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This is actually a two part question. Would there be a purpose to a compressor in an electric turbofan where there is no need for a combustion chamber, and if not, is there then a purpose for a bypass as well?

Sorry if I'm unclear, as i am not an industry professional perhaps my wording may not be clear. What I mean to say is that in a regular turbofan engine there are compressors that push air into a combustion chamber with higher density (presumably to get more potential energy per volume of air) where fuel is introduced and ignited to create higher pressure/kinetic energy to run the turbines, which in turn move the front compressors and the fan. However, in an electrically driven fan, since there is no combustion happening, and the fan is driven by an electric motor, does the engine then need the compressors? Do they perform any benefit in a system that does not use combustion to create pressure?

Then if not, is there any benefit to the bypass system in an electrically driven fan engine? Or does it make more sense to simply switch to a ducted fan system?

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  • $\begingroup$ unclear what you are asking. $\endgroup$
    – niels nielsen
    Jan 7, 2019 at 7:22
  • $\begingroup$ Sorry if I'm unclear, as i am not an industry professional perhaps my wording may not be clear. $\endgroup$
    – No One
    Jan 7, 2019 at 7:51
  • $\begingroup$ The "rear compressors" are called turbines and are not compressors at all since they actually decompress the flow; you can look up this terminology with a cursory Wikipedia search. $\endgroup$
    – AEhere supports Monica
    Jan 7, 2019 at 12:05
  • $\begingroup$ yes thank you for the correction. $\endgroup$
    – No One
    Jan 7, 2019 at 22:50

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No. The only purpose of the compressor is to provide high pressure air for the combustion chamber and turbine. If there is no combustion chamber and no turbine, then you do not need a compressor. Just drive a big ducted fan (or propellor, your choice) with your electric motor.

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There won't be an electric turbofan as it doesn't make sense to make one. A jet engine is designed to burn fuel and turn it into propulsion, compressors squash air so it can be mixed with fuel. If you take the fuel away and replace it with an electric motor an engine would be designed along completely different principles.

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  • $\begingroup$ It would be just a fan or propeller. $\endgroup$
    – Tim Nevins
    Jan 7, 2019 at 16:34
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    $\begingroup$ @TimNevins. Except....electric turbofans are being made. See eurekamagazine.co.uk/design-engineering-news/…. The graphic in the story shows a fan driven by a 2kW motor, exactly as described in the question. And, several other demonstrator aircraft with electric engines are also planned. Cheers. $\endgroup$
    – Penguin
    Jan 8, 2019 at 11:39
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Yes, if you want to go super sonic.

This effectively gives you the performance characteristics of a low-bypass turbofan or a turbojet:

1) low cross section and high thrust to cross section ratio (low supersonic drag)

2) achieving very high nozzle velocity by jetting the high pressure flow out of the nozzle (useful at high speed)

3) Flow increases pressure but not velocity when moving through the engine, so that all stages operates in the subsonic region. Important if your intake is not far from transonic when the airplane is supersonic.

4) Poor economy.

In the perceivable future it's hard to imagine any jet engine not powered by a turbine (piston ICE, electric, nuclear, etc, any shaft engine except a turbine).

Especially the focus now on electric airplanes is to improve range, and both supersonic and jet kills the range, so practically the answer is still "No".

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  • $\begingroup$ so basically if I was looking at an engine for subsonic, there's no benefit to having either a compressor, or a by-pass system? Just stick with a normal ducted fan or prop? $\endgroup$
    – No One
    Jan 7, 2019 at 22:59
  • $\begingroup$ @No One . Yes. Just like turbine counterparts, if a prop can do, then prop. $\endgroup$
    – user3528438
    Jan 8, 2019 at 3:43

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