Air /or other gas/ is fed into vacuum filed large cylinder/piston
combination. Work done in the process at constant temperature (apprx.) and
variable expansion ratio by the smaller cylinder/piston. It is then
compressed by the large cylinder/piston under a bit higher temperature and
pushed out. When compressing the air / gas / the expansion ratio is smaller
than when it is taken in (on average).
You can play with the simulator, but only two parameters are adjustable.
It assumes the small cylinder operates 6 degrees below when doing work, while the large cylinder
operates 4 degrees above when pushing the air out. A very efficient linear actuator is needed
for the larger cylinder.