Don Stauffer writes:

Sport Pilot wrote:
You can only get so much speed when you inject the fuel through the

combustion or expansion cycle. High speed diesels get more speed by
injecting more of the fuel early. But an aircraft engine doesn't need
to turn more than 2500 RPM so we should be able to get the benifit of
the longer burn time.



True, but even 2500 rpm is a high speed Diesel. When we speak of low
speed Diesels, those are like the big ship and stationary engines that
run maybe 800 rpm max.


I once had the opportunity to visit the engine room of one of the big
ferries cruising between Sweden and Finland. It had four engines and
two props.

The idle speed was 100 rpm and full speed was 150 rpm.

I could not hear any difference between 100 and 150 rpms. But then I
never knew what noise came from the propulsion engines. There were a
lot of other helper engines making a lot of noise.

The props were geared 2:1, so they did 75 rpms at full speed.

Thomas