The present study examines the development of miscible displacements in homogeneous porous media with a non-constant, time-dependent injection velocity. Numerical simulations for a sinusoidal injection velocity model are conducted to determine the effects of different variables on the efficiency of the displacement. The evolutions of nonlinear fingers with time are analyzed by plotting concentration fields, transversely averaged concentration profiles and sweep efficiency curve. Both the displacing process (injection process) and inverse displacing process (production process) are considered. Convection, transverse dispersion mechanisms, magnitude and frequency of the velocity changes are analyzed and the results are compared with those of a constant injection velocity process.