Periodic Reporting for period 1 - EnFoRCe (Effects of Electric Fields on tuRbulent Combustion)
Período documentado: 2020-10-01 hasta 2022-09-30
The ability of electric fields to modify the behavior of hydrocarbon flames is well-known since the first decades of the 20th century. Even weak electric fields can provide significant energy to ionized species, that are naturally produced inside a flame, and modify the behavior of a burning mixture. Over the years, it has been experimentally demonstrated that imposing an electric field it is possible, for instance, to augment the laminar premixed-flame speed, to extinguish liquid-pool fires and jet diffusion flames, to induce instabilities in premixed flame, or to vary lift-off heights of jet diffusion flames. However, this technology has never been utilized outside a research laboratory, mainly because the knowledge of the fundamental phenomena involved in electrified flames is still insufficient to formulate predictive models necessary to effectively design a flame control system.
Although the recent strive to use renewable energy sources, the combustion of hydrocarbons is still one of the main sources of energy for our society. The need to push the envelope of the current state of the art toward more green and efficient technologies constantly faces the limitations posed by combustion instability. In this context, experimental studies have shown that the application of an external electric field is an economic and efficient way of extending the stability limits of a flame. This technique of controlling a combustion process is particularly interesting from an industrial point of view is its ease of implementation in existing combustion chambers and the low amount of electric energy required to operate the system.
This project numerically analyses electrified methane-air flames impinged by an external electric field. The main objective of this analysis is to shed light on the fundamental physics involved in the electric-field/turbulent-flame interaction. By using high-fidelity calculations and some of the most recent supercomputers in the World, the analysis carried out in this project will be able to access details of turbulent electrified flames that are not measurable with experiments. Moreover, a new open-source solver and models for the numerical analysis of electrified flames have been developed and released.
The results of this project have shown that turbulence can create significant fluctuations in the electric charge field produced by a flame. The presence of these fluctuations influences the distribution of the electric force exerted on the flow and consequently the ability of electric fields to control combustion. The dominant challenges in modeling the underlying phenomena have been identified and will be addressed in future works.
Although the recent strive to use renewable energy sources, the combustion of hydrocarbons is still one of the main sources of energy for our society. The need to push the envelope of the current state of the art toward more green and efficient technologies constantly faces the limitations posed by combustion instability. In this context, experimental studies have shown that the application of an external electric field is an economic and efficient way of extending the stability limits of a flame. This technique of controlling a combustion process is particularly interesting from an industrial point of view is its ease of implementation in existing combustion chambers and the low amount of electric energy required to operate the system.
This project numerically analyses electrified methane-air flames impinged by an external electric field. The main objective of this analysis is to shed light on the fundamental physics involved in the electric-field/turbulent-flame interaction. By using high-fidelity calculations and some of the most recent supercomputers in the World, the analysis carried out in this project will be able to access details of turbulent electrified flames that are not measurable with experiments. Moreover, a new open-source solver and models for the numerical analysis of electrified flames have been developed and released.
The results of this project have shown that turbulence can create significant fluctuations in the electric charge field produced by a flame. The presence of these fluctuations influences the distribution of the electric force exerted on the flow and consequently the ability of electric fields to control combustion. The dominant challenges in modeling the underlying phenomena have been identified and will be addressed in future works.
The work performed during the project can be mainly organized into three sections: software development, model development, and electrified combustion theory.
The first section dealt with implementing all the features required to accurately compute electrified flames in a Navier-Stokes rately. An open-source fluid dynamics solver was chosen as a baseline, namely the Hypersonic Task-based Research (HTR) solver. HTR is a compressible Navier-Stokes solver with an innovative software infrastructure that makes it particularly efficient in using new supercomputers with heterogeneous architectures. The software development activities included the formulation and implementation of new models of reactions that are required to predict the rate of hydrocarbon combustion and the medication of the charged species fluxes to take into account the ion wind induced by an external electric field. The results of this activity have been condensed in the journal paper, Di Renzo “HTR-1.3 solver: Predicting electrified combustion using the hypersonic task-based research solver”. Computer Physics Communications 272 (2022), and partially presented at the 2021 Division of Fluid Dynamics meeting of the American Physical Society in Phoenix. Moreover, the newly developed version of the HTR solver is freely available at https://github.com/stanfordhpccenter/HTR-solver.
Although the recent developments in the computational capabilities of the nowadays supercomputers and the efficiency of the numerical tool deployed in this project, the prediction of electrified remains a very challenging problem. Accurate numerical predictions of electrified flames could require the transport of hundreds of different chemical species, which reacts through thousands of chemical reactions. For this reason, part of this action has been dedicated to the development of new chemical models that could accurately predict electrified flames with a reduced number of species. Using chemical mechanisms reduction techniques that have been developed at CERFACS, a new reaction mechanism has been formulated for methane-air flames starting from a very detailed description of the chemistry. The details of this mechanism and the main results that have shown its capabilities have been presented in Di Renzo & Cuenot “A reduced chemical mechanism for the simulation of electrified methane/air flames”. Combustion and Flame 244 (2022).
The third and final part of the project consisted in putting together the results achieved in the chemical model and software development to perform the first direct numerical simulation of an electrified turbulent diffusion flame. The canonical mixing layer configuration, shown in the attached figure, has been selected to provide a highly controlled environment whereby all the physical phenomena happening in the electrified turbulent flame could be identified and studied in depth. The results of the carried-out calculations have been presented at the 14h European Fluid Mechanics Conference in Athens, Grece, and have been submitted for publication.
The results of this project will be useful for scientists interested in electrified combustion and might lead to the formulation of reduced-order models able to predict the behavior of electrified flames in burners utilized in industrial applications.
The first section dealt with implementing all the features required to accurately compute electrified flames in a Navier-Stokes rately. An open-source fluid dynamics solver was chosen as a baseline, namely the Hypersonic Task-based Research (HTR) solver. HTR is a compressible Navier-Stokes solver with an innovative software infrastructure that makes it particularly efficient in using new supercomputers with heterogeneous architectures. The software development activities included the formulation and implementation of new models of reactions that are required to predict the rate of hydrocarbon combustion and the medication of the charged species fluxes to take into account the ion wind induced by an external electric field. The results of this activity have been condensed in the journal paper, Di Renzo “HTR-1.3 solver: Predicting electrified combustion using the hypersonic task-based research solver”. Computer Physics Communications 272 (2022), and partially presented at the 2021 Division of Fluid Dynamics meeting of the American Physical Society in Phoenix. Moreover, the newly developed version of the HTR solver is freely available at https://github.com/stanfordhpccenter/HTR-solver.
Although the recent developments in the computational capabilities of the nowadays supercomputers and the efficiency of the numerical tool deployed in this project, the prediction of electrified remains a very challenging problem. Accurate numerical predictions of electrified flames could require the transport of hundreds of different chemical species, which reacts through thousands of chemical reactions. For this reason, part of this action has been dedicated to the development of new chemical models that could accurately predict electrified flames with a reduced number of species. Using chemical mechanisms reduction techniques that have been developed at CERFACS, a new reaction mechanism has been formulated for methane-air flames starting from a very detailed description of the chemistry. The details of this mechanism and the main results that have shown its capabilities have been presented in Di Renzo & Cuenot “A reduced chemical mechanism for the simulation of electrified methane/air flames”. Combustion and Flame 244 (2022).
The third and final part of the project consisted in putting together the results achieved in the chemical model and software development to perform the first direct numerical simulation of an electrified turbulent diffusion flame. The canonical mixing layer configuration, shown in the attached figure, has been selected to provide a highly controlled environment whereby all the physical phenomena happening in the electrified turbulent flame could be identified and studied in depth. The results of the carried-out calculations have been presented at the 14h European Fluid Mechanics Conference in Athens, Grece, and have been submitted for publication.
The results of this project will be useful for scientists interested in electrified combustion and might lead to the formulation of reduced-order models able to predict the behavior of electrified flames in burners utilized in industrial applications.
This project has improved multiple aspects of the state of the art of electrified combustion.
A new and efficient solver capable of taking into account the effects of an electric field on a three-dimensional diffusion flame has been developed and made available open source. Considering that most of the previous calculations on electrified combustion have been performed in one- and two-dimensional configurations using in-house solvers that are not shared with the rest of the scientific community, this project has not only demonstrated the capability of performing large-scale calculations in this field but also produced a tool that is freely available and that enables any researcher to perform similar calculations.
A new chemical model for the prediction of electrified methane-air flames has been formulated and published. This model contributes to significantly reducing the computational cost of electrified combustion simulations without penalties on the accuracy of the calculations.
The tools mentioned above have allowed the first numerical simulation of a diffusion flame impinged by an external electric field shedding light on multiple aspects of this interaction.
These new findings are already in use to formulate future electrified combustion models capable of predicting this interaction in industrial burners.
A new and efficient solver capable of taking into account the effects of an electric field on a three-dimensional diffusion flame has been developed and made available open source. Considering that most of the previous calculations on electrified combustion have been performed in one- and two-dimensional configurations using in-house solvers that are not shared with the rest of the scientific community, this project has not only demonstrated the capability of performing large-scale calculations in this field but also produced a tool that is freely available and that enables any researcher to perform similar calculations.
A new chemical model for the prediction of electrified methane-air flames has been formulated and published. This model contributes to significantly reducing the computational cost of electrified combustion simulations without penalties on the accuracy of the calculations.
The tools mentioned above have allowed the first numerical simulation of a diffusion flame impinged by an external electric field shedding light on multiple aspects of this interaction.
These new findings are already in use to formulate future electrified combustion models capable of predicting this interaction in industrial burners.