Monday, May 23, 2016

Stirling Engines

I am no mechanic, but some aspects of machinery intrigue me. One is the Stirling engine. Why? Well, to me it is almost like perpetual motion, and it is a machine that is virtually silent and non-polluting when in operation. So silent is it that the Swedes and now others use it for submarine stealth under water where it will generate electricity to power the boat – in silence.
There are snags. Powerful machines are heavy, and they work at a constant speed. So for jobs like pumping water, making electricity, or spinning a ventilation fan, they are excellent – though not as efficient as an electric motor or the far more complicated and polluting internal combustion engine (like in a car).
Being an externally powered engine, it is free to use almost any source of heat, like the sun’s rays and from any normally wasted surplus heat (like water-cooling water), right down in scale to a nightlight or electric bulb. (I have seen a very small one work with the heat from a mug of hot coffee.)
So what is this rather odd machine?
For a beta type engine, take an enclosed metal cylinder with an external heat source at one end and vanes or other cooling method at the other. In this cylinder is a loosely-fitting piston on a rod, called a displacer. Heat one end of the cylinder and the air (or other gas) inside will expand, pushing the displacer toward the cold end, where the colder air pressure within the sealed container will shunt it back to the hot end. In the process an internal power piston will move in and out, hinged and connected to an external flywheel via a rod through a seal, also through which the displacer is hinge- connected to a different part of the flywheel’s circumference (actually at 90 degrees on the wheel).
So, apply heat to one end, spin the wheel, and off she goes – hopefully.
The colder the external air temperature the better.
It takes no skill to operate. A farmer, for instance, who lights a fire at the hot end, can pump water with a Stirling engine and go away to work knowing that the pump will work until the fire goes out, with no damage done or attention needed. Simplicity is the engine’s strength.
Ever since Robert Stirling, a Scottish minister, invented and patented his engine in 1816, there have been countless innovations, configurations and variations of the principle. Many patents have been lodged, there being continued interest in its use and development.
Above is the way I understand it, and as a layman in these matters I still sense that a certain amount of magic is also involved.