[tjohns]

And to be clear, "knocking" means engine detonation, which very quickly leads to catastrophic engine failure. Which is something that you don't want while in flight.

Until now, the only alternative was to fly a turbine-powered aircraft that can run on Jet-A. The problem with those is that turbines are far too expensive, and terribly inefficient at low altitude - both of which have kept them out of reach for most of general aviation.

[jsmith45]

Admittedly Turboprops can be somewhat more efficent at lower altitudes than turbojet and turbofan engines. But still not terribly efficient at say sightseeing or cropdusting altitudes, and they are still a lot more expensive than avgas engines (and that is not even accounting for the fact that the aircraft designed to use them are bigger and more expensive than many avgas based prop planes).