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Standard Unleaded vs Premium Unleaded 

 

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 Post subject: Re: Standard Unleaded vs Premium Unleaded
Posted: Wed Sep 08, 2010 2:07 pm 
Getting Side Ways
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Age: 26

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Joined: 4th Sep 2009

Ride: 92 EB s

Location: DORRIGO
NSW, Australia

Well in my experiances with the falcon.
E10. Put 20bucks in to try it. I got home and to school the next day. 30ks. And it was gone. Plus the terrible idle and hard starts.

91ron. Regular. At mobles and bp.rough idle. Poor economy.

Pulp at bp and moble is way to expencive for what it is.

Im a shell man now. 91 is cheaper then bp, 95 seems to run my car as well as the bp 98 but with better economy and cheaper. And v-power is simply the bomb.
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 Post subject: Re: Standard Unleaded vs Premium Unleaded
Posted: Wed Sep 08, 2010 4:56 pm 
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VIC, Australia

BP Ultimate or Caltex 98 for me.
It depends largely on what area/state you live in as to fuel quality between servos

 

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 Post subject: Re: Standard Unleaded vs Premium Unleaded
Posted: Wed Sep 08, 2010 4:58 pm 
Parts Gopher
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Location: Morisset
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Steady ED wrote:
BP Ultimate or Caltex 98 for me.
It depends largely on what area/state you live in as to fuel quality between servos


ditto for me!

 

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 Post subject: Re: Standard Unleaded vs Premium Unleaded
Posted: Wed Sep 08, 2010 11:28 pm 
Stock as a Rock
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Ride: 1995 EF Futura, 1971 ZD Fairlane

Location: Morisset
NSW, Australia

vortex 98, mobil premium 98, or bp ultimate, shell v power i got 650 out of a tank, ran normal unleaded the other week, had no choice E10 s**t EVERYWHERE!! and i got 530, for the sake of like 5 bucks extra a tank your actually saving money because thats like 100kms more to a tank your getting running premium which is what about 10bucks worth of fuel roughly. depends where you get it though ive had s**t batches of premo at times.

 

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 Post subject: Re: Standard Unleaded vs Premium Unleaded
Posted: Thu Sep 09, 2010 2:26 am 
Getting Side Ways
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my old NC fairlane ran well on E10
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 Post subject: Re: Standard Unleaded vs Premium Unleaded
Posted: Sun Sep 12, 2010 11:45 am 
Getting Side Ways
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Location: Hamilton
New Zealand

paul09 wrote:
I'm a chem engineering student and have been told by a few lecturers, in a car which is not tuned for 98ron (ie e-series falcons) performance difference will be minimal, however there should be a small economy improvement, BUT they recommended running a full tank of premium just once a year because of the extra cleansing properties...they said there's no need to run it all year in a car which is designed for regular..


As for e10.... I work at a shell servo part time and am a chemical engineering uni student full time...and I'm against E10, it is both less economical AND makes negligible difference to the emissions...it's just a government ploy to appear as if they're doing something about the environment...

So here's the chemistry approach, for fuel economy:

Combustion of Ethanol:
C2H5OH + 6*(O2) ---> 3*(H2O) + 2*(CO2), this reaction produces 1368kJ per mole of ethanol heat energy.
1mole of ethanol is ~46grams. So Ethanol produces 29.74kJ heat per gram.

Normal petrol is a mixture of hydrocarbons ranging from 5-carbon chains to 12-carbon so we'll take an average of 8, octane.

Combustion of Octane:
2*(C8H18) + 25*(O2) ---> 18*(H2O) + 16*(CO2), this reaction produces 5430kJ per mole octane.
1mole of octane is ~114g. So octane produces 47.63kJ heat per gram.

You can see that octane produces a lot more energy per gram than ethanol...



You have some of the basics right but forgot some others, namely density (this has a partial correcting factor on mass [& therefore energy] delivery of ethanol based fuels because fuel is added on a volume basis rather than a weight basis) and charge cooling (ethanol has a much greater heat of vaporisation than petrol, so it has a much greater cooling effect in the combustion chamber which reduces the tendency for pre-ignition [anti-work]). But the whole situation can be boiled down to 2 descriptions.

1. Octane rating is a measurement of the fuels ability to resist detonation. There are 3 octane scales, RON (what we use in NZ/AUS, somewhat meaningless except in the laboratory), MON (this actually reflects real-world driving under load) & (RON+MON)/2 (what the Yanks use). Now higher octane fuels burn rate is slower than lower octane fuels, and peak engine output relies on getting the correct spark lead time to maximise combustion chamber pressure just after TDC. So if the spark timing isn't changed to reflect the different fuels burn speed, the peak cylinder pressure will occur (for higher octane fuels) later in the combustion cycle & less work will be extracted from the fuel. So the highest power output from an engine will be obtained by using the lowest octane fuel possile that still allows for optimum spark advance. For a normally aspirated SBF this is typically around 34°BTDC at WOT. Changes to engine configuration (eg compression ratio, volumetric efficiency, EGR, operating temperature, combustion chamber and piston crown design etc) effect the ability for that engine to acheive optimum spark advance with a given fuel's octane rating, hence the need for fuels with different octane ratings.

So in summary, unless your engine NEEDS higher octane fuel to acheive optimum spark advance, don't run higher octane fuel. It costs more and you actually extract less power from it. But if you do need higher octane fuel to acheive optimum spark advance, the extra cost per litre is generally offset by a greater energy extraction per litre. Which all boils down to if your engine is unmodified, use the fuel originally specified, if it's modified then some experimentation will be needed.

2. Combustion creates heat and gases (which the heat expands), this in turn pushes the pistons down & rotates the crank. This is the basis of the heat engine our car uses to turn chemical energy into kinetic energy. It does this by reacting a combustable liquid with oxygen. Carbon - Carbon and Carbon - Hydrogen bonds in the fuel are broken and Carbon - Oxygen (CO2) and Hydrogen - Oxygen (H2O) bonds are formed. The difference in bond energies is liberated as heat and noise.

Alcohols (ethanol, methanol etc) are oxygenated hydrocarbons. An oxygen molecule has already been inserted into the hydrocarbon. So they are already "partially burnt" & there isn't as much energy liberated when they are burnt in our engines. This is the major reason why they yield less energy per gram.

I'm an industrial chemist with 25 years hot rodding experience.

 

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