Chris Cosman wrote:

My question is, since diesel fuel is heavier than gas is the HP/pound of fuel
still about the same?

The HP/lb depends not only on the fuel, but also on the engine.  Recall thast
engine's can be rated by the BSFC.  That's HP / lb / hour.

If you want to talk about energy available per pound, that would be Btu/lb.
Gasoline and diesel are roughly equivalent on a Btu/lb basis (both in the range
of 18,000-19,000 Btu/lb), but since diesel is denser, diesel has more Btu/gal
(128,400) than gasoline (115,000).  See:

http://afdc.nrel.gov/pdfs/fueltable.pdf

It's also easy to see that adding oxygenates (ethanol, methanol, or MTBE) lowers
the energy per gallon of gasoline.  Less energy per gallon equals more gallons
per hour for the same HP in a given engine.  Yet another reason to avoid alcohol
when using mogas to fly.

Now if we could just find a safe way to carry pure hydrogen...  :-)

Russell Kent

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