Fuel prices--BTU's per gal.

I think it was 1995, at Oshkosh, I attended a forum on the differences
between auto fuel and avgas. It was presented by a fellow who owned
and operated one of the few refinerys which produce avgas.

IIRC, a refinery turns crude oil into different hydro-carbons. They
are all solvents, and all support combustion. They are ranked from
light to heavy, based on how many hydrogen atoms there are per each
carbon atom. Butane has two hydrogen, and octane has eight. The
heaviest is asphalt, which is the goo left after all lighter fuels are
driven off, has the most energy per lb, but is the most difficult to
ignite.

Auto fuel is a blend which includes the asphalt, as well as butane in
the winter. Avgas has only three components, which do not include
those at either end of the spectrum (ashalt and butane). So avgas
does not leave the residue that old auto fuel will, nor does the
engine start as easily, nor does it produce as much power.
Because the avgas does not have the lighter components, it does not
vapor lock as readily either.

The octane rating compares the tendency of an engine to knock, based
on the speed of the flamespread. Higher octane ratings mean only that
the fuel burns more slowly, as if lead were added. It does not mean
that the fuel has more power, only that engines can have a higher
compression ratio without knock, so the engine can utilize more of the
energy in the fuel. The lowest octane rating, that will not knock,
makes the most power.

If that fellow gives his talk again, you will certainly enjoy the
hour.

George wrote:
I think it was 1995, at Oshkosh, I attended a forum on the differences
between auto fuel and avgas. It was presented by a fellow who owned
and operated one of the few refinerys which produce avgas.

IIRC, a refinery turns crude oil into different hydro-carbons. They
are all solvents, and all support combustion. They are ranked from
light to heavy, based on how many hydrogen atoms there are per each
carbon atom. Butane has two hydrogen, and octane has eight. The
heaviest is asphalt, which is the goo left after all lighter fuels are
driven off, has the most energy per lb, but is the most difficult to
ignite.

It isn't the number of hydrogen atoms per carbon atom. It is the number
of carbon atoms fundamentally as the number of hydrogen atoms is defined
by the bond structure. Octane has 8 carbon atoms, but only 18 hydrogen
atoms which isn't even close to an 8 to 1 ratio.


Auto fuel is a blend which includes the asphalt, as well as butane in
the winter. Avgas has only three components, which do not include
those at either end of the spectrum (ashalt and butane). So avgas
does not leave the residue that old auto fuel will, nor does the
engine start as easily, nor does it produce as much power.
Because the avgas does not have the lighter components, it does not
vapor lock as readily either.

The octane rating compares the tendency of an engine to knock, based
on the speed of the flamespread. Higher octane ratings mean only that
the fuel burns more slowly, as if lead were added. It does not mean
that the fuel has more power, only that engines can have a higher
compression ratio without knock, so the engine can utilize more of the
energy in the fuel. The lowest octane rating, that will not knock,
makes the most power.

And burn speed is not related to octane rating.

Two fundamental errors from the "expert", eh? Makes me question just
how expert he really is.

Matt

On May 29, 8:55 pm, Matt Whiting wrote:
George wrote:
I think it was 1995, at Oshkosh, I attended a forum on the differences
between auto fuel and avgas. It was presented by a fellow who owned
and operated one of the few refinerys which produce avgas.

IIRC,

snip makes the most power.

And burn speed is not related to octane rating.

Two fundamental errors from the "expert", eh? Makes me question just
how expert he really is.

Matt


OK Matt, Which "expert" are you trying to insult?

The author who went to a one hour forum about twelve years ago, or the
poor guy who gives a talk at Oshkosh, which may or may not be
remembered accurately by anybody twelve years later ?

Personally, I am glad that you know how many carbon atoms are in
octane, but if you do know so much, why not share it without insult?
We don't have enough space for me to list all the data I've forgotten
these last 12 years or so, even if I could.

George wrote:
On May 29, 8:55 pm, Matt Whiting wrote:
George wrote:
I think it was 1995, at Oshkosh, I attended a forum on the differences
between auto fuel and avgas. It was presented by a fellow who owned
and operated one of the few refinerys which produce avgas.
IIRC,

snip makes the most power.
And burn speed is not related to octane rating.

Two fundamental errors from the "expert", eh? Makes me question just
how expert he really is.

Matt


OK Matt, Which "expert" are you trying to insult?

Neither. I was simply stating a fact that I don't trust an expert that
gets two fundamental things that wrong.


The author who went to a one hour forum about twelve years ago, or the
poor guy who gives a talk at Oshkosh, which may or may not be
remembered accurately by anybody twelve years later ?

Personally, I am glad that you know how many carbon atoms are in
octane, but if you do know so much, why not share it without insult?

There was no insult.

Matt