Stirling Engine’s Day in the Sun?
The Stirling engine was invented by a Scottish clergyman in 1816 as a potential replacement for the steam engine. Its particular genius is that it is a closed cycle regenerative gas system, making it highly efficient and able to be powered by virtually any heat source. Commercial adoption since its conception has been limited, but some engineers believe it has a killer current application — powering far-flung villages that are not on power grids.
From a user’s point of view the Stirling approach has two advantages. One is that because, like a steam engine, a Stirling is an external-combustion engine, it can run on a variety of fuels. Both designs can thus be powered by wood, dried animal dung or more or less anything else that will burn.
The second advantage is that a free-piston engine suffers little wear and tear, so it should be able to run for a decade or more without servicing. (One of the Oxford group’s designs has already survived for 15 years in the harsh environment of space.) This is because cylinder and piston are in line with the alternator that they drive in order to produce the electricity, eliminating the need for a crankshaft, and also because an external-combustion engine does not have to withstand the continual explosion of fuel inside its cylinder, so it can use special bearings that greatly reduce wear.