The Stirling engine patented by Robert Stirling in 1816 has been in limited use by industry since it’s inception. The essential element of the Stirling cycle is compression of a fixed amount of working gas in a cool chamber. The cool compressed gas is then transferred to a hot chamber, heated from an external source, where the gas expands and drives a piston to perform work. By cooling the expanded hot gas within a radiator, it then can return to the cool chamber for the cycle to repeat.

Stirling engines can convert heat into work because the expanding hot gas delivers more work energy than needed to compress the same amount of cool working gas. Rapid heat removal of the expanded working gas, in a closed cycle engine, requires a large radiator limiting its applications.

The efficiency of the Stirling cycle is typically 15 to 20 percent greater than that of the internal combustion engine. Trochilic Quad Cycle engines are leveraged over the reciprocating Stirling engine in that its internal running friction is radically lower and energy loss due to piston mass delta is essentially eliminated.

In the late 1830ies, development of the Erickson cycle took the Stirling cycle one step further by going to open cycle. That is operation with external combustion; as in the Stirling engine, but at atmospheric input pressure and return of exhaust gases to the atmosphere. At the time, these engines were called caloric or hot air engines. Steam and the internal combustion engines were evolving in that era as well and they met with greater commercial acceptance.

One limiting factor for the external combustion engine for automotive applications was the problem of heat latency. That is, the engine does not respond instantly to changes in input heat. This problem is largely circumvented by a hybrid version of the Trochilic engine. It can run on ether or both internal and external combustion simultaneously and at any percentage of input power from either source.

The Trochilic Stirling engine provides more useful output power for the applied heat because of its energy efficient rotary motion but in solar applications is as vulnerable, as all energy-collecting systems are to the lack of sunlight. With the melding of all the earlier innovations and trochilic motion a new kind of engine has evolved that can run on both internal and external combustion.

This approach lends itself to solar power generation for days of limited solar energy, as well as provides for uniform power output. The need for battery backup and storage is limited to special requirements. It should be clear that, for this flexibility, the hybrid Trochilic runs in open cycle at some loss in efficiency. The pure Trochilic Stirling can adapt to this type of operation but requires an intermediate heat conducting fluid such as sodium, excepting alternate heat sources.