Experiments have been performed in a two-dimensional (2D), planar Mach 2 wind tunnel to study injection and combustion processes around a simulated projectile base. Lateral injection and external burning (EB) of hot fuel-rich reaction products from solid propellants, axial base injection (BI) of helium and nitrogen, and combined EB and BI have been studied. Test results show that the two base pressure rise mechanisms associated with EB and BI can be superimposed. Moreover, the base pressure rise associated with combined EB and BI was found to be higher than with EB or BI alone.