  A two-component fluid representing dark energy is studied. One of the
components has a polytropic form, while the other has a barotropic form. Exact
solutions are obtained and the cosmological parameters are constrained using
supernova type Ia data. In general, an open universe is predicted. A big rip
scenario is largely preferred, but the dispersion in the parameter space is
very high. Hence, even if scenarios without future singularities can not be
excluded with the allowed range of parameters, a phantom cosmology, with an
open spatial section, is a general prediction of the model. For a wide range of
the equation of state parameters there is an asymptotic de Sitter phase.
