Pub Date : 2022-11-07DOI: 10.1080/13647830.2022.2136038
M. Valorani, R. Malpica Galassi, P. P. Ciottoli, H. Najm, S. Paolucci
The size and complexity of multi-scale problems such as those arising in chemical kinetics mechanisms has stimulated the search for methods that reduce the number of species and chemical reactions but retain a desired degree of accuracy. The time-scale characterisation of the multi-scale problem can be carried out on the basis of local information such as the Jacobian matrix of the model problem and its related eigen-system evaluated at one point P of the system trajectory. While the original problem is usually described by ordinary differential equations (ODEs), the reduced order model is described by a reduced number of ODEs and a number of algebraic equations (AEs), that might express one or more physical conservation laws (mass, momentum, energy), or the fact that the long-term dynamics evolves within a so-called Slow Invariant Manifold (SIM). To fully exploit the benefits offered by a reduced order model, it is required that the time scale characterisation of the n-dimensional reduced order model returns an answer consistent and coherent with the time-scale characterisation of the N-dimensional original model. This manuscript discusses a procedure for obtaining the time-scale characterisation of the reduced order model in a manner that is consistent with that of the original problem. While a standard time scale characterisation of the (original) N-dimensional original model can be carried out by evaluating the eigen-system of the ( ) Jacobian matrix of the vector field that defines the system dynamics, the time-scale characterisation of the n-dimensional reduced order model (with n
{"title":"The spectral characterisation of reduced order models in chemical kinetic systems","authors":"M. Valorani, R. Malpica Galassi, P. P. Ciottoli, H. Najm, S. Paolucci","doi":"10.1080/13647830.2022.2136038","DOIUrl":"https://doi.org/10.1080/13647830.2022.2136038","url":null,"abstract":"The size and complexity of multi-scale problems such as those arising in chemical kinetics mechanisms has stimulated the search for methods that reduce the number of species and chemical reactions but retain a desired degree of accuracy. The time-scale characterisation of the multi-scale problem can be carried out on the basis of local information such as the Jacobian matrix of the model problem and its related eigen-system evaluated at one point P of the system trajectory. While the original problem is usually described by ordinary differential equations (ODEs), the reduced order model is described by a reduced number of ODEs and a number of algebraic equations (AEs), that might express one or more physical conservation laws (mass, momentum, energy), or the fact that the long-term dynamics evolves within a so-called Slow Invariant Manifold (SIM). To fully exploit the benefits offered by a reduced order model, it is required that the time scale characterisation of the n-dimensional reduced order model returns an answer consistent and coherent with the time-scale characterisation of the N-dimensional original model. This manuscript discusses a procedure for obtaining the time-scale characterisation of the reduced order model in a manner that is consistent with that of the original problem. While a standard time scale characterisation of the (original) N-dimensional original model can be carried out by evaluating the eigen-system of the ( ) Jacobian matrix of the vector field that defines the system dynamics, the time-scale characterisation of the n-dimensional reduced order model (with n","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"26 1","pages":"1185 - 1216"},"PeriodicalIF":1.3,"publicationDate":"2022-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46351053","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 : 2022-10-20DOI: 10.1080/13647830.2022.2137062
A. Newale, Pushan Sharma, S. Pope, P. Pepiot
Large eddy simulation (LES)/ Probability Density Function (PDF) approaches are now well established and can be used for simulating challenging turbulent combustion configurations with strong turbulence chemistry interactions. Transported PDF methods are known to be computationally expensive compared to flamelet-like turbulent combustion models. The pre-partitioned adaptive chemistry (PPAC) methodology was developed to address this cost differential. PPAC entails an offline preprocessing stage, where a set of reduced models are generated starting from an initial database of representative compositions. At runtime, this set of reduced models are dynamically utilised during the reaction fractional step leading to computational savings. We have recently combined PPAC with in-situ adaptive tabulation (ISAT) to further reduce the computational cost. We have shown that the combined method reduced the average wall-clock time per time step of large-scale LES/particle PDF simulations of turbulent combustion by 39%. A key assumption in PPAC is that the initial database used in the offline stage is representative of the compositions encountered at runtime. In our previous study this assumption was trivially satisfied as the initial database consisted of compositions extracted from the turbulent combustion simulation itself. Consequently, a key open question remains as to whether such databases can be generated without having access to the turbulent combustion simulation. Towards answering this question, in the current work, we explore whether the compositions for forming such a database can be extracted from computationally-efficient low-dimensional simulations such as 1D counterflow flames and partially stirred reactors. We show that a database generated using compositions extracted from a partially stirred reactor configuration leads to performance comparable to the optimal case, wherein the database is comprised of compositions extracted directly from the LES/PDF simulation itself.
{"title":"A feasibility study on the use of low-dimensional simulations for database generation in adaptive chemistry approaches","authors":"A. Newale, Pushan Sharma, S. Pope, P. Pepiot","doi":"10.1080/13647830.2022.2137062","DOIUrl":"https://doi.org/10.1080/13647830.2022.2137062","url":null,"abstract":"Large eddy simulation (LES)/ Probability Density Function (PDF) approaches are now well established and can be used for simulating challenging turbulent combustion configurations with strong turbulence chemistry interactions. Transported PDF methods are known to be computationally expensive compared to flamelet-like turbulent combustion models. The pre-partitioned adaptive chemistry (PPAC) methodology was developed to address this cost differential. PPAC entails an offline preprocessing stage, where a set of reduced models are generated starting from an initial database of representative compositions. At runtime, this set of reduced models are dynamically utilised during the reaction fractional step leading to computational savings. We have recently combined PPAC with in-situ adaptive tabulation (ISAT) to further reduce the computational cost. We have shown that the combined method reduced the average wall-clock time per time step of large-scale LES/particle PDF simulations of turbulent combustion by 39%. A key assumption in PPAC is that the initial database used in the offline stage is representative of the compositions encountered at runtime. In our previous study this assumption was trivially satisfied as the initial database consisted of compositions extracted from the turbulent combustion simulation itself. Consequently, a key open question remains as to whether such databases can be generated without having access to the turbulent combustion simulation. Towards answering this question, in the current work, we explore whether the compositions for forming such a database can be extracted from computationally-efficient low-dimensional simulations such as 1D counterflow flames and partially stirred reactors. We show that a database generated using compositions extracted from a partially stirred reactor configuration leads to performance comparable to the optimal case, wherein the database is comprised of compositions extracted directly from the LES/PDF simulation itself.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"26 1","pages":"1239 - 1261"},"PeriodicalIF":1.3,"publicationDate":"2022-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45804593","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 : 2022-10-20DOI: 10.1080/13647830.2022.2136039
Wenliang Zhou, Qizhao Lin
With the increase of bioenergy crops and the rapid development of agriculture, the total amount of solid waste is increasing rapidly. This study quantified the pyrolytic performance and gaseous products of spent coffee grounds (SCG), Chinese medicine residue (CMR), vinasse (VI) and camellia oil shell (COS) by using (derivative) thermogravimetric ((D)TG), Fourier transform infrared spectrometry (FTIR) and mass spectrometry (MS) analyses. There are two main stages of mass loss: volatilisation of volatiles and continuous decomposition of macromolecules. At a heating rate of 20°C/min, COS has the slowest pyrolysis rate compared to the other three. Model-free methods: Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) were used to calculate the activation energy (E) of samples with different conversion rates (α). SCG and VI have the highest average activation energy (about 240kJ/mol), followed by CMR (200kJ/mol), and COS the lowest (175kJ/mol). FTIR was mainly used to detect functional group types (including hydroxyl, carbonyl, aldehyde and ester groups, etc.), while MS co-detected the characteristics of condensable/non-condensable gases (including H2O, CO2, NOx, SOx, C6H6, C7H8, C9H8 and other major gas emissions, pollutants and hydrocarbons). Nitrogen oxides are produced in the range of 500–800°C. SCG and VI emit more gas pollutants than CMR and COS.
{"title":"Pyrolysis of four waste biomasses and elucidation of reaction kinetics and pyrolytic products","authors":"Wenliang Zhou, Qizhao Lin","doi":"10.1080/13647830.2022.2136039","DOIUrl":"https://doi.org/10.1080/13647830.2022.2136039","url":null,"abstract":"With the increase of bioenergy crops and the rapid development of agriculture, the total amount of solid waste is increasing rapidly. This study quantified the pyrolytic performance and gaseous products of spent coffee grounds (SCG), Chinese medicine residue (CMR), vinasse (VI) and camellia oil shell (COS) by using (derivative) thermogravimetric ((D)TG), Fourier transform infrared spectrometry (FTIR) and mass spectrometry (MS) analyses. There are two main stages of mass loss: volatilisation of volatiles and continuous decomposition of macromolecules. At a heating rate of 20°C/min, COS has the slowest pyrolysis rate compared to the other three. Model-free methods: Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) were used to calculate the activation energy (E) of samples with different conversion rates (α). SCG and VI have the highest average activation energy (about 240kJ/mol), followed by CMR (200kJ/mol), and COS the lowest (175kJ/mol). FTIR was mainly used to detect functional group types (including hydroxyl, carbonyl, aldehyde and ester groups, etc.), while MS co-detected the characteristics of condensable/non-condensable gases (including H2O, CO2, NOx, SOx, C6H6, C7H8, C9H8 and other major gas emissions, pollutants and hydrocarbons). Nitrogen oxides are produced in the range of 500–800°C. SCG and VI emit more gas pollutants than CMR and COS.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"26 1","pages":"1217 - 1238"},"PeriodicalIF":1.3,"publicationDate":"2022-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47450875","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 : 2022-10-13DOI: 10.1080/13647830.2022.2132015
S. Yakush, O. Korobeinichev, A. Shmakov, T. Bolshova, S. Trubachev
Gas-phase combustion of methylmethacrylate (MMA) monomer is an essential stage of solid polymethylmethacrylate (PMMA) combustion, which is of interest in many applications. A skeletal kinetic scheme for MMA combustion in air is proposed including 44 irreversible elementary reactions for 29 species. The mechanism is derived from the reduced kinetic scheme for MMA oxidation comprised of 263 reactions for 66 components. In this work, the mechanism predictive capabilities are demonstrated by solving the self-ignition problem, as well as the premixed flame propagation problem for MMA-air mixtures. It is shown that the skeletal mechanism overpredicts the ignition delay times due to significant simplification of the MMA decomposition stage reaction pathways. The flame propagation speed is predicted reasonably for lean and nearly-stoichiometric mixtures, but overpredicted for fuel-rich mixtures. Also, a diffusion flame representing the cup burner of liquid MMA is simulated in two-dimensional statement of the problem, the results are shown to agree well with the measurements and numerical simulations performed earlier on the basis of a detailed kinetic scheme. The skeletal mechanism can be used in the numerical simulations of gas-phase combustion of MMA, including the problems of flame propagation over the solid PMMA polymer.
{"title":"A reduced kinetic scheme for methyl methacrylate gas-phase combustion","authors":"S. Yakush, O. Korobeinichev, A. Shmakov, T. Bolshova, S. Trubachev","doi":"10.1080/13647830.2022.2132015","DOIUrl":"https://doi.org/10.1080/13647830.2022.2132015","url":null,"abstract":"Gas-phase combustion of methylmethacrylate (MMA) monomer is an essential stage of solid polymethylmethacrylate (PMMA) combustion, which is of interest in many applications. A skeletal kinetic scheme for MMA combustion in air is proposed including 44 irreversible elementary reactions for 29 species. The mechanism is derived from the reduced kinetic scheme for MMA oxidation comprised of 263 reactions for 66 components. In this work, the mechanism predictive capabilities are demonstrated by solving the self-ignition problem, as well as the premixed flame propagation problem for MMA-air mixtures. It is shown that the skeletal mechanism overpredicts the ignition delay times due to significant simplification of the MMA decomposition stage reaction pathways. The flame propagation speed is predicted reasonably for lean and nearly-stoichiometric mixtures, but overpredicted for fuel-rich mixtures. Also, a diffusion flame representing the cup burner of liquid MMA is simulated in two-dimensional statement of the problem, the results are shown to agree well with the measurements and numerical simulations performed earlier on the basis of a detailed kinetic scheme. The skeletal mechanism can be used in the numerical simulations of gas-phase combustion of MMA, including the problems of flame propagation over the solid PMMA polymer.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"27 1","pages":"139 - 152"},"PeriodicalIF":1.3,"publicationDate":"2022-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46643102","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}
A hybrid particle/finite volume algorithm has been formulated for zone-adaptive modelling of turbulent reactive flows to achieve both high fidelity in predictions and high computational efficiency. Specifically, a computationally economical species transport model via finite volume algorithm is employed as the base model for the whole computational domain, while the advanced transported probability density function (TPDF) method via Lagrangian particle tracking is employed only for regions with intense turbulence-chemistry interaction. The ‘PDF regions’ can be updated dynamically based on local flow and flame characteristics, and are compatible with complex geometric structures such as separated multi blocks, non-convex, and multi-connected regions. A two-way particle/finite volume submodel coupling is formulated to ensure the composition consistency in submodels in the PDF regions and to impose the correct interface conditions for composition and mass flow rate on the boundary of the PDF regions. The spatial partition and particle algorithms for time-varying PDF regions are demonstrated and the convergence characteristics of the adaptive modelling are investigated specifically for the variation of statistical error and bias with the number of particles per cell. The proposed zone-adaptive hybrid particle/finite volume algorithm has been numerically validated in a turbulent hydrogen/air non-premixed jet flame. It is shown that the predictions from zone-adaptive modelling are almost identical to those of stand-alone TPDF, illustrating the preservation of prediction accuracy but with significantly less computational cost.
{"title":"Consistent submodel coupling in hybrid particle/finite volume algorithms for zone-adaptive modelling of turbulent reactive flows","authors":"Tianwei Yang, Yuchao Yin, Hua Zhou, Yi Mo, Yuxuan Chen, Zhuyin Ren","doi":"10.1080/13647830.2022.2133636","DOIUrl":"https://doi.org/10.1080/13647830.2022.2133636","url":null,"abstract":"A hybrid particle/finite volume algorithm has been formulated for zone-adaptive modelling of turbulent reactive flows to achieve both high fidelity in predictions and high computational efficiency. Specifically, a computationally economical species transport model via finite volume algorithm is employed as the base model for the whole computational domain, while the advanced transported probability density function (TPDF) method via Lagrangian particle tracking is employed only for regions with intense turbulence-chemistry interaction. The ‘PDF regions’ can be updated dynamically based on local flow and flame characteristics, and are compatible with complex geometric structures such as separated multi blocks, non-convex, and multi-connected regions. A two-way particle/finite volume submodel coupling is formulated to ensure the composition consistency in submodels in the PDF regions and to impose the correct interface conditions for composition and mass flow rate on the boundary of the PDF regions. The spatial partition and particle algorithms for time-varying PDF regions are demonstrated and the convergence characteristics of the adaptive modelling are investigated specifically for the variation of statistical error and bias with the number of particles per cell. The proposed zone-adaptive hybrid particle/finite volume algorithm has been numerically validated in a turbulent hydrogen/air non-premixed jet flame. It is shown that the predictions from zone-adaptive modelling are almost identical to those of stand-alone TPDF, illustrating the preservation of prediction accuracy but with significantly less computational cost.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"26 1","pages":"1159 - 1184"},"PeriodicalIF":1.3,"publicationDate":"2022-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45902153","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 : 2022-09-16DOI: 10.1080/13647830.2022.2121663
V. Kurdyumov, C. Jiménez
The purpose of this work is to demonstrate that there are different stable configurations of lifted edge flames for the same set of parameters. It is shown that when a fuel jet is injected surrounded by oxidiser streams of equal velocity, there are configurations with symmetric and non-symmetric flame structures with respect to the symmetry line of the problem. These two kinds of solutions are both stable and the actual realisation of one or another solution depends on the initial conditions, in particular on the flame ignition parameters. It is shown that this multiple solution phenomenon takes place when the fuel Lewis number is less than unity. The influence of the Zel'dovich number and the injection flow rate is also investigated.
{"title":"Lifted jet edge flames: symmetric and non-symmetric configurations","authors":"V. Kurdyumov, C. Jiménez","doi":"10.1080/13647830.2022.2121663","DOIUrl":"https://doi.org/10.1080/13647830.2022.2121663","url":null,"abstract":"The purpose of this work is to demonstrate that there are different stable configurations of lifted edge flames for the same set of parameters. It is shown that when a fuel jet is injected surrounded by oxidiser streams of equal velocity, there are configurations with symmetric and non-symmetric flame structures with respect to the symmetry line of the problem. These two kinds of solutions are both stable and the actual realisation of one or another solution depends on the initial conditions, in particular on the flame ignition parameters. It is shown that this multiple solution phenomenon takes place when the fuel Lewis number is less than unity. The influence of the Zel'dovich number and the injection flow rate is also investigated.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"26 1","pages":"1114 - 1129"},"PeriodicalIF":1.3,"publicationDate":"2022-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41979022","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 : 2022-08-22DOI: 10.1080/13647830.2022.2111275
Pushan Sharma, A. Newale, P. Pepiot
Probability Density Function (PDF) methods, which allow for the direct integration of chemical kinetics, are well established to accurately simulate turbulent flames with strong turbulence-chemistry interactions. While adaptive chemistry techniques have been proven effective in reducing the high CPU cost and memory requirements associated with the handling of chemistry in such simulations, performance metrics have mostly been focussed on the primary oxidation pathways converting fuel to major products. In contrast, this work investigates the ability of adaptive techniques, in this case, the pre-partitioned adaptive chemistry (PPAC) approach, to handle secondary kinetics pathways that are parallel, but tightly coupled to the main oxidation process, taking formation as a case study. PPAC relies on a partitioning of the composition space into a user-specified number of regions, on which specialised reduced models are generated using the Directed Relation Graph with Error Propagation (DRGEP) reduction technique. The direct application of that methodology to a mix of hydrocarbon oxidation and nitrogen-related targets is shown to yield excessively detailed region-specific reduced mechanisms in order to properly capture both the main oxidation and the secondary formation processes, thereby decreasing the benefits of the adaptive approach. To address this issue, a sequential approach is proposed for the generation of the region-specific reduced mechanisms, in which the primary combustion pathways relevant for each region are identified first, followed by the selective addition, directly at the reduced level, of any secondary pathways relevant for that region using a recently developed build-up technique. This new strategy is assessed in the context of propane combustion in a partially stirred reactor (PaSR) and methane combustion in the Sandia Flame D configuration, demonstrating in both cases the benefits of the sequential approach for reduced model generation.
{"title":"Efficient treatment of secondary kinetic processes for pre-partitioned adaptive chemistry approaches","authors":"Pushan Sharma, A. Newale, P. Pepiot","doi":"10.1080/13647830.2022.2111275","DOIUrl":"https://doi.org/10.1080/13647830.2022.2111275","url":null,"abstract":"Probability Density Function (PDF) methods, which allow for the direct integration of chemical kinetics, are well established to accurately simulate turbulent flames with strong turbulence-chemistry interactions. While adaptive chemistry techniques have been proven effective in reducing the high CPU cost and memory requirements associated with the handling of chemistry in such simulations, performance metrics have mostly been focussed on the primary oxidation pathways converting fuel to major products. In contrast, this work investigates the ability of adaptive techniques, in this case, the pre-partitioned adaptive chemistry (PPAC) approach, to handle secondary kinetics pathways that are parallel, but tightly coupled to the main oxidation process, taking formation as a case study. PPAC relies on a partitioning of the composition space into a user-specified number of regions, on which specialised reduced models are generated using the Directed Relation Graph with Error Propagation (DRGEP) reduction technique. The direct application of that methodology to a mix of hydrocarbon oxidation and nitrogen-related targets is shown to yield excessively detailed region-specific reduced mechanisms in order to properly capture both the main oxidation and the secondary formation processes, thereby decreasing the benefits of the adaptive approach. To address this issue, a sequential approach is proposed for the generation of the region-specific reduced mechanisms, in which the primary combustion pathways relevant for each region are identified first, followed by the selective addition, directly at the reduced level, of any secondary pathways relevant for that region using a recently developed build-up technique. This new strategy is assessed in the context of propane combustion in a partially stirred reactor (PaSR) and methane combustion in the Sandia Flame D configuration, demonstrating in both cases the benefits of the sequential approach for reduced model generation.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"26 1","pages":"1098 - 1113"},"PeriodicalIF":1.3,"publicationDate":"2022-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44430284","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 : 2022-08-17DOI: 10.1080/13647830.2022.2110945
Simret Kidane Goitom, M. Papp, M. Kovács, T. Nagy, I. G. Zsély, T. Turányi, László Pál
Optimisation of detailed combustion mechanisms means that the corresponding kinetic model is fitted to experimental data via optimising their important rate and thermodynamic parameters within their domain of uncertainty. Typically, several dozen parameters are fitted to several hundred to several thousand data points. Many numerical optimisation methods have been used, but the efficiency of these methods has not been compared systematically. In this work, parameters of an H2/O2/NO x mechanism (214 reaction steps of 35 species) were fitted to 1552 indirect (ignition delay times measured in shock tubes and concentrations measured in flow reactors) and 755 direct measurements. Three test cases were investigated: (1) fitting the Arrhenius parameters of 2 reaction steps to 732 data points; (2) fitting the Arrhenius parameters of 4 reaction steps to 1077 data points; (3) fitting the Arrhenius parameters of 10 reaction steps to 2307 data points. All 3 cases were investigated in 2 ways: fitting the A-parameters only and fitting all Arrhenius parameters (5, 11 and 29 parameters, respectively). A series of global (FOCTOPUS, genetic algorithm, simulated annealing, particle swarm optimisation, covariance matrix adaptation evolutionary strategy (CMA-ES)) and local (simplex, pattern search, interior-point, quasi-Newton, BOBYQA, NEWUOA) optimisation methods were tested on these cases, some of them in two variants. The methods were compared in terms of the final error function value and number of error function evaluations. The main conclusions are that the FOCTOPUS resulted in the lowest final error value in all cases, but this method required relatively many error function evaluations. As the task became more difficult, more and more methods failed. A variant of the BOBYQA method looked stable and efficient in all cases.
{"title":"Efficient numerical methods for the optimisation of large kinetic reaction mechanisms","authors":"Simret Kidane Goitom, M. Papp, M. Kovács, T. Nagy, I. G. Zsély, T. Turányi, László Pál","doi":"10.1080/13647830.2022.2110945","DOIUrl":"https://doi.org/10.1080/13647830.2022.2110945","url":null,"abstract":"Optimisation of detailed combustion mechanisms means that the corresponding kinetic model is fitted to experimental data via optimising their important rate and thermodynamic parameters within their domain of uncertainty. Typically, several dozen parameters are fitted to several hundred to several thousand data points. Many numerical optimisation methods have been used, but the efficiency of these methods has not been compared systematically. In this work, parameters of an H2/O2/NO x mechanism (214 reaction steps of 35 species) were fitted to 1552 indirect (ignition delay times measured in shock tubes and concentrations measured in flow reactors) and 755 direct measurements. Three test cases were investigated: (1) fitting the Arrhenius parameters of 2 reaction steps to 732 data points; (2) fitting the Arrhenius parameters of 4 reaction steps to 1077 data points; (3) fitting the Arrhenius parameters of 10 reaction steps to 2307 data points. All 3 cases were investigated in 2 ways: fitting the A-parameters only and fitting all Arrhenius parameters (5, 11 and 29 parameters, respectively). A series of global (FOCTOPUS, genetic algorithm, simulated annealing, particle swarm optimisation, covariance matrix adaptation evolutionary strategy (CMA-ES)) and local (simplex, pattern search, interior-point, quasi-Newton, BOBYQA, NEWUOA) optimisation methods were tested on these cases, some of them in two variants. The methods were compared in terms of the final error function value and number of error function evaluations. The main conclusions are that the FOCTOPUS resulted in the lowest final error value in all cases, but this method required relatively many error function evaluations. As the task became more difficult, more and more methods failed. A variant of the BOBYQA method looked stable and efficient in all cases.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"26 1","pages":"1071 - 1097"},"PeriodicalIF":1.3,"publicationDate":"2022-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47975009","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 : 2022-08-01DOI: 10.1080/13647830.2022.2105259
Andrew F. Ilersich, K. Schau, J. Oefelein, A. Steinberg, M. Yano
We present and assess a method to reduce the computational cost of performing ensemble-based data assimilation (DA) for reacting flows in multiple-query scenarios, i.e. scenarios where multiple simulations are performed on systems with similar underlying dynamics. The accuracy of the DA, which depends on the accuracy of the sample covariance, improves with the ensemble size, but results in a commensurate increase to computational cost. To reduce the ensemble size while maintaining accurate covariance, we propose a data-driven approach to augment the covariance based on the statistical behaviour learned from previous model evaluations. We assess our augmentation method using one-dimensional model problems and a two-dimensional synthetic reacting flow problem. We show in all these cases that ensemble size, and thus computational cost, may be reduced by a factor of three to four while maintaining accuracy.
{"title":"Augmenting covariance estimation for ensemble-based data assimilation in multiple-query scenarios","authors":"Andrew F. Ilersich, K. Schau, J. Oefelein, A. Steinberg, M. Yano","doi":"10.1080/13647830.2022.2105259","DOIUrl":"https://doi.org/10.1080/13647830.2022.2105259","url":null,"abstract":"We present and assess a method to reduce the computational cost of performing ensemble-based data assimilation (DA) for reacting flows in multiple-query scenarios, i.e. scenarios where multiple simulations are performed on systems with similar underlying dynamics. The accuracy of the DA, which depends on the accuracy of the sample covariance, improves with the ensemble size, but results in a commensurate increase to computational cost. To reduce the ensemble size while maintaining accurate covariance, we propose a data-driven approach to augment the covariance based on the statistical behaviour learned from previous model evaluations. We assess our augmentation method using one-dimensional model problems and a two-dimensional synthetic reacting flow problem. We show in all these cases that ensemble size, and thus computational cost, may be reduced by a factor of three to four while maintaining accuracy.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":"26 1","pages":"1041 - 1070"},"PeriodicalIF":1.3,"publicationDate":"2022-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43281593","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 : 2022-07-13DOI: 10.1080/13647830.2022.2095927
S. Singh, Jithin Edacheri Veetil, Neeraj Kumbhakarna, R. K. Velamati, Sudarshan Kumar
The effect of hydrogen (H2) addition on the flame dynamics of premixed methane/air mixtures in a microchannel was investigated through two-dimensional numerical computations using a detailed chemistry model. Detailed numerical simulations were performed in a 2 mm diameter tube with 120 mm length and a hyperbolic wall temperature gradient condition. All numerical computations were performed at stoichiometric mixture conditions with a fixed inlet velocity of 15 cm/s. Flame repetitive extinction and ignition (FREI) has been observed to appear at various mixture conditions. The frequency of FREI shows a non-monotonic variation for CH4/air mixtures with H2 addition. The time taken for completion of one FREI cycle increases with H2 addition. The maximum temperature and heat of the reaction were observed to decrease with hydrogen addition. The effect of diameter on the FREI cycle was studied by comparing the numerical results for 1, 1.5, and 2 mm diameter tubes. As the diameter is reduced from 2 mm to 1 mm, the FREI frequency increased, and the maximum temperature decreased owing to increased heat loss through channel walls. The location of the ignition and extinction shifted downstream for 1 mm tube, as compared to a 2 mm diameter tube.
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