There is also a ‘new generation’ of aircraft engines around, i’ve seen a brochure and photos of one of the pre-production ones here in the UK. The engine is a development of the Wankel rotary system but is supposedly more efficient. The engine is in the process of certiication i believe (currently a single rotor system is on a microlight). The great advantage of Wankel engines is that they can be turbo compounded, a turbo can be attached to the crank to increase the power for a smaller engine size. These engines are also meant to be able to un on any fuel.