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So a professor tells me that the best vehicle's engine efficiency is about....

S

SwiftWind

Platinum Member
20%....but most people don't take care of their cars and their cars usually run around 10%-15% due to no oil changes, air filters, fluids flush, etc....

Question 1:
whoa, is that really the best efficiency you can get out of a car?

Question 2:
How much efficiency are we looking at with hybrid cars? or hydro cars?

Question 3:
Uh, whats the best efficiency ever reached with anything? (motor, engine, machine, electricity, whatever).

 
Originally posted by: Ronstang
Originally posted by: SwiftWind
Originally posted by: Ronstang
How are you quantifying efficiency?
Click to expand...

Work in/work out x 100%...

or, in this case, amount of fuel burned vs fuel actually being used.
Click to expand...

Then he is an idiot.
Click to expand...

fuel being used? 😕 That's retarded, it's all being used

We need a little deeper explanation of wtf 20% is supposed to mean
 
Originally posted by: Ronstang
Originally posted by: SwiftWind
Originally posted by: Ronstang
How are you quantifying efficiency?
Click to expand...

Work in/work out x 100%...

or, in this case, amount of fuel burned vs fuel actually being used.
Click to expand...

Then he is an idiot.
Click to expand...

Care to explain? I didn't post this to bash my teacher, I posted this to find the answer.
 
Yep, I'm pretty sure it's based on the energy stored in the fuel, minus the exhaust heat, compared to the mechanical work done by the engine. So basically, you're counting the energy stored in the bonds of the fuel (heat of combustion, I believe... it's been a while since I did any Chemistry) and using that as your "energy in". You can measure the horsepower integrated over some finite time to get the "energy out".

You'll note that a car's exhaust manifold is usually quite hot... that's waste heat. In theory, if you add up the work done, energy of the waste heat, and energy lost to friction, you should come pretty close to the heat of combustion.

The equation given in the link above for a Carnot cycle (e = 1-(Tc/Th), where Tc and Th are the temperatures of the cold gas and hot gas respectively) tells us that efficiency is basically (Th-Tc)/Th, where Th-Tc is basically the work done (where work includes friction).
 
I believe that number has more to do with the efficiency of the combustion reaction that powers the car. Lots of energy is lost during combustion in the form of heat that goes unused, and possibly in other ways... I don't really remember. Our bodies are powered by a similar processes (very similar actually, as we use oxygen to "burn" fuel) but we are MUCH more efficient (maybe three times, or 50-60%, correct me if I'm wrong).
 
What about those engines which had like 3 moving parts... Some asian car manufacturer made those...
 
Engines themselves are around 30% efficient. So once you factor in drivetrain losses and other crap I can believe 20%.
 
Originally posted by: Accipiter22
Originally posted by: Ronstang
Originally posted by: SwiftWind
Originally posted by: Ronstang
How are you quantifying efficiency?
Click to expand...

Work in/work out x 100%...

or, in this case, amount of fuel burned vs fuel actually being used.
Click to expand...

Then he is an idiot.
Click to expand...

yeah what a moron, it's like tottttally 30%.....pfft 20...what a loser..
Click to expand...

realistically its about 20%, IDEAL (carnot) engines are 30%
 
You don't lose 5-10% by not changing oil/flushing the fluids/changing the air filter.

Question 1: Over 30%, but that depends on how much R&D and money you have and want to spend.

Question 3: Over 50%.
 
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