Patent Design

Gas Engine Patents of Note

| November/December 2003

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.