Question

If the efficiency of a gasoline engine is 25%, what happens to the missing 75% of the energy in the fuel?

Answer 1

The 75% energy which does not do any useful work gets dissipated as thermal energy in gasoline engines.

Explanation:

The efficiency of any engine like gasoline engine is the ratio of work done in contrast to heat or energy provided.

Gasoline engines are internal combustion engine. The thermal efficiency is calculated of these engines.

work done or efficiency= $\frac{work done}{heat absorbed}$

         or heat absorbed is divided by heat used in doing work

the friction and in other forms heat gets lost.

In gasoline engine about 65 to 75 % heat gets emitted without any useful work done. The heat gets lost in friction, air turbulence, noise and work input to turn on the engine. After the dissipation of heat in it only 25% is used up by vehicle having gasoline engines.