Otto Cycle
The first gasoline-powered engine was modeled on the steam engine, and was the first practical alternative to it as a power source. In the steam engine, expanding steam inside a cylinder pushed up a piston, which then returns to its original position when the steam is allowed to escape and the steam supply is cut off. A steam engine is said to have a two-stroke cycle, since the piston moves twice (through one cycle) with each blast of steam.
The two-stroke gasoline engine used a mixture of ignited gasoline and air in place of the hot steam above. The piston was attached to a crankshaft with U-shaped sections called cranks via connecting rods attached to the bends. With these cranks, the crankshaft converted the up-and-down motion of the piston into rotating mechanical energy. A two-stroke engine did not have much power, however, because it required a precisely-timed combustion of the gasoline/air mixture. Too soon or too late damped the piston and so decreased the rotary power delivered through the crankshaft.
The German engineer Nikolaus August Otto (1832-1891) built his first gasoline-powered engine in 1861. Three years later he formed a partnership with Eugen Langen, and together they formed the Deutz Gas Engine Factory, developing an improved engine that won a gold medal at the Paris Exposition of 1867.
In 1876 Otto built an internal combustion engine utilizing a four-stroke cycle. (Some attribute this invention to Otto's chief engineer, Franz Rings.) The four-stroke cycle has been patented in 1862 by the French engineer Alphonse Beau de Rochas, but since Otto was the first to build a working engine on its principle, it is commonly called the Otto cycle.
The piston in a four-stroke cycle moves up-and-down down twice in each cycle. The four distinct events in the four-stroke engine are commonly labeled the intake, or induction stroke, the compression stroke, the explosion, or power stroke, and the exhaust stroke. It has two valves, the intake valve, through which the gas-air fuel mixture enters the cylindrical chamber, and the exhaust valve, through which the exhaust gasses leave.
1. In the intake stroke, the gas-air mixture is drawn into the chamber, through the intake valve, as the piston moves down the chamber.
2. In the compression stroke, the piston comes back up the chamber with both valves closed, compressing the gas-air mixture to a very small volume.
3. In the explosion stroke, the compressed gas-air mixture is ignited via an electric spark, and the mixture explodes. The piston is driven back down the chamber, the stroke that sends power to the crankshaft.
4. In the exhaust stroke, the exhaust valve is opened and the piston comes back up the chamber, pushing the spent gasses out of the chamber. The exhaust valve closes, the intake valve opens, and the cycles begins again.
Otto's engine produced 3 horsepower and ran at 180 revolutions per minute. It was a great improvement in reliability, efficiency, and quietness, and was an immediate success. More than 30,000 of these "Otto Silents" were built during the next 10 years.
Otto's patent was revoked in 1886 when Beau de Rochas' earlier patent was brought to light. The Otto cycle was a starting point for later developments in the internal combustion engine, such as the Stirling engine, where the mixture is burned not in the piston chamber but in a separate combustion chamber.
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