Brake Mean Effective Pressure
This is the average effective cylinder pressure that does useful work calculated from the brake horse power.
The work accomplished during one engine cycle divided by the engine swept volume. It is essentially the engine torque normalized by the engine displacement. The word ′brake′ denotes the actual torque/power available at the engine flywheel as measured on a dynamometer. Thus, BMEP is a measure of the useful power output of the engine.
Where
BMEP = Brake Mean Effective Pressure [Nm-2 = Pa]
T = Torque [Nm]
nc = number of revolutions per cycle [for a 4-stroke engine nc = 2 and for a 2-stroke engine nc = 1]
Vd = displacement volume [m3]
This is easily re-written so that it works for engine displacements in litres:
Where
Vlitres = displacement volume [litres]
From the above equations you can see that the peak BMEP is achieved at peak torque. In most engines peak torque is achieved below peak power.
| Naturally aspirated four-stroke diesels | 700 to 900 kPa |
| Naturally aspirated spark-ignition engines | 850 to 1050 kPa |
| Turbocharged automotive spark ignition engines | 1250 to 1700 kPa |
| Turbocharged automotive four-stroke diesels | 1400 to 1900 kPa |
See also: Brake Specific Fuel Consumption, Indicated Mean Effective Pressure, Mean Effective pressure.
Subjects: Automotive Engines