Investigation of combustion oscillations in a lean gas turbine model combustor

This contribution is a continuation of ASME-GT2006-90300. While still working at atmospheric pressure, the range of operating conditions was extended to more realistic reduced mass flows to reproduce the engine pressure loss and air preheat up to 700K. The thermoacoustic behaviour of the burner was mapped over that operating range. Two different types of oscillations were observed for flames anchored at the nozzle or lifted from it. Both exhibited a frequency dependence on the Strouhal number for constant reduced mass flows. For a selected operating point with the lifted flame at a preheat temperature of 600K and a reduced mass flow of 0.3kg K-0.5/(s bar), the thermoacoustic behaviour of the burner was characterised by phase locked Particle Image Velocimetry as well as phase locked OH- and OH-T- LIF measurements and correlated to the acoustic pressure signal obtained by microphones. The combined data showed pulsating combustion being supported through periodic reignition of the main flame zone by a recirculating volume of hot, OH-rich gas, the cycle time being connected to the observed frequency. The characterization of the preheated operating point was completed with a heat balance investigation quantifying the non-adiabatic combustion conditions of the uncooled combustor.