I feel a bit stupid for asking this, but I simply cannot wrap my head around how a jet engine directs its thrust backwards.
A piston engine opens and closes valves, such that air is alternately sucked in and compressed to create force. That makes sense and I understand how it works.
But with a jet engine there are no valves opening and closing, so why doesn’t the air that is sucked in just get pushed right back out from the thrust generated? How can an engine simultaneously suck in air from the front and force it out the back?
It makes no sense to me :-/
In: Engineering
The combustion in a jet engine does not increase the pressure of the gas, only the volume. The combustion chamber expands towards the rear to allow the gasses to expand without increasing in pressure. The pressure on the inlet side of the combustion chamber is actually slightly higher then on the exhaust side, but the area is much smaller. So there is a lot more gas exiting the combustion chamber then entered it, even though it is at roughly the same pressure.
The pressure is generated from the turbine in front of the combustion chamber. You know how a turbo in a piston engine will compress the gas before it enters the cylinder so the compression ratio in the cylinder can be lower. A jet engine basically have such a big turbo that their compression ratio is 1. This big turbine in the front to compress the air that much is driven by the exhaust fan at the back, just like in a piston engine turbo. And because the exhaust have so much more volume then the intake air it will generate a lot more force on the exhaust fan then it takes to run the intake turbine.
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