Critical Design Parameters for Pylon-Aided Gaseous Fuel Injection Upstream of a Flameholding Cavity

The Air Force Institute of Technology and the AFRL are investigating means to increase the efficiency of fuel-air mixing into supersonic flow. Previous work has shown much promise in increasing the penetration and mixing of a fuel-air mixture into the freestream by injecting fuel behind small triangular pylons. Pylon-aided fuel injection has also shown to lift the fuel plume off the combustor floor; this floor-gap prevents the ignition of fuel seeded in the boundary layer. In this paper twenty-one pylons of varying widths, heights, and lengths were examined in four specific test matrices within a CFD environment. Pylons in test matrix 1 maintained a constant height and length while varying the pylon width. Test matrix 2 and 3 varied the absolute height of two different pylons from test matrix 1; scaling the pylons height and maintaining a constant leading edge wedge angle and width to height ratio. The final test matrix varied the length of pylons while keeping the height and width fixed. Pylons with a width less than 3-diameters featured a fuel plume dominated by two sets of counter-rotating vortices. These pylons provided large amounts of penetration and floor gap with minimal impact on flammable fuel plume area (Af). The 4,5, and 6-diameter wide pylons resulted in flow structures dominated by one large set of vortices with minimal penetration and large Af values. Variations in pylon length had no discernable impact on the mixing metrics. Aerodynamic loses were minimal for all pylon configurations and did not correlate to the absolute size of the pylons tested