As a gasoline engine is running, an amount of gasoline containing 14,800 J of chemical potential energy is burned in 1 s. During that second, the engine does 3,700 J of work.

Question

(a) What is the engine's efficiency (in percent)?

 

(b): The burning gasoline has a temperature of about 5,000°F (3,000 K). The waste heat from the engine flows into the air at about 86°F (303 K). What is the Carnot efficiency (in percent) of a heat engine operating between these two temperatures? (in percentage)

Answer 1

Efficiency = Work output /Heat Input ( 100) %

In this case W= 3700J

Heat Input = 14800 J

Efficiency = 3700/14800( 100) = 25%

For Carnot's Engine

Efficiency = 1 - T2/T1 ( T1 = Temperature of source, T2 = Temperature of Sink)

= 1- 303/3000 = (3000-303) /3000 = 0.899

% efficiency = 89.9%