On the mechanisms of flame kernel extinction or survival during aeronautical ignition sequences: Experimental and numerical analysis
Résumé
A detailed study of ignition mechanisms in aeronautical burners is presented. Even in global lean conditions, liquid fuel injection leads to a strong stratification of the mixture and the whole range of equivalence ratio may be encountered in the burner. The observation of ignition sequences in a representative lab-scale combustion chamber, from both experiment and numerical simulation, reveals a variety of scenarios leading to success or failure. In particular the occurrence of quenching events after the successful creation of a kernel flame is a key mechanism for the outcome of the sequence. A first analysis leads to a classification of ignition/extinction scenarios, based on similar time evolutions and trajectories of the flame kernel. It is found that this classification is much dependent on the sparking location. Then a deeper analysis allows to decompose all scenarios in a succession of more simple, generic mechanisms which are independent of the geometry. This decomposition is a useful tool to describe, understand and predict ignition sequences, being successful or not, in any combustion chamber geometry.