  Nova outbursts play an important role in the chemical evolution of galaxies,
especially they are the main source of synthetic $^{13}\rm C$, $^{15}\rm N$,
$^{17}\rm O$ and some radioactive isotopes like $^{22}\rm Na$ and $^{26}\rm
Al$. The enrichment of He in nova ejecta indicates that the accreted material
may mix with the He-shell (He-mixing). The purpose of this work is to
investigate how the He-mixing affects the nova outbursts in a systematic way.
We evolved a series of accreting WD models, and found that the mass fraction of
H and He in nova ejecta can be influenced by different He-mixing fractions
significantly. We also found that both the nova cycle duration and ejected mass
increase with the He-mixing fractions. Meanwhile, the nuclear energy production
from $p$-$p$ chains decreases with the He-mixing fraction during the nova
outbursts, whereas the CNO-cycle increases. The present work can reproduce the
chemical abundances in the ejecta of some novae, such as GQ Mus, ASASSN-18fv,
HR Del, T Aur and V443 Sct. This implies that the He-mixing process cannot be
neglected when studying nova outbursts. This study also develops a He-mixing
meter (i.e. $\rm He/H$) that can be used to estimate the He-mixing fraction in
classical nova systems.

Solar and Stellar Astrophysics