How does the fuel efficiency of a jet engine compare to that of an internal combustion engine?

Question

Assuming optimal conditions for both types of technology...

Answer 1

I think you need to try to campare apples to apples. If you took a recip engine of 600 horses and compared it to something of considerable power in a turbo-prop, like a Walter, You would see considerable efficiencies in the turbine powered version. For the space and weight, a turbo-prop is much more efficient than a recip of half the output. Which is why it is becoming popular to convert piston singles with a turbo-prop.

Answer 2

There are several factors you need to consider when talking about fuel economy... If you just want to compare how much fuel is burnt per hour of operation, there is no competiton... The jet burns much more fuel per hour than the piston engine, but you're comparing apples to oranges.

When you factor in the weight of the aircraft and the weight of the cargo (passengers or boxes), the jet engine turns out to be more efficient for moving big, heavy airplanes with lots of passengers or cargo on board, at relatively high speeds, while a piston engine will be more fuel efficient in moving a lightweight airplane. with little cargo or passenger load at much slower speeds.

It just depends on what you want to do with your money and time.

Answer 3

If were talking brake thermal efficiency, I'm almost positive that a jet is more efficient. One of those HBF engines on any modern jet puts out tens of thousands of horsepower (70,000?) It may only get a mile per several gallons, but it makes a whole lot of power!

A reciprocating engine has an efficiency of about 33%.
A jet engine has an efficiency of about 40%, although I can't find data to prove it...

Answer 4

For what it's worth...
In researching experimental helicopters (Rotorway) there is the internal combustion engine seeming to run at about 9 gallons per hour where the Solar turbine conversion runs at about 12 gallons per hour (but with reportedly more power). From what I have heard, the big advantage is less moving parts and more choices of fuel for the turbine.