Engine, machine for converting energy into motion or mechanical work. The energy is usually supplied in the form of a chemical fuel, such as oil or gasoline, steam, or electricity, and the mechanical work is most commonly delivered in the form of rotary motion of a shaft. Engines are usually classified according to the form of energy they utilize, as steam, compressed air, and gasoline; the type of motion of their principal parts, as reciprocating and rotary; the place where the exchange from chemical to heat energy takes place, as internal combustion and external combustion; the method by which the engine is cooled, as air-cooled or water-cooled; the position of the cylinders of the engine, as V, in-line, and radial; the number of strokes of the piston for a complete cycle, as two-stroke and four-stroke; the type of cycle, as Otto (in ordinary gasoline engines) and diesel; and the use for which the engine is intended, as automobile and airplane engines. Engines are often called motors, although the term motor is sometimes restricted to engines that transform electrical energy into mechanical energy (see Electric Motors and Generators). Other specialized engines are the windmill, gas turbine, steam turbine, and rocket and jet engines.
Automobile engines get their power from burning fuel such as gasoline, diesel, or alcohol. The combustion, electrical, lubricating, and cooling systems need to work together to make the engine run smoothly and deliver power efficiently to the vehicle. The basic functions and interactions of these engine systems are shown in this series of slides. Many modern engines have a fuel injection system instead of a carburetor.
The combustion system turns fuel into the power that propels the car. In this diagram, the fuel injector sprays fuel into the intake manifold, where it mixes with air on its way into the cylinders. Inside the cylinders, the fuel-air mixture is compressed by the pistons as they pump upward. Spark plugs ignite the compressed fuel in a small explosion, which drives the pistons downward. Each piston connects to the crankshaft and as the pistons move up and down, the crankshaft turns. The crankshaft transfers this power to the transmission, which ultimately turns the axles and wheels.
The lubricating system reduces the friction produced by the engine’s moving parts, which may rub against each other thousands of times per minute. The main lubricant in an automobile engine is motor oil, which is held in an oil pan underneath the engine. A pump circulates the oil through tubes called galleries to all the moving parts of the engine. Before the oil circulates to the engine, it passes through an oil filter, which strains particles from the oil.
The electrical system manages the engine and provides the electricity necessary to keep the engine running. A key turning in the ignition allows electricity to flow from the battery to the starter. The starter includes a small motor that turns the crankshaft and sets the pistons in motion. As the crankshaft turns, it provides power to the alternator, which converts the turning power to electricity. This electricity ignites the spark plugs, recharges the battery, and operates the car’s lights, radio, and other electrical features. Most new cars also use small computers called electronic control units to monitor and regulate many of the car’s functions.
The cooling system draws heat away from the engine block, which would otherwise warp at the temperatures generated by combustion and friction. The water pump circulates engine coolant, a mixture of water and antifreeze, through the non-moving parts of the engine to absorb heat. The coolant routes through tubes in the radiator, where heat passes through the tubes into thin metal fins. A fan blows through the fins to increase the rate of cooling.