Grumman-581 wrote:
On Tue, 15 Aug 2006 16:40:11 GMT, Larry Dighera
wrote:
How does the energy density of LNG compare to ethanol?

It's less than gasoline, but I'm not sure how it compares to
ethanol... Do you mean LNG or LPG though?

Propane has an octane rating of 110 to 120... Sounds great, right?
Unfortunately, the weight of the tanks is what would probably get
us... Our tanks would have to be built quite a bit sturdier to handle
the increased pressure... Although typical operating pressures are
around 130 psi, tanks are typically rated to over 300 psi...

With LNG, you need either higher pressure or a cooling system...


LNG, as used in the Beech system (Beech Aircraft really did the
pioneering work on LNG, of course it went nowhere....) was stored at
very low temperature at approximately atmospheric pressure in a dewar
type insulated tank. It's important to understand that methane-natural
gas- is an incondensible gas for all intents and purposes, like oxygen
and nitrogen but unlike propane, nitrous oxide, carbon dioxide, ammonia
which can be stored at human-habitable ambient temperatures at
pressures feasible for storage tanks.

Methane and propane can be burned in an IC engine in similar fashion
once they are a gas, but at very different fuel-air mixtures. Methane
is approximately 108 octane and propane is in the 103-106 range
depending on exactly what's in it (LP motor fuel is nothing like
reagent grade and contains methane, butane, methanol, and lots of
other junk).

LNG would be practical but the cost of distribution would be high and
the fuel system is fairly complex, at least in the Beech system. CNG
has no range to speak of. LPG is very practical for all sort of ground
vehicles and has been done successfully in helicopters, but large
volume storage in fixed wing aircraft is problematic. A fixed wing
aircraft designed around a fuselage LP tank as a stressed member might
make some sense.