History of the Stirling
When in 1816, the Scottish minister Robert Stirling patented the Stirling cycle, he could hardly have foreseen that his invention would be experimented with in the years to come for such sophisticated applications as artificial hearts, high performance automotive engines and space station power plants. The earliest applications of the Stirling were low power output prime movers, water pumps and kerosene fans. These devices enjoyed great popularity in the latter half of the nineteenth century because of their great reliability, safety, long life and ease of use. Thousands of Stirling cycle machines were manufactured in the United States and Europe before the advent of the internal combustion engine.
Around the beginning of the twentieth century, cheap refined fossil fuels and engines which utilized them began to erode the market of the Stirling, which, it seemed, just could not improve sufficiently to compete with the gasoline engines. Despite their undeniable qualitative advantages over the noisy, oily, unreliable gasoline engines, Stirlings began to lose ground. The one most important reason? The Stirling relies very heavily on efficient heat transfer for its performance. With the materials and processes at the disposal of the early twentieth century engineers, they could not get the stirling to even approximate the power-to-weight ratio of the internal combustion engine.
In the 1940's and 1950's, N. V. Philips of The Netherlands started the interest in modern Stirlings. The rising price of fossil fuels together with the realization of the environmental damage caused by internal combustion engines induced many others to follow suit. The automotive industry started working on an automobile engine for their twenty-first century vehicles. NASA is working on the design of a nuclear-powered Stirling power plant for the commercial space stations of the coming century. The U.S. Department of Defense is engaged in a multi-million dollar development program for free-piston Stirling alternators for field use because of the tremendous qualitative advantage they have over conventional gen-sets. Oil and gas exploration companies and the medical profession are also investigating various possibilities with the Stirling.
What differentiates these modern-day Stirlings from their nineteenth century counterparts is the use of high-temperature alloys and manufacturing processes previously unknown. These have enabled engineers to improve the power to weight ratio of the Stirling by up to 200 times over that of the 19th century Stirlings. And with the uncertainties of gasoline cost and supply, the Stirling once again makes sense.
While most research organizations are pursuing exotic applications for the Stirling which will not be commercially viable before well into the next century, Stirling Technology pursued a very different path. It combined the availability of high-tech materials and processes and computer-aided design with the traditional uses for the Stirling to produce a practical device manufactured for everyday use. This user-oriented product is the ST-5.
