Define :

i) Brake thermal efficiency – It is defined as the ratio of heat equivalent to brake power per unit time to the heat supplied to the engine per unit time Brake thermal efficiency = B.P./ mf x C.V. 

ii) BSFC – It is the mass of fuel required to develop 1 kW brake power for a period of one hour. It is inversely proportional to the brake thermal efficiency. BSFC = Mass of fuel consumed in kg/hr / Brake power in kW