Any fuel has energy that can be dangerous if suddenly released.
Hydrogen has properties conducive to sudden energy release.
1. It is the smallest atom, most able to leak through the minutest passages.
2. In general it loves to react with other materials. It embrittles metals making pressure vessels easy to fracture.
3. It cannot be readily liquified, requiring very high pressure vessels (350 bars is over 5,000 psi).
4. It is the easiest gas to ignite - a little bit of static charge will do.
5. Hydrogen burns with a colorless almost invisible flame. By the time you notice a fire, it's already too late. The only nice thing about a hydrogen fire is that the product, water, is basically non-toxic, though everything else engulfed will give off toxic fumes.
Weather services used hydrogen for their weather balloons most of the 20th century using electrolyzers. Despite all the training and modern safety precautions taken, accidents still occured alarmingly often. As a result, most weather services have changed to using helium. Helium is a non-starter for fuel.
Basically, TJ, this is an engineering exercise. In fact, the people we talked to at Aston Martin used those exact words. As many commenters here have pointed out, hydrogen power isn't practical and it isn't new. Personally, I think the automakers are treating this as it should be treated -- as long-term research. Luckily, no state is trying to force the technology with passage of laws mandating that the auto companies build these vehicles.
Billvon, thanks for saying the same things that I stated in another blog today, except that your explanations werer a bit clearer, and I didn't mention the fire and explosions issues. Hydrogen is one of those things that seems like a good idea until you look at the implementation of it. Are we engineers the only ones who can see problems, or what?
My feeling is that it would be real interesting to know how the aston-martin race car places in the race.
Hello napelou, What if you could generate enough H2 "on-board" to satisfy the needs of a blended mixture; i.e. fuel and H2--whether that fuel is biogas, diesel, low lead, etc etc? Seems to me that would be a significant breakthrough and would possibly eliminate the need for fueling stations. (Other than gasoline.)
naperlou: If you remember just a few years back, SHELL OIL CO. sponsored print advertisements & other media ads showcasing their hydrogen dispensing kiosks in Finland. IF my memory serves me, they included a highly modified FORD vehicle in the ad also.
Hydrogen sounds like the ideal fuel. It's light, it can be used with fuel cells, the only reaction product is water, heck, most of the universe is made of hydrogen! And it just sounds very sexy.
But there are several things that make hydrogen a pretty poor fuel overall.
1) We don't have any. This is the big one. Very little exiats on Earth in molecular form (H2.) That means we have to make it, and that takes energy. Which means that hydrogen is not really a fuel - it is more like an energy carrier, a way to put energy into place A and extract it at place B.
2) It's hard to make. Electrolysis isn't very efficient; an electrolyzer that can hit 70% is a pretty good one. We can make it via thermal dissociation, but to do that we'd really need new nuclear reactor technologies (high temperature gas reactors to be specific.) And that's a ways out. We can break it down from natural gas, but that requires (you guessed it) natural gas.
3) It leaks like crazy. It leaks through materials that would otherwise be considered impervious, due to its very small molecular size. So you need to go to extremes in terms of pipe and tank wall thickness, seals, valves etc. And even then you will inevitably get leaks. Which leads to:
4) Danger of explosion. Natural gas (a flammable gas that most people are familiar) is explosive; if you mix it with air at ratios between 5 to 15%, it will explode when an igniton source is present. We're fortunate that it only explodes within this range, or else the gas pipes in your house would explode every time you had some plumbing work done and some air got into your gas lines. As long as MOST of the gas in the pipe is natural gas you are safe.
Hydrogen isn't like that. Its ignition energy is much lower and it will explode over a range of 4% to 75%. So it will explode over a range more than five times greater than natural gas, and the explosion will be easier to set off. Examples of industrial accidents where just a small amount of air got into a hydrogen tank - rsulting in a massive explosion - are common.
5) It's hard to store. Since it is so light you have to compress it a lot more - and more compression means a more expensive, more dangerous tank that gives you less range overall. You can also liquefy it, but due to its low liquefication temperature this takes a lot of energy.
Most of these problems can be solved by adding a carbon to the mix, so that intead of H2 molecules you have CH4 (methane) molecules. This results in a denser, easier to store, less leaky, less dangerous gas. It also has the benefit that we currently have a lot of this fuel (natural gas) and it can be made quite easily from animal wastes and garbage. Many farms power themselves from the methane collected from anaerobic digesters.
And if we ever do find a good source of hydrogen? Combine hydrogen and atmospheric CO2 to give us methane and water via the Sabatier reaction. We will have a carbon-neutral source of natural gas that will easy to store and use - and we already have a quite extensive infrastructure to store, transport and use it.
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