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The compression effect of the jet engine blades is what ignites the fuel. I don't think that part is replaceable, it's what makes a jet engine a jet engine. T

The compression effect of the jet engine blades is what ignites the fuel. I don't think that part is replaceable, it's what makes a jet engine a jet engine. The hot gasses from the fuel burn produce thrust, and also sends rotational force back into the turbine blades to keep the compression effect going.

Toutouxc 5y ago
> The compression effect of the jet engine blades is what ignites the fuel Not exactly, the igniter ignites the fuel initially, and after a short while the combustion becomes self-sustaining (i.e. new fuel is evaporated and heated above its autoignition temperature by all the residual heat around it). The igniters are turned off after a while and are only turned on again under certain conditions (high risk of flameout for a variety of reasons). Also the "hot gasses from the fuel burn produce thrust" part has slowly become more and more incorrect, because nowadays in airliners we use what's called high-bypass turbofans where the primary purpose of the hot engine core is not to generate thrust, but to drive a turbine connected to the huge fan in the front, which sends most of the air AROUND the core ("high-bypass") in order to create thrust. The core does produce some thrust, but the air coming out of it is pretty fast and creates more noise, so we try not to have too much of that. And the core itself doesn't really need to burn fuel, you could rip the combustion chamber out and put a nuclear-reactor-fed heat exchanger there and it would work the same. Or a beefy electric motor that would drive the fan and also utilize its waste heat to imitate a very-high-bypass turbofan.
- stadium 5y ago
  Thanks for the detailed explanation. I am not connected to the aerospace industry. In the context of retrofitting an electric motor where the fossil fuel combustion happens today, it still doesn't seem possible. > Or a beefy electric motor that would drive the fan Isn't that what Weight is doing with their motor? Motor attached to fan blades to produce thrust?
idiotsecant 5y ago
The compression is the easiest part to emulate. The hard part is the enormous amount of heat you need to generate and quickly transmit into that compressed fluid. Combustion is great on both accounts for that, but you could do it electrically as well given a sufficient power supply.
- stadium 5y ago
  > The hard part is the enormous amount of heat you need to generate and quickly transmit into that compressed fluid. Without a combustible fuel in the picture, isn't it more efficient for the kinetic energy of an electric motor to directly spin fan blades or turboprop propellers, vs converting that energy to heat?
  - idiotsecant 5y ago
    Maybe! There are certainly some operational regimes where it would be less efficient to spin props than it would be to shoot out hot gas, but they might be places where an electric aircraft wouldn't ever operate.

Toutouxc 5y ago

> The compression effect of the jet engine blades is what ignites the fuel Not exactly, the igniter ignites the fuel initially, and after a short while the combustion becomes self-sustaining (i.e. new fuel is evaporated and heated above its autoignition temperature by all the residual heat around it). The igniters are turned off after a while and are only turned on again under certain conditions (high risk of flameout for a variety of reasons). Also the "hot gasses from the fuel burn produce thrust" part has slowly become more and more incorrect, because nowadays in airliners we use what's called high-bypass turbofans where the primary purpose of the hot engine core is not to generate thrust, but to drive a turbine connected to the huge fan in the front, which sends most of the air AROUND the core ("high-bypass") in order to create thrust. The core does produce some thrust, but the air coming out of it is pretty fast and creates more noise, so we try not to have too much of that. And the core itself doesn't really need to burn fuel, you could rip the combustion chamber out and put a nuclear-reactor-fed heat exchanger there and it would work the same. Or a beefy electric motor that would drive the fan and also utilize its waste heat to imitate a very-high-bypass turbofan.

stadium 5y ago
Thanks for the detailed explanation. I am not connected to the aerospace industry. In the context of retrofitting an electric motor where the fossil fuel combustion happens today, it still doesn't seem possible. > Or a beefy electric motor that would drive the fan Isn't that what Weight is doing with their motor? Motor attached to fan blades to produce thrust?

idiotsecant 5y ago

The compression is the easiest part to emulate. The hard part is the enormous amount of heat you need to generate and quickly transmit into that compressed fluid. Combustion is great on both accounts for that, but you could do it electrically as well given a sufficient power supply.

stadium 5y ago
> The hard part is the enormous amount of heat you need to generate and quickly transmit into that compressed fluid. Without a combustible fuel in the picture, isn't it more efficient for the kinetic energy of an electric motor to directly spin fan blades or turboprop propellers, vs converting that energy to heat?
- idiotsecant 5y ago
  Maybe! There are certainly some operational regimes where it would be less efficient to spin props than it would be to shoot out hot gas, but they might be places where an electric aircraft wouldn't ever operate.