The Combustion and Plasma research activities aim to study energy systems and processes that involve intense heat sources such as combustion (burners, furnaces, boilers, combustion turbines, combustion engines, etc.) and plasma arcs and electrical discharges (arc welding, circuit breaker, plasma torch, discharge lamps, thin film deposition reactors, etc.).
Conventionally, increased energy efficiency and a reduction in harmful emissions have served as the driving forces behind all combustion-related research. Our conventional combustion business is based on these principles. Nevertheless and in the future we will also be interested in fuel cells which represent a worldwide interest in the field of energy for sustainable development.
In the field of plasmas, worldwide interest is oriented towards the control of phenomena out of thermodynamic and chemical equilibrium for the development of a multitude of industrial applications such as electrical switching devices, plasma reactors, and energy-efficient lamps that produce light with great consistency.

Objectifs du programme de recherche:

The objectives of the Combustion and Plasma research program are:

• * The establishment of theoretical, numerical and experimental tools for the study of transfers in reactive flows in combustion and plasmas.
• * The use of the tools put in place and the knowledge acquired to control and optimize several industrial systems and processes (burners, combustion turbines, fuel cells based on hydrocarbons, discharge lamps, electrical cut-off devices, plasma reactors).

Methodology and approach envisaged for carrying out the research program:

The methodology and approach envisaged for carrying out the research program are developed below for the various sub-themes: 

1. Combustion conventionnelle:

   The simulation of turbulent diffusion flames in a gaseous medium using flamelet concept models is currently well-established. With the aim of expanding our expertise, we are considering applying this approach to premixed flames. In a first step, we will numerically study the thermochemical structure of laminar premixed flames. Subsequently, our focus turns to turbulent premixed flames and potentially partially premixed flames.Considering the significant role of radiative exchanges in flame stabilization and particle preheating, we have begun developing a model for evaluating these exchanges in a gaseous medium laden with particles.
   We can currently predict the distribution of radiative fluxes in a cylindrical enclosure containing a gas laden with solid particles. The medium is assumed to be gray, absorbing, emissive, and diffusive. In collaboration with the Laboratory of Energetics and Thermal and Applied Mechanics (Nancy), we are working to improve our code by using appropriate phase functions for particle scattering and considering the nature, size, and concentration of the particles. To account for the spectral dependence of radiation, the medium will be approximated as a gray medium by bands.
   The concentration of particles in two-phase media involves determining their position. In this context, numerical simulations predicting the transport and dispersion of solid particles in a turbulent air jet are currently underway. In a first step, it was assumed that only the mean flow affects the particles. Currently, we are considering, to deduce particle dispersion, taking into account interactions between particles and turbulent velocity fluctuations. The theoretical tools put in place will then be used for simulating droplet vaporization in a hot air jet. It is evident that this study is only a first step toward understanding combustion in Diesel engines.
   Aware of the dangers to humanity caused by pollutant species, especially nitrogen oxides emitted by hydrocarbon combustion, we have analyzed the mechanisms of their formation and reduction methods. In the case of the "staged combustion" technique for NOx reduction, we modeled the combustion chamber of a gas turbine by an appropriate combination of a set of ideal reactors. Currently, another NOx reduction method called "Flameless oxidation" has emerged. It involves creating recirculation of combustion products through fresh reactants, resulting in a diffuse reaction zone without temperature peaks. This leads to a reduction in NOx formation. We plan to combine our turbulent flow calculation code with the ChemKin code to numerically study this technique.
   Furthermore, convinced of the need for experimental studies at LESTE, we are considering equipping ourselves with an experimental setup to achieve low NOx combustion. In this regard, and in collaboration with the Rouan team (CORIA, France), we plan to simulate and design a low NOx Natural Gas - Air burner. The French team will be responsible for manufacturing this burner. In principle, this burner will be equipped with a series of small natural gas injectors distributed around a central axis and an annular air jet.

2. Slow combustion in fixed bed and synthetic combustio:
    We have developed a numerical simulation code for the flow and transfers in fixed bed burners. This code is validated by comparison with experimental results obtained at the University of Berkeley. Currently, we plan to use this code to analyze the different techniques of thermal treatment of solid waste (combustion, incineration, thermolysis). Particular attention will be given to pollution problems.We also plan, within the framework of a collaboration with Professor Calos Fernandez Pello of the University of California at Berkeley, to use this code to study the combustion of mixtures of solid powders in a fixed bed for the manufacture of composite materials for various industrial applications. such as catalysts, electrical insulators, etc.
    
3. Fuel Cells and Hydrocarbon Reformers:
   The fuel cell is a system that allows the silent production of electricity from, essentially hydrogen, without polluting emissions and without moving parts. Hydrogen storage is one of the technological obstacles to be solved for the commercial use of these fuel cells.
   Currently, great interest is granted to SOFC cells (Solid Oxide Fuel Cells) which can use as fuel a hydrocarbon directly and/or a mixture of hydrogen, CO and hydrocarbon. These batteries are less expensive, but their electrical efficiency remains lower than that of batteries using pure hydrogen. Hence the interest of integrating a process for transforming hydrocarbons into hydrogen.
   The planned study consists of the modeling and numerical simulation of heat and mass transfers with the reaction kinetics in the SOFC pile and during the transformation of the hydrocarbon (natural gas, methanol, gasoline, diesel, etc.) for the supply of these batteries.
    
4. Arc and Discharge Plasma:
   In the physics of ionized media, the electric arc occupies a very special place because of the number and importance of its applications (arc lamp, plasma torch, arc welding, circuit breaker, laser, etc.). Engineers quickly saw the interest that could be drawn from this phenomenon, capable of transforming electrical energy into light or thermal energy and of behaving like a reactor of choice for certain applications (deposition of thin layers, etching of electronic chips , waste treatment, etc.). The production of circuit breakers requires a long and costly series of tests on the one hand for their development and on the other hand for their qualification. The objective of our study is to produce a numerical simulation code for breaking in an SF6 circuit breaker; it is essentially a simulation of the electric arc and its interaction with the gas and the electrodes. The numerical simulation code that needs to be validated will reduce the number of tests needed and help size the electrical switchgear. The modeling involves certain characteristics which are necessary to know. It is therefore necessary to carry out experiments to determine these characteristics and validate the digital code.
   In the field of lighting, the high-pressure mercury discharge lamp has been and remains widely used. Research and improvement of the characteristics of light sources in terms of efficiency have led to the introduction of metal additives (thallium, indium, etc.) in the form of halides (iodide in general) into landfills. A first work was devoted to the evaluation of the transport coefficients in the plasma of a high pressure discharge lamp in mercury doped with thallium iodide. Within the framework of the CHAPMAN-ENSKOG theory, the coefficients of diffusion and thermal conductivity were calculated.
   We now plan to numerically study the natural convection and the radiative phenomena in the lamp, as well as the electrical and thermal instabilities which can be harmful in certain cases.
   Concerning plasma reactors, we are interested in radiofrequency discharges in NH3/SiH4 mixtures for the deposition of thin films of silicon nitrides. The objective of our study is the establishment of a computer code for the numerical simulation of plasma reactors.
   First of all, a bibliographic study on chemical vapor deposition processes of thin films by the "PECVD" method (Plasma Enhanced Chemical Vapor Deposition) will be carried out. Next, we will focus on the mathematical formulation.
   The discretization of the equations will be carried out by finite volume methods based on finite elements in axisymmetric configuration. After validating the code, we will use it to simulate plasma reactors.

Opportunities for promoting research results:

The digital tools developed and the results obtained will make it possible to optimize and design several systems and processes (burners, ovens, electrical contactors and switches, fuel cells, plasma reactor, lamps, etc.) and therefore can be directly valued.