A Stirling Performance

In 1816, a Scottish parson and part-time inventor named Robert Stirling patented a new engine for pumping water out of mines and quarries. It could run on almost any fuel, he boasted--including whisky. Indeed the parson had such faith in his engine that he often cut his Sunday sermons short to work on it. For all his enthusiasm, though, when Stirling died in 1878 at the age of 88, his engine was still unperfected. Soon it was totally overshadowed by the newer gasoline-powered internal combustion engine.

Now, as Detroit seeks fuel-saving, less-polluting alternatives to the modern auto engine, Stirling's machine has taken on new life. The Ford Motor Co. plans to test experimental models as possible competitors for the Wankel rotary engine, which is already standard equipment on Japanese-produced Mazdas and will be offered as an option on the General Motors Vega next year.

Detroit for a long time considered the Stirling engine too bulky and expensive for passenger cars. Ford's interest was revived by the work of the giant Dutch electronics firm, N.V. Philips, which has tested Stirling prototypes in boats, large pumps (to help dry out Holland during 1952's devastating floods) and even buses. In 1972, impressed by the Dutch results, Ford signed an agreement with Philips for joint development of a Stirling engine for passenger cars.

Shuttling Gas. Unlike typical internal combustion engines, the Stirling engine is powered by heat from an external source. In the Ford-Philips design (see diagram), hydrogen gas is heated by a burner, which can run on virtually any kind of fuel. The sealed-in hydrogen then expands, enters one cylinder and pushes a sliding piston. As the piston moves, it forces gas out of the other end of the cylinder; the emerging gas is cooled and then moves toward an adjacent cylinder where heat is applied once more and the process is repeated. As the gas shuttles between interconnected cylinders, the pistons move back and forth and piston rods push against a so-called swash plate, or disk.

The swash plate, in turn, forces a drive shaft to rotate.

Engineers point out that a Stirling engine would be quieter than an equivalent internal combustion engine, would emit less noxious fumes, and would use fuel more economically. Lacking any need for valves or cams, it would also have fewer parts. Jack Collins, manager of Ford's alternative-engines program, concedes that the Stirling is still a long way from being ready for passenger car use; for one thing, an adequate burner has not yet been developed.

But Ford hopes to test Stirling engines soon in four medium-sized Torinos. If all goes well, says Collins, the Rev. Stirling's old dream might yet become reality--perhaps as early as the 1980s.

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