A car engine burns fuel to turn the wheels. Its exhaust pipe blows out hot gas, and its radiator sheds heat into the passing air.
Could a well enough built engine keep all that heat and turn every joule of fuel energy into useful work?
Some of the input heat always ends up in the cooler surroundings instead.
Put numbers on one engine. Suppose it takes in 900 J from burning fuel and delivers 270 J of useful work.
The other 630 J leaves as heat: through the exhaust, the radiator, and the hot engine block. 900 - 270 = 630.
A better built engine can shrink that 630 J. It can never shrink it to 0 J.
This is a limit of nature, not a limit of engineering.
Q: A gas lawn mower's engine takes in 600 J from its fuel and delivers 180 J of useful work. Say where the remaining energy goes.
The engine takes in 600 J and delivers 180 J as useful work.
600 - 180 = 420. The remaining 420 J cannot have disappeared.
No device converts all the heat it takes in into useful work, so the 420 J ends up in the cooler surroundings as heat.
420 J leaves to the surroundings as heat, through the hot engine parts and the exhaust.
Q: A portable generator is rebuilt with the best available parts. Its owner expects it to now turn all its fuel energy into electrical output. Judge the expectation.
No real device converts all the heat it takes in into useful work.
A rebuild can shrink the generator's wasted share.
Some of the input heat still ends up in the cooler surroundings.
The expectation is wrong: even the rebuilt generator sends some of its fuel's energy into the surroundings as heat.
A go-kart engine takes in heat from burning fuel. What happens to the part of that heat that does not become useful work?
Mirek says: 'Even a perfectly maintained motorcycle engine sends some of its fuel's energy into the surroundings as heat.' Is he correct?
A dirt bike engine takes in 750 J from its fuel and delivers 225 J of useful work. Enter the energy that ends up in the surroundings as heat, in J.
Which statement about real engines is correct?
A snow blower's engine is rebuilt with the best parts available. What does the rebuild change?
A camp generator's engine takes in 1400 J from its fuel and delivers 420 J of useful electrical output. Enter the heat that leaves to the surroundings, in J.