Sterling Engines

The Sterling heat engine was invented by Robert Stirling in 1816. He was a reverend in the Scotland who built heat engines in his home workshop. His Heat Economiser was patented in 1816. The engine incorporates ideas of reduced fuel consumption compared with the current steam engines.

Further development to the engine happened when his younger brother suggested using pressurized gas as the working fluid. Additional patents in 1827 and 1840 were for improvement to the design.

A closed cycle with external heating engine that has a power piston, a displacer to move the enclosed air between the hot and cold ends a regenerator in now called a Stirling Cycle Engine.

Air in the engine is cyclically heated (by an alcohol burner) and expands to push the power piston (shown in blue) to the right. As the power piston moves to the right, the yellow linkage forces the loose-fitting, red "piston" (on the left half of the machine) to displace air to the cooler side of the engine. The air on the cool side loses heat to the outside world and contracts, pulling the blue piston to the left. The air is again displaced, sending it back to the hotter region of the engine, and the cycle repeats.

Stirling Engines work on a temperature difference between the hot end and the cooling fins. Any source of heat could be used. Refrigerant on the cold end may be needed for long term use or if the barrier conducts too much heat. On a finely machined Stirling engine, the temperature difference can be as low a just a few degrees- the heat from your hand can be enough to power the flywheel.

Stirling Engines are most commonly found in waste heat recovery systems. Power plants that generate hot water could be used to power several heat engines for no additional cost after setup. However, the power generated by these engines would be only a fraction of what the steam turbine is putting out. Set up costs are high enough that waste heat recovery systems are not too common.

Interests in heat engines may increase because they minimize the cost per unit energy being produced. For large scale power production, Stirling Engines are too expense to make. Given current energy shortages and rising environmental concerns, heat engines may become more attractive.

The most common application of Stirling Engines is water pumping. Even Robert Stirling modified his engine to pump water from a stone quarry.