OH planar laser-induced fluorescence imaging in a hydrocarbon-fueled scramjet combustor

Planar laser-induced fluorescence (PLIF) imaging of OH has been completed through the piloting section of a hydrocarbon-fueled scramjet. This pilot consists of flush-wall fuel injection followed by a recess, or cavity, in one wall. Images were obtained for both gaseous (ethylene) and liquid (JP-7) fuel combustion. For the gaseous-fuel tests, ethylene as introduced through four flush-wall, low-angle injectors placed upstream of the cavity. For the liquid-fuel tests, injection was normal to the crossflow through seven injectors (four in the bottom wall, three in the top wall). Introducing a small amount of aas into the liquid in the bottom wall injectors enhanced atomization of the liquid column. Flight conditions between Mach 4 and 5 anti dynamic pressures between 23.9 and 71.7 kPa are simulated. Instantaneous images show the dynamics of the combustion process, suggest the process is premixed in nature, and reveal the presence of large-scale structures. Average images at different axial locations show the effects of total temperature and dynamic pressure on the combustion process. Increasing temperature broadens the time-averaged flame zone, while increasing dynamic pressure tends to force the flame against the combustor sidewall. At a given axial location, the time-averaged reaction zone for ethylene is larger than thai for JP-7.