An engineer from Tula, Mikhail Shchuchkin, has developed a scheme for an unusual engine. In search of a way to increase the efficiency of a piston engine, he proposed a new power unit in which the engine cylinders operate part of the time according to the Carnot cycle (ICE), and part of the time according to the Stirling cycle.
The promising unit will have three cylinders — two hot cylinders and one cold one. Fuel is supplied to one hot cylinder for four cycles, and it heats up.
The second hot cylinder simultaneously operates as a Stirling engine paired with the cold cylinder. For the next four strokes, the roles change: fuel is burned in the second hot cylinder, and the first one operates according to the Stirling cycle.
But that's not all. Shchuchkin will connect a second Stirling engine to the first engine. Its crankshaft rotates twice as slowly, and it draws energy from the exhaust gases generated in the first half of the engine.
From "Pervy Tekhnichesky":
The editorial board found several contradictions in the promising engine. The idea of combining an ICE and a Stirling engine within one sleeve to utilize wall heat looks good on paper.
However, in practice, energy costs for compression, parasitic volumes in valves, and thermodynamic loads can completely negate the expected increase in efficiency. The system clearly lacks testing on a "live" prototype.