Experimental investigation of aerodynamics and structure of a swirl-stabilized kerosene spray flame with laser diagnostics

Abstract

A gas turbine model combustor was equipped with an industrial Lean Premixed fuel injection system operating with liquid commercial kerosene (Jet-A1) at atmospheric pressure. Large optical accesses enable joint Particle Image Velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) measurements at repetition rates up to 5 kHz and 10 kHz, respectively. Using these diagnostics, flame topologies and non-stationary events were investigated in operating conditions representative of the ones encountered in real aeronautic propulsion systems. The flame shape was analyzed in terms of interactions between the different flame zones responsible for flame stabilization in confined swirled flames. Data processing of the strain rate and vorticity fields highlighted the existence of two shear layers that interfere differently with the inlet air/fuel mixing jet. An inner shear layer (ISL) between the Inner Recirculation Zone (IRZ) and the fresh inlet flow is located at the upper base of the fuel spray. An Outer Shear Layer (OSL) is also identified between the Outer Recirculation Zone (ORZ) and the fresh incoming flow. Spanwise-oriented vortices are produced from this latter, with a growth rate function of the free stream speed ratio (fresh incoming reactants and the flow circulating inside ORZ). The detailed analysis of the shear layers gives new insight on the flame structures obtained from OH-PLIF data. Finally, high-speed simultaneous measurements of flow velocity and OH distributions highlighted unusual flame pinching mechanisms leading to the release of subsequent unburned pockets propagating in the burned gases.