Re: air - fuel ratio

> >
> >        If you read your engine textbook you will find that the RON
rating is
> > made under light load conditions just as you describe. You are correct
to
> No it is not. Apparently you do not know under what conditions the
> octane ratings are obtained. Contrary to what you said both the Motor
> method and Research method are obtained at WOT. Do I really need to list
> the specifics of methods used?


WOT? It's a test engine there is no throttle adjustment per se. The
engine runs at 600 RPM. Does that sound like WOT? The engine load
conditions are described as light (according to ASTM) as a result 
it yields a  different (higher) octane number than the
MON test which is not a light load test (again according to ASTM). 
	And by the way the test engines that are still used today
were designed something like 80 years ago - so exactly how much does an 
80 year old push rod and carb engine tell you about how a modern 
engine will perform with respect to fuel economy. Oh that's right your 
textbook says it doesn't have anything to do with fuel economy . Well DUH!

        The point is motorists don't know what the RON octane number 
is for the fuel in their gas tanks. Or more to the point they don't what
the octane number is that could be useful when driving for fuel economy,
Thus if
you change pumps in the interest of getting better fuel economy you have
no idea
if you are really increasing or decreasing the knock characteristics of
the fuel 
at light load conditions. 



> 
> > The fuels properties to knock under light loads is exactly what the
> > RON test determines. Engines do knock under light loads even if you
think
> > they don't ( and even if you can't hear it) and that does impact on
gas
> > mileage.
> Interesting assertion here. Please provide a source for this. In my 30
> years of engine testing this is a new "fact" for me. And in much of my
> testing, I have acquired and viewed the in-cylinder pressure data and
> have not seen this.


 

 The RON test is done under light load. It does indeed detect knock under
those
conditions. How can you  claim an engine can't knock under
light load? The test protocol is all well do***ented. 
What isn't do***ented is the results of that part of the test that would 
actually be useful for increasing fuel economy.


> 
> >
> >       The problem is you don't have any idea what the RON rating is
for the
> > fuel in your gas tank and it can vary quite a lot for any given posted
> > pump octane rating. But in spite of the fact that you have no idea
what
> > the octane is in your gas tank under those conditions that could
> > potentially be giving you better mileage, you are positive it has no
> > affect on mileage cause you read something in a book.

> This is absurd.

What specifically is absurd? Are you saying it's absurd that I said you
read a book?

It's not absurd to say that you don't know how octane interacts with fuel
mileage in your own car. You have made it clear that for the specific
types of driving conditions that would lead to fuel economy you don't know
what the specific octane characteristics are of the fuel in your car's
tank. Sure, you may know what the octane characteristics of the fuel are
when you punch it to pass some guy who is going 65, but that has nothing 
to do with good fuel economy.

You dismiss textbook information that has been verified 
over and over just because it doesn't fit your pet theory.

What have I dismissed in textbooks? As far as I know they are pretty
silent on
the issue. The octane ratings are designed to benefit auto manufacturers
so they
can build cars that don't get harmed by the fuel. The octane rating system
as it
is now in North America makes it close to impossible for motorists to use
the
displayed octane numbers as a guide to purchasing for fuel economy. But
that
doesn't mean it has to be that way or that it always will be that way. 

-jim


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