Some very impressive modeling work lies behind this paper, but leaves the reader with many questions which Dr. Mahkamov may care to answer.

We are told that the Biomass Stirling Engine “has been experimentally tested” and that “experimental data, which is available (where?) of the mechanical brake power output and speed, indicates that”—these “are reasonably close to those predicted by using the 3D CFD model.” Could the author provide the figures so that we can judge for ourselves how close is “reasonably close?”

One observes that, with fluid flow losses included, the $γ$ engine achieves an inferior predicted performance to the modified $α$, whether using the second-order model, or the 3D CFD model.

 Mode 2nd order 3D CFD $γ$ $250W$ $737W$ $4Hz$ $3.33Hz$ $α$ $2.970W$ $3.870W$ $7Hz$ $5Hz$
 Mode 2nd order...