performance of the rocket motor 100 with reference still to fig1 an injector 122 communicates with the combustion chamber 110 for injecting a liquid phase oxidizer from the liquid fuel tank 101 into the combustion chamber 110 in use the oxidizer is injected into the combustion chamber 110 via the injector 122 the injected oxidizer is gasified and flows axially along the combustion port 120 this forms a boundary layer edge 125 over the exposed surfaces of the solid fuel grain 130 the boundary layer edge 125 is usually turbulent in nature over a large portion of the length of the combustion port 120 a diffusion flame zone 135 exists within the boundary layer edge 125 which diffusion flame zone 135 extends over the entire length of the solid fuel 130 the heat generated in the flame which is located approximately 20 30 of the boundary layer thickness above the fuel surface is transferred to the wall mainly by convection the wall heat flux evaporates the solid fuel and the resultant fuel vapor is transported to the flame where it reacts with the oxidizer which is transported from the free stream by turbulent diffusion mechanisms the unburned fuel that travels beneath the flame the unburned oxidizer in the free stream and the flame combustion products mix and further react in the mixing chamber 115 the hot gases expand through a nozzle 140 to deliver the required thrust the u201c wagon wheel u201d solid fuel grain configuration shown in fig2 can provide a beneficial ratio of exposed surface area to cross sectional area for the solid fuel grain however the wagon wheel design has disadvantages for example due to the slow burning rate.