Cars and other land vehicles require an engine in order to run. Most car engines today work by a four-stroke internal combustion system. There are four main stages of converting fuel into a force that can propel the car, so there are four strokes to the combustion system of car engines. This four stoke cycle is also referred to as the Otto cycle, named after Nikolaus Otto who invented the four stroke cycle in 1867. This four-stroke cycle occurs in every cylinder of a car engine.



The intake stage of the four stroke combustion cycle involves the opening of the air intake valve which allows air to flow in to mix with the gasoline inside the car engine. The piston at the top of the cylinder moves down so that this can happen. This movement allows in great amounts of the air and gasoline mixture. The intake valve then closes and shuts in the gas and air mixture.

In the compression portion of the four stroke combustion cycle, the piston moves upwards in order to compress the mixture of air and gasoline together. By compressing the gas and air mixture, the energy released will be much more powerful. The compression ratio for a diesel engine is 20:1 whereas the compression ratio for a gasoline engine is 10:1.

In the combustion part of the four stoke cycle, at the very moment that the piston reaches the top of the cylinder a spark is released that ignites the mixture. This spark comes from the spark plug. As a result of this explosion of energy, the piston is driven downward, turning the crankshaft and powering the car.

Spark plugs are electrical devices that fit snugly into the cylinder head. Spark plugs have insulated center electrodes which are connected by heavily insulated wires to an ignition coil or magneto circuit. Together this forms a spark gap inside each cylinder.

During the exhaust stroke of the four stroke system, the exhaust valve is opened and the burned ash from the blast of burnt mixture is released out of the cylinder and into the tail pipe. This part happens just as the piston moves back to the original top position and is continually repeated.

Internal combustion engines are divided into compression-ignition engines and spark-ignition engines. Spar-ignition engines require a spark to begin combustion, whereas in compress-ignition engines (diesel engines), the fuel/air mixture is compressed until it spontaneously ignites. Compression-ignition engines sometimes use glow plugs to improve problems with starting in cold weather.

There are nearly as many different types of engines as there as cars. Car engines vary in size as well as cylinder arrangement. The engine size of a car largely depends upon the number of cylinders and the displacement each cylinder produces. For example, a car engine containing six cylinders, each with a displacement of 500cc/half a liter, will be considered a 3 liter engine. This is calculated by multiplying displacement by the number of cylinders.

Cylinder arrangements may be flat, in a V-arrangement, side by side, as well as other arrangements. In the flat arrangement, the cylinders are placed next to each other horizontally. In a side by side arrangement, the cylinders will be placed next to each other vertically in a line. In a V-arrangement, cylinders are arranged vertically into a V shape.