Engine Friction and Lubrication

Engine Friction: The difference between the indicated horse power and the brake horse power (useful power) available at the outlet shaft.
The increase in compression ratio leads to increase the friction losses so the lower compression ratio is the lower friction losses.
The friction power dissipates as heat to cooling system.
Engine friction is also greatly affected by engine speed. The mechanical efficiency, which is defined as the ratio of brake horse power and indicated horse power, can be as high as 85% for carefully designed low speed engine having a piston speed of up to about 600 m/min. but is very
difficult to get a mechanical efficiency better than 75% for high speed engine having a piston speed of about 800 m/min.
Total engine friction
Defined as the difference between ihp and bhp, includes the power required to drives the compressor or a scavenging pump and the power required to drive engine auxiliaries such as oil pump, coolant pump and fan, etc.
If the power to drive compressor and auxiliaries is neglected, the total engine friction can be divided into five main components. These are:
1. Crank case mechanical friction.
2. Blowby losses (compression - expansion pumping losses).
3. Exhaust and inlet system throttling losses.
4. Combustion chamber pumping loop losses.
5. Piston mechanical friction.