Don Stauffer in Minnesota wrote:
>
> On May 6, 4:51 pm, jim <".sjedgingN0sp"@[EMAIL PROTECTED]
> wrote:
>
> >
> > But octane is far more im****tant to fuel economy and performance. That
is
> > more im****tant to how much energy goes to the wheels.
> >
>
> Not true. Thermal efficiency aids BOTH performance and fuel economy.
> A higher CR without detonation will provide more power without any
> increase in fuel flow rate.
Not sure exactly why you are disagreeing with my statement. I agree that
thermal efficiency is the issue. HOWEVER, I think CR is only one element
of many in the equation. But you do seem to at least grasp that octane
does play a role. That role is going to be much more apparent as price of
fuel continues to climb.
If you look at the big picture refining higher octane base blend motor
gasoline requires more barrels of crude to produce. In addition, as it
happens each of those gallons of that higher octane fuel contains slightly
less energy. So high octane base blend gasoline by its very nature is
energy inefficient even before you get it to the engine. But the calculus
is complicated. Gaining 5% energy efficiency inside the engine at a loss
of 10% of the energy from the source crude is not really a winning thermal
efficiency equation and it is going to inevitably cost you more.
The point is these cost benefit calculations are already being made, but
they are not being made with thermal efficiency in mind. That is, the
tradeoffs are being calculated but the goal is to maximize the oil
industry and government's interests. Unfortunately, that often works
directly against thermal efficiency.
>
> If we had higher octane fuels without serious environmental
> consequences, we could have better fuel milage. The higher CR that
> modern fuels allow is one reason fuel milage is better on a ton-mile
> per gallon basis than it was pre-WW2.
Where did you come up with that? It is my observation that 1940 cars were
pretty heavy and quite fuel efficient compared to cars in the 50's of the
same weight. Not that anyone cared in the 50's about fuel efficiency, but
fuel efficiency was an issue before WW2 so cars were designed to be more
fuel efficient. It wasn't until the early 70"s that anyone much cared
about fuel efficiency. Increased Fuel efficiency in the late 70's and
eighties was mostly achieved by shedding weight.
-jim
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