Answer:Both are correct
Explanation:
Both are correct because
Mechanical efficiency is the dimensionless term which is the ratio of brake horsepower to the Indicated horse Power
Where brake power is the Power obtained at the crankshaft and
Indicated horsepower is the power obtained in the combustion chamber and this power is the loss in the form of friction.
Volumetric efficiency is the ratio of actual fuel intake to the maximum air fuel that could be taken.