Air rushing through the inlet is compressed between the sides of the tube and the torpedo-shaped body, whose nose is pointed at the front. Its wider part, which sits inside the engine, slows incoming air down to subsonic speeds. Fuel is then sprayed into the air stream, and the mixture is ignited as it flows past a flame inside the combustion chamber. The resulting hot gasses are then ejected out of a nozzle in the back, yielding plenty of thrust. The first Hyper-X plane is slated for a trial run over the Pacific Ocean next month.
Ramjets have a couple of important limits.
One is that they don't work until the engine is moving at high speeds, so you need a way to get the plane moving at Mach speeds in the first place. One way to do that is to combine a ramjet and a turbine engine in the same housing. Then you run the turbine portion of the engine until you are moving through the air fast enough for the ramjet to work efficiently. Once you reach that speed, you can shut the turbines down and let the ramjet do all the work. The other problem is that as you approach speeds of Mach 6 or so, the air flowing into the inlet is moving so quickly that it creates a supersonic shock wave as it is compressed inside the engine.