Mechanical efficiency of Engine!
Mechanical efficiency is defined as ratio of brake power (Power obtained at crank shaft) to the indicated power (Power generated at piston).
Mechanical efficiency = Brake power (BP)/ Indicated power (IP)
As BP is always less than IP because IP= BP + FP, so value obtained is in fractions . Therefore it will be multiplied with 100 to get percentage value.
Mechanical efficiency = (BP/ IP) X 100
It can also be defined as ratio of brake thermal efficiency to indicated thermal efficiency.