Question

Why brake thermal efficiency is very less ? Can it be improved by simply increasing the compression ratio

Answer 1

The brake thermal efficiency is very less because of friction between the elements. No it can not be improved by increasing compression ratio.

The break thermal efficiency is given as

η_br=$\frac{BP}{Fuel energy}$

In actual when the fuel is burnt, it generates some power on the piston, which is known as indicated power, however some part of this power is lost in friction, due to friction between, cylinder and piston, friction between other couplings and connection, due to which available power is less than the indicated power, known as break power.

Thus break power is less due to friction between the elements, and it can not be improved by increasing compression ratio.