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Engine power is the power that an engine can develop. It can be expressed in power units, most commonly kilowatt, metric horsepower (often abbreviated PS), 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 ...
During testing, the output torque and rotational speed are measured to determine the brake horsepower. Horsepower was originally measured and calculated by use of the "indicator diagram" (a James Watt invention of the late 18th century), and later by means of a Prony brake connected to the engine's output shaft
is the motor constant [1] (sometimes, motor size constant).In SI units, the motor constant is expressed in newton metres per square root watt (/): = where is the motor torque (SI unit: newton–metre)
The torque is then related to the lever length, shaft diameter and measured force. The device is generally used over a range of engine speeds to obtain power and torque curves for the engine, since there is a non-linear relationship between torque and engine speed for most engine types. Power output in SI units may be calculated as follows:
The horizontal axis shows the rotational speed (in rpm) that the crankshaft is turning, and the vertical axis is the torque (in newton-metres) that the engine is capable of providing at that speed. Torque forms part of the basic specification of an engine: the power output of an engine is expressed as its torque multiplied by the angular speed ...
The power band of an internal combustion gasoline automobile engine typically starts at midrange engine speeds (around 4,000 RPM) where maximum torque is produced, and ends below the redline after reaching maximum power (typically between 6,200 RPM and 6,800 RPM). Diesel engines in cars and small trucks may develop maximum torque below 2,000 ...
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Torque measurement is somewhat complicated since there are two machines in tandem - an inline torque transducer is the preferred method of torque measurement in this case. An eddy-current or waterbrake dynamometer, with electronic control combined with a variable frequency drive and AC induction motor, is a commonly used configuration of this type.