Unsteady Aspects of Lean Premixed Prevaporized Gas Turbine Combustors: Flame-Flame Interactions

This work quantifies several sources of unsteadiness that exist within a Lean PremixedPrevaporized (LPP) gas turbine combustor that was operated at elevated pressures using Jet-A fuel. Flame-flame interactions and shear layer vortex shedding, which can be sources of combustion instabilities, are quantified with PIV and PLIF diagnostics. Flame-flame interactions occur because LPP aircraft combustors employ a premixed Main flame that is anchored by the non-premixed Pilot flame. The measured degree of unsteadiness is the standard deviation of: a) flame surface density, b) flame length, c) vorticity in shear layer, and d) recirculation zone size. The flame surface density profile was broad, indicating that large flame motions occur. Flame length increases non-linearly with fuel flowrate. Intense vortices in the shear layer are more than twice the average vorticity, indicating the need for unsteady modeling. Chamber pressure and liquid fuel flow rates were varied. Velocity fields for the five reacting cases were similar but they differed from the two non-reacting cases. Heat release causes the recirculation zone shape to change from ellipsoidal (for the reacting cases) to toroidal (for the non-reacting cases). Methods were developed to image Jet-A spray flames at 3 atm. using formaldehyde fluorescence.