Where it all began: The Otto
A drawing from August Otto’s 1877 U.S. patent, no. 194,047, for his “Improved Gas-Motor Engine.” It was the world’s first practical 4-stroke engine design.
By the mid-1860s, the race was on to develop and perfect a gas-powered engine. Although steam engines had been providing the power to fuel a rapidly industrializing world, they were not without their limitations: Chief among them, the requisite for a large boiler to hold water and fuel to heat the water to steam. Engineers knew that if they could control an explosion of fuel driving a piston, they could create an engine with far-reaching capacity and application.
In the early 1860s, German engineer Nicolaus August Otto and industrialist Eugen Langen formed N.A. Otto & Cie, with the express purpose of designing and building internal combustion engines. By 1866 their company had produced its first - and in fact the first - practical gas engine, the Otto-Langen atmospheric engine. Not unlike firing a cannon ball, the engine worked by exploding a charge to drive a piston vertically. The piston had a cogged rack for a connecting rod, which engaged a pinion gear at the top of the cylinder to turn a flywheel, translating its linear force to rotational motion. The suction created by the piston's extended rise, along with the piston's substantial weight, pulled the piston back down its bore, driving the pinion as it did so.
The Otto-Langen was a commercial success, and along with versions built under license, it is thought perhaps as many as 5,000 examples were built until production ended in about 1878. It was, however, noisy and grossly inefficient (the largest, 3 HP engines stood over 10 feet tall and weighed close to 5,000 pounds), as there were no real means for controlling the explosion of gas to drive the piston.
Otto continued experimenting, and in 1876 he designed and built the world's first 4-stroke engine. Originally called the Otto cycle, its design quickly became known for its principal four strokes of intake, compression, combustion and exhaust.
Shown here is Otto's first United States patent for his engine, no. 194,047, granted Aug. 14, 1877. A reading of Otto's patent shows he clearly understood the need to control the point of ignition and to create a spreading flame front, rather than an instantaneous explosion, as in the Otto-Langen.
His patent notes the engine's introduction of "an intimate mixture of combustible gas or vapor and air … together with a separate charge of air or other gas, that may or may not support combustion, in such a manner and in such proportions that the particles of combustible gaseous mixture are more or less dispersed in an isolated condition … so that on ignition, instead of an explosion ensuing, the flame will be communicated gradually."
In operation, a slide valve admitted a charge of air, followed by a concentrated fuel/air charge, and finally opened a channel for a pilot flame to ignite the concentrated charge, setting off the process of combustion to drive the piston. A sideshaft controlled the operation of the slide valve and the exhaust valve (a standard poppet valve), and a flyball governor driven off the sideshaft regulated speed. It is a design familiar to every gas engine collector, its basic construction echoed in every engine that followed.
It's impossible to overstate the importance of Otto's engine, for it set the stage for a new order in motive power, becoming in short order the dominant form of power for industry, farm and home. From basic operating principle to working design, it set the standard for the construction of efficient gas-powered engines and in the process forever changed the world.
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