Why is Hydrogen so difficult to compress?

Question

I have read that the main problem with a hydrogen powered car is that the gas is very difficult to compress.

Another question I have is, if you were to have a hydrogen vehicle, and were to leave it hot temperatures, could the fuel storage tank explode? I ask because I thought maybe since the tank is already containing a really high pressure, the heat could cause the fuel to further expand and possibly shear the storage tank.

And last question, do vehicles using a hydrogen fuel cell or a hydrogen combustion engine both require a highly compressed supply of hydrogen? I'm a little confused with this hydrogen fuel cell idea.

I ask all this because I have to write a persuasive essay, and thought a good topic would be why Hydrogen Vehicles are not the future for motor vehicles. In my opinion it's just another attempt by the gas companies to divert attention away from a much more efficient fully electric car, which they could not continue making money on after purchase of the vehicle.

Answer 1

A Hydrogen gas is no more difficult to compress than any other gas

No the storage tanks would not explode. If you fired a bullet at it from close range it would bounce off

The tanks are made of carbon fiber which is virtually impervious to heat

Hydrogen tanks for cars come in 2 types 5,000 pounds per square inch  (PSI)

and 10,000 pounds per square inch (PSI)

A test was recently done

setting light to a petrol car and a hydrogen car

the petrol car had a 1/16th of an inch hole drilled into a fuel line

The Hydrogen car had to have 3 safety devices disabled to allow the testers to make the gas leak

Both cars were set on fire

The petrol car burned to a molten shell within minutes

The Hydrogen car vented off flames straight up in the air before another safety device shut the gas off

The temperature in the Hydro cars interior never went above 78 degrees Fahrenheit (warm room temperature)

Answer 2

That last answer was great.

btw: hydrogen can be produced using renewables, as well as from coal and other fossils... in the proposed new economy where hydrogen plays a significant role... where does the hydrogen come from?

Answer 3

Okay--good questions, BTW.

Hydrogen isn't any harder to compress than any other gas--but here's te problem: how much gas you have (by weight) in a given volume depends on the molecular weight.  Oxygen, for example, weighs about 1.4 kilograms per cubic meter at normal air pressure--it has an a molecular weight of 32.  But hydrogen is the lighetest element--the molecular weight of the H2 molecule is only 2--so, there's only 0.09 kg/m^3  So--to store  a lot of hydrogen--you need to compress it a lot more than other gases.  for instance--if your fuel tank wre one cubic meter ( a LOT bigger than todays gas tanks, at 30 times normal pressure (about 440 psi) you could store 42 kg of oxygen.  To get that much hydrogen, the pressure has to be about 7000 psi (500 times normal pressure)  

We can do that--but figuring out how to build a tank like that at a cost that people can afford is going to take years of research.  In addition--this goes to another of your questions--if the tank ruptures for any reason, that much pressure will make it explode--and when it does, it would be very likely to  ignite, reacting with atmospheric oxygen--making for an even bigger explosion.  And several times as powerful as a gas tank exploding in one of todays cars. So tanks for cars like this will also need to be very reliable--which makes the technological challenge even tougher.

We really don't need to worry about what would happen on a hot day.  The heat won't start a fire--and the expansion as the hydrogen heated would be no more than4-5 %--if they can figure out how to build the fuel tanks at all, making it that much stronger won't be a big deal.

The hydrogen fuel cells don't have to operate at high pressure, however (not anything like the tank has to have), and that we already can build, though they do need to be cheaper.  It's not likely that a car engine will burn the hydrogen directly.  The reason is that hydrogen burns at VERY high temperatures--the combustion chamber would be very difficult to build.  the fuel cells are just a lot easier.

A last point--why go to all this trouble?  The answer is this: although, besides being very "clean" hydrogen is very efficient, there's that low molecular weight.  The only way to store enough hydrogen for the car to have a decent range is to use those very high pressures.; even then, such cars will probably not have as much range as todays cars.