Design of the multi-cylinder Stirling engine arrangement with self-start capability and reduced vibrations

The Franchot engine is a double acting Stirling engine that has a freely controllable phase angle and no shuttle and axial conduction losses but is inferior to the Siemens and free piston Stirling engines in terms of its ability to self-start. In addition, the Franchot engine is not widely used with the reliable slider crank mechanism due to vibrations. Here, the multi-cylinder Franchot engine is thermodynamically and mechanically studied with the simple slider crank mechanism with the aim of improving the self-start capability and to reduce the vibrations. Both instantaneous power and engine arrangements are used to judge the mechanical performance for different engine parameters and configurations. The optimal phase shifts and phase angles are derived and it is shown that both are governed by the number of cylinders. The theoretical analysis shows that by increasing the number of cylinders, different engine vibrations are reduced and the engine becomes self-starting. Hence, the Franchot engine can be superior to the Siemens engine, particularly due to the ability to remove the rocking couples for engines with more than two phases. Thus, the engine operation is stabilised and the simple slider crank mechanism can be used with the multi-cylinder Franchot engine.