An adaptation of a primitive-variable finite-differ ence computer program was accomplished in order to predict the reacting flowfield in a solid-fuel ramjet. The study compares the predictions of the primitive-variable computer model with predictions of an earlier stream function-vorticity computer model and with empirical data. The new model was found to be more readily adaptable to different geometric configurations and flow conditions. Flowfield calculations were made both within the fuel grain and the aft mixing chamber. Addition of the aft mixing chamber decreased the effect of fuel grain inlet velocity on boundery-laye r thickness and the radial location of the flame zone within the fuel grain.