Someone asked for the relative energies of natural gas compared to
Gasoline. What I've been able to gather is :
1 cu/ft NG=1028 BTU
1 gal Gasoline=125000 BTU
C. Smith

Those are "sit and burn" BTUs.

In actuality, the efficiency of gasoline as a motor fuel is very low,
while the efficiency of natural gas is very high.  Otherwise, a NG or
propane-fueled car would have pretty much no range or power.  There are
gas-powered Crown Vics in service as police cruisers!

Gasoline must be stable as a liquid, then rapidly broken down and
vaporized before it will burn, so most of a gallon of gas provides no
power.  Natural gas must simply be heated, and a far higher percentage
burns.

Keith W

Well there is still the high BTU per cubic foot of gasoline.
The tank needed for NG is also big and heavy.

Paul Lamar
-----------------------------------
Can't resist responding to this -- too much misinformation in Keith's
response.

1.    Nominally gasoline is 'octane' C8H18, although in practice it is a
wide variety of carbon containing species, including ring structures
(aromatics) and both shorter and longer chains than octane.  The energy is
derived from converting the C to CO2 and the H to H2O.  Carbon going to
carbon-dioxide is more energy rich than hydrogen going to water.

2.    Natural gas is nominaly CH4, although in fact it contains some 2,3
and
even 4 chain carbon atoms in small quantities. Less carbon = less energy /
mole.

Almost all Natural gas vehicles use compressed storage (CNG), not cryogenic
LNG.  The range of those Crown Vics IS reduced from a normal Crown Vic
running on gasoline, the reason that they can be used is that they are
FLEET
vehicles that can come back to a local site for refill. It requires a very
high pressure pump to fill them, they also have very little trunk space
left
after you put in the CNG tank

The EFFICIENCY of combustion in the (properly designed and tuned) engine is
almost identical between the two fuels.  The gasoline does need to
vaporize,
which cools the incoming air some, but the statement that gasoline is very
low efficiency and NG is very high is just not true.

The POWER of engines running on NG is reduced from that on gasoline, there
are large stationary engines that can be run either on diesel, or with
ignition systems on gasoline or natural gas. The NG units are derated from
the liquid fuel units.

The attraction of natural gas is not that it is more EFFICIENT, but that it
is somewhat more domestic, is less of a greenhouse producing fuel (it still
does have carbon in it).

Bill Schertz
KIS Cruiser #4045
N343BS

To clarify (or in other words, what I was trying to say) is that I was
comparing mass to mass.  A pound of NG (by mass) is pretty much a pound
of methane.  You burn it and you get a lot of power and a little soot
(and the soot of methane is mostly water vapor).  A pound of gasoline
(in liquid state) includes a lot of compounds which are not intended to
provide power, but are there to keep the volatiles from separating
before they are supposed to (thus to eliminate detonation), to reduce
soot, etc.

When you burn it in open air, the gasoline has the time to burn more of
the component chemicals, and does it so quickly that it usually can't
get enough air, burns poorly and that's when you see the black smoke
that they love when doing special effects.  The same gasoline burned in
the same open air, but in a regulated flow which is properly adjusted,
burns very cleanly with little smoke (example: Coleman lantern).  The
volatiles boil off and burn at the proper temperatures, consumed to a
far greater percentage than in a car engine.

In a car engine, everything is mixed together, trapped in a confined
space, and forced to burn within a few milliseconds.  This leaves a lot
of those compounds unburned, which is why you can smell gas engine
exhaust to a far greater level than the exhaust from a Coleman stove (to
be fair, Coleman fuel is also free of most of the non-volatile chemicals
necessary for motor fuel).  The amount of unburned and
partially-consumed chemicals is so great that we force the car's exhaust
through a superheated grid which breaks them down and burns them without
extracting any power, simply because the alternative is to dump them
into the environment as vapors.

Natural gas, however, is a single primary compound with trace amounts of
contaminants.  It will burn uniformly if it burns at all.  Thus, in an
engine, more of the fuel mass provides actual power.

When you show me something that only uses a small percentage of a lot of
stored energy -- then throws the rest away -- I call that "inefficient."
When you show me something that uses a high percentage of a little
stored energy, I call that "efficient," even if the total power is less
than the inefficient fuel.  An SR-71 was an incredible machine, but
would anyone claim it to be as fuel-efficient as a sailplane?

Efficiency has nothing to do with how much energy is in a fuel, but
instead with how much energy you can take out and put to work.

Keith W