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Theoretical Study of Plasma in the Ignition/Combustion Transition Phase of a Gas Engine

par Laurence Laffont - publié le , mis à jour le

Andriniaina HARRY SOLO’s thesis defense, intitled "Étude théorique d’un plasma dans la phase de transition allumage/combustion d’un moteur à gaz" ("Theoretical Study of Plasma in the Ignition/Combustion Transition Phase of a Gas Engine") took place on October, 18th 2020.

Jury :
Mrs Anne BOURDON - LPP, CNRS - Rapporteur
Mr Vincent RAT - IRCER, CNRS - Rapporteur
Mr Laurent FULCHERI - Mines, Paris Tech - Reviewer
Mr Olivier EICHWALD - LAPLACE, University of Paul SABATIER - Reviewer
Mr Pierre FRETON - LAPLACE, University of Paul SABATIER - Thesis supervizor
Mr Jean-Jacques GONZALEZ - LAPLACE, University of Paul SABATIER - thesis co-supervizor

Abstract :
The spark ignition in thermal engines, leading up to the initiation of combustion, is characterized by several processes which happen during short periods of time (a few milliseconds at max). The knowledge and control of the physicochemical phenomena involved are key elements to optimize the system. Using numerical tools, a more detailed description and understanding of the mechanisms governing the medium can be investigated. This thesis is related to this topic and is focused on analysing the chemical species’ evolution of an air-methane stoichiometric mixture according to the medium characteristics.
The work is based on three main stages.
The first step concerns the development of a calculating tool of the chemical composition and thermodynamic properties. The method is based on mass action law and on the resolution under the local thermodynamic equilibrium hypothesis for a given pressure or mass density. Corrective terms (of Debye-Hückel and virial) enabling to assimilate the gas to real fluid are integrated into the system of equations.
The second step is devoted to the development of the 0D model, based on the resolution of the species’ conservation equation. This approach leads to studying the possible presence of departures from equilibrium according to various cooling rates of the medium.
The last step concerns the implementation of a 1D transient hydro-kinetic coupling model applied to ignition. It is developed upon an axisymmetric cylindrical geometry. The results show typical evolutions of temperature and radial propagations of pressure. Depending on those parameters, the species’ behavior is analyzed and discussed in comparison to equilibrium. The departures from equilibrium of the densities highlighted for some initial choices of parameters by the coupling model open perspectives to the direct calculation of the plasma properties.