Name: Johnny
Status: educator
Grade: 9-12
Location: MO
Country: N/A
Date: 12/21/2005
Question:
What is a reasonable guess to what it cost per mile to
operate a subcompact car on hydrogen?
Replies:
I do not think a satisfactory answer exists because it depends upon what
the inputs of the cost model is. For example: 1. At present there are few
(if any) processes/devices for producing hydrogen in large amounts
required at a cost that is even approximately equal to hydrocarbon fuels.
Is the cost per mile going to include the cost of reconfiguring the auto
engine and/or designing one. 3. There are only beginning to become
available systems to store adequate amounts of hydrogen on/in and
automobile -- the technology so far just is not there yet. At present
storing hydrogen as a liquid (theoretically the best way) is not feasible
because it boils at 20 kelvins (about -253 C.). This presents material
design problems since many metals absorb hydrogen and become brittle, and
of course insulation of the storage vessel would be a challenge as would
trying to store it at high pressure. 4. The combustion temperature of
hydrogen is very high. Assuming air is used as the oxidant, the nitrogen
which is carried along will no doubt produce NOx gases which would have to
be removed from the exhaust as it is today.
s
It is possible to look up the heats of combustion reactions of: 2 H2 +
O2 = 2 H2O and
2 C8H18 + 25 O2 = 16 CO2 + 18 H2O (C8H18 = octane, being a prototype
hydrocarbon in gasoline) and compare the heat produced on a weight basis of
fuel. However, that is not a valid comparison because all of the costs of
hydrogen fuel have to be input. It is the overall cost/benefit that matters.
Heat / unit mass of fuel is only one of the factors involved.
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