TEXT: The Internal Combustion Engine

Combustion is a word for fire or burning; an internal combus­tion engine is one in which a fire inside the engine itself makes the engine work. Despite its polluting emissions, this is one of the most significant inventions of all time, especially because of its primary uses as a portable power source. The steam engine uses a fire in a boiler rather than inside the engine; for this reason steam engines are sometimes called external combustion engines.

Experiments with internal combustion go back to the seven­teenth century. The first fuel tried was gunpowder, with a predictably explosive result. Other experiments were made with different kinds of gases including hydrogen which is explosively combustible. It was not until the second half of the nineteenth century that the development of petroleum products made possible today's internal combustion engine. Kerosene for lamps and stoves was the product first sought from petroleum while gasoline seemed nothing more than a dangerous by-product. But after other fuels had been tried it was gasoline that emerged as the most practical for internal combustion.

The first genuinely marketable internal combustion engine was the work of a German inventor, Nicolas August Otto. The Otto device was a four-stroke engine in which each piston made four movements (two up and two down) for each combustion in the cylinder using gasoline vaporized and mixed with air in a carburetor. It utilized a cycle in which the combustible mixture is

drawn into the cylinder of an internal combustion engine on a suction stroke, is compressed and ignited by a spark plug on a com­pression stroke, burns and performs work on an expansion stroke, expels combustion products on an exhaust stroke.

Since only the third stroke produces work, the piston needs help over the other strokes. This is given by a flywheel attached to the crankshaft. The flywheel in effect stores energy from the power stroke; this energy then carries the piston through the three strokes until the next power stroke caused by the combustion is repeated.

Another necessary component of the four-stroke engine is a camshaft which controls the cams that open or close valves to let gases in and out of the cylinder. The camshaft makes one revolution for every two of the crankshaft since the valves open only on every other stroke.

The engine designed by Otto was an immediate success. When he died in 1891, 30,000 of his engines had been sold, but they were suitable only for stationary use. Another German, Gottlieb Daimler, pioneered in adapting the Otto engine so that it could be used to power vehicles. By 1900 automobiles appeared with increasing frequency, first on the streets of Europe and then in the United States. This series of inventions has changed daily life for most people as much as any other in our history. It has made possible great industries, provided con­venient transportation for millions of people and established new patterns of living.

The automobile emerged and developed because of the ingenuity of many different inventors. As an addition to the basic four-stroke engine, increasingly efficient carburetors were designed. The first improved carburetors replaced coal gas with petroleum products like benzene and gasoline. Another develop­ment was the use of several cylinders rather than the one in the first Otto engines. At various times automobile engines have had from two to sixteen cylinders; the standard numbers today are four, six, and eight. Other problems solved to achieve the efficiency of modern automobiles include ignition systems that cause combus­tion several hundred times a minute and cooling systems for cylinders rapidly heated by this combustion. Methods that employ both air and water to cool the engine have been engineered though most modern cars are water-cooled.

Automobiles had just gained wide acceptance when inventors began to experiment with the internal combustion engine as a source of power for flying machines. Flight is one of our oldest dreams but the reality of powered flight transcending the bonds of wind, air currents, and gravity belongs entirely to the twentieth century. The first successful flight in a powered aircraft was made by two Americans, Wilbur and Orville Wright, in December of1903 at Kitty Hawk, North Carolina. They put a gasoline engine into a glider and this fragile contrivance flew for twelve seconds. In time for World War I (1914-1918) airplanes had been developed for use as weapons. The decades of the 1920s and 1930s saw the beginning of commercial aviation. When World War II (1939-1945) exploded air power was a major factor for victory and defeat.

Before the development of mod­ern jet engines, to be explored in the next unit, airplanes were powered by gasoline internal combustion engines; these were light and powerful, both necessary conditions for flight. They used a radial engine with cylinders arranged around a central point like the spokes of a wheel. One cylinder was joined to the crank by a master connecting rod; the other cylinders were joined by hinged rods to the master connecting rod rather than to the crank. The crankshaft connected to a propeller which, as previously described, makes a helical motion that almost literally "screws" the plane through the air.

Another type of internal combustion engine is the diesel engine, named for its German inventor, Rudolf Diesel. In a diesel engine air is compressed to a very small proportion of its original volume; this causes the air to become so hot that combustion takes place when fuel is injected into the cylinder. Diesel engines have several advantages: they do not require a spark, they operate with cheaper fuel than other internal combustion engines, and they have a higher thermal efficiency thereby developing more power in ratio to the amount of fuel used.

Diesel engines have gained wide acceptance for many heavy duty vehicles, including ships, trucks, heavy equipment, and some types of passenger cars. Diesel locomotives have almost completely replaced steam engines on railroads. As an example of the complexity of modern machinery, diesel engines are used to provide power to run electric generators whose electricity is then used by the electric motors that perform the actual work on diesel locomotives!