  Context. Classical novae are explosive phenomena that take place in stellar
binary systems. They are powered by mass transfer from a low-mass main sequence
star onto a white dwarf (either CO or ONe). The material accumulates for 10+4 -
10+5 yr until ignition under degenerate conditions, resulting in a
thermonuclear runaway. The nuclear energy released produces peak temperatures
of about 0.1 - 0.4 GK. During these events, 10-7 - 10-3 Msun enriched in
intermediate-mass elements (with respect to solar abundances) are ejected into
the interstellar medium. However, the origin of the large metallicity
enhancements and the inhomogeneous distribution of chemical species observed in
high-resolution spectra of ejected nova shells is not fully understood. Aims.
Recent multidimensional simulations have demonstrated that Kelvin-Helmholtz
instabilities that operate at the core-envelope interface can naturally produce
self-enrichment of the accreted envelope with material from the underlying
white dwarf at levels that agree with observations. However, such
multidimensional simulations have been performed for a small number of cases,
and much of the parameter space remains unexplored. Methods. Here we
investigate the dredge-up, driven by Kelvin-Helmholtz instabilities, for white
dwarf masses in the range 0.8-1.25 Msun and different core compositions
(CO-rich and ONe-rich substrates). We present a set of five numerical
simulations performed in two dimensions aimed at analyzing the possible impact
of the white dwarf mass (and composition) on the metallicity enhancement and on
the explosion characteristics. Results. We observe greater mixing (about 30 per
cent higher when measured in the same conditions), at the time we stop the
simulations, and more energetic outbursts for ONe-rich substrates than for
CO-rich substrates and for more massive white dwarfs.
