Left Coast Mogas (Ping! Jim Weir)

[Darrel Toepfer]

Gleaned from the CPA ATIS 8.24:

THE PRICE OF MOGAS IN CALIFORNIA. . .
I've been touring California for the past week and was amazed to find
Mogas in Modesto for $2.29/gal. I'm told it's the only place in
California you can get it.
Bill Whatley

[RST Engineering]

I saw that in the CPA letter last week and I just haven't had the time to
call Modesto to figure out how they get pure gasoline.

Jim


"Darrel Toepfer" > wrote in message
t...
> Gleaned from the CPA ATIS 8.24:

> Mogas in Modesto for $2.29/gal. I'm told it's the only place in
> California you can get it.
> Bill Whatley

[Robert M. Gary]

There seem to be few places in California where MOGAS is still legal.
Most of California requires additives to automotive gas that the FAA
explicity prohibits under any STC.

-Robert

[RST Engineering]

Mystery solved. Modesto gets its mogas (don't call it auto gas any more
says the distributor) from an outfit called Boyett Petroleum in Modesto.
Anybody can get it from the refineries over in the Bay area or from Reno, no
problem. It is just that it is illegal to use it in automobiles, but
perfectly legal in off road vehicles. All California highway vehicles are
restricted to a 5.5% gasahol mixture or diesel.

Repeat, ANY DISTRIBUTOR can get pure mogas from the refinery in 8000 gallon
lots if they want it in California. Now the problem seems to be convincing
a few airports to go through the hassle to get it in small quantities so
that it doesn't sit for six months and break down.

Jim




"Robert M. Gary" > wrote in message
ups.com...

> There seem to be few places in California where MOGAS is still legal.
> Most of California requires additives to automotive gas that the FAA
> explicity prohibits under any STC.

[Robert M. Gary]

I wonder if the small quantities will cause the price required to cover
the overhead of the tank, etc more than the price of the higher volume
100LL? When I had the Aeronca Chief (65hp cont) the engine ran MUCH
better on MOGAS than 100LL. The automotive detergents helped keep the
engine clean along with the hotter burning lower octane.

-Robert

[john smith]

Robert M. Gary wrote:
> I wonder if the small quantities will cause the price required to cover
> the overhead of the tank, etc more than the price of the higher volume
> 100LL? When I had the Aeronca Chief (65hp cont) the engine ran MUCH
> better on MOGAS than 100LL. The automotive detergents helped keep the
> engine clean along with the hotter burning lower octane.

What makes you think the lower octane burns hotter?
How does the difference in octane additive make the fuel burn hotter?

[[email protected]]

On Tue, 21 Jun 2005 02:35:08 GMT, john smith > wrote:

>Robert M. Gary wrote:
>> I wonder if the small quantities will cause the price required to cover
>> the overhead of the tank, etc more than the price of the higher volume
>> 100LL? When I had the Aeronca Chief (65hp cont) the engine ran MUCH
>> better on MOGAS than 100LL. The automotive detergents helped keep the
>> engine clean along with the hotter burning lower octane.
>
>What makes you think the lower octane burns hotter?
>How does the difference in octane additive make the fuel burn hotter?

Some people insist low octane fuel burns FASTER, which might put more
heat in the cyl - but I have seen info from fuel engineers
thatndisputes this theory.

[Cub Driver]

The Cubs at Hampton NH airfield were STC'ed for mogas when 80 octane
became unavailable. The general feeling was that the engines had a
tendency to stall in cold weather. (They certainly did have such a
tendency, whatever the cause.) Furthermore, the instructors didn't
like the smell of it (the instructor sits in the front seat of a Cub).

Hampton still sells mogas (at one point it was cheaper on the field
than at the gas stations all around) but the STCs have been removed
and the Cubs run on 100LL.


-- all the best, Dan Ford

email (put Cubdriver in subject line)

Warbird's Forum: www.warbirdforum.com
Piper Cub Forum: www.pipercubforum.com
the blog: www.danford.net
In Search of Lost Time: www.readingproust.com

[Allen]

> wrote in message
...
> On Tue, 21 Jun 2005 02:35:08 GMT, john smith > wrote:
>
>
> Some people insist low octane fuel burns FASTER, which might put more
> heat in the cyl - but I have seen info from fuel engineers
> thatndisputes this theory.

I was always told the higher octane burns faster, and is consumed in a
shorter duration, thus a lower temperature.

Allen

[Dave Butler]

wrote:

> Some people insist low octane fuel burns FASTER, which might put more
> heat in the cyl - but I have seen info from fuel engineers
> thatndisputes this theory.

Higher octane fuel is used to make the flame-front advance more slowly and
smoothly across the combustion chamber, thus eliminating "knock". The flame
starts at the spark plug and fans out from there. What you want is less of an
explosion, and more of a steady increase in pressure in the combustion chamber.
That's what higher octane does.

Disclaimer: not a professional in this field.

[George Patterson]

Allen wrote:
>
> I was always told the higher octane burns faster, and is consumed in a
> shorter duration, thus a lower temperature.

Other way 'round on the burn rate. From a motorcycle performance site -

"The higher the octane, the slower the speed of the burn; the lower the octane
the faster the burn. If the burn is too fast, uncontrolled combustion can
occur. This most often is heard as “pinging” and is commonly referred to as
detonation. This is because instead of burning through top dead center of the
combustion stroke, the entire charge is ignited too early and explodes in the
chamber and acts as a bomb. Conversely, if the speed of the burn is too slow,
it continues after the useful work can be done in the motor and manifests itself
as poor throttle response, reduced power output and increased emissions and fuel
consumption. An engineering fact: THE MOST HORSEPOWER IS MADE AT THE THRESHOLD
OF DETONATION. We have often gained horsepower on the dyno and felt improved
starting and driveability going from Premium grade gas to Regular. This change
was recently quantified in a customer’s Ducati M900 by reducing the cranking
time to start-up from 15 to 3 revolutions, although part of the improvement is
explained below."

George Patterson
Why do men's hearts beat faster, knees get weak, throats become dry,
and they think irrationally when a woman wears leather clothing?
Because she smells like a new truck.

[nrp]

I understand that octane is really a measure of the resistance to self
ignition in the pressure/temperature map. High temperatures or high
pressures will cause self ignition (actually this is detonation), but
octane gives us a way to measure the combinations of pressure and
temperature that also causes self ignition. It isn't measured directly
but instead octane is measured as an equivalent fuel mixture based
evaluation using an extra rugged variable compression ratio lab engine
under various conditions.

As the piston approaches TDC, the pressures and temperatures in the
cylinder rise due to adiabatic compression. If the
pressure-temperature combination ever reaches the limit supposedly
defined in the above map, the whole air-fuel charge detonates
violently. The ignition is not controlled by the magneto anymore as
the whole charge expolodes at once. With detonation, the turbulence
inside the cylinder is so violent that the combustion boundary layer
next to the cylinder head is scrubbed away, causing the cylinder head
to receive even more heat - which quickly leads to a runaway situation.

I doubt octane has anything to do with the rate of flame propagation
except that if detonation should occur, there really isn't a flame
front.

Pinging is different. With it there is charge ignition from
non-sparkplug sources that are usually the glowing (or at least extra
hot) embers inside the combustion chamber. These multiple ignition
sources cause the pressures to rise more rapidly than simply the spark
ignition, and things could deteriorate into detonation if it persists
long enough. With pinging there is still a flame front, although it is
from more sources so the pressures will rise more quickly.

It has taken a long time for me to understand the difference between
detonation and pinging. Detonation quickly wrecks engines and grossly
feeds on itself.

[John Galban]

nrp wrote:
>
> It has taken a long time for me to understand the difference between
> detonation and pinging. Detonation quickly wrecks engines and grossly
> feeds on itself.

Pinging is the knocking sound you hear when the air fuel mixture
ignites or explodes prematurely when the piston is still compressing
the mixture. I think the effect you describe as pinging is commonly
called pre-ignition. It differs from detonation in that there is an
alternate ignition source in the cylinder. Both pre-ignition and
detonation can cause an engine to ping or knock.

In an aircraft engine, detonation usually comes from using gasoline
with a lower than required octane rating (a.k.a. anti-knock index).
Pre-ignition is usually the results of cylinder contamination by bits
of carbon, or ash residue from using automotive type oils.

John Galban=====>N4BQ (PA28-180)

[Corky Scott]

On 21 Jun 2005 11:44:26 -0700, "nrp" > wrote:

>As the piston approaches TDC, the pressures and temperatures in the
>cylinder rise due to adiabatic compression. If the
>pressure-temperature combination ever reaches the limit supposedly
>defined in the above map, the whole air-fuel charge detonates
>violently. The ignition is not controlled by the magneto anymore as
>the whole charge expolodes at once. With detonation, the turbulence
>inside the cylinder is so violent that the combustion boundary layer
>next to the cylinder head is scrubbed away, causing the cylinder head
>to receive even more heat - which quickly leads to a runaway situation.
>
>I doubt octane has anything to do with the rate of flame propagation
>except that if detonation should occur, there really isn't a flame
>front.

>Pinging is different. With it there is charge ignition from
>non-sparkplug sources that are usually the glowing (or at least extra
>hot) embers inside the combustion chamber. These multiple ignition
>sources cause the pressures to rise more rapidly than simply the spark
>ignition, and things could deteriorate into detonation if it persists
>long enough. With pinging there is still a flame front, although it is
>from more sources so the pressures will rise more quickly.
>
>It has taken a long time for me to understand the difference between
>detonation and pinging. Detonation quickly wrecks engines and grossly
>feeds on itself.

Pinging, which is heard only in automobiles, not aircraft engines (too
noisy to hear it), is the sound of detonation. What's happening
inside the combustion chamber is that once the spark plug starts the
flame front, it spontaneously ignites in other areas (due to heat and
pressure) and the flame fronts collide together causing turbulence
which bangs off the combustion chamber walls and gives you that
"pinging" sound.

When the fuel/air mixture ignites as the piston is rising up, that is
something wholy different and FAR more dangerous than detonation.
That's called "Pre-ignition". Pre-ignition will destroy an engine in
a matter of a few seconds. Detonation results in overheating (and
eventual damage if not corrected) which is detectible and can be
countered.

Pre-ignition pulverizes pistons, turns them to pieces of their former
selves.

John Deakin did a series of hugely informative articles on engine
mixture and what happens inside the combustion chamber on AVWeb in the
columns section. The articles are all still there.

Corky Scott