I know that it is an aeroplane and not a helicopter but I've flown a PA28 fitted with a 1.7 litre diesel in Germany and there is a DA40 flying in Austria with the same engine. Diamond hope to bring the diesel version to market sometime later this year. In addition they hope to fly a diesel twin (aeroplane) at ILA Berlin later in the year. SMA are also producing aero diesel engines.. .<a href="http://www.thielert.com/en/index.html" target="_blank">Thielert</a>