  Based on an isospin dependent transport model IBUU, effects of high density
behavior of nuclear symmetry energy in the proton-rich reaction
$^{22}$Si+$^{22}$Si at a beam energy of 400 MeV/nucleon are studied. It is
found that the symmetry energy affects $\pi^{+}$ production more than
$\pi^{-}$. More interestingly, comparing with neutron-rich reactions, for
$\pi^{-}/\pi^{+}$ and dense matter's N/Z ratios, effects of symmetry energy in
the proton-rich reaction both show contrary behaviors. The practical experiment
by using the proton-rich reaction $^{22}$Si+$^{40}$Ca to study nuclear symmetry
energy are also provided.
