Warning! - Long post.
To summarize - SUCK, SQUEEZE, BANG, BLOW - that's all you really need to know.
No need for Raven to get out his books, I can tell you what you need to know. It is my job after all! (check my profile).
The 'SC' in scramjet does not, as he said, stand for 'single combustion' it actually stands for 'supersonic combustion' and as for his point about increasing the compression for the afterburner - NONSENSE! There is no afterburner on a scramjet. However, if there were an afterburner it would not be necessary to increase compression prior to ignition - it doesn't happen that way in a standard Gas Turbine (jet) engine.
Here is an explanation:
Standard 'Gas Turbine engine'
There are four types Turbo Jet, Turbo fan, Turbo prop and Turbo shaft but they all work on the same principle and that principle is much the same as the internal combustion engine in a car. Infact, the gas turbine engine is sometimes referred to as a single stroke internal combustion engine, which is what it is.
It works like this:
Air is brought into the engine at the intake where it meets the compressor. That increases its pressure and temperature while reducing its velocity. The reduction in velocity is essential because if the aircraft is travelling supersonic then the air must be slowed to subsonic speeds, otherwise a shock wave could be formed inside the engine - stalling it.
The compressor is basically a series of fans set inside a diverging cone. The fans are made of rotors and stators. The rotors turn which draws the air in at an enormous rate (easily enough to suck in a man if he stands to close - it has happened!) the air then hits the stators which are much like the rotors but they do not turn - their job is to maintain the straight airflow (front to back) so they face in the opposite direction to rotors. They also direst the airflow on to the next set of rotors.
The air then gets fed into the combustion chamber where it is met by a constant supply of fuel. unlike a car engine there is no ignition taking place after start up. A high energy spark is used to start the combustion process at engine start up but is no longer needed once the enigine is running because there is a constant supply of fuel and air - therefore constant combustion! Combustion reduces the pressure of the air whilst vastly increasing temperature and velocity.
After combustion the air goes through the tubine. Which much like the rotors in the compressor is a series of 'fans' but unlike the rotors they are not drawing the air through them but instead have the air forced through them which turns them.
The turbines are connected to the rotors by a central shaft. So the air coming out of the engine turns the rotors in the compressor which draws the air in! So you see, as long as fuels is fed to the combustion chamber the engine needs nothing else to keep it running.
The afterburner is the last thing the air passes through before leaving the engine. It is optinal to fit an engine with an afterburner as they are not really necessary.
All the afterburner is, is a series of fuel pipes and nozzels that sit in the airflow at the back of the engine because of that they get in the way of the airflow and reduce its efficiancy. However when in use they greatly increase thrust. The afterburner works simply by squirting fuel into the airflow. The air is still hot enough to ignite the fuel and so any unburnt oxygen left in the air is now ignited.
The downsides to the afterburner are: As I said above they reduce efficiancy when not in use and also they vastly increase fuel rate, so they are only used in two instances - 1) increased thrust for take off and 2) combat situations where a fast getaway 'could be handy'.
I said there were four types - they are:
1) Turbo Jet, which is as described above.
2) Turbo Fan - much like a turbo jet but its 'stage one' compressor has an vastly increased diameter which blows are in a bypass duct around the engine bypassing the internal workings completely. One reason for this is to aid cooling of the engine but it also (suprisingly) provides more thrust than the air going through the engine. The downside to the Turbo Fan is its increased diameter.
3) Turbo Shaft - Used in helicopters. The turbo shaft engine has a lot more turbine stages which removes the thrust completely. It does however, give a much greater torque to the central shaft which is then used to drive the helicopters rotor blades.
4) Turbo Prop - Like a turbo shaft but this time the power is used to drive a propeller at the front of the engine and it is this the powers the aircraft.
THE RAMJET
The ramjet does away with all the working parts of the engine. Instead it works by compressing the air simply by the internal shape of the engine.
The air is again slowed to subsonic speeds before combustion but this time it is done by the shape of the intake.
The ramjet can accelerate an aircraft to musch greater speeds than a standard jet engine and it is also much lighter. The downside to using ramjets is that they need the aircraft to be moving before they can work because they don't have the compressor to draw the air in.
Another name for a ramjet would be an air breathing rocket. It works on exactly the same principle as a rocket but where a rocket carries its own oxygen supply for combustion, a ramjet using the oxygen in the air.
THE SCRAMJET
The scram jet is basically a ramjet that allows the air to maintain its supersonic speeds. New designs in the internal shape of the engine prohibit the build up of shockwaves.
Finally (at last) as for dreams of flying to the moon at these speeds like some of the posts above suggest. Well, you really wouldn't want to travel there that
slowly!
The X43A is the fastest
air breathing aircraft to ever have flown - the space shuttle orbits the earth at a relative speed of Mach 25!
1001001 S.O.S.
