Cerfacs Enter the world of high performance ...

Abstract:

In order to improve the efficiency of gasoline engines, one efficient solution resides in engine downsizing which consists in the diminution of the engine size with the adjunction of a compressor to keep the power output. When the downsizing level is important, the high pressure and temperature levels promote autoignition phenomena such as knocking or rumble that can damage the engine. This kind of combustion, still misunderstood, is a limit to further use downsizing. In this thesis, Large Eddy Simulation is used to study this kind of abnormal combustions. The objective is to propose a numerical methodology able to reproduce its apparition and to understand its mechanisms. Auto-ignition is a combustion regime very sensitive to the variations of local thermodynamic conditions. Precise numerical methods and appropriate models, especially for thermal boundary conditions must be used. The first part of this manuscript presents the proposed numerical methodology and in particular two aspects implemented during this thesis: an auto-ignition model that permits to reproduce auto ignition delays with reduced kinetic schemes and a coupling methodology between combustion chamber and cylinder head in order to obtain realistic temperature fields for the boundary conditions. The second part of this manuscript presents the results of two numerical studies that reproduce some operating points from an experimental engine database. The first study is performed using combustion models from the literature and aims at reproducing experimental behavior for various parametric variations impacting the combustion. The second study is performed thanks to the numerical models implanted in this thesis in order to evaluate the impact of the thermal boundary conditions on the mechanisms leading to abnormal combustions.

Jury:

Olivier COLIN              IFP Energies Nouvelles, Rueil-Malmaison              Referee
Fabrice FOUCHER      Laboratoire PRISME, Orléans                                Referee
Jacques BORÉE          Institut Pprime, Poitiers                                          Member
Philippe GUIBERT       Université Pierre et Marie Curie, Jussieu                Member
Frédéric RAVET           RENAULT, Boulogne-Billancourt                             Invited member
Thierry POINSOT        IMFT, Toulouse                                                        Advisor
Olivier VERMOREL     CERFACS, Toulouse                                               Co-advisor