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

摘要

This work quantifies several sources of unsteadiness that exist within a lean premixed prevaporized 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 particle image velocimetry and planar laser-induced fluorescence diagnostics. Flame-flame interactions occur because lean premixed prevaporized aircraft combustors employ a premixed main flame, which is anchored by the nonpremixed pilot flame. The measured degree of unsteadiness is the standard deviation of flame surface density, flame length, vorticity in shear layer, and recirculation zone size. The flame surface density profile was broad, indicating that large flame motions occur. Flame length increases nonlinearly with fuel flow rate. 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 nonreacting cases. Heat release causes the recirculation zone shape to change from ellipsoidal (for the reacting cases) to toroidal (for the nonreacting cases). Methods were developed to image Jet-A spray flames at 3 atm using formaldehyde fluorescence.