AVGAS

[Garfield Willis]

On Thu, 08 Jun 2000 10:35:37 -0400, Joe Curran <espace at MIT.EDU> wrote:

>AVGAS is leaded, 106 octane, and a bit expensive. Being leaded, it is
>also bad for you and everyone else.

Oh goodie, something I know something about (well, somewhat).

Just to toss in another mite (why not, when can you have *too* much
info? :), the reason why the most common Avgas (100LL - blue in color)
is actually 106+octane, is that there are two different octane rating
systems, RON and MON, and aviation still uses the older MON system,
hence it's rated at 100 octane MON, and around 106-110 if measured using
the RON system. The other less easily found highly-leaded Av fuel, the
so-called 100/130 (red in color), also bears a MON rating of 100 like
the 100LL, but is a significantly different formulation of the lead
carrier (more about this below).

[Actually, I guess to be squeeky precise, Mogas is rated using a
composite of RON & MON, whereas Avgas is still rated in straight MONs]

So WHY you say does it say "100/130"? What's the second number for?
Well, the ASTM suggested pilots would be less confused and less liable
to erroneous refueling, if just the first number was used, so when the
100 octane stuff was reformulated (sposedly to reduce the lead some,
hence the nomenclature "low lead" for 100LL, which of course still has
tons of lead in it), they dropped the second rating number, and just
went to "100LL".

OK, so you're still tapping yer feet, and wondering, WHAT IS that second
number? Here's a quote from an aviation book close at hand: "Take for
example 100/130. The first number (100) is the minimum antiknock rating
of the fuel in the lean mixture (remember, pilots lean to slightly rich
of peak EGT when cruising, for max economy); the last number (130) is
the minimum antiknock rating in the full-rich mixture (the mix setting
used by pilots during TO & climbout, for max power).

And here's the full spread of fuels and colors available at airports:

Grade		Color

80/87		Red
100LL		Blue
100/130	Green
115/145	Purple (getting scarce these days; only found at larger fields)

OK, but most of this crap is Av related, you say; why would an
automotive/racing bloak care? One lil tidbit I can pass along of
potential interest, is that it's a notorious commonplace in Av circles,
that the 100LL is far more prone to lead-fouling and lead-promoted
corrosion than the older 100/130 it replaced. I would think this would
recommend the 100/130 over the 100LL for auto racing fuel mixing, IF you
can get it.

Just a nit perhaps, but an interesting one.

Oh and yes Paul, all of the leaded racing fuels are contaminants for O2
sensors. The longevity of a WB O2 sensor in leaded environment is a
highly disputed figure; a vendor may say "20hrs", if they're tryna cover
their warrantee butts like Horiba does, or they'll say "possibly upwards
of a couple hundred hours, depending on installation position of the
sensor", if they're trying to sell their WOT WB O2 option into the
racing marketplace. Heh, my my how the specs change depending on your
prespective, eh?

Guys have actually been using O2 sensors in experimental aircraft for
some time now (and running 100LL), and one fellow in our own group
reported last year that by carefully selecting a mounting place for the
O2 sensor shielded somewhat from the direct exh blast (in this guy's
case, in a cross-over pipe, but you get the idea), he's had them last
for MANY hundreds of hours. YMMV.

Gar


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