. Bukrina","doi":"10.1080/13647830.2023.2241421","DOIUrl":"https://doi.org/10.1080/13647830.2023.2241421","url":null,"abstract":"In the present work, we propose a new variant of the model of the composite synthesis under surface heating. We believe that the formation of the composition occurs at the level of reaction cell. The diffusion-controlled process of reduction of one material by another from an oxide is described in the framework of the problem with moving boundaries. It is assumed that the formation of the matrix composition is carried out by the diffusion mechanism. From the position of interfaces, we find the relative volume fractions of oxide phases and the fraction of volume occupied by the matrix. The averaging method of the analysis results at the reaction cell level makes it possible to use these data at the macroscopic level. Volume fractions of phases and average matrix composition (obtained by averaging over the area occupied by the matrix) provide values reflecting the composition of the composite at the macro level. The problem is solved numerically in dimensionless formulation. Dimensionless complexes of physical quantities are distinguished. The estimation of these parameters is performed. The conditions of correctness of the proposed approach are established from comparison of temporal and spatial scales of thermal and diffusion phenomena. A numerical algorithm for the joint solution of macro- and mesolevel problems has been developed. The proposed algorithm makes possible the investigation of the dynamics of composition changes at all points. The model is supplemented by the calculation of stresses and strains from the data on composition and temperature changes in reaction cells. Averaged values of stresses are transferred to macro level.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42547632","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-07-07DOI: 10.1080/13647830.2023.2232338
F. Williams, V. Nayagam
The influence of adding a seventh important elementary step to a six-step mechanism, previously employed for describing the asymptotic structure of normal-alkane droplet combustion supported by cool-flame chemistry in the negative-temperature-coefficient (NTC) range, is investigated by analytical methods. A development paralleling the classical activation-energy-asymptotic (AEA) analysis of the partial-burning regime, accompanied for the first time by an AEA analysis for a negative activation energy, to account properly for the removal of an important intermediate species, is pursued to make predictions of the combustion process, resulting in a revised asymptotic structure that agrees better with computational predictions based on detailed chemistry.
{"title":"Updated asymptotic structure of cool diffusion flames","authors":"F. Williams, V. Nayagam","doi":"10.1080/13647830.2023.2232338","DOIUrl":"https://doi.org/10.1080/13647830.2023.2232338","url":null,"abstract":"The influence of adding a seventh important elementary step to a six-step mechanism, previously employed for describing the asymptotic structure of normal-alkane droplet combustion supported by cool-flame chemistry in the negative-temperature-coefficient (NTC) range, is investigated by analytical methods. A development paralleling the classical activation-energy-asymptotic (AEA) analysis of the partial-burning regime, accompanied for the first time by an AEA analysis for a negative activation energy, to account properly for the removal of an important intermediate species, is pursued to make predictions of the combustion process, resulting in a revised asymptotic structure that agrees better with computational predictions based on detailed chemistry.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44746145","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-06-20DOI: 10.1080/13647830.2023.2226658
A. Bayliss, E. Shafirovich, V. Volpert
Recently, it has been proposed to develop space power systems based on filtration combustion of metal powders with oxygen supplied by a chemical oxygen generator. The experiments with lithium and magnesium powders at natural infiltration of oxygen have shown propagation of both counterflow and coflow combustion waves. However, natural filtration combustion of metal powders at relatively low pressures is not sufficiently understood. In the present paper, we investigate the natural coflow combustion waves propagating through a porous medium. The porous matrix is made of metal particles that react with oxygen flowing from the open end of the sample to the reaction zone where it is consumed forming a condensed product which also has a porous structure. The gas flow is due to the pressure difference between the pressure at the open end and that in the reaction zone (the so-called natural filtration). The open end is where the sample is ignited, so that the gas flows through the reaction products, i.e. in the same direction as the combustion wave propagates (coflow filtration). Our mathematical model involves the conservation of energy equation and gas mass, solid reactant mass, and gas momentum balances, as well as an equation of state, and appropriate boundary and initial conditions. It is studied analytically under the combustion front approximation. When the reaction zone is close to the open end, there is sufficient amount of oxygen in the reaction zone and the reaction is controlled by kinetic factors (the kinetic regime of propagation). As the reaction moves away from the open end, it is gas supply that becomes a limiting factor (filtration regime). Both kinetic and filtration regimes of propagation as well the transition between them are analytically studied in this paper.
{"title":"Coflow filtration combustion waves","authors":"A. Bayliss, E. Shafirovich, V. Volpert","doi":"10.1080/13647830.2023.2226658","DOIUrl":"https://doi.org/10.1080/13647830.2023.2226658","url":null,"abstract":"Recently, it has been proposed to develop space power systems based on filtration combustion of metal powders with oxygen supplied by a chemical oxygen generator. The experiments with lithium and magnesium powders at natural infiltration of oxygen have shown propagation of both counterflow and coflow combustion waves. However, natural filtration combustion of metal powders at relatively low pressures is not sufficiently understood. In the present paper, we investigate the natural coflow combustion waves propagating through a porous medium. The porous matrix is made of metal particles that react with oxygen flowing from the open end of the sample to the reaction zone where it is consumed forming a condensed product which also has a porous structure. The gas flow is due to the pressure difference between the pressure at the open end and that in the reaction zone (the so-called natural filtration). The open end is where the sample is ignited, so that the gas flows through the reaction products, i.e. in the same direction as the combustion wave propagates (coflow filtration). Our mathematical model involves the conservation of energy equation and gas mass, solid reactant mass, and gas momentum balances, as well as an equation of state, and appropriate boundary and initial conditions. It is studied analytically under the combustion front approximation. When the reaction zone is close to the open end, there is sufficient amount of oxygen in the reaction zone and the reaction is controlled by kinetic factors (the kinetic regime of propagation). As the reaction moves away from the open end, it is gas supply that becomes a limiting factor (filtration regime). Both kinetic and filtration regimes of propagation as well the transition between them are analytically studied in this paper.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42917635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-06-20DOI: 10.1080/13647830.2023.2224755
F. Nmira, Antoine Bouffard, J. Consalvi
This article reports flamelet/transported PDF (TPDF) simulations of the well-documented ethylene/air turbulent non-premixed jet flame investigated experimentally at Sandia. The transported PDF equation is solved with the Stochastic Eulerian Field method. The soot production is modelled by a validated three equation PAH-based soot model that predicts the mean soot aggregate properties at low computational time and includes a detailed description of the soot production processes. Gas and soot radiation is modelled using the rank-correlated full-spectrum k model. The turbulence/chemistry/soot production/radiation interactions are taken into account by means of the PDF method. Simulations are run by considering or not soot differential mixing. Based on recent conclusions drawn from Direct Numerical Simulations (Zhou et al., Proc. Combsut. Inst. 38 (2021) 2731–2739), soot differential mixing is modelled by neglecting soot mixing owing to sufficiently large mixing timescales. When soot differential mixing is considered, model predictions reproduce reasonably well the exhaustive set of experimental data, including flame structure, soot statistics and radiative outputs without adjusting parameters. In particular, the predictions demonstrate for the first time the capability of RANS/TPDF models to capture the soot intermittency. On the other hand, neglecting the soot differential mixing produces notable reductions in mean and fluctuating soot volume fraction and soot intermittency. Scatter plot analysis shows that the effects of soot differential mixing are more pronounced in regions of the mixture fraction space where soot surface growth and soot oxidation dominate the soot production, affecting these processes in a non-negligible manner. In an opposite way, soot nucleation and PAH condensation are much less significantly affected. Model results show also that disregarding soot differential mixing reduces the mean soot emission as well the soot emission turbulence/radiation interaction.
本文报道了在桑迪亚实验研究的乙烯/空气湍流非预混射流火焰的小火焰/传输PDF（TPDF）模拟。采用随机欧拉场方法求解传输PDF方程。烟尘产生是通过一个经过验证的基于PAH的三方程烟尘模型进行建模的，该模型预测了低计算时间下的平均烟尘聚集特性，并包括烟尘产生过程的详细描述。使用秩相关全谱k模型对气体和烟尘辐射进行建模。湍流/化学/烟尘产生/辐射相互作用通过PDF方法考虑在内。通过考虑或不考虑烟灰差异混合来运行模拟。根据直接数值模拟的最新结论（Zhou et al.，Proc.Combsut.Inst.38（2021）2731–2739），由于混合时间尺度足够大，通过忽略烟灰混合来模拟烟灰差分混合。当考虑烟灰差分混合时，模型预测在不调整参数的情况下合理地再现了详尽的实验数据集，包括火焰结构、烟灰统计和辐射输出。特别是，预测首次证明了RANS/TPDF模型捕捉煤烟间歇性的能力。另一方面，忽略煤烟差异混合会显著降低平均和波动的煤烟体积分数以及煤烟间歇性。散点图分析表明，在混合物分数空间的区域中，烟灰表面生长和烟灰氧化主导了烟灰的产生，烟灰差异混合的影响更为明显，以不可忽略的方式影响这些过程。相反，烟灰成核和PAH冷凝受到的影响要小得多。模型结果还表明，忽略煤烟差异混合会降低平均煤烟排放以及煤烟排放湍流/辐射相互作用。
{"title":"Flamelet/transported PDF simulations of ethylene/air jet turbulent non-premixed flame using a three-equation PAH-based soot production model","authors":"F. Nmira, Antoine Bouffard, J. Consalvi","doi":"10.1080/13647830.2023.2224755","DOIUrl":"https://doi.org/10.1080/13647830.2023.2224755","url":null,"abstract":"This article reports flamelet/transported PDF (TPDF) simulations of the well-documented ethylene/air turbulent non-premixed jet flame investigated experimentally at Sandia. The transported PDF equation is solved with the Stochastic Eulerian Field method. The soot production is modelled by a validated three equation PAH-based soot model that predicts the mean soot aggregate properties at low computational time and includes a detailed description of the soot production processes. Gas and soot radiation is modelled using the rank-correlated full-spectrum k model. The turbulence/chemistry/soot production/radiation interactions are taken into account by means of the PDF method. Simulations are run by considering or not soot differential mixing. Based on recent conclusions drawn from Direct Numerical Simulations (Zhou et al., Proc. Combsut. Inst. 38 (2021) 2731–2739), soot differential mixing is modelled by neglecting soot mixing owing to sufficiently large mixing timescales. When soot differential mixing is considered, model predictions reproduce reasonably well the exhaustive set of experimental data, including flame structure, soot statistics and radiative outputs without adjusting parameters. In particular, the predictions demonstrate for the first time the capability of RANS/TPDF models to capture the soot intermittency. On the other hand, neglecting the soot differential mixing produces notable reductions in mean and fluctuating soot volume fraction and soot intermittency. Scatter plot analysis shows that the effects of soot differential mixing are more pronounced in regions of the mixture fraction space where soot surface growth and soot oxidation dominate the soot production, affecting these processes in a non-negligible manner. In an opposite way, soot nucleation and PAH condensation are much less significantly affected. Model results show also that disregarding soot differential mixing reduces the mean soot emission as well the soot emission turbulence/radiation interaction.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43594496","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-06-14DOI: 10.1080/13647830.2023.2218621
F. Bisetti
Unsteady counterflows are employed to understand and model the effect of turbulence on flames. We present a novel numerical approach for the simulation of one-dimensional unsteady counterflow flames with fourth order spatial discretization and up to fourth order time discretization. The approach couples a three-stage Lobatto IIIa formula for boundary value problems and variable-order, variable time step size Backward Differentiation Formulas for time integration. The framework is explained in detail, its computational performance is analysed, and its use is demonstrated for the case of stochastic forcing of premixed counterflow flames, whereby the imposed rate of strain is a multi-scale lognormal discrete random process with exponential autocorrelation. High-order spatial and temporal discretization make the approach well-suited for the accurate and computationally efficient simulation of the effect of turbulence on flames, which are characterised by large amplitude stochastic fluctuations of the local rate of strain.
{"title":"High-order methods for the simulation of unsteady counterflow flames subject to stochastic forcing of large amplitude","authors":"F. Bisetti","doi":"10.1080/13647830.2023.2218621","DOIUrl":"https://doi.org/10.1080/13647830.2023.2218621","url":null,"abstract":"Unsteady counterflows are employed to understand and model the effect of turbulence on flames. We present a novel numerical approach for the simulation of one-dimensional unsteady counterflow flames with fourth order spatial discretization and up to fourth order time discretization. The approach couples a three-stage Lobatto IIIa formula for boundary value problems and variable-order, variable time step size Backward Differentiation Formulas for time integration. The framework is explained in detail, its computational performance is analysed, and its use is demonstrated for the case of stochastic forcing of premixed counterflow flames, whereby the imposed rate of strain is a multi-scale lognormal discrete random process with exponential autocorrelation. High-order spatial and temporal discretization make the approach well-suited for the accurate and computationally efficient simulation of the effect of turbulence on flames, which are characterised by large amplitude stochastic fluctuations of the local rate of strain.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45612766","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2023-05-18DOI: 10.1080/13647830.2023.2212637
Qun Hu, Lipo Wang
The spray flame in a laminar counterflow is influenced by various setup conditions, for instance the strain rate and liquid droplet parameters, including the initial temperature, size distribution, hydrodynamics and the vaporisation history. With some reasonable simplification, the two phase governing equations can be reformulated as equations in the single gas phase with reconstructed spray-related source terms. Numerical solutions assume interesting similarity features, such as the (almost) independence of the evaporation path after mapping onto a newly defined quantity R, constructed from sensible enthalpy and mixture fraction. In this regard, the dimensionality of free parameters describing the structure of the spray flame can be hopefully reduced, which then provides a different scenario to understand the spray combustion physics. The flame regime diagram is also elaborated in the present framework.
{"title":"Structure and similarity properties of the laminar counterflow spray flame","authors":"Qun Hu, Lipo Wang","doi":"10.1080/13647830.2023.2212637","DOIUrl":"https://doi.org/10.1080/13647830.2023.2212637","url":null,"abstract":"The spray flame in a laminar counterflow is influenced by various setup conditions, for instance the strain rate and liquid droplet parameters, including the initial temperature, size distribution, hydrodynamics and the vaporisation history. With some reasonable simplification, the two phase governing equations can be reformulated as equations in the single gas phase with reconstructed spray-related source terms. Numerical solutions assume interesting similarity features, such as the (almost) independence of the evaporation path after mapping onto a newly defined quantity R, constructed from sensible enthalpy and mixture fraction. In this regard, the dimensionality of free parameters describing the structure of the spray flame can be hopefully reduced, which then provides a different scenario to understand the spray combustion physics. The flame regime diagram is also elaborated in the present framework.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2023-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42628960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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