Originally posted by Figher Master FIN
After the air has gotten in the engine it goes through the compressor wich makes the air more dense (I'm not sure so explain)
Now here comes my first question, is the air compressed because it burns better? After the air and the fuel burns they start to make the turbine spin
which again sucks more air in the engine.
The "gases" that the fuel and the air make are very expandable, wich means that they take a lot of room in the open wich makes them the perfect fuel
because they create lots of thrust.
My last question is more about the throttle, how can a pilot actually make a plane go slower and faster with a jet-engine plane. Does it have
something to do with the compressor or the turbine or the fuel injector?
- Yeah, the compressor basically keeps shoving the air into a smaller and smaller volume, with conservation of mass dictating a constant mass flow
mass flow rate = rho * A * V
the area [A] decreasing, velocity [V]... well, it effectively chokes and cannot increase further, thus making the density [rho] have
- The turbine rotors have to be spinning to start with to turn the compressor, there is no clutch on a turbine. Yes, the air is compressed because it
burns much, much
better. Current turbofans have a operating pressure ratio of around 30, but at such high pressures, there are problems with
emissions, specifically NOx [IIRC]
- The mixing of the air and fuel is very important to minimise unburnt combustant, and alot of R&D goes into combustor designs. Yes, as you say, when
the gases do combust, they produce a large expansion of air, which is key to the operation of a turbine [and an internal combustion engine for that
- The turbine is balanced with the compressor [for anyone wondering about fans etc I'll use a single spool turbojet design], more power to the
turbine = more power to the compressor = more air in the front.
If the pilot increases the throttle by say 5%, more fuel is dumped into the combustor, more energy is extracted by the turbine blades, leading to more
energy for the compressor, which drags in more air, leading to a further improvement in power. This will eventually balance out through drag on the
Certain engines must be treated with care though, if the pilot increases the throttle by 50% too quickly, too much energy can be absorbed by the
turbine, spinning the compressor too fast - causing it to stall as there is not enough mass flow through the engine. The engines on the F-14A were
notorious for having stall happy engines.