Momentum and energy injection by a supernova remnant into an
  inhomogeneous medium
  We investigate the effect of mass-loading from embedded clouds on the
evolution of supernova remnants and on the energy and momentum that they inject
into an inhomogeneous interstellar medium. We use 1D hydrodynamical
calculations and assume that the clouds are numerous enough that they can be
treated in the continuous limit. The destruction of embedded clouds adds mass
into the remnant, increasing its density and pressure, and decreasing its
temperature. The remnant cools more quickly, is less able to do PdV work on the
swept-up gas, and ultimately attains a lower final momentum (by up to a factor
of two or more). We thus find that the injection of momentum is more sensitive
to an inhomogeneous environment than previous work has suggested, and we
provide fits to our results for the situation where the cloud mass is not
limited. The behaviour of the remnant is more complex in situations where the
cloud mass is finite and locally runs out. In the case of multiple supernovae
in a clustered environment, later supernova explosions may encounter higher
densities than previous explosions due to the prior liberation of mass from
engulfed clouds. If the cloud mass is finite, later explosions may be able to
create a sustained hot phase when earlier explosions have not been able to.
