I was thinking of designing a very simple and small Paraffin rocket engine as an experiment. One thing that I don't understand about these designs is how you efficiently use your oxidizer without a large amount being shot through the rocket unburned. With a solid fuel like this, how do you efficiently mix it to ensure it burns in the right place where it can add thrust?
EDIT: I liked the answer down below, but found this great public chapter about hybrid rockets that had some good illustrations: https://web.stanford.edu/~cantwell/AA283_Course_Material/AA283_Course_Notes/AA283_Aircraft_and_Rocket_Propulsion_Ch_11_BJ_Cantwell.pdf