21st Century Overview - Engines

The car engine provides the power to move the car by changing chemical energy contained in gasoline into mechanical energy of the engine pistons.   It is an Internal Combustion (IC) engine that in principle has not changed since its invention in the latter part of the 19th century.   However, since that time it has been improved greatly in power and reliability.   Also, unlike earlier IC engines, it runs quietly and smoothly.   Basic engine operation is described below.   Engine Detail provides more information.

Engine as it appears in the car.   It is mounted in the front of a front-wheel drive (FWD) car and in the rear of a rear-wheel drive (RWD) car.   Air and gasoline enter the cylinder of the engine where the oxygen in the air and the gasoline are ignited by a spark.   The ignited gasoline explodes into gases that expand to push down the piston, which turns a crankshaft that turns the wheels through the transmission and driving axles.   The engine has many precision working parts as described at Engine Detail.

Engine showing parts.   The most common car engine is the 4-stroke, spark-ignition piston engine using gasoline as a fuel.   ("4-stroke": "stroke" is the distance traveled by the piston, either up or down.   There are 4 strokes in 1 complete firing cycle.)     Most engines use water to cool them, but some less powerful engines are cooled by air.   The common name for this engine is "gasoline engine", although it can use other kinds of fuels, e.g., alcohol & natural gas.   (Diesel, 2-stroke, and other engines are described at power.)

Engine parts work together to transform chemical energy contained in the gasoline into piston motion (mechanical energy). The piston is connected to a connecting rod that is connected to the crankshaft.   Thus, the linear (up and down) mechanical motion of the piston is converted into the rotational motion of the crankshaft.   When open, the intake valve takes in a combination of air (for oxygen) and fuel (gasoline) to be combusted above the piston.   The exhaust gases are pushed out through the exhaust valve by the rising cylinder following combustion.

Pistons turn the crankshaft, thus changing linear up-and-down motion to rotary motion.   The crankshaft is connected to the drive train, which turns the car wheels.

Engine configurations are classified by their number of cylinders and their arrangement.   An engines has 4, 5, 6 8, 10, and 12 cylinders into which the pistons are located, although 4, 6, and 8 are the most common.   The V-engine reduces the length of the engine while the slant-engine reduces the engine height.   Opposed-engines ("boxer-engines") have a low center of gravity for greater stability and tend to run more smoothly under all operating conditions.   The size and therefore potential power of the engine is approximated by the sum of the displacements (volumes) of the cylinders, usually expressed in cubic centimeters (cc) or liters (l), e.g., 3300 cc = 3.3 l.   The engine power may also be given more precisely as measured horsepower (hp).