Modélisation numérique des phénomènes se déroulant lors de l’inflammation initiale du mélange dans un moteur à allumage commandé

Abstract

The spark discharge produce by a spark plug is a complex phenomenon studied experimentally and numerically since the end of the 20th century, although his principle has been used inside spark-ignition engines since its creation in 1860. The first numerical studies aren’t so much detailed and are limited by the use of 1D and 2D models. Some decade later, the phenomenon is better understood and exploited to be useful in reducing polluting gaz emissions and optimizing the ignition and discharge parameters. Improved modeling techniques now allow the development of more complex 3D models to study some unknown processes of spark discharges. The goal of this study is to model a spark discharge and the following ignition of the mixture. The Navier-Stokes equations are solved by the Star-CCM+ software with a compressible, laminar and unsteady numerical model. In order to create the full complex discharge model used for the ignition study, a much simple model is first designed to determine the mesh parameters needed to modeling the discharge. A model using the flame front of the methane air combustion is then used to validate the mesh. A new discharge model is developed based on an energy deposition cylinder growing with variable radius. Different heat transfers to the spark plug are then tested and compared during a discharge. The heat transfer condition combining adiabatic and isothermal conditions provides the most convincing results with regard to the shape and development of the flame, highlighting the importance of vorticity and flow vortices in the creation of the flame. Furthermore, the discharge model presented in this study is confronted with a more classic model of constant geometry deposition cylinder. Finally, different energy levels of discharges are tested in order to understand the role of flow intensities on the structure of the flame. It is concluded that a more energetic discharge accelerates the development of the flame but also intensifies the vorticity at the outlet of the electrodes.

Date	12 Dec 2022
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Patrice Seers (Supervisor)