I.C. Engines

Indicated and Brake Power

$W_{cycle,cyl} = k\:\textrm{(Spring rating)} \times\frac{\textrm{Swept volume}}{\textrm{Length of diagram}} \times\textrm{Net area}$ $I.P. = \frac{1}{2}W_{cycle,cyl}\times\frac{Rev}{sec}\times Nu.\,of\;Cylinders$ $B.P. = (F \times R)\times\omega = \uptau \times \omega$

Mechanical efficiency of an engine is given by:

$\eta_{mech} = \frac{B.P.}{I.P.}$

Whereas thermal efficiency is

$\eta_{Th,i} = \frac{I.P.}{m_{fuel}H_{comb}}$ $\eta_{Th,b} = \frac{B.P.}{m_{fuel}H_{comb}}$