Staged multipoint injection is being introduced as an interesting technology to control uncontrolled flow and flame dynamics in Lean Premixed Prevaporized (LPP) swirled burners in GT. The BIMER combustor has been operated for many years to shed light on the complex phenomena related to two-stage multipoint LPP burners, as well as to build an experimental database for the validation of numerical developments. The BIMER injection system is composed of a pilot stage, where 15% of the global air mass flowrate goes through a swirler and fuel is injected through a pressurized nozzle, and a multipoint stage, where the rest of the air flows through a second swirler and fuel is injected in a « jet-in-crossflow » configuration at the swirler vanes’ exits. The staging factor is defined as the ratio of fuel mass flowrate injected through the pilot stage over the total fuel mass flowrate.

During the experimental campaigns, flame shape transitions and a consequent hysteresis cycle were observed as a function of the staging factor. After ignition in a low power operating point, a V-shaped flame is stabilized and keeps its V shape after the air and fuel mass flowrates are increased to reach the nominal operating power. Then, as the staging factor is reduced, the V flame transitions to a M-shaped flame. When the staging factor is re-increased to a certain value, the M flame flashes back and transitions to the initial V shape. However, the role of the operating conditions during ignition on creating the conditions for the stabilization of the initial flame V flame and, thus, for the existence of a hysteresis cycle, has not been investigated yet. Therefore, the objective of this paper is to use Large Eddy Simulations (LES), performed with the AVBP solver with a Lagrangian modeling for the liquid-phase, to study the influence of the operating conditions on the resulting flame shape during ignition.

Two operating conditions are simulated: the experimental ignition operating point, a low-power low flowrate condition, and the nominal operating point with a much higher power and much higher flowrates. Both operating points have an equivalence ratio of 0.7. Two simulations are performed for each operating point, one where the ignition kernel is initiated at the Outer Recirculation Zone (ORZ) and the other one where it is initiated at the Central Recirculation Zone (CRZ). In all cases the fuel is injected only through the pilot injector (staging factor of 100%). For the low power point, both ORZ and CRZ ignitions will lead to the stabilization of a V-flame, that keeps its V shape after the conditions were changed to the nominal operating point, as in the experiments. When igniting directly on the nominal operating point, the ORZ ignition will result in a M-shaped flame, while the CRZ one will result in a tulip shape. Thus, a link between the ignition operating conditions and the resulting flame shape is verified for the BIMER combustor. Assumptions are then made and verified to explain the mechanisms that causes the different flame shapes.


LES of the Ignition of a Two-Phase Staged Swirling Burner: Influence of Ignition Location and Operating Conditions on the Flame Shape

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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