Meaning | Concept | Definition:
Engine displacement is a measure of volume in an internal combustion engine. Although it is not directly proportional to the total power produced, it normally correlates strongly with the power output.
As cylinders move within an engine, they work by displacing a certain volume of air. All internal combustion engines have a certain volume displaced per cylinder. High engine displacement will generally result in low fuel consumption, and a number of governments have used the figure as a basis for taxes.
An internal combustion engine burns fuel in cylinders to produce energy. A piston compresses the air inside a cylinder, while fuel, typically gasoline, is injected into the air. A spark plug ignites fuel into compressed air, further increasing the air pressure inside the cylinder.
This high-temperature, high-pressure gas pushes the piston down a distance called the stroke. The piston is connected directly to the vehicle’s transmission, which in turn can turn the wheels.
Engine displacement refers to the volume swept by all the pistons in an engine. It does not include the volume of air above the piston where the initial spark is fired. It can be calculated with the following formula:
Engine displacement = ? / 4 * (cylinder diameter) 2 * stroke * number of cylinders
In essence, this is the total volume that all cylinders can change by. The figure only refers to the volume displaced by the pistons, so it is the internal diameter of the cylinder that should be used in this calculation.
However, the cylinders of an internal combustion engine never reach their maximum volume at the same time. Their positions are staggered so that more continuous energy can be produced, rather than bursts of energy.
Engine displacement is usually expressed in liters, but can also be expressed in cubic centimeters (cc) or cubic inches. Many motorcycle and lawn equipment engines have a total displacement of less than a liter, so the cc figure is preferred.
Economy class cars generally have four cylinders with total displacements between one and two liters. Eight-cylinder sport utility vehicles (SUVs), on the other hand, can have displacements greater than six liters. Total engine displacement is often incorporated into a vehicle’s name.
In some countries, engine displacement has a legal meaning. Engine sales are frequently taxed based on displacement, rather than total horsepower.
For this reason, it is common to see offsets slightly below some threshold value. However, many countries, such as Sweden, are beginning to tax vehicles based on total carbon dioxide emissions rather than engine displacement.