Further Enhancements to the Thermodynamic Cycle and Engine Efficiency.
In previous engines of this type, cooling is accomplished by using relatively poor heat exchangers to reject heat at temperatures significantly above room temperature. Since the efficiency of the engine is affected by the difference between hot and cold side temperatures, this relatively high "cold" side temperature limits the efficiency of an engine operated at a given hot side temperature.
Rather than use still more energy to boost the hot side temperatures we have lowered the cold side temperature very dramatically, to a value well below zero degrees Fahrenheit. We use a specially designed chiller to accomplish this. Furthermore, we recover not only the heat rejected by the engine, but also the heat used in running the chiller, and reinsert it into the input heat stream.
The combined result of this is that the engine operates at a much higher Temperature differential between the hot and cold sides, and yet does not require extremely high temperatures, and does not waste the energy used in accomplishing the chilling.
Another important aid to efficiency is the manner in which the engine is throttled. Previous external combustion engines usually vary the temperature of the hot side to throttle the engine, raising the temperature to increase the power output. However, this results in lower thermodynamic efficiency when running at partial throttle, and also slows the throttle response.
We throttle the engine by adding or removing working fluid, while keeping the hot and cold side temperatures constant. Thus, at any given power output level, we still have the greatest possible Temperature differential between the hot and cold sides - maintaining efficiency.