Have you heard about Duke Engines, they are an axial engine which are smaller and lighter than a traditional internal combustion engine. These 5 cylinder engines develop the same power as a traditional 6 cylinder engine despite being >30% lighter.
Have look at the video below to see the internal movements of the engine work to produce power in this barrel shaped engine. It transfers the reciprocal motion of the piston to rotational movement of the crankshaft is a very unusual way.
According to the Duke website, these engines have several advantages including being able to run on all automotive fuels, “or indeed any of the alternatives currently proposed as replacements for petroleum-based fuels, such as Bio-Fuels, Hydrogen, LPG, CNG, etc.”
These engines are not currently commercially available but Duke are working to refine axial engine technology and overcome the technical challenges which are in the way of making these engines available in commercial applications.