Introduction:
Engine friction if defined as the difference between the indicated horse-power (power at piston top as produced by the combustion gases) and the brake horse-power (useful power) available at the output shaft, i.e.
f.p.= i.p.-b.p
TOTAL ENGINE FRICTION:
1. Crankcase mechanical friction.
2. Blow by losses (compression-expansion pumping loss).
3. Exhaust and inlet system throttling losses.
4. Combustion chamber pumping loop losses.
5. Piston mechanical friction.
Crankcase Mechanical Friction: Crankcase mechanical friction can further be sub-divided into:
(1) Bering friction,
(2) Valve gear friction, and
(3)Pump and miscellaneous friction.
Blow by Losses: Blow by is the phenomenon of leakage of combustion products past the piston and piston rings from the cylinder to the crankcase.
Exhaust and Inlet Throttling Loss: The standard practice for sizing the exhaust valve is to make them acertain percentage smaller than the inlet valves.
Piston Mechanical Friction: Piston mechanical friction can be sub-divided into:
1. Viscous friction
2. Non-viscous friction
a) Friction due to ring tension
b) Friction due to gas pressure forces behind the ring.
EFFECT OF ENGINE VARIABLES ON ENGINE FRICTION
Motoring Method:
In the motoring method, engine is driven with the help of an external motor. The power consumed by this motor, if corrected for mechanical and other losses of the motor, gives the fp of the engine.