Four-Stroke Engine Invented

In 1876, the German engineer Nikolaus August Otto built a working engine that compressed a fuel-air mixture before igniting it, using the four-stroke cycle of intake, compression, power, and exhaust. Often called the Otto cycle, this design became the basis for most gasoline engines. It turned the internal combustion engine from a noisy curiosity into a practical, efficient power source, and it made possible the lightweight engines that later drove automobiles and aircraft.

Internal combustion had been explored for decades. In the 1860s, the Belgian-born engineer Étienne Lenoir produced a gas-fired engine that ran without compression and was inefficient. Otto, a former salesman with no formal engineering training, began experimenting with such engines and in 1864 founded a company with the industrialist Eugen Langen. Their 1867 atmospheric engine, which used the vacuum created by a cooling explosion, was more efficient than Lenoir's and won a prize at the Paris Exposition. Yet it was large, slow, and limited in power. Meanwhile, the French engineer Alphonse Beau de Rochas had described the four-stroke principle in an 1862 pamphlet, though he did not build an engine from it.

Otto's company, Gasmotoren-Fabrik Deutz, produced the engine in 1876, with the engineer Franz Rings and a young Gottlieb Daimler among those working at the firm. Compressing the charge before ignition made combustion more complete, so the engine extracted more work from the same amount of fuel. It ran on illuminating gas and was sold as a stationary power source for workshops and small factories, which could not afford a steam engine. Thousands were sold within a few years.

Otto's patent did not last. Challengers pointed to Beau de Rochas's earlier description, and in 1886 a German court invalidated a key patent claim, opening the way for competitors. Historians still debate how much credit Otto deserves, since the idea of the cycle predated him, but there is little doubt that he was the first to turn it into a commercially successful machine.

The legacy came quickly. Daimler left Deutz and, with Wilhelm Maybach, developed a compact, high-speed gasoline engine in the 1880s. Around the same time Karl Benz, working independently, built his own engine and a motor vehicle. Over the following century the four-stroke engine powered cars, motorcycles, trucks, boats, and generators, reshaping transport, cities, and economies. Its environmental costs, notably carbon emissions and air pollution, have since become a central reason that modern engineers are seeking alternatives.