Engine power

Engine power is the power that an engine can put out. It can be expressed in power units, most commonly kilowatt, pferdestärke (metric horsepower), or horsepower. In terms of internal combustion engines, the engine power usually describes the "rated power", which is a power output that the engine can maintain over a long period of time according to a certain testing method, for example ISO 1585. In general though, an internal combustion engine has a power take-off shaft (the crankshaft), therefore, the rule for shaft power applies to internal combustion engines: Engine power is the product of the engine torque and the crankshaft's angular velocity.
Definition.
Power is the product of torque and angular velocity:
Let:
Power is then:
In internal combustion engines, the crankshaft speed formula_7 is a more common figure than formula_8, so we ca use formula_9 instead, which is equivalent to formula_8:
Note that formula_7 is per Second (s−1). If we want to use the common per Minute (min−1) instead, we have to divide formula_7 by 60:
Usage.
Numerical value equations.
The approximate numerical value equations for engine power from torque and crankshaft speed are:
International unit system (SI).
Let:
Then:
Technical unit system (MKS).
Then:
Imperial unit system.
Then:
Example.
A diesel engine produces a torque formula_27 of 234 N·m at formula_7 4200 min−1, which is the engine's rated speed.
Let:
Then:
or using the numerical value equation:
The engine's rated power output is 103 kW.