  It has been proposed that mixing induced by convective overshoot can disrupt
the inward propagation of carbon deflagrations in super-asymptotic giant branch
stars. To test this theory, we study an idealized model of convectively bounded
carbon flames with 3D hydrodynamic simulations of the Boussinesq equations
using the pseudospectral code Dedalus. Because the flame propagation timescale
is much longer than the convection timescale, we approximate the flame as fixed
in space, and only consider its effects on the buoyancy of the fluid. By
evolving a passive scalar field, we derive a {\it turbulent} chemical
diffusivity produced by the convection as a function of height, $D_{\rm t}(z)$.
Convection can stall a flame if the chemical mixing timescale, set by the
turbulent chemical diffusivity, $D_{\rm t}$, is shorter than the flame
propagation timescale, set by the thermal diffusivity, $\kappa$, i.e., when
$D_{\rm t}>\kappa$. However, we find $D_{\rm t}<\kappa$ for most of the flame
because convective plumes are not dense enough to penetrate into the flame.
Extrapolating to realistic stellar conditions, this implies that convective
mixing cannot stall a carbon flame and that "hybrid carbon-oxygen-neon" white
dwarfs are not a typical product of stellar evolution.
