Experimental investigation of porous injectors for liquid propellant rocket engines

Three different injector heads have been tested using a LOX/H₂ subscale combustion chamber at the European High Pressure Research and Technology Test Facility P8. For reference purposes, a first configuration based on a classical shear coaxial injector head with 13 elements has been investigated. The second configuration consists of a planar porous faceplate made from sinter bronze and 68 implemented single LOX tubes. Hydrogen was injected through the porous faceplate whereas liquid oxygen enters the combustion chamber in a classical parallel showerhead configuration at moderate injection velocities. With the third configuration, a hemispherical shaped faceplate has been used in order to increase both the mechanical strength and the hydrogen injection area. In addition, the LOX tubes have been modified from a parallel to a far downstream impinging arrangement in order to enhance the combustor wall compatibility. Liquid oxygen was injected at 120K whereas the hydrogen injection temperature was about 50K with the porous configurations and about 90K with the coaxial injector head. c^*-efficiency data have been gathered as well as some basic information on the axial heat flux distribution during steady state operation. All three configurations have been operated at combustion chamber pressures up to 80bar and propellant mixture ratios between 1.5 and 6. In addition to steady states, ramp-tests have been performed in order to investigate the throttling capabilities of the porous injectors.