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purely mechanical engines


forufes
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a mechanism to store mechanical energy then release it, like wounding a giant spring then having a full seize car go 100 miles.

the closest i found was NASA's human powered plane.

did you hear of anything similar?

Humans use chemical energy (combustion)... They convert sandwiches, apples and milk to CO2, water, poo, urine :)

So that doesn't count as a purely mechanical engine.

 

I'm afraid that you can't store much energy like that. A giant spring might get you a few meter... or a giant flywheel spinning at a horribly high speed might work too (let's not include the safety issues yet).

 

Does a compressed air engine count? There's no reaction, but the storage is by compressing air... not sure if that counts as "mechanical".

Edited by CaptainPanic
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Humans use chemical energy (combustion)... They convert sandwiches, apples and milk to CO2, water, poo, urine :)

So that doesn't count as a purely mechanical engine.

 

I'm afraid that you can't store much energy like that. A giant spring might get you a few meter... or a giant flywheel spinning at a horribly high speed might work too (let's not include the safety issues yet).

 

Does a compressed air engine count? There's no reaction, but the storage is by compressing air... not sure if that counts as "mechanical".

 

There is a lot of research going on into flywheel energy storage. There is also quite a lot of history regarding transport. For more info google - flywheel energy storage -

Edited by TonyMcC
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There is a lot of research going on into flywheel energy storage. There is also quite a lot of history regarding transport. For more info google - flywheel energy storage -

As far as I know, the flywheel storage is meant to store energy, for example at a traffic light, and to turn it back into a forward motion of the vehicle when the light turns green.

 

Back-of-the-envelope calculation to find the weight of a flywheel to do 100 miles in a fuel efficient car:

Wikipedia states that energy density can be "360-500 kJ/kg".

"The high energy densities often cited with flywheels can be a little misleading as commercial systems built have much lower energy density, for example 11 W·h/Kg, or 40 kJ/kg."

 

Taking the upper (non-commercial) value of 360-500 kJ/kg, I conclude that we would need a flywheel of 100 kg to replace the energy value of 1 kg of gasoline (about 40 MJ/kg).

 

An ordinary fuel-efficient car would need 8 liters of gasoline to do the 100 miles (160.9344 kilometers) as asked in the OP.

Ordinary engines have an efficiency of 20%, while flywheels have up to 90%. So, while the fuel-efficient car would use the 8 liters, the flywheel-car would require 4.5 times less energy to do the same distance. It would require 1.8 liters of gasoline-equivalent.

 

So, I conclude that to do 100 miles, you would need a flywheel of 180 kg... which is possible.

 

We should note that this is with the future-tech flywheel. A common commercial flywheel stores about 10 times less, so it would weigh 1800 kg, which is too much.

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Flywheels, I feel, are somewhat udervalued - I hope that there will be more flywheel talk-about (also on this forum). But the flywheel is not ideal car-energy-source. The flywheel is ideal when you need lots of mechanical power (energy release in short time).... Also, I beleive, in space missions, flywheels could be easier to deploy (zero gravity, vacuum) - could be used to convert small-power energy source (like PV cells) to on-peek-demand high-power source.

 

CaptainPanic - be merciful to non-gasoline energy sources. Don't 'kill' them by comparing them to gasoline... Gasoline is certainly unbeatable by all counts - anything compared to gasoline seems plain useless. Gasoline looks like "out of this world". We were blessed.

 

(And yes, I would certainly count compressed air as a mechanical energy source.)

 

 

 

 

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CaptainPanic - be merciful to non-gasoline energy sources. Don't 'kill' them by comparing them to gasoline... Gasoline is certainly unbeatable by all counts - anything compared to gasoline seems plain useless. Gasoline looks like "out of this world".

 

Indeed. 10^8 J/gallon (~35 MJ/liter). It's really hard to compete with that.

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One comment on flywheels... By the time you get one large/fast enough to store significant quantities of energy (like, for a 100 mile trip), you now have one hell of an interesting problem when it comes to the handling of your automobile. The gyroscopic forces are going to be significant. What's going to happen when you try to drive on an inclined/crowned/etc. road?

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If you are just talking about the energy source the output of our giant fusion reactor, 93 million miles away, is enormous. Obviously it is the cost at the pump or meter or whatever that really counts. SM

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CaptainPanic - be merciful to non-gasoline energy sources. Don't 'kill' them by comparing them to gasoline... Gasoline is certainly unbeatable by all counts - anything compared to gasoline seems plain useless. Gasoline looks like "out of this world". We were blessed.

 

Hmm... Although I agree that comparing new technology to fossil energy sources feels like cheating, I feel that this time I was left with no choice:

 

1. It was not my question - I just answered the OP's question after TonyMcC put me on the track of flywheels... to leave gasoline out of the answer would be silly. The OP asked about a car going 100 miles.

2. I just showed that there IS actually a future for flywheels in cars. It's not yet perfect, but it's not utterly impossible either.

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A car that could use a flywheel -> maybe a dragster racing car (was there any effort on making one, if anybody knows?).

 

The gyroscopic forces are going to be significant. What's going to happen when you try to drive on an inclined/crowned/etc. road?

 

Yes, this seems like a problem... On the other hand, a military fighter aircraft seems quite agile despite the fact that jet engines spin very fast. I have no idea how jet engines are not torn apart when an aircraft changes pitch.

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the function i know of flywheels in cars is to start them up.

an inline crank rocker four bar mechanism can maintain its motion from a linear force input, however, starting its motion from a linear force input might get troublesome since the crank rocker can be in its toggle position, which is why they have the flywheel.

think of it this way; you can't get your bicycle moving if the peddle you're pushing is in its lowest position, you have to bring it to its mid position to be able to turn it by pushing it.

your leg is the bar connected to the piston cylinder...[hope i made it clear]

 

but what i had in mind, is like a mechanical battery, big or small, to which you input mechanical work then retrieve that mechanical work, i didn't think of fluids really, but more of a solid mechanism.

 

something like this:stock-photo-mn-in-a-wind-up-pedal-car-on-white-background-6126793.jpg

 

i also didn't mean 100m\h as a velocity, but just 100miles as a distance before needing to wind up the mechanism.

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  • 2 weeks later...

Compressed air is viable and currently being commercialised. Look up the Tata.

Well, seeing as you're being more generous with the type of vehicle used let's run some back of envelope equations again.

CaptainPanic already showed a flywheel is borderline viable at high speed. It would work quite well at lower speeds, especially as this avoids the gyroscopic problem to an extent.

 

Let's look at spring power.

A very efficient 50cc scooter can go about 100 miles on 2-3 litres, or 25MJ at the back wheel. You could probably halve that, or better if you were willing to do the journey at 30km/h

Springs produce around 0.0003MJ/kg so being generous, that would mean about 3000-8000kg of spring. This is a lot more than a scooter's 50kg.

 

If you were willing to go a little slower, and build something like

then you might do a bit better.

The latest record is 10,000 miles per gallon, or ~2,500 miles per litre. Even highly efficient engines will still be around 50% efficient, most of the gains are from reducing friction/air resistance.

That's 2MJ per 100 miles, or ~700kg of spring.

This means that it's probably within our technology to do 100 miles (or at least 10 miles) on a very flat track with a spring powered car, but it would be a prohibitively expensive engineering project.

 

We could also cheat and use the not-quite-available-yet-but-soon-we-promise win button for all engineering projects.

If this is true, long carbon nanotubes would be roughly on par with batteries as an energy store, and cars capable of travelling 100miles at incredibly high performance (they do not suffer from power draw limits like batteries) would be possible with this single additional technology.

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