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
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
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
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
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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