You know, I see no reason why both haves (cylinders) have to be the same size. Further still only one cylinder would work fine if rocking arm gets a push at the right time much like a kids swing to keep it going form a electromagnet or such. Only needs to be strong enough for compression. Dont know what to call it would t be a “duality” in this case. Its a type of 2 stoke without 2 stroke fuel. Could run on LPG, Methane, Diesel….. Main use pumps, blade-less fan pushing air or generating electric.