Mechanical efficiency of IC engine

[aruneswaran]

what is the equation for the mechanical efficiency of an internal combustion engine?

what are the formulas for 'ip' for 4-stroke and 2-stroke engines?
thank you

 

[brewnog]

Mechanical efficiency n:

n = (Pb / Pig) = 1-(Pf / Pig)

Where Pb is the brake power, Pig is gross indicated power, and Pf the friction power.

What do you mean by ip? Indicated pressure?