The Stirling cycle engine was invented in 1816 by Robert Stirling. But due to its low power output it never gained widespread use. It was however ideally suited for powering fans and pumps in remote and hot climates, where electricity was unavailable.
The theory behind the operation of the Stirling engine is based on the thermodynamic principle of the Carnot Cycle. However in the Ideal Stirling cycle, the two constant volume processes are not adiabatic (thermally insulated.) Figure 1 shows a P-V diagram of an ideal Stirling cycle. Where a fixed quantity of gas is subjected to four processes.
Figure 1. The ideal Stirling Cycle. Click on a path to view how the process works.
- Process 1-2 is an isothermal (constant temperature) expansion at temperature THot. The volume increases, the pressure falls, and a quantity of heat Qin is absorbed by the working fluid from the heat source.
- 2-3 is a constant volume process where heat Qout is rejected and the pressure drops.
- Process 3-4 is an isothermal compression at temperature TCold, with more heat rejected to a heat sink at the same temperature. The pressure rises and the volume decreases.
- In 4-1 more heat is added at a constant volume thus increasing the pressure to its initial value, at which point the cycle can be repeated.
- The amount of work produced is represented by integration of the area between the higher and lower temperatures.
