The basic idea is very simple: start with the most efficient engine and reduce it greatest energy loss. The world’s most efficient engine is a two-stroke diesel used in ships and locomotives. Their biggest energy loss is heat in the exhaust. YankeeDiesel uses that heat to power the supercharger.
Turbochargers work almost the same way. They use exhaust gases to force extra air into four-stroke engines. Turbochargers improve efficiency but do not work on two-stroke engines. They require a supercharger.
To get the extra power, YankeeDiesel has a secondary expansion chamber wrapped around the combustion chamber. Now the combustion gases can expand a second time. The expanding gases power the supercharger and the best place for a supercharger is also wrapped around the combustion chamber. Unfortunately their movements are out of phase – when one needs to move up, the other wants to move down. The only way out of this dilemma is to make the combustion chamber reciprocate. Then everything comes together.
To make a reciprocating combustion chamber, we need opposed cylinders and each cylinder shares a planetary crankshaft. The reciprocating piston and connecting rods are gone. Now the reciprocating combustion chamber acts directly against the crank pin. The videos below show this motion.