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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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.
{"title":"Flame dynamics of premixed CH4/H2/air flames in a microchannel with a wall temperature gradient","authors":"S. Singh, Jithin Edacheri Veetil, Neeraj Kumbhakarna, R. K. Velamati, Sudarshan Kumar","doi":"10.1080/13647830.2022.2095927","DOIUrl":"https://doi.org/10.1080/13647830.2022.2095927","url":null,"abstract":"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.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2022-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47822029","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 : 2022-06-28DOI: 10.1080/13647830.2022.2085181
Donald Scott Stewart, Kibaek Lee, A. Hernández
Through the use of carefully designed numerical experiments on an explosive system, that use predictive models for subcomponents and multi-material simulation, we demonstrate enhanced reactivity by energy trapping in regions of the reactive flow that were previously shocked. Particles and inclusions are placed in designed patterns in an explosive matrix. New capabilities in additive manufacture make it possible to consider novel designs, that we refer to as ‘reactive metamaterials’. For a fixed amount of energy delivered by a shock impactor, an explosive that normally would not detonate, will detonate when particles are included. Enhanced reactivity correlates precisely with a change in the partition of energy from kinetic to internal, via reflective processes and flow stagnation in high pressure systems. We analyse cases associated with high shock impedance tantalum particles, and void inclusions, individually and placed in a test array. High impedance reflectors trap energy in regions of pre-shocked material. Whereas void shock collapse causes depressurisation of the material along with rapid material flow, and high pressure spot formation related to the jet impact blast. We analyse how these limiting cases of high impedance particle arrays and void arrays partition specific kinetic and internal energy, during the shock impact transient on the system of matrix explosive and embedded particle/voids. Both generate specific flow fields, pressure and temperature cycles in the matrix material over interval times, determined by the particle/void size and placement. Design variations of the configurations presented here can be tested by both experiment and simulation, and can be searched for optimal designs, aided by modern machine learning search methods.
{"title":"Enhanced reactivity by energy trapping in shocked materials: reactive metamaterials for controllable output","authors":"Donald Scott Stewart, Kibaek Lee, A. Hernández","doi":"10.1080/13647830.2022.2085181","DOIUrl":"https://doi.org/10.1080/13647830.2022.2085181","url":null,"abstract":"Through the use of carefully designed numerical experiments on an explosive system, that use predictive models for subcomponents and multi-material simulation, we demonstrate enhanced reactivity by energy trapping in regions of the reactive flow that were previously shocked. Particles and inclusions are placed in designed patterns in an explosive matrix. New capabilities in additive manufacture make it possible to consider novel designs, that we refer to as ‘reactive metamaterials’. For a fixed amount of energy delivered by a shock impactor, an explosive that normally would not detonate, will detonate when particles are included. Enhanced reactivity correlates precisely with a change in the partition of energy from kinetic to internal, via reflective processes and flow stagnation in high pressure systems. We analyse cases associated with high shock impedance tantalum particles, and void inclusions, individually and placed in a test array. High impedance reflectors trap energy in regions of pre-shocked material. Whereas void shock collapse causes depressurisation of the material along with rapid material flow, and high pressure spot formation related to the jet impact blast. We analyse how these limiting cases of high impedance particle arrays and void arrays partition specific kinetic and internal energy, during the shock impact transient on the system of matrix explosive and embedded particle/voids. Both generate specific flow fields, pressure and temperature cycles in the matrix material over interval times, determined by the particle/void size and placement. Design variations of the configurations presented here can be tested by both experiment and simulation, and can be searched for optimal designs, aided by modern machine learning search methods.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2022-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48641275","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 : 2022-06-26DOI: 10.1080/13647830.2022.2090443
Pabitra Badhuk, R. Ravikrishna
Phosphorus-based chemical compounds such as trimethylphosphate (TMP) and dimethylmethylphosphonate (DMMP) are widely used as fire suppressants. The detailed chemical kinetic mechanism by Jayaweera et al. [1] is frequently used to describe the flame inhibition process. The elementary reaction steps can be categorised into inhibitor molecule decomposition steps and radical recombination steps. The present work shows that the inhibitor decomposition process can be adequately represented by a single irreversible step for TMP. Subsequently, graph-based mechanism reduction techniques and sensitivity analysis are employed to extract the key catalytic inhibition reactions. The resultant skeletal kinetic mechanism consists of 4 species and 7 reactions. The present work also proposes a global mechanism containing 3 species and 3 reactions. In the global model, flame inhibition is described by a 2-step model. These models are validated in premixed and diffusion flame environments. Excellent agreement with the experimental measurements and detailed model predictions are obtained. Development of the skeletal/global models reduces the computational time by around 82% compared to the detailed model.
以磷为基础的化合物，如三甲基磷酸盐(TMP)和二甲基膦酸盐(DMMP)被广泛用作灭火剂。Jayaweera et al.[1]详细的化学动力学机理常被用来描述抑焰过程。基本反应步骤可分为抑制剂分子分解步骤和自由基重组步骤。本研究表明，缓蚀剂的分解过程可以用一个不可逆的步骤来充分表征。随后，采用基于图的机理还原技术和灵敏度分析提取关键的催化抑制反应。生成的骨架动力学机制由4种物质和7种反应组成。本工作还提出了一个包含3种物质和3种反应的全局机制。在全局模型中，火焰抑制用两步模型来描述。这些模型在预混火焰和扩散火焰环境下得到了验证。与实验测量结果和详细的模型预测结果非常吻合。与详细模型相比，骨架/全局模型的开发减少了约82%的计算时间。
{"title":"Development and validation of skeletal/global mechanisms describing TMP-based flame inhibition","authors":"Pabitra Badhuk, R. Ravikrishna","doi":"10.1080/13647830.2022.2090443","DOIUrl":"https://doi.org/10.1080/13647830.2022.2090443","url":null,"abstract":"Phosphorus-based chemical compounds such as trimethylphosphate (TMP) and dimethylmethylphosphonate (DMMP) are widely used as fire suppressants. The detailed chemical kinetic mechanism by Jayaweera et al. [1] is frequently used to describe the flame inhibition process. The elementary reaction steps can be categorised into inhibitor molecule decomposition steps and radical recombination steps. The present work shows that the inhibitor decomposition process can be adequately represented by a single irreversible step for TMP. Subsequently, graph-based mechanism reduction techniques and sensitivity analysis are employed to extract the key catalytic inhibition reactions. The resultant skeletal kinetic mechanism consists of 4 species and 7 reactions. The present work also proposes a global mechanism containing 3 species and 3 reactions. In the global model, flame inhibition is described by a 2-step model. These models are validated in premixed and diffusion flame environments. Excellent agreement with the experimental measurements and detailed model predictions are obtained. Development of the skeletal/global models reduces the computational time by around 82% compared to the detailed model.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48570377","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 : 2022-06-16DOI: 10.1080/13647830.2022.2086068
Pragneshkumar Rajubhai Rana, K. Narayanaswamy, Sivaram Ambikasaran
Ignition delay time (IDT) is an important global combustion property that affects the thermal efficiency of the engine and emissions (particularly NO ). IDT is generally measured by performing experiments using Shock-tube and Rapid Compression Machine (RCM). The numerical calculation of IDT is a computationally expensive and time-consuming process. Arrhenius type empirical correlations offer an inexpensive alternative to obtain IDT. However, such correlations have limitations as these typically involve ad-hoc parameters and are valid only for a specific fuel and particular range of temperature/pressure conditions. This study aims to formulate a data-driven scientific way to obtain IDT for new fuels without performing detailed numerical calculations or relying on ad-hoc empirical correlations. We propose a rigorous, well-validated data-driven study to obtain IDT for new fuels using a regression-based clustering algorithm. In our model, we bring in the fuel structure through the overall activation energy ( ) by expressing it in terms of the different bonds present in the molecule. Gaussian Mixture Model (GMM) is used for the formation of clusters, and regression is applied over each cluster to generate models. The proposed algorithm is used on the ignition delay dataset of straight-chain alkanes (C H for n = 4 to 16). The high level of accuracy achieved demonstrates the applicability of the proposed algorithm over IDT data. The algorithm and framework discussed in this article are implemented in python and made available at https://doi.org/10.5281/zenodo.5774617.
{"title":"A data-driven framework to predict ignition delays of straight-chain alkanes","authors":"Pragneshkumar Rajubhai Rana, K. Narayanaswamy, Sivaram Ambikasaran","doi":"10.1080/13647830.2022.2086068","DOIUrl":"https://doi.org/10.1080/13647830.2022.2086068","url":null,"abstract":"Ignition delay time (IDT) is an important global combustion property that affects the thermal efficiency of the engine and emissions (particularly NO ). IDT is generally measured by performing experiments using Shock-tube and Rapid Compression Machine (RCM). The numerical calculation of IDT is a computationally expensive and time-consuming process. Arrhenius type empirical correlations offer an inexpensive alternative to obtain IDT. However, such correlations have limitations as these typically involve ad-hoc parameters and are valid only for a specific fuel and particular range of temperature/pressure conditions. This study aims to formulate a data-driven scientific way to obtain IDT for new fuels without performing detailed numerical calculations or relying on ad-hoc empirical correlations. We propose a rigorous, well-validated data-driven study to obtain IDT for new fuels using a regression-based clustering algorithm. In our model, we bring in the fuel structure through the overall activation energy ( ) by expressing it in terms of the different bonds present in the molecule. Gaussian Mixture Model (GMM) is used for the formation of clusters, and regression is applied over each cluster to generate models. The proposed algorithm is used on the ignition delay dataset of straight-chain alkanes (C H for n = 4 to 16). The high level of accuracy achieved demonstrates the applicability of the proposed algorithm over IDT data. The algorithm and framework discussed in this article are implemented in python and made available at https://doi.org/10.5281/zenodo.5774617.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2022-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47743440","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 : 2022-06-16DOI: 10.1080/13647830.2022.2083525
S. Tomasch, N. Swaminathan, Christoph Spijker, I. S. Ertesvåg
This study presents an algebraic combustion closure for Large eddy simulation (LES) exhibiting attributes of simplicity and simultaneous accuracy under realistic combustion conditions. The model makes use of the interlink between the reaction and dissipation rates in premixed turbulent combustion but relaxes the thin flame assumption by considering finite-rate chemistry effects in the small-scale turbulence structure. The core idea of the approach is to approximate the reaction progress in the unresolved spectrum of wave lengths and to use it within a filtered reaction rate expression. The model is implemented in OpenFOAM 4.0 and is tested on a turbulent, premixed flame behind a bluff-body, applying an LES approach for turbulence modelling. The cross comparison of velocity, temperature and composition data with experiments and a well-investigated combustion model in literature reveals competitive performance of the new model. Especially in the near-field of the bluff body flame, corresponding to thin and moderately thickened flame regions, its ability to capture the flame structure is highly promising. The chosen, partly explicit approach to recover the temperature from the transported sensible enthalpy, involving a strong coupling between filtered reaction and heat release rate, also shows advantages over obtaining the temperature from presumed probability density functions.
{"title":"Development of a turbulence dissipation based reaction rate model for progress variable in turbulent premixed flames","authors":"S. Tomasch, N. Swaminathan, Christoph Spijker, I. S. Ertesvåg","doi":"10.1080/13647830.2022.2083525","DOIUrl":"https://doi.org/10.1080/13647830.2022.2083525","url":null,"abstract":"This study presents an algebraic combustion closure for Large eddy simulation (LES) exhibiting attributes of simplicity and simultaneous accuracy under realistic combustion conditions. The model makes use of the interlink between the reaction and dissipation rates in premixed turbulent combustion but relaxes the thin flame assumption by considering finite-rate chemistry effects in the small-scale turbulence structure. The core idea of the approach is to approximate the reaction progress in the unresolved spectrum of wave lengths and to use it within a filtered reaction rate expression. The model is implemented in OpenFOAM 4.0 and is tested on a turbulent, premixed flame behind a bluff-body, applying an LES approach for turbulence modelling. The cross comparison of velocity, temperature and composition data with experiments and a well-investigated combustion model in literature reveals competitive performance of the new model. Especially in the near-field of the bluff body flame, corresponding to thin and moderately thickened flame regions, its ability to capture the flame structure is highly promising. The chosen, partly explicit approach to recover the temperature from the transported sensible enthalpy, involving a strong coupling between filtered reaction and heat release rate, also shows advantages over obtaining the temperature from presumed probability density functions.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2022-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48252076","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 : 2022-05-30DOI: 10.1080/13647830.2022.2080122
Zhuang Ma, Chen Wang, Gaofeng Wang, Tao Cui, Yao Zheng
Critical slowing down phenomena occur during the transition process of various dynamical states, such as bifurcations. The eigenvalues of dynamical systems can be regarded as an indicator of critical slowing down of impending bifurcation. Adaptive, locally linear models can extract local eigenvalues of the nonlinear dynamical system by segmenting a full-time series into multi-windows, and eigenvalue spectrum analysis is based on the eigenvalues. The state transition between different combustion states occurs through bifurcation processes. In this paper, we investigate critical slowing down in the bifurcation process of backward-facing step combustor. We performed a series of experiments by fixing the air mass flow and varying the fuel mass flow from the lean blowout condition to a thermoacoustic instability condition with a quasi-steady change, and the combustion state varying versus the change of the operation conditions exhibit a quasi-Hopf bifurcation process. The measured pressure fluctuations were treated by the local linear model to analyse the eigenvalue spectrum. The real parts of the eigenvalues approximate zero gradually when the equivalence ratio increases, and this tendency corresponds to the critical slowing down. Furthermore, the commonly used early warning signals were also used to support the analysis results of the eigenvalue spectrum.
{"title":"Experimental investigation on critical slowing down of premixed combustion in a backward-facing step combustor","authors":"Zhuang Ma, Chen Wang, Gaofeng Wang, Tao Cui, Yao Zheng","doi":"10.1080/13647830.2022.2080122","DOIUrl":"https://doi.org/10.1080/13647830.2022.2080122","url":null,"abstract":"Critical slowing down phenomena occur during the transition process of various dynamical states, such as bifurcations. The eigenvalues of dynamical systems can be regarded as an indicator of critical slowing down of impending bifurcation. Adaptive, locally linear models can extract local eigenvalues of the nonlinear dynamical system by segmenting a full-time series into multi-windows, and eigenvalue spectrum analysis is based on the eigenvalues. The state transition between different combustion states occurs through bifurcation processes. In this paper, we investigate critical slowing down in the bifurcation process of backward-facing step combustor. We performed a series of experiments by fixing the air mass flow and varying the fuel mass flow from the lean blowout condition to a thermoacoustic instability condition with a quasi-steady change, and the combustion state varying versus the change of the operation conditions exhibit a quasi-Hopf bifurcation process. The measured pressure fluctuations were treated by the local linear model to analyse the eigenvalue spectrum. The real parts of the eigenvalues approximate zero gradually when the equivalence ratio increases, and this tendency corresponds to the critical slowing down. Furthermore, the commonly used early warning signals were also used to support the analysis results of the eigenvalue spectrum.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2022-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47650839","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}
To build a set of complete kinetic parameters of oxygenated fuels kinetic model on Pt catalyst, methanol was used as an example to carry out the catalytic oxidation kinetics experiment of oxygenated fuels on Pt/ZSM-5 catalyst. The Power law model and Langmuir–Hinshelwood (L–H) model were established to characterise the catalytic oxidation reaction of methanol. Then the oxidation kinetics of methanol, ethanol, dimethyl ether (DME) and n-butanol on Pt/ZSM-5 was studied under the same experimental conditions. It was found that the reaction orders of fuel molecules (methanol is −0.14) were much less than that of oxygen (1.23) in Power law model. The adsorption constants of fuel molecules were higher than that of oxygen in L–H model. The adsorption characteristics of alcohols on Pt were similar, but the reaction orders of alcohols were not consistent. The adsorption constants and adsorption heat of dimethyl ether were much larger than that of alcohols. The intrinsic reaction rates of four oxygenated fuels on Pt/ZSM-5 were compared at the same input power: r methanol r DME r ethanol r n-butanol. In general, methanol is a suitable oxygenated fuel in the design and development of catalytic micro-combustor.
{"title":"Kinetics of catalytic oxidation of oxygenated fuels on Pt/ZSM-5 catalyst","authors":"Yanyi Yao, Wei-juan Yang, Xing Zhang, Xiaoyu Zhu, Jun Cheng, Junhu Zhou","doi":"10.1080/13647830.2022.2063194","DOIUrl":"https://doi.org/10.1080/13647830.2022.2063194","url":null,"abstract":"To build a set of complete kinetic parameters of oxygenated fuels kinetic model on Pt catalyst, methanol was used as an example to carry out the catalytic oxidation kinetics experiment of oxygenated fuels on Pt/ZSM-5 catalyst. The Power law model and Langmuir–Hinshelwood (L–H) model were established to characterise the catalytic oxidation reaction of methanol. Then the oxidation kinetics of methanol, ethanol, dimethyl ether (DME) and n-butanol on Pt/ZSM-5 was studied under the same experimental conditions. It was found that the reaction orders of fuel molecules (methanol is −0.14) were much less than that of oxygen (1.23) in Power law model. The adsorption constants of fuel molecules were higher than that of oxygen in L–H model. The adsorption characteristics of alcohols on Pt were similar, but the reaction orders of alcohols were not consistent. The adsorption constants and adsorption heat of dimethyl ether were much larger than that of alcohols. The intrinsic reaction rates of four oxygenated fuels on Pt/ZSM-5 were compared at the same input power: r methanol r DME r ethanol r n-butanol. In general, methanol is a suitable oxygenated fuel in the design and development of catalytic micro-combustor.","PeriodicalId":50665,"journal":{"name":"Combustion Theory and Modelling","volume":null,"pages":null},"PeriodicalIF":1.3,"publicationDate":"2022-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48000950","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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