High Octane Fuel - Do you need the "Good" stuff?
|
|
Author:
Swami |
Publishing date: 07.11.2002 07:35 |
| The swami has been hearing a lot of nonsense around the gas
pumps these days. People are tanking up with the "good" stuff
because the commercials imply that it's better for their engine.
When the oil companies use superlatives like "Super", "Extra"
and "High"...well it must be better, right? And of course they
wouldn't be charging $0.10 - $0.20 more unless they were putting
some really good stuff in there, right? Sorry...
|
The swami has been hearing a lot of nonsense around the gas
pumps these days. People are tanking up with the "good" stuff
because the commercials imply that it's better for their engine.
When the oil companies use superlatives like "Super", "Extra"
and "High"...well it must be better, right? And of course they
wouldn't be charging $0.10 - $0.20 more unless they were putting
some really good stuff in there, right? Sorry...
"High Octane" is not synonymous with "good" or "better", and
does not mean that it is better for your engine! And the chances
are pretty good you don’t need high octane fuel in your scooter.
High-octane fuels only become necessary when your engine has a
high compression ratio. It’s a very long and complicated
story…that the swami will make short.
First important fact that you must accept:
All gasoline, regardless of its’ octane rating, have pretty much
the same amount of energy per gallon. What!!! "Sacrilege" you
say? Well, actually, some higher-octane fuels have a few LESS
percent energy per gallon…so as not to argue over this small
point, for the sake of this discussion we will all agree that
the automotive gasoline that you buy at the pump, regardless of
octane rating, has the same amount of potential energy.
Second important fact that you must accept:
Octane is NOT a measure of power but of the fuels’ resistance to
ignition from heat. A higher-octane fuel also, under identical
combustion chamber conditions, will burn slower.
How can this be? If all of the above is true, how do we get more
power out of high octane gasoline? We do, don’t we?
Well…yes we do. Here’s how:
But first you must understand "heat of compression". There is a
2,000 year old fire starting device that still amazes the swami.
A length of bamboo was hollowed out leaving one end capped. A
stick, about the same length as the bamboo, was whittled down
until it fit snugly into the bamboo cylinder. A bit of dried
grass or wood shavings were placed in the bottom of the bamboo
cylinder and the snugly fitting stick was violently rammed down
the bamboo tube. The heat generated from rapidly compressing the
air in the tube was sufficient to ignite the tinder.
The same thing can happen in the cylinder of an engine. The
piston, quickly squeezing the fuel/air mixture into a small
space, can generate enough heat of compression to ignite the
fuel well before the spark plug fires, with unpleasant results.
If the fuel prematurely ignites while the piston is on its’ way
up, the burning of the fuel, in conjunction with the rising
piston, creates even more pressure, resulting in a violent
explosion. This explosion is equivalent to hitting the top of
the piston with a very large hammer. If you want to be able to
see through the top of your piston, ignore those sounds that are
usually called: "pre-ignition", "ping" or "engine knock". Trust
me on this one; in his reckless youth, using this method, the
swami turned a few pistons into paper weights.
What we really want is a very rapid burn of the fuel, not an
explosion. And we want the burning of the fuel to take place
while the piston is in a better position to convert this
pressure into productive work, like on its’ way down. Think of
this burning as a very fast "push" on the top of the piston.
Despite the violent noises you hear from some exhaust systems,
it really is a rapid push on the top of the piston making the
crankshaft go around, not explosions.
So that we can ignite the fuel at exactly the right time with
the spark plug, instead of from the heat of compression, they
put stuff into gasoline to keep it from igniting prematurely.
The more resistant the fuel is to ignition from the heat of
compression, the higher its’ octane rating.
Are you with me so far?
Higher compression ratios = higher combustion chamber pressures
= higher heat… and it is with these higher combustion chamber
temperatures that the magic happens.
At higher temperatures the fuel is burned more efficiently. So,
while it’s true that the higher-octane fuel does not posses any
more energy than low octane fuel, the increased octane allows
the extraction of more of the potential energy that has always
been there. Conversely, lower compression ration engines utilize
a little less of the fuel energy potential (2-4% reduction) but
there is also less heat generated in the combustion process.
So how do you know if you need high-octane fuel? The swami
suggests you look in the owners’ manual! Manufacturers really do
want you to get the maximum efficiency out of your engine. They
do their best to give a good balance between horsepower and
engine life. It’s in their best interests to do so.
There is ABSOLUTELY NO BENEFIT to using a higher octane than
your engine needs. The only benefit is increased profits to the
oil companies that have cleverly convinced some of the public
that their new "Super-Duper, Premium-High-Test, Clean-Burning,
Used-By-Famous-Racing-Types-All-Around-The-World,
Extra-Detergent-Laden-Keep-Your-Pipes-Clean, Extra-High-Octane"
fuel is your engines’ best friend. The swami is telling you the
truth, don’t listen to that talking cartoon car.
The swami hears people insisting that they got better mileage,
better acceleration, and less dental plaque by switching to a
high-octane fuel. The swami reminds these people that in every
pharmacy is a special miracle pill that is often prescribed by
doctors, it works wonders because people believe that it works
wonders; it’s called a "placebo". The swami warns: never confuse
faith with physics!
If you are getting pinging or knocking with what should be the
correct octane for your engine, start by checking the ignition
timing, also check that the spark plug is the correct heat
range. For 2-strokes, check for excessive carbon build-up on the
top of the piston, the carbon takes up space and increases the
compression ratio.
If all is well and correct, and you still are getting knocking,
then try the next higher octane. You won’t go faster, you won’t
go farther, but you will prevent an unsightly hole in your
piston.
This subject is a whole lot more complicated than the swami
wants to bother with. If you are curious to know more, put some
of these words into your search engine and enjoy the education:
Antiknock Index
Octane
Stoichiometric Combustion
Thermal Efficiency
Flame Front
Highest Useful Compression Ratio
Compression Ratio
Placebo |
External Source
Source Name: Scooter Swami
Source URL:
http://www.bajajusa.com/octane_text.htm
|
