What Percent of Energy from Gasoline is Actually Used to Move the Car?

Question

I've heard that only less than 30% of the energy released from burning gas in a car is used to move the car and the rest is released as heat and other forms of energy. Forgot where I've heard this and I cannot find anything about this on the internet. Can anyone confirm this and possibly provide a source?

Answer 1

I read that the gas guzzlers get only ab out 15 per cent to the wheels.

Answer 2

from what I understand, and based on my education in the automotive industry, you are correct, it is roughly 30 -35%

Answer 3

You're correct. I don't have the numbers, but about 1/3 is turned into heat, 1/3 is lost due to friction, and the last 1/3 makes the power.

Answer 4

Gas cars break down like this:

1/3 of the energy goes out the radiator as waste heat

1/3 of the energy goes out the exhaust pipe as waste heat

1/3 of the energy actually turns the crank shaft

Now subtract from that final third the power to turn the water pump, oil pump, alternator, power steering pump and air conditioning.  Then loose some more energy through friction losses in the drive train.  If the car has an Automatic Transmission (A/T) add a little bit more loss to turn the fluid pump and the energy loss in the torque converter while the car is stopped.  That constant push you feel while the A/T is in gear is lost energy exiting in the form of heat in the transmission fluid.  That's why A/T have oil coolers.

So only 20% to 25% of the total energy in that gallon of gas actually goes to pushing the car forward.  I've seen estemates as low as 15%.  See the waste?

While in an electric car you have very little waste heat to get rid of.  There is only 1 moving part on the motor.  Also electric motors are much more efficient at converting input energy to torque.  And torque is what pushes you down the road, not RPM.

Answer 5

Depends on the vehicle. But, even the most fuel efficient cars only get about 41% use of gasoline vapors. At least, I thought I heard that before.

Answer 6

Some book I bought back in the '70's had a chemistry equation that showed if you calculated 100% combustion efficiency for gasoline by chemical means, you would get a 1:64 ratio of gas to air, rather than the standard 1:14 ratio most carburetors ran. Why? Because, valves would burn up at higher ratios ( more lean, less heat removal from engine parts, hence they overheated and burned ). I can't find that book, I KNOW I have it somewhere. But that works out to about a 22% efficiency. Most of the gasoline is actually used as a COOLANT to cool the valves and piston tops, the rest is fuel. How does that work? Simple - gasoline is SPRAYED into the intake, either by carburetor, or Fuel injector...as a liquid. Liquids don't burn, gases do. So, the gas droplets only vaporize partially, the rest absorbs the heat and turns to pollutants, because the oxygen can't get to the center of the droplets to completely burn the molecules of gasoline. And if you DO vaporize them completely, then you burn engine parts due to lack of cooling efficiency. Now, the lower you go in compression, the less effect this has. Rumors of 100 MPG carburetors back in the 1930's - 1940s may have been true, because cars often only ran 5 or 6:1 compression ratios, not the 9:1 or 8.5:1 of today's cars, so much less heat.

  Anyway, I've been wanting to find that book, and get a real chemist to confirm the authenticity of the claim of  efficiency. But I have yet to find it again. It's packed away in the attic or basement somewhere, I'm sure.  Keep searching, though. I'll bet any decent chemist could figure out the formula for it, though.

- The Gremlin Guy -