Iíve always liked Stirling engines . They only require heat to run so can use any fuel/heat source. This one is a ďBohm HB9Ē which uses a methylated spirit burner as the heat source.
I could not square buying the kit for this one either (see Knotax KS90) unless it was used for 3DS Max practice, so here it is. Itís built to a high polygon count as I intend to animated the assembly process. Even the screw threads and tapped holes are modeled. It is also used my first render using Ambient Occlusion and HDRI lighting.