Suggested clarifications I think Gilles objection to using ports as classification is that it may be confused with the number of valves promoted by post petrol engine manufactures I suggest usine Dual cycle instead of four port and Single cycle instead of two port The avec chariots ans sans chariots designs could be used in either layout The AC would be better suited to an internal combution engine but would also suit say an gas pump or expander due to the greater change in volume through the cycle The possible use as an internal combustion engine has recieved the most attention It has many more uses pneumatic motor steam engine refrigerant expander pump etc As far as I can see development is currently focused on the dual cycle which is better suited to the majority of these uses so perhaps the internal comustion engine should be presented as a simply possible use of the single cycle configuration Photo detonation HCCI SCCI ATAC really warrant a seperate page with a mention here that the Quasiturbine is better suited to it than current engine designs due to the quick compression rate at tdc It is theoretically possible to use different fluids in the pump as long as cross contamination is not a problem You could use hydrolic oil to pump air as long as it doesn t matter if your compressed air is full of hydrolic oil The fact the rotor is exposed to both cycles there will be a layer or oil on the face plate when it is on the air side Seals and tolerances would also have to be right for the thinner fluid meaning an increase in friction compared to puming a thicker fluid There isn t any evidence this has been tested however