in which W is the total of utile work done by the run (within joules), and "energy" is the quantity of energy (agaaround, in joules) utilized to start a run.

An efficiency of Unity (100%) is impossible - a second law of thermodynamics prohibits it. Theoretically, a reciprocal annihilation of matter and antimatter would become all effective, however a collection of the discharged energy would does'nt be.