  A highly efficient gas-kinetic scheme with fourth-order accuracy in both
space and time is developed for the Navier-Stokes equations on triangular
meshes. The scheme combines an efficient correction procedure via
reconstruction (CPR) framework with a robust gas-kinetic flux formula, which
computes both the flux and its time-derivative. The availability of the flux
time-derivative makes it straightforward to adopt an efficient two-stage
temporal discretization to achieve fourth-order time accuracy. In addition,
through the gas-kinetic evolution model, the inviscid and viscous fluxes are
coupled and computed uniformly without any separate treatment for the viscous
fluxes. As a result, the current scheme is more efficient than traditional
explicit CPR methods with a separate treatment for viscous fluxes, and a fourth
order Runge-Kutta approach. Furthermore, a robust and accurate subcell finite
volume (SCFV) limiting procedure is extended to the CPR framework for troubled
cells, resulting in subcell resolution of flow discontinuities. Numerical tests
demonstrate the high accuracy, efficiency and robustness of the current scheme
in a wide range of inviscid and viscous flow problems from subsonic to
supersonic speeds.
