Otto's Practical Internal Combustion Engine

Date May, 1876

In his efforts to improve the efficiency of the Lenoir engine, Nikolaus August Otto built the first four-stroke piston cycle, internal combustion engine. As the prototype for all modern internal combustion engines, Otto’s engine helped to revolutionize transportation.

Locale Deutz, German Empire (now in Germany)

Key Figures

• Nikolaus August Otto (1832-1891), German engineer and inventor
• Étienne Lenoir (1822-1900), Belgian-French inventor
• Eugen Langen (1833-1895), German technician and businessman
• Alphonse Beau de Rochas (1815-1893), French engineer and inventor
• Gottlieb Daimler (1834-1900), German engineer and inventor
• Wilhelm Maybach (1846-1929), German engineer, automobile builder, and industrialist
• Carl Benz (1844-1929), German mechanical engineer and inventor
• William Crossley (1844-1911), British car manufacturer
• Francis Crossley (1839-1897), British car manufacturer

Summary of Event

While a young man, Nikolaus August Otto developed a keen interest in technology and mechanical objects. After dropping out of high school at the age of sixteen, he became a traveling salesman. During one of his trips, he heard about an internal combustion engine that had been developed by Étienne Lenoir in 1860. It was a two-stroke engine that drew in a mixture of fuel and air during the first stroke. The mixture was ignited by a low-tension electric ignition, and it expanded during the second stroke, impelling the pistons. The Lenoir engine was not very efficient and was limited to relatively small sizes, because it had to be cooled by a water jacket placed around the cylinder.

Otto attempted to improve the Lenoir engine using a carburetor that he had invented. He then conducted several experiments with a four-stroke engine, but his initial attempts failed. In 1861, he filed for a patent for his own two-cycle gasoline engine. In 1864, Otto was joined in his engine-building efforts by German industrialist Eugen Langen. They became partners and formed the first engine manufacturing company in the world, N. A. Otto and Company, in Cologne, Germany. Between 1866 and 1876, the company manufactured a free-piston, atmospheric, two-cycle engine that was much more efficient than the Lenoir engine. The engine’s piston movement was independent of the main shaft. Its fuel mixture was ignited with an open flame in the combustion chamber. This flame-ignition system would be used by a number of engine manufacturers until around 1900.

Rather than generating power from the gaseous fuel explosion itself, the operational cycle of the Otto-Langen engine developed its power from atmospheric pressure. Production engines never exceeded three horsepower. A two-horsepower engine weighed almost four thousand pounds and stood about 10.5 feet tall. Competing against fourteen other gas engines, N. A. Otto and Company was awarded a gold medal for its engine at the World’s Fair in Paris in 1867. Less than five thousand Otto-Langen engines were manufactured. Almost half of those were built by a British company owned by William and Francis Crossley . The Otto-Langen engine was not yet a reasonable alternative to the steam engine, because it was much noisier and could generate only a few horsepower. It was an important stepping-stone, however, toward the development of a four-stroke engine.

In 1869, N. A. Otto and Company built a new factory, the Gasmotorenfabrik (fuel-powered engine factory), in Deutz, Germany. Two prominent German engineers, Gottlieb Daimler and Wilhelm Maybach, joined N. A. Otto and Company in 1872. With their assistance and returning to some of the ideas that he had experimented with in 1861, Otto built the first practical alternative to the steam engine in May, 1876. It was a four-stroke piston cycle, internal combustion engine.

Otto’s engine carried out four piston strokes in one cycle. During the first stroke, an intake valve opened, the piston moved outward in the cylinder, and the pressure inside the cylinder dropped. The lowered pressure caused a fuel mixture of air and vaporized gasoline to be sucked into the cylinder. When the cylinder reached its maximum volume, the intake valve closed and the pressure increased. In the second stroke, the piston moved inward. This inward motion of the piston in the cylinder compressed the gasoline-air mixture, which in turn raised the temperature of the mixture. Since the compression stroke occurred very quickly, only a small amount of the energy was transferred to the environment.

Near the end of the compression stroke, the fuel mixture was ignited and the power stroke initiated. During this third stroke, the ignited gas expanded rapidly, increasing the pressure against the piston and driving it outward to produce mechanical work. This process again occurred rapidly, so little energy was lost to the environment. At the end of the power stroke, the exhaust valve was opened. The hot exhaust gases were expelled through the exhaust valve during the final stroke, the exhaust stroke. The piston moved inward in the cylinder and the temperature and pressure decreased. The cycle then started over again.

The Otto engine was much more efficient than the Lenoir engine and could be made in much larger sizes. The four-stroke piston cycle became known as the Otto cycle. It became the prototype used by modern internal combustion engines. The efficiency of an engine may be measured as the net work produced during a cycle divided by the heat that is absorbed during ignition. For a typical compression ratio of eight to one, the theoretical maximum efficiency achievable is 56 percent. In practice, as a result of friction, conductive heat loss, and the incomplete combustion of the fuel, efficiencies are about 20-30 percent. In order to control the speed of the engine, Otto and his colleagues tried various ways to regulate the action of the intake and exhaust valves, as well as a variety of methods for regulating the gas-air ratio.

Otto was granted a patent for his four-stroke engine in 1877. The English licensees for manufacturing N. A. Otto and Company engines were the Crossleys . They built many thousands of Otto engines, and they sold more than thirty thousand of them between 1876 and 1886.

Otto’s patent for the Otto engine was revoked in 1886, when it was discovered that French inventor Alphonse Beau de Rochas had described the four-cycle principle in 1861 in a rather obscure, privately published pamphlet. From all available evidence, Otto developed his engine independently of the work done by Beau de Rochas. Nevertheless, he was left without a defendable patent. Many manufacturers began building engines based on the Otto cycle.

Carl Benz established the first practical automobile manufacturing company in 1885 and used the Otto engine design in his automobiles. Daimler and Maybach, who left N. A. Otto and Company in 1882, formed their own company. Daimler used the Otto engine to build the first gas-engine motorcycle in 1885. In 1890, Maybach used the Otto engine design to manufacture the first four-cylinder internal combustion engine. With the Otto cycle as a model, Rudolf Diesel developed the diesel engine in 1893. It was an internal combustion engine that used high compression ignition instead of flame or electric ignition.

Significance

Otto’s four-stroke engine provided the first practical alternative to the steam engine. Since steam engines were too expensive and not well suited for portable or small applications, the Otto engine marked the beginning of a new era of industrial development and laid the foundation for the manufacture of modern engines. By 1886, more than thirty thousand Otto engines had been sold. By 1890, the Otto internal combustion engine had been developed to the point where it was suitable for small fabrications and powerful enough for most portable, remote operations. As a result, it was universally adopted for the production of petroleum-fueled automobiles. The diesel engine developed in 1893 is an internal combustion engine that resulted from Otto’s design. By 1900, internal combustion engines were beginning to replace steam engines for electric generation and were being used in all but the largest installations by 1915.

Modern internal combustion engines are the most commonly used engines for mobile propulsion systems. A wide variety of internal combustion engines has been developed for a variety of applications. These include reciprocating engines, such as the two-stroke, four-stroke, and diesel engines, as well as rotary engines, such as the Wankel engine. The gas turbine, jet engine, ramjet engine, and rocket engine, meanwhile, are internal combustion engines in which combustion occurs continuously. They are all patterned after Otto’s invention. Internal combustion engines are used in almost all automobiles and motorcycles, many boats, and a wide variety of aircraft and locomotives. In jet aircraft and large ships, they occur mostly in the form of gas turbines. They are also used for electric generators and in a variety of industrial applications.

Bibliography

Baierlein, Ralph. Thermal Physics. Cambridge, England: Cambridge University Press, 1999. Explains the basic thermodynamic principles associated with the operation of Otto’s internal combustion engine.

Lumley, John L. Engines: An Introduction. Cambridge, England: Cambridge University Press, 1999. Describes the operation of a variety of engines, including the four-stroke engine.

Pulkrabek, Willard W. Engineering Fundamentals of the Internal Combustion Engine. Upper Saddle River, N.J.: Pearson/Prentice Hall, 2004. Discusses the history, operating principles, and applications of the internal combustion engine.

Schroeder, Daniel V. An Introduction to Thermal Physics. New York: Addison Wesley Longman, 2000. Reviews Otto’s development of the practical internal combustion engine, the components of the Otto cycle, and the efficiency of the Otto engine.

Sturge, M. D. Statistical and Thermal Physics: Fundamentals and Applications. Natick, Mass.: A K Peters, 2003. Sturge reviews some of the important history of the internal combustion engine, including the detailed operation and practical limitations of the Otto cycle.