# Ways a Car can be More Efficient?

1. Nov 7, 2009

### T.O.E Dream

Why can't a car use the movement of it's axle or wheels and use that to generate electricity? For example there are magnets on the axle and as it moves it create electricity in a coil around it?

I know that energy cannot be created nor destroyed but I don't see how it violates it? I mean the axle moves why not use the that motion to create electricity? Please try to keep your answer simple. Thanks.

2. Nov 7, 2009

### xxChrisxx

Capturing electricity from a rotating axle will take it away from driving the car forward.

When you set up a field, the act of generating electricity creates a megnetic field that acts as a brake. I can''t remember which way around the fields are created as i'm not too good with electrical stuff.

Of course a KERS system could be used, which occurs when the car is on overrun. That'd work.

3. Nov 7, 2009

### Pengwuino

As xxChrisxx stated, power will be taken away from actually propelling the car meaning you'll need to run the engines even harder to produce the same locomotion.

4. Nov 7, 2009

### Bob S

Do you plan to tie this to the grid? How long is your extension cord?
Bob S

5. Nov 7, 2009

### T.O.E Dream

Oh well. I which there was a way around the problem.

But what about having an air intake system that uses the fast moving air to spin turbines that can create electricity. Will the drag cancel everything out or is there a way to avoid drag?

6. Nov 7, 2009

### Staff: Mentor

This is similar to the way regenerative braking works...

7. Nov 7, 2009

### xxChrisxx

Cars don't go fast enough to have air to spin turbines.

Just think of it like this, you are creating power to make motion. If you try to recover any power FROM the motion, you will have a net loss in efficiency (if you intend to use this electricity to create motion that is) as you are creating more steps.

You only gain efficiency when you capture energy from something that you don't want. eg turbocharging the high enthalpy exhaust gas would otherwise be thrown a way. --> net gain. (not in fuel efficieny but power per unit)

The key is to tap into motion/whatever when you ARENT generating power. Eg, regenerative braking. Or overrun down a hill.

Last edited: Nov 7, 2009
8. Nov 7, 2009

### T.O.E Dream

Okay this might be really stupid but I need to ask it.

Is it possible that you can convert the heat that a system gives off. To say it differently, imagine that when a wheel creates friction with the floor and energy is loss in the form of heat, can you recover the heat that it just created? I understand that even if you can recover it you can't do anything with it, but it doesn't violate the fact that energy cannot be created nor destroyed.

9. Nov 7, 2009

### xxChrisxx

Yep using lost heat, say through the brake discs would yield a gain.

10. Nov 7, 2009

### Staff: Mentor

The exhaust from a car is also very hot and provides a large opportunity for heat recovery. I've heard Mercedes is working on a steam turbine heat recovery cycle for the exhaust.

11. Nov 7, 2009

### trini

you could transmit the generated energy using wireless transmission but that would involve massive radiation fields all over the place, not a good idea, and yes they do use the car's engine to drive magnets, that's where most of the electricity in your car comes from.

12. Nov 7, 2009

### mgb_phys

A few military vehicles use thermoelectrics to generate electricity from the exhaust heat.

13. Nov 7, 2009

### T.O.E Dream

Speaking of recovering heat do you think that we might develop a technology where we can recover heat from room temperature objects? So that we can get energy from the heat of the air or something like that?

14. Nov 7, 2009

### Staff: Mentor

No, you need a temperature difference to make heat flow from one place to another - and to caputre and use it.

15. Nov 8, 2009

### T.O.E Dream

Yeah, I thought of that after I asked the question. But why aren't we use termoelectricty in power plants and in cars?

16. Nov 8, 2009

### Staff: Mentor

What's thermoelectricity? Cars and power plants take chemical energy and turn it into mechanical energy to turn generators.

17. Nov 8, 2009

### T.O.E Dream

What I mean is that why can't powerplants and cars use thermoelectric generators to create electricity from the heat of the exhaust or waste.

18. Nov 8, 2009

### xxChrisxx

They can, from a thermodynamics point of view. It's just practicalities that limit its usage. Making something small enough to package into the exhaust system is a pain.

So it's possible, just hard atm.

19. Nov 8, 2009

### T.O.E Dream

What about in a power plant, they don't need to make it small. How effective would it be.

20. Nov 8, 2009