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In Reply to: RE: Toyota poised to unleash another revolution, just like the Prius was. posted by tinear on November 19, 2014 at 07:05:31
if we generate the hydrogen in situ (e.g., by electrolysis of water) in some sort of time/energy/cost-efficient manner.
that said...
I guess carrying a tankful of compressed hydrogen gas really isn't any scarier than carrying around 20 gallons of gasoline. I think there's a "Hindenburg effect" that makes folks like me a little extra-leery of hydrogen as a fuel (and probably irrationally so).
Energy density of the fuel is the bugear, methinks, for any alternatives to the good ol' fossil fueled internal combustion engine.
It's the big limiter for batteries (there's an absolute physical limit to how many watt-hours one can get from a battery per unit mass of the electrochemically-active species used).
I do wonder about the energy density of hydrogen (kcal per mole, or gram or gallon or whatever measure you prefer) vs. fuels like even gasoline (not to mention Diesel fuel, which packs a lot of available energy into a gallon of goop).
all the best,
mrh
Follow Ups:
The numbers I found were in Mega Joule per kilogram.Hydrogen 120MJ/kg
Gasoline 44.4MJ/kg
The numbers are effectively reversed if you use Joule per volume as liquid hydrogen is a lot less dense than gasoline.
Edits: 11/19/14
on a weight basis, there are a lot of moles of hydrogen and "all" of hydrogen is combustible, so to speak (i.e., H2 + 1/2(O2) --> H2O; "it all counts") but the physical density of H2 is low (unless extremely compressed/very cold). Gasoline has the good manners to be a liquid (albeit barely) at room temperature, with relatively high density.
I WAS indeed too lazy to look (as I confessed) :-P
all the best,
mrh
...but I think the energy per vol for H2 would be worse than even liq. H2. I read that in the Toyota, the H2 would be stored as a very high pressure gas (10,000 psi). Since only liq. He is colder than liq. H2, a liquid H2 fuel tank would be very expensive, and would probably be constantly venting H2 gas.
I think that I often do that after I sup on Mexican cuisine.
all the best,
mrh
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all the best,
mrh
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