h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I recently read a headline that proclaimed "Scientists Find Way to Convert Sunlight to Fuel!"

"Really?" I thought, putting another log on the fire.

Baron Grim


I can't seem to get away from sodding flame arrestors today! Shall we start talking about pressure relief valves as well just so I feel like I'm still at work?

The thing with flame arrestors is it assumes that the petrol tank is still intact and the fire flashes back and that you can get air into the internals of the petrol tank in the right mix for the fuel to burn.

The vapour space above the fuel in a petrol tank should be too rich to ignite.

As I said, the fuel arrestors were regarding portable gas cans. For in car fuel tanks, the entire tank is filled with a metal mesh. When set on fire, all the tank will do is burn, not explode as there isn't any confined space large enough for the vapor to accumulate enough to reach that point where it could explode.

>>>that's why noone in their right mind is trying to invent a hydrogen fuel generator that actually stores the hydrogen<<<

Erm - not exactly true...

http://automobiles.honda.com/fcx-clarity/

This little thing is the future, not those ruddy Prius, which are wonderfully fuel efficient if you happen to drive them in town and horrendously inefficient if you're in a hurry to get anywhere on a motorway. And not battery powered cars with their restricted range and environment-raping batteries.

Honda have already got approval to put them on the road from the US authorities, and they've even started leasing them out in Southern California... The only thing stopping global introduction tomorrow is a lack of re-fueling points.

OK, well I did say I was unaware of what actual engineers were up to. In chemistry talks (and it's chemists who develop all this technology at the outset) I've never seen anything except conceptualised devices that store water and generate the hydrogen as you go along.
If one of those things was a in a crash, better get the tin hat on.

"devices that store water and generate the hydrogen as you go along"

There's a problem right there. How do you generate the hydrogen? By using electricity? Generated how? From a battery? Why not just use the battery directly?

The entire point of a hydrogen car is that you generate the hydrogen centrally, efficiently, then distribute it to the car owners. It's all about where and when you convert the energy and in what form you transport it.

It's all about collecting solar energy and converting it into kinetic energy. You first have to concentrate the solar energy, by, for instance, have a tree convert it into a hydrocarbon, then have the tree lie down for a couple of hundred million years or so until it's nice and concentrated, then you can burn it.

You can EITHER burn it centrally and concentrate the energy into a battery OR burn it centrally and concentrate the energy into compressed hydrogen OR simply dole it out and let people burn it as and when they actually need the kinetic energy.

Storing water would mean burning the oil to charge a battery which would split the hydrogen which you would then burn to convert into kinetic energy. There's a bunch of steps there you don't need.

Even if you didn't burn oil to charge the battery, but used solar power, you're still convert solar to battery to hydrogen to kinetic, when you could just use the battery directly.

"With decent sized electric cars at around £15-20k, they are no more expensive than petrol-driven cars"

The difference is petrol driven cars have significant residual value - they go on being able to run on petrol for ten or twenty years or more, depending on how well you look after them. Whereas in an electric car a significant proportion of the cost is the battery, and those things don't last forever... and the cost proportion and lifetime are things that look unlikely to change in the near future.

Right now you can buy a new petrol engine car, run it for three years, and trade it in for about half what you paid for it (I've done this several times). How happy would be be paying £15k or even £10k for a petrol engined car if you knew that after about three to five years of normal use you'd need to replace the entire engine and drive train, at a cost of several thousand pounds? How much do you think that car would be worth, second hand, when everyone knows it would need a replacement engine? The lifetime costs of a petrol engined car are well understood. Right now, I don't think many people understand the true lifetime costs to the owner of the current crop of electric cars. Or maybe they do... and that's why hardly anyone is buying one.

All good points. Thinking about it a bit more I think they don't usually use water but other solid fuel equivalents of hydrogen - e.g. metal hydrides that release H2 gas readily. I think it was me who put that in there as I was trying to think of a reasonably cheap/readily available source of H2.

Also, probably for many of the reasons mentioned above, most of the hydrogen cells I've sen discussed have not been for the purpose of propelling a car. They have been for other things.

Just to eb a semantic pain in the (_!_)


Whisky

<>>>that's why noone in their right mind is trying to invent a hydrogen fuel generator that actually stores the hydrogen<<<

Erm - not exactly true...

http://automobiles.honda.com/fcx-clarity/>

Whisky: that is not a hydrogen fuel generator, that's a storage tank. It's proven technology.




No problem in storign hydrogen really as is seen above...I'd just want to know that what ever happened to the car the bottle wouldn't blow up...I don't fancy seeing a H2 tank in a fire on a motorway and slowly building up gas pressure...where the hell would you emergency the hydrogen off to?!?!?!

Here is an interesting article about on board hydrogen generation and the fact that it's not viable at present...

http://green.autoblog.com/2008/08/04/why-on-board-hydrogen-generators-wont-boost-your-mileage/

Hmm, yeah I should have known that really shouldn't I

Incidentally pure hydrogen, as with petrol just burns - it's the mix of hydrogen and oxygen that does the big high-end explosive stuff.

Surely if you just had pure hydrogen it wouldn't do anything? You have to have some oxygen for it to burn - do you mean the right proportions of oxygen and hydrogen?

Canadian inventor and entrepreneur Dr. Geoffrey Ballard
was running buses on hydrogen fuel cells in Vancouver
way back in the 1990s.

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

He sold the automotive side of the business to Ford
and is concentrating now on stationary power systems
and low mileage fork-lift type devices - leaving Ford
holding the bag on the road-going patents that he admits
are not viable.

"Can you make hydrogen fuel at a price point that makes
any sense to anybody? And the answer to that to date
has been No."


~jwf~

The reaction of hydrogen to burn also requires oxygen yes.

But to get a full on detonation - much different there are plenty of online vids if you google - requires a premixed mixture of hydrogen and oxygen. And yes it needs to be of the right proportions. But the expalision limits of H2-O2 mixtures are pretty relaxed. If you ignite a balloon full of hydrogen it burns. If you ignite one with a mixture as above - kaboom!

Expalision???? Whut? Bloody autocorrect I didn't even know that was a word!

Explosion

Ah it's not. Just my usual klutz typing

Orcus: you aren't *quite* correct in your explanations above...however, it's Friday night and I've already spent 4hours doing pressure relief stuff so I'll leave it this time!

Conflagration and detonation are to do with wave front speeds and stuff like that.

Apologies if already mentioned but how about using a wind turbine to crack water into hydrogen to power your car?

Here is how hydrogen fuel cells actually work:

http://www.ballard.com/fuel-cell-applications/backup-power.aspx

As Ballard discovered they are great for stationary applications
but not so much for road transport.


~jwf~

What if it isn't windy? And what about wind direction? At what stage do the forces of the car travelling forward overcome any forces created by simply the movement of the wind?

And I don't think you could posit using the force of the car moving through the air to create the wind either...

>Orcus: you aren't *quite* correct in your explanations above...however, it's Friday night and I've already spent 4hours doing pressure relief stuff so I'll leave it this time!

Conflagration and detonation are to do with wave front speeds and stuff like that.<


I talk chemist, you talk engineer - such is life. I'm no explosions expert - that's just what I was taught at school and a little beyond.
I have seen what I described with balloons and a cattle prod up close an personal but I can see that there is a grey area somewhere between rapid burning and detonation that merges them into one phenomenon I suppose. This is probably a more important issue to those that need to know and I'm glad you know more about it than me