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Engine displacement is the measure of the cylinder volume swept by all of the pistons of a piston engine, excluding the combustion chambers. [1] It is commonly used as an expression of an engine's size, and by extension as an indicator of the power (through mean effective pressure and rotational speed ) an engine might be capable of producing ...
For vehicles where the above formula cannot be applied (e.g. electric vehicles), the tax horsepower is derived from the effective engine power (which is defined by law as the maximum power that the engine can provide after being used at full power from 30 minutes, which is normally lower than the rated engine power).
Speed has dropped out of the equation, and the only variables are the torque and displacement volume. Since the range of maximum brake mean effective pressures for good engine designs is well established, we now have a displacement-independent measure of the torque-producing capacity of an engine design – a specific torque of sorts.
Engine displacement is calculated based on bore, stroke length and the number of cylinders: [1] displacement = π ( 1 / 2 × bore ) 2 × stroke × n cylinders. The stroke ratio, determined by dividing the bore by the stroke, traditionally indicated whether an engine was designed for power at high engine speeds or torque at lower engine ...
Absolute cylinder pressure is used to calculate the dynamic compression ratio, using the following formula: = where is a polytropic value for the ratio of specific heats for the combustion gases at the temperatures present (this compensates for the temperature rise caused by compression, as well as heat lost to the cylinder)
If other units are used, the constant is different. When using coherent SI units (watts, newtons, and metres per second), no constant is needed, and the formula becomes P = Fv. This formula may also be used to calculate the power of a jet engine, using the speed of the jet and the thrust required to maintain that speed.
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Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the equivalent volume of the fresh air drawn into the cylinder during the intake stroke (if the gases were at the reference condition for density) to the volume of the cylinder itself.