Hydrodynamical simulations of binary systems undergoing common envelope evolution have generally failed to achieve the levels of envelope ejection and orbital inspiral needed to produce observed post-common-envelope binaries, particularly binary white dwarfs. Energy released by hydrogen and/or helium recombination in the expanding envelope has been invoked as a potential source of energy, and recently Nandez and Ivanova have found using smoothed particle hydrodynamics (SPH) simulations that this mechanism may work if the energy can be trapped and used to do work. However, it is not clear whether this condition actually obtains in real systems. To gain insight into this question, we are conducting adaptive mesh refinement (AMR) simulations of common envelopes with radiation diffusion and an equation of state that includes hydrogen and helium partial ionization. We present simulations of red giant-white dwarf systems with parameters similar to those studied by Nandez et al. and discuss the efficiency of envelope ejection in these systems, examining its connection to the relative locations of the photosphere and partial ionization zones.