WeberFan wrote:BIG HUGE SNIP... (Emphasis mine)PeterZ wrote:That is unless it is possible to make jets/turbo props without electricity. Re-starting en engine in flight may not be possible, but can it even get started with assistance groundside? Can an ignition system be created witout electricity? Will using chemical agents work as igniters? I have no clue what is possible in that direction.
Yep...It's possible.
Speaking as an aerospace engineer now...
A lot of what goes on in turbojet engines is mechanically driven once the motor is started. So, when you're getting ready to start it on the ground, you need a way to rotate the engine, which will then drive all the accessories (like the hydraulic pumps and - the one I was really thinking of - the fuel pump). The fuel pump delivers high-pressure fuel to the burner cans. The fuel injectors vaporize the fuel and allow it to mix with the combustion air being drawn through the engine intake and compressed. So now you have a highly-combustible fuel-air mixture in the burner cans.
The final step is ignition. While an electrical / spark ignitor is the most common, you could also use a "shotgun shell" ignitor (common with earlier piston engines and diesels). Once it's going, it'll keep going so long as you have a continuous supply of air and fuel.
As to restarting a motor in the air (and assuming you've "got some sky underneath you"), you can nose over to get enough airspeed so you have ram air up the intake to spin the motor (and thus drive all the accessories like the fule pump). Another shotgun shell ignitor and voila.
So jets don't need an ignitor after the initial ignition? I thought that might be the case, but wasn't sure.