  In this work we revisit constraints on K-inflation with DBI kinetic term and
power-law kinetic term from reheating. For DBI kinetic term we choose monomial
potentials, $V\propto \phi^n$ with $n=2/3\,,1\,,\,2$ and $4$, and natural
inflaton potential, and for power-law kinetic term we choose quadratic, quartic
and exponential potentials. The phase of reheating can be parameterized in
terms of reheating temperature $T_{re}$, number of e-folds during reheating
$N_{re}$ and effective equation of state during reheating $w_{re}$. These
parameters can be related to the spectral index $n_s$ and other inflationary
parameters depending on the choice of inflaton kinetic term and potential. By
demanding that $w_{re}$ should have a finite range and $T_{re}$ should be above
electroweak scale, one can obtain the bounds on $n_s$ that can provide bounds
on tensor-to-scalar ratio $r$. We find, for K-inflation with DBI kinetic term
and quadratic and quartic potentials, that the upper bound on $r$ for
physically plausible value of $0\le w_{re} \le 0.25$ is slightly larger than
the Planck-2018 and BICEP2/Keck array bound, and for $n=2/3$ and $1$, the
reheating equation of state should be less than $0$ to satisfy Planck-2018
joint constraints on $n_s$ and $r$. However, natural inflation with DBI kinetic
term is compatible with Planck-2018 bounds on $r$ and joint constraints on
$n_s$ and $r$ for physically plausible range $0 \le w_{re}\le 0.25$. The
quadratic and quartic potential with power-law kinetic term are also compatible
with Planck-2018 joint constraints on $n_s$ and $r$ for $0\le w_{re} \le 1$.
However, for exponential potential with power-law kinetic term, the equation of
state during reheating $w_{re}$ should be greater than $1$ for $r-n_s$
predictions to lie within $68\%$C.L. of joint constraints on $n_s$ and $r$ from
Planck-2018 observations.
