Time resolved diagnostics for the study of ignition in a two phase burner

National audienceThe need to be able to predict the ignitability of gas turbine combustor is limited by a lack of knowledge of the physical processes involved and complexity of the ignition process. The need to ensure ignition in the event of a flame extinction determines, to some extent, the operating envelope of an airplane. Ignition is a highly transient process and success/failure of ignition depends on a large number of parameters. Thus, in the current study, it is attempted to measure various physical parameters simultaneously, with high spatial and temporal resolution before and after the deposition of energy. The present research concerns the study of ignition of a two stage multi-point injection burner using dodecane. The air flow rate is 10~g/s and is preheated at 473 K and averaged equivalence ratio is set at 0.70. The use of a laser induced spark for ignition allows for easier change in the location of the spark. High speed (20 kHz) PIV measurements are performed by capturing the Mie scattering of the fuel droplets inside the combustion chamber before and after spark energy deposition. Laser induced plasma spectroscopy is used to measure concentration in the region of the spark. A Helium-Neon laser is passed through the burner close to the injector, in order to measure the frequency of the precessing vortex core. Images of the laser induced sparks are also acquired using an intensified CCD camera, to look at possible presence of droplets inside as well as the initial spatial extension of the spark. Moreover, the energy of the laser beam entering the burner is also measured. In the present study, only one position of the plasma is analyzed. All the simultaneous measurements provide a quantitative measure of some physical conditions required for successful ignition and criteria are proposed to explain failure versus success of ignition