Scott,
1) Does AVgas and MOgas have the same energy potential and weight?
For all practical purposes, "Yep" and "Yep".
I know diesel fuel has more potential energy but also
weighs more and
needs to be considered in the calculations.
6.1 lb/gal and 19,500 BTU/LB for Diesel, 6.05 lb/gal and
20,380 BTU/LB for
Gasoline (average values)
2) Could you explain to a slow learner {:>) exactly what
the octane rating
means. Not how to calculate it but what the fuel does.
(i.e. compare 100
octane to 50 octane)
Long story but higher octane means the fuel has a greater
resistance to
ignition. It's actually HARDER to ignite which lets us
advance timing, run
higher compression and other fun things that increases overall engine
efficiency. Higher octane numbers have NOTHING to do with the energy
content. Fortunately for the gas station owners, most folks
don't believe
that and run the higher priced gas thinking they are doing
good things for
their car.
3) When comparing AVgas motors to MOgas engines, do we need
to compensate
for weight or octane?
Nope. Just can't tune them the same. Higher octane will
let you TUNE the
engine for higher HP (within limits). Feeding high octane
fuel to a "low"
performance engine (your basic car engine) doesn't hurt a
thing but gives
you NO advantages, just higher cost and slightly increased
maintenance
(plugs and sensors).
Feeding low octane fuel to a highly "strung" engine (race car, high
performance aircraft engines, etc) and the engine will
eventually self
destruct from detonation.
And Paul is absolutely correct in that O2 sensors usually
die quickly if
they see ANY lead.
Also keep in mind that 100LL (Low Lead) has a VERY high lead
content. The
LL description is a hold over from when it was compared to
110 octane and
other aviation fuels seldom seen any more.
Steve Webre
Broussard, LA
Actually Steve, many modern cars will have more power with premium fuel,
latest autoweek quoted a Honda engineer as saying that the new
accord V6,
while not requiring premium fuel would gain 10HP using it.
Also, the Oz sensors don't seem to die quickly at all using
100LL, according
to Tracey and others on the list.
Other than that I totally agree with you.
Hans
Depending on how you look at it, Hans and Steve's arguments are either
identical but looking from different directions, or apples and oranges.
Higher octane fuel in an engine that's not computer controlled will keep
the knocking away...and allow a higher-compression engine designed to
squeeze a bit more power from the fuel to do that without destroying itself.
Slower burning fuel (higher octane) provides a slower, more controlled
'burn' and a smooth(er) pressure increase that's properly timed. The charge
is less likely to ignite from a hot (but non-firing) sparkplug, or from
carbon deposits in the combustion chamber.
Computer control in a lower compression engine will allow the computer to
continually adjust the timing to get the most energy out of the gas. The
Bosch system in my gas VW would retard the timing for low-octane fuel (with
decreased economy and power) and advance the timing until the knock sensor
stated reporting noises, then retard the timing a bit until things ran
smoothly...increased power and economy and no detonation.
I've heard that modern cars can benefit from some lower grade fuel now
and again - gives the computer a chance to reset it's 'custom'
injection/ignition map... It's amazing how much better my '88 Jetta would
run after a 'lobotomy'...had some slowly-dying sensors filling the ECU's
memory with doo-doo (yeah, a technical term).
FWIW
Andy Hecker
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