The Brayton Cycle Engine
Students of gas-powered engines know that Nicolaus Otto (1832-1891) is credited as the father of the four-cycle engine that still serves us today, powering just about every kind of motorized machine imaginable. Introduced in 1876 as the Otto Silent engine, Otto's engine was a revolution in the making, and its introduction heralded a new age in mechanical power.
Lesser known, however, is the engine scheme designed by one George Bailey Brayton (1839-1892) of Boston, Mass., in 1872. Writing in American Gasoline Engines Since 1862, engine historian C.H. Wendel claims that Brayton's engine was the 'first commercially successful engine of purely American design.'
A two-stroke engine, Brayton's patented design hinged on the used of a charging cylinder to pull in and compress the fuel/air charge. The compressed charge was stored in a receiver and then admitted into the combustion chamber. The combined charging cylinder and power cylinder worked simultaneously; a charge being pulled in as the power cylinder dropped to the bottom of its stroke, then compressed as the power cylinder rose on its power stroke.
The compressed fuel/air charge was admitted into the bottom of the power cylinder through a cam-actuated valve. On its way to the power cylinder it passed through a chamber where it was ignited by a constant flame as it entered the power cylinder. Receiver pressure was always greater than combustion pressure, and a series of wire-gauze diaphragms kept the burning charge from reversing directions.
The resultant burning and expansion of the fuel/air charge pushed the piston up for its power stroke, and spent gases were exhausted through a mechanically actuated valve. Combustion was continuous, not instantaneous, and this cycle of constant cylinder pressure came to be known as the Brayton Cycle. In his book Internal Fire, author Lyle Cummins writes that most of Brayton's production engines used a separate charging cylinder. Because of its design, Brayton's engine could be run on liquid or vapor fuel.
Although not clear in the patent drawings shown here, the piston was connected to a flywheel 'by means of the common crank and links ... in any convenient way.' Cummins says that in production engines the piston was connected to the crankshaft via a rocking beam arrangement.
The cylinder was water jacketed, and thermosiphon cooling was employed to keep operating temperatures in check.
Brayton's engine as depicted in his 1872 patent. The charging receiver is at right. Charge volume was controlled by a simple gate valve at the bottom of the receiver, and a linkage-actuated valve (visible between the receiver and the cylinder) admitted the fuel/air charge into the combustion chamber.
The design evidently suffered from poor efficiency, but Brayton continued development of his engine and introduced numerous variations based on this basic design. Brayton built and marketed engines under the banner of the Brayton Petroleum Engine Co., Boston, Mass., and the Pennsylvania Ready Motor Co. of Philadelphia, Pa., produced engines following Brayton's design. Some double-acting engines were built, and Brayton was said to be working on an improved oil-burning engine when he died in 1892.
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