The ramjet is an air-breathing propulsion engine, which relies on the ram effect for compressing the entering air, thus, eliminating the need for a compressor. Ramjets have no moving parts, the entering air is compressed aerodynamically is mixed with the fuel and ignited. Finally, the burned gases accelerate in a converging-diverging nozzle generating thrust.
In the present research, the ramjet engine fuel is kerosene gel in which boron particles have been added. Boron has 140% energy per unit mass in comparison to hydrocarbon fuels and 300% energy per unit volume. Gelled kerosene provides the means that contain the boron powder and prevents particle sedimentation.
An early study of Hadad et al. showed the high performance potential of a boron loaded ramjet engine with specific impulse higher than 2,000 s. The scope of the present study is to evaluate the performance of a ramjet loaded with boron and to investigate the effect of the various parameters, such as bypass ratio and boron content. The study uses a commercial numerical CFD solver (FLUENT) to simulate a 3D combustion chamber of a ramjet with an aft burner in which bypass air is injected.
Boron ignition and combustion has been modelled using King’s model. The model divides the combustion of the boron into two stages. Initially, the boron particles are covered by a boron-oxide thin layer that prevents from ambient oxygen to reach the boron core and react. After the removal of the boron oxide layer, combustion begins releasing the chemical energy of the boron particles.
The simulation of the boron combustion is time dependent and deals with the particle phase separately from the CFD simulation. In each time step the diameter of the boron particles and the heat release are calculated. The particle distribution is polydisperse and the particles are injected into the flowfield together with the gel fuel.
The results include the temperature, velocity and particle distribution flowfield and eventually the performance of the ramjet is derived.
