Honda FCX Clarity 5.97 MPG!

(M.A. Stewart) wrote in

See, this is why that Mars lander crashed...got to get your units right.
Hydrogen is a gas. Your can't have a gallon of, um, gas.

Is 171 liters liquid or compressed gas...was it 171 liters of gas at sea
level?

The Chemistry Guy

 

Well you can. Take a gallon bottle of milk. Drink the milk. You are left
with a gallon of air in the bottle.

IIRC, it was 2500 PSI, which is about 130 times atmospheric pressure.

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?).

Jeff

 

Well you can. Take a gallon bottle of milk. Drink the milk. You are left
with a gallon of air in the bottle.

IIRC, it was 2500 PSI, which is about 130 times atmospheric pressure.

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?).

Jeff

 

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/services/hydrogen.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-clarity/fuel-cell/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

 

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/services/hydrogen.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-clarity/fuel-cell/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

 

How many moles is that?

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

 

How many moles is that?

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