Honda FCX Clarity 5.97 MPG!

On Mar 31, 6:31 pm, (M.A. Stewart) wrote:
> Jeff ) writes:
> > Justbob30 wrote:
> >> So, what is your source of this information? per Honda, it gets closer
> >> to the equivalent of 60 MPG with a range of 270 miles, are you sure your
> >> decimal point is not in the wrong place?
>
> >>http://automobiles.honda.com/fcx-cla...ll/comparison/
> >>http://automobiles.honda.com/fcx-cla...ked-questions/
>
> > I don't see where either say the vehicle gets 60 MPG. Rather, one graph
> > says it has 60% efficiency, which means 60% of the energy in the
> > hydrogen is converted to motion compared to about 20% in a gasoline engine.
>
> > In the NY Times article
> > (http://automobiles.honda.com/images/...s/NY_TIMES.pdf) it
> > does say that it gets the equivalent of 68 MPG, meaning that it goes 69
> > miles on amount of energy as there is in a gallon of gasoline.
>
> >> "M.A. Stewart" > wrote in message
> ...
> >>> Yikes... the Honda FCX Clarity (H2 fuel cell) gets 5.97 MPG (U.S. gallon)
> >>> on liquid H2 (or is it H?).
>
> >>> What does a U.S. gallon of hydrogen cost?
>
> >>> --
>
> I got the information from a Canadian magazine called 'Driven'.
> It's a glossy, overpriced, psuedo car magazine. The Mar. 2008
> edition on page 69 states a 171 litre fuel tank with a 435 kilometre
> range. That works out to 5.97 MPG (U.S.).
>
> 171 L = 45.178 U.S. Gal
>
> 435 Km = 269.7 miles
>
> Did the mag mess up?
>
> What's a gallon of H2 cost?
>
> --

i don't think they ever mentioned about liquid H2 (LH2) to be used in
the Clarity. In fact, storing and transfering LH2 is very dangeous.

I beleive that the car uses compressed gaseous H2 instead. But how
much pressure is needed to store enough H2 for a 270 miles trip?

So i did some calculations based on these premises:

1) the volume ratio, liquid H2 at boiling point to gaseous H2 at
normal temperature, is 1/848
http://www-safety.deas.harvard.edu/s....html#physical

2) the volumetric energy density of LH2 is one quarter of that of
gasoline
http://en.wikipedia.org/wiki/Liquid_hydrogen

3) a fuelcells-powered vehicle has three times the energy efficency of
that of a gasoline-powered vehicle.
http://automobiles.honda.com/fcx-cla...ll/comparison/

Now, let's say a gallon of gasoline gives a Honda Accord 35 miles,
then by energy content and engine's efficiency, a gallon of LH2 would
yield (35/4)x3 = 27 miles for a Honda Clarity
Then by volume ratio, i see that i would need 848 gallons of gaseous
H2 to go 27 miles on the Clarity
So to cover a distance of 270 miles, i would need a volume of 848 x
(270/27) = 8,480 gallons of gaseous H2 at standard atmospheric
pressure (1 atm)
Assuming a constant temperature, then by Avogadro's law, to compress
that volume to a fixed 45.2 gal container, a pressure of 8,480/45.2
= 187.6 atm = 2,748 psi is needed.

That looks like doable

Jeff > wrote in
news:Xy3Qj.6011$WU.1276@trndny08:

>
> Well you can. Take a gallon bottle of milk. Drink the milk. You are
> left with a gallon of air in the bottle.
>
How many moles is that?

>> Is 171 liters liquid or compressed gas...was it 171 liters of gas at
>> sea level?
>
> IIRC, it was 2500 PSI, which is about 130 times atmospheric pressure.
>
>> The Chemistry Guy
>
> The chemistry guy who knows that gases take up space and can be
> measured in gallons or litres (although that is useful unless you know
> the temperature and pressure - remember the ideal gas laws?).


As you said a 'gallon of <insert name of gaseous element>' is meaningless
without context.