The effects of mixture stratification at the intake port and gaseous fuel injection on the flow field and fuel-air mixing in a two-dimensional rotary engine model have been investigated by means of a two-equation model of turbulence, an algebraic grid generation method and an approximate factorization time-linearized numerical technique. It is shown that the fuel distribution in the combustion chamber is a function of the air-fuel mixture fluctuations at the intake port The fuel is advected by the flow field induced by the rotor and is concentrated near the leading apex during the intake stroke. During compression, the fuel concentration is highest near the trailing apex and lowest near the rotor. The penetration of gaseous fuel injected into the combustion chamber during the compression stroke increases with the injection velocity and results in recirculation zones between the injector and the leading apex and between the injector and the trailing apex. However, most fuel vapor is advected by the velocity field induced by the rotor and is concentrated near the leading apex. The fuel concentration near the trailing apex and rotor is small except at high injection velocities.