Originally Posted by
Jackonicko
How much more environmentally friendly is a modern turboprop than an equivalent sized turbojet, in terms of environmental impact?
Roughly 30% lower fuel burn per passenger seat/mile?
Lower flying and less likely to contrail?
Lower flying and releasing emissions at a 'better' height?
A better 'neighbour' in terms of noise?
Is there an environmental argument for making greater use of turboprops for short haul?
How do the new generation of Open Rotor Fans/Unducted fans/Propfans compare?
Any thoughts?
What am I missing?
The word "turbojet" is more usually used to describe aero jet engines with low bypass ratios. A pure turbojet accelerates a small volume of gas to a very high velocity (think military fighters and early jet airliners). All modern commercial types use turbofan engines which compared to a turbojet accelerate a large volume of air but nowhere near as fast as a turbojet engine. This is the reason for the much larger engine diameters these days compared to forty years ago - as an aside this is, indirectly, the reason for disasters with the 737 Max.
From my own experience, the latest narrowbody engines when flown at low cost indices at similar altitudes are burning roughly the same amount of fuel per seat kilometer as large turboprops albeit there has been more progress and research in turbofan engines compared to commercial turboprop engines. I would expect the next generation of airliner turboprop engines might widen the gap again.