Engine Indicators, Power, Tuning
Posted: Fri Aug 31, 2018 12:42 pm
These devices are instruments designed to make a record of engine cylinder pressure vs piston stroke, and that information allows determination of the work performed during the engine's stroke. Multiplying by the rate of strokes occurring over a standard period of time, then you have the rate of doing work per unit of time, in other words, the power, typically "horsepower" back in the day.
The "indicated Horsepower", derived from the instrument is actually more than the actual power, because there is engine friction in the rotating machine. If one applies a "Prony Brake", a device that measures actual power of an engine, one can determine the real engine output, stated as "Brake Horsepower". Hence the two typical abbreviation terms, IHP and BHP. In our typical engines, friction is around 10%, so if you have an indicator showing 10 IHP, you would find the actual engine crankshaft power at about 9 BHP.
Calculating the engine's power is according to the long established PLAN formula: IHP = P x L x A x N /33,000, where:
P is average differential pressure across the piston, Pounds Force per square inch. Should be a fraction of main steam pressure
L is the length of stroke, in feet
A is the area of the cylinder bore, in square inches
N is the number of power strokes per minute, depends on engine RPM, number of cylinders, if engine is single or double acting.
33,000 is the number of ft-LBf work that a draught horse can perform in one minute, according to James Watt
Early Engine indicators are elegant machines with clever mechanisms to record cylinder "Indicator Diagrams". Later versions were designed for typical IC engines, and had to be capable of much faster recordings. Today, virtually all commercial indicators are electronic devices.
Now for LEON to carry on this topic
The "indicated Horsepower", derived from the instrument is actually more than the actual power, because there is engine friction in the rotating machine. If one applies a "Prony Brake", a device that measures actual power of an engine, one can determine the real engine output, stated as "Brake Horsepower". Hence the two typical abbreviation terms, IHP and BHP. In our typical engines, friction is around 10%, so if you have an indicator showing 10 IHP, you would find the actual engine crankshaft power at about 9 BHP.
Calculating the engine's power is according to the long established PLAN formula: IHP = P x L x A x N /33,000, where:
P is average differential pressure across the piston, Pounds Force per square inch. Should be a fraction of main steam pressure
L is the length of stroke, in feet
A is the area of the cylinder bore, in square inches
N is the number of power strokes per minute, depends on engine RPM, number of cylinders, if engine is single or double acting.
33,000 is the number of ft-LBf work that a draught horse can perform in one minute, according to James Watt
Early Engine indicators are elegant machines with clever mechanisms to record cylinder "Indicator Diagrams". Later versions were designed for typical IC engines, and had to be capable of much faster recordings. Today, virtually all commercial indicators are electronic devices.
Now for LEON to carry on this topic
