Ways a Car can be More Efficient?

[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.

 

[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.

 

[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.

 

[Bob S]

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.

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

 

[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?

 

[russ_watters]

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

 

[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.

 

[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.

 

[xxChrisxx]

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

 

[russ_watters]

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.

 

[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.

 

[mgb_phys]

The exhaust from a car is also very hot and provides a large opportunity for heat recovery.

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

 

[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?

 

[russ_watters]

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

 

[T.O.E Dream]

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

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

 

[russ_watters]

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

 

[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.

 

[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.

 

[T.O.E Dream]

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

 

[xxChrisxx]

Well in a power plant this sort of thing is already used.

look up cogeneration plants. exhaust steam after the lowest pass turbine is used to heat things.

http://en.wikipedia.org/wiki/Cogeneration

 

[T.O.E Dream]

Well in a power plant this sort of thing is already used.

look up cogeneration plants. exhaust steam after the lowest pass turbine is used to heat things.

http://en.wikipedia.org/wiki/Cogeneration

When you say it's used to heat "things" what exactly do you mean. Is the heat used to make electricity?

 

[mgb_phys]

When you say it's used to heat "things" what exactly do you mean. Is the heat used to make electricity?

No it's normally used to heat surrounding housing/offices or sometimes glasshouses.
The efficency for energy generations is proportional to the temperature difference so it's not really worth it for steam that is only just above boiling point.

 

[xxChrisxx]

When you say it's used to heat "things" what exactly do you mean. Is the heat used to make electricity?

Electiricty generation is a pretty inefficient process compared to heat generation. The idea of coegeneration plants is that surrouding buildings don't use the electiricy already generated for heating. They use the waste heat from the electricity generating process.

 

[russ_watters]

Note that thermoelectric generators are also very inefficient, so it is not better to try to use thermoelectrics directly (as opposed to using turbines, etc.).

 

[Noja888]

Sorry to stray from using the heat of a car to convert it to something useful. But...

Did anyone see the episode of "Mythbusters" where they put golf ball divots on a cars' exterior to create turbulence? They increased the mileage per gallon from 26 to 29.7 (between 3 to 4 miles per gallon better). And they were just using a clay "skin" to make the divots and to do the testing. I imagine a well researched application of this would yield better results.

I also heard that someone made a flywheel that spun on magnetic bearings/field (no friction). But if the flywheel let go it had enough force to break out of its containment and possibly kill someone.

 

[Lsos]

look up cogeneration plants. exhaust steam after the lowest pass turbine is used to heat things.
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They also have "combined cycle" plants, which are like cogeneration plants, except the exhaust is in fact used to make more electricity. A gas turbine's exhaust is over 500 deg C, which is still plenty to derive work from. This exhaust is used to make steam and power a traditional steam cycle plant. The efficiencies of these plants are quite high, reaching up to around 60%.

http://en.wikipedia.org/wiki/Combined_cycle

And to answer T.O.E Dream's question,

But why aren't we use termoelectricty in power plants and in cars?

Well, they do. I'm not so sure about the term "termoelectricity", but most power plants work by making electricity from a temperature difference. It just so happens that complex, elaborate machines (turbines, generators, boilers, pumps, etc.) are the best way to do this.

It should also be noted that however you go about getting this electricity from the heat, there will always be "waste heat", as in heat that you have to reject because it just isn't enough to do anything with. Power plants dump out water that's around 10 deg C warmer than the surrounding water. But...what can you do with 10 degrees? I'm sure if you tried hard enough you could get something...but you'll always get to the point where it just isn't worth it anymore.

As long as it is worth it, people will do it, as in the "combined cycle" plant I mentioned above.

Also, there might be more direct methods to get electricity from heat difference, but I imagine they aren't nearly as efficient or practical as traditional methods. Otherwise they would be used more extensively.

 

[xxChrisxx]

The point is with combined cycle plants the gas turbine exhaust is much higher temp as you say. After this is put through a steam cycle, the exhaust may still be 100 degrees.

Waste heat connot always be used for generating electricity, below a certain temperature it just becomes terribly inefficient to do so. Thats is when CHP (combined heat and power) is used.

With CHP plants you can get a utisliation ratio of near to 1 (never quire 1 due to unavoidable losses). This is kind of like saying 100% efficiency (although we don't say efficency for CHP).

But good points, it's all about using what would otherwide be thrown away. Until it becomes enecominic to use.

 

[LURCH]

...But good points, it's all about using what would otherwide be thrown away. Until it becomes enecominic to use.

And on that point, going back to increased effifiency in automobiles, I wonder if the car makers couldn't find a way to use Ferriday shock absorbers (my term). A linear generator could use magnetic resistance to dampen oscilations from bumps in the road, and generate ellectricity, rather than throwing that energy away as heat. Sort of a "regenerative shock absorber," one might say.

 

[xxChrisxx]

It's a good idea, it's possible to gain energy from that from a themo point of view.

The problem with many of these ideas is econimics and practicalities. Realistically how much energy are you going to recoup from the shock absorber moving say half an inch to an inch a few times a minute? Is that then really worth the expendature on a more complicted damper?

I suspect this is the reason why many energy recouping ideas are just ignored, the benefits vs cost just doesn't justify it.

 

[J.ofalltrades]

The problem with many of these ideas is econimics and practicalities. Realistically how much energy are you going to recoup from the shock absorber moving say half an inch to an inch a few times a minute? Is that then really worth the expendature on a more complicted damper?

/QUOTE]

I remember reading a while back (Popular Science I think) about Bose developing a magnetic shock that did just that. After all, with 5 - 10 shakes, you can charge one of those battery-less flashlights enough for ten minutes worth of light. Encase the shock in a magnetic field and store the energy and presto change-o you have enough energy for headlights or your radio or what-have-you.