Free field realization of WBCn and WG2 algebras

We study the BRST cohomology in the quantum hamiltonian reduction of affine Lie algebras of non-simply laced type. We obtain the free field realization of the Wg-algebra for g = B2, B3, C3 and G3. The WC3 algebra is shown to be equal to the WB3 algebra at the quantum level by duality transformation.