Re: More on Top Tier gasoline
- From: jim <"sjedgingN0sp"@m@xxxxxxx>
- Date: Thu, 31 Jul 2008 11:31:22 -0500
"C. E. White" wrote:
"jim" <"sjedgingN0sp"@m@xxxxxxx> wrote in message news:1217464847_9@xxxxxxxx
....
Octane is a measurement of how hard it is to catch the fuel on fire,
not how much heat energy the fuel contains.
No it is a rating indicating how much the fuel theoretically has a
tendency to detonate. As a counter example to your claim, hydrogen
catches fire much easier than any gasoline component yet it has an
octane rating much higher than any gasoline component.
Actually hydrogen is not a good example to use. It has a high RON rating
(research method) and a low MON rating (motor method). In an Otto Cycle
engine hydrogen tends to pre-ignite and therefore acts like a low octane
gasoline.
Right that is a very definite issue with hydrogen but not an fatal
one. Pre-ignition is not the same thing as detonation altho it may
cause detonation.
Engines have been designed to deal with that. That means high
compression engines that take advantage of hydrogen's octane and are
very efficient compared to gasoline powered engines.
It is theoretical limit because there is no way to predict with
certainty how any particular blend of fuels will work in any
particular engine. Testing in an engine is still the method for
determining octane even though today they can determine the exact
molecular composition of the fuel.
If someone really want to know how their particular vehicle responds
to any particular gasoline you have to try it and see. It's true the
vast majority of vehicles will see only diminishing returns for octane
levels above what the manufacture recommends. But how much your engine
varies from the norm can only be determined by doing controlled tests.
And as I said before - how you drive will have an effect as well. Someone
who almost never drives at WOT is likely to see less of a difference than
someone who routinely drives hard.
Yes depending on what exactly the fuel is composed of. The current
octane rating system is not intended to help motorists with fuel
economy. It is intended to help the oil companies and auto mfgs. sell
there products.
The heat energy will be
about the same in all grades of gas. If ethanol is used as the octane
booster then 91 octane will have slightly less heat energy since
ethanol contains about 30% less heat energy than gasoline.
Even when no ethanol is present on average higher octane fuel contains
less energy than low octane. It is just in the nature of the gasoline
fractions that the ones that contribute the most to detonation (for
example heptane) also contain the most energy. But the energy content
is for all practical purposes irrelevant. If energy content was all
that was important for fuel economy then you would burn diesel in your
gas engine.
I was taught that higher octane gasoline had a lower energy content than
regular when I was in college - 30+ years ago. However since then I have
seen many credible sources saying this is not true.
From http://www.api.org/aboutoilgas/gasoline/gasoline-octane.cfm :
That looks more like a biased opinion not a credible source. The API
is doing a lot of bad mouthing of fuels that contain less heat content
but produce more useful output energy. If you are interested, the API
and SAE do publish figures on heating values for the various classes
of components in gasoline. So you can look at the raw data and judge
for yourself rather than reading the spin they put on that data.
"Gasoline with a higher heating value (energy content) provides better fuel
economy. Traditionally, premium gasoline has had a slightly higher heating
value than regular, and, thus, provides slightly better fuel economy, but it
is difficult to detect in normal driving. There can be even larger
differences in heating value between batches of gasoline from the same
refinery, between summer and winter volatility classes, or between brands of
gasoline from different refineries because of compositional differences. The
differences are small and there is no practical way for the consumer to
identify gasoline with a higher-than-average heating value."
When they say traditional they mean 50 years ago when the world was
awash in high quality sweet crude oil and large amounts of lead were
used for boosting octane. The reality is octane is achieved in much
different way today and if you look at the class of components that go
into premium compared to what goes into regular from many refineries
the components with higher octane tend to also have less energy. That
doesn't mean it isn't possible to create blends where regular has the
same heat content as premium - it just isn't the current reality.
But the heat content really has nothing to do with fuel economy. Put
some diesel in your gasoline engine and see how much that extra heat
content helps your mileage.
The point I'm making is not that premium is cost effective, but that
you really don't know how any particular engine will respond without
trying it - there are just too many variables for sweeping predictions
to be valid. And this is more true today than in the past because of
the changes engine management systems and changes in fuel. Not because
premium is better but because regular in many places is worse than it
was in the past.
-jim
Other interesting references:http://www.sciam.com/article.cfm?id=fact-or-fiction-premium-g
http://www.consumerenergycenter.org/transportation/consumer_tips/regular_vs_premium.html
http://ask.cars.com/2007/07/premium-gasolin.html
http://www.cartalk.com/content/features/premium/myths.html
http://www.caranddriver.com/reviews/hot_lists/high_performance/features_classic_cars/regular_or_premium_feature+t-test_results+page-2.html
or http://tinyurl.com/6pwz27
It is my opinion that if your car was designed to run on regular, running
premium is a waste of money. Although the engine may be able to adjust some
parameters to increase performance and fuel economy, the changes will be
minor. On the other hand, if your car was designed to run on premium
(because of turbocharging/supercharging, a higher compression ratio, or
other inherent design factors) then running regular may drastically effect
your performance and fuel economy even if the PCM can adjust parameters to
protect the engine from excessive pre-ignition.
Regards,
Ed White
----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= - Total Privacy via Encryption =---
.
- Prev by Date: Re: Galvanized conduit or iron pipe from the plumbing section as a breaker bar extender?
- Previous by thread: Galvanized conduit or iron pipe from the plumbing section as a breaker bar extender?
- Index(es):
Relevant Pages
|
