# Is a turboprop or a turbofan more eco-friendly?

If we compare them, which one wins? Why? And, what about CO2 emissions?

• – fooot Feb 2 '18 at 1:09
• Global warming isn't top of your worries when you have all the planes dumping all the toxins, pounds of lead per GA airplane per hour for starters. – user3528438 Feb 2 '18 at 2:14
• You need to define what, in addition of C02, you want to compare (under the unclear wording eco-friendly). For instance, what about noise? – mins Feb 2 '18 at 8:28
• Yes. The answer is yes. – J Walters Feb 2 '18 at 17:09

To compare them we need to compare the same mission (we can't compare an A380 against a regional turboprop).

For 82-86 passengers on a 1,100 km (600 NM) trip, the turboprop comes out on top (for this mission).

2.79 L/100 km/seat (Bombardier Dash 8 Q400)
3.44 L/100 km/seat (Embraer E-Jet E2-175)


Note: a Boeing 787-9 flies 304 passengers over 9,208 km at 2.31 L/100 km/seat.

From slowest to fastest, the economical choice would be turboprop, turbofan, and turbojet. Above ~700 km/h, the turboprop starts to lose.

### The why:

• Turboprop: The core runs at near full power, and with a reduction gear, the propeller runs at a slow speed suited for slow flight. If the blade tips reach Mach 1, efficiency starts to go down (at a fixed RPM, blades fly faster the faster the plane).
• Turbofan: Same principle, but instead of a reduction gear, a low-pressure spool is used. And with the nacelle/shroud, the fan can run faster and move more air.
• Turbojet: The core provides the propulsive power directly, this solves the slow exhaust of the turbofan in supersonic flight.

The common theme: gas turbine cores run best near their full power. That makes a turbojet bad at slow speed / low power.

Fuel mileage and image source: Wikipedia article 'Fuel economy in aircraft' (well sourced).