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Are Free-piston Engines Here ?
Page 77
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THE larger free-piston-turbine binations now have a fuel economy comparable with that of similar-sized oil engines. Large units operating in ships and stationary power plants have an overall efficiency of 37 per cent., which is in the exact range of good oilengine practice.
This was stated by Mr. Arthur F. Underwood, manager of General Motors Research Staff Activities, at a recent meeting of the Society of .Automotive Engineers' New York section.
--Smaller units,
(page 418).
resembling the twocylindered free-piston gasifier in General Motors' experimental car (XP-500), would operate with oil-fuel economy "within the immediately foreseeable future," he declared.
Savings of this form of power, essentially an oil-powered pump or air compressor connected to a gas turbine, were based on its versatile fuel appetite. A large test unit of 1,250 gas h.p. had been operated on petroleum fuels ranging from petrol to bunker C crude and shale oils.
The turbine unit which produced the power from a free-piston gasifier operated at a maximum temperature of 900° F.—low enough to obviate the need for high-temperature alloys for turbine blades. This low temperature also permitted engineers to use two or more identical gasifier ants to pump gases into a single power turbine.
So far as the future of the free-piston engine was concerned, Mr. Underwood believed it would appear first where oil engines were now used, particularly Units up to 400 b.h.p.