Abstract
Staged multipoint injection has been developped as an interesting technology to control flow and flame dynamics in Lean Premixed Prevaporized (LPP) swirled gas turbine burners. The BIMER combustor, a two-staged swirling burner composed of a pilot stage and a multipoint stage, has been operated for many years to shed light on the complex phenomena related to such kinds of burners, as well as to build an experimental database for the validation of numerical developments. During the experimental campaigns, several flame archetypes have been encountered, flame shape transitions and a consequent hysteresis cycle were observed depending on the liquid fuel splitting between the stages. As each flame archetype presents different combustion characteristics and thermoacoustic behavior, it is highly relevant to understand how to stabilize such archetypes. In this optics, the objective of the present paper is to investigate ignition as a way to control the final flame archetype. By means of Large Eddy Simulations, we explore different operating conditions and have a direct insight into the flame propagation process. Two operating conditions are simulated: a low and a high flow rate condition. Two simulations are performed for each operating point, one where the ignition kernel is initiated in the Outer Recirculation Zone (ORZ) and the other one where it is initiated in the Central Recirculation Zone (CRZ). In all cases the fuel is injected only through the pilot injector, as in the ignition process during experiments. For the low power point, both ORZ and CRZ ignitions lead to the stabilization of a V-flame. When igniting on the high power operating point, the ORZ ignition results in a M-shaped flame, while the CRZ one results in a tulip shape. These different behavior are analyzed and discussed in the final part of the paper.
