This topic acurred to me, because I work with scroll compressors and I try to understand perhaps more about physics that are involved in such a machine.
The truth is I had these day's the idea to try to build a scroll engine based on a scroll expander, that would would work on any known fuel(combustible) that exists. I am speaking of an engine that would work, from my point of view, as an invertet ventilator system. If my air ventilator works as an compressor, than my engine would work in the oposite way as a dynam using the shape of the van.
The main idea is to use the scrolls compressor mobile part shape, like a wind mill that transforms energy of the moving gas(due to expansion) for creating working force.
Of course using an shock expansive gas as gazoline type fuel would probably result in the the destruction of the scroll, perhaps a redesigning of the scroll compressor would solve this problem. I mean the redesigning of the scroll in the way that it would enable the expansion gas to be used in the most efficient way posssible, whithout creating shocks in the system and almost any expanding energy not to be dissipated in a shock. For this you would need an a shape that is similar to the scroll compressor but wich goal is to calm down the energy of the shock and and transform it along the spiral into working force.
The oiling system of such an engine would be the second bigest problem, but still it can be solved. As well as the fact that this engine would need to have a friction area between the mobile and fixed scroll which would result in an, most probabily, imposibilty of designing an hermeticly closed space between the two scrolls.
PS: Sorry for my english
