In 1853, John Ericsson constructed a huge 300. hp hot air engine that ran on the Ericsson cycle. It had pistons 14.0 ft in diameter and it consumed 2.00 lbm of coal per indicated horsepower hour.
Assuming a heating value for coal of 13.0 × 103 Btu/lbm and that the engine was reversible, determine the thermal efficiency of this engine.