Large eddy simulations of a liquid fuel swirl burner: flame characterization for pilot and multipoint injection strategies
Résumé
A laboratory-scale swirling burner fueled with dodecane is studied numerically using large eddy simulations. The burner is composed of two stages, allowing the use of two different injector types (namely pilot and multipoint) in order to study the influence of droplet size and initial position with fixed geometry and delivered power. For a chosen lean operating point, the two liquid injection types are tested, highlighting a dramatic influence on the flame stabilization process. When fuel is injected through the multipoint stage, evaporation and mixing are enhanced and a partially premixed mixture enters the combustion chamber. The flame then takes an ‘M’ shape, mainly controlled by the large inner and outer recirculation zones associated with this highly swirling flow and in which trapped burnt gases guarantee permanent ignition of the fresh mixture entering the chamber. The situation is much more complex when fuel is solely injected through the pilot nozzle. Due to the large amount of liquid fuel present in the pilot zone, premixing is not achieved and the flame must stabilize itself mainly in a hybrid combustion regime. This is only possible thanks to a very complex situation in this region, where hot evaporated fuel is trapped in front of the nozzle and oxygen is mainly coming from the large central recirculation zone. In that case, the flame takes a ‘tulip’ shape, with a stabilization point inside the injection device. Both flame shapes are compared using scatterplots and flame dynamics are analyzed.