I was interested in the above paper since the engine involved incorporates the same spherical rocker arm seals as were used on the valve mechanism of a solar thermal water pump which I built and tested in the 1980s (Solar Energy, 31(5), pp. 523–525). This form of transverse rocker beam drive and seal design was suggested to me by Richard Kinnersly, the designer of the Stirling engine, which is the subject of Dr. Mahkamov’s paper.

Although conversion of the engine to $α$ mode may increase the power output, there are other considerations, relating to the realization of a practical engine. Given that the engine uses dry lubrication, temperature and pressure stresses on the rings of the (hot) expansion piston in $α$ mode may be such as to compromise their operating life. Engine design involves more than thermodynamics and fluid flow....