Could a 200-year-old engine solve today's petrol crisis?
A LITTLE-known invention by a Church of Scotland minister almost 200 years ago could help to reduce the world's insatiable and ever-growing appetite for oil.
As prices on the oil markets continue to approach their highest for 21 years - threatening a repeat of the fuel protests of four years ago - a leading expert on the Stirling engine has claimed it could reduce petrol and diesel consumption in motor vehicles by more than half.
Dr Peter Waddell, a retired reader in mechanical engineering at Strathclyde University, believes the internal combustion engine - workhorse of the western world for more than a century - could be replaced by a modern interpretation of Robert Stirling's 1812 engine.
He claims that, using new advances in technology, the Stirling engine could easily match a modern petrol or diesel engine of a similar capacity, but with an improvement in efficiency of about 30 per cent.
Robert Stirling was a Church of Scotland minister who invented the Stirling engine because steam engines of his day often blew up, killing and maiming people who happened to be close by.
His new type of engine could not explode and produced more power than steam engines then in use. In 1816 he received his first patent for a new type of "air engine".
The engines he built and those that followed eventually became known as "hot air engines" and continued to be called that until the 1940s when other gases such as helium and hydrogen were used as the working fluid. As opposed to the modern internal combustion engine, the Stirling engine is an external combustion engine and uses the "Stirling Cycle".
This means that the gases inside never leave the engine. There are no exhaust valves that vent high-pressure gases, as in a petrol or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet.
Although they have very limited application in their present stage of development, they are used in some submarines, refrigerators and auxiliary power units for yachts.
The Stirling Cycle uses an external heat source - which could be anything from petrol to solar energy to the heat produced by decaying plants. No combustion takes place inside the cylinders of the engine.
However, until recently the main problem with the technology was that engineers could never get any power out of them.
Dr Waddell said: "The problem is that you have to work under pressure. As the pressure increases the power output does so dramatically as well.
"But as helium is prohibitively expensive, you have an enclosed mass of hydrogen under high pressure.
"If that leaks out and there is a spark you are on potentially lethal ground. It would cause a catastrophic explosion."
Rubber seals to prevent the gas leakage were always seen as the Achilles heel of the Stirling engine, as they leaked under pressure, posing significant danger.
Using liquid sealant, Dr Waddell and his research team at Strathclyde University cracked the problem to the point where they could "blow the engine apart due to pressure, without losing any of the volatile gas".
He added: "Having discovered the key to working the engine under high pressure we started to get absolutely brilliant results, and proved the principle that it works.
"It would be totally feasible to make the Stirling engine work now.
"Ford gave up in the early 1990s because they could not seal the hydrogen under high pressure.
"With our success it has already been proven that, cylinder capacity to cylinder capacity, you could get as much power out of a Stirling as you could with a petrol engine.
"The problem was that it would cost a pile of money to re-tool up to build Stirling engines," said Dr Waddell.
"It is as good as the petrol or diesel engine and could replace the current internal combustion engine in most cars without any problem at all."