Detailed laser-based investigation of a laboratory scale liquid fuel burner
Résumé
This paper presents detailed measurements obtained in a laboratory scale liquid fuel burner facility operating at atmospheric pressure. Time resolved planar imaging techniques are used to describe both density and velocity of droplets under non-reacting and reacting conditions in a liqui fuel burner. The fuel can be injected either through a pressurized nozzle or through multiple orifices. The ratio between the mass flux in the pressurized nozzle to the total mass flux is defined as staging ratio. Depending on this parameter, different flame shape can be obtained as well as different acoustic frequencies. As the flame stabilization process depends also on the initial conditions, it is possible to have two different flame shapes with the same mass fluxes conditions. The spectral analysis shows a strong peak around 2481 Hz for non-reacting cases and 2518 Hz in reacting cases. Detailed analysis based on cross power spectral density approaches or on dynamic mode decomposition shows the circulating nature of this structure, clearly associated to the precessing vortex core. A similar analysis is performed in reacting conditions, showing the reminiscence of the PVC structure and showing the different structure of the mode related to acoustics. PVC may be either amplified or damped depending on the flame position. Finally, detailed PIV measurements show the velocity fields of the two modes, making possible to understand better the role of the PVC.