bigdyno said:
I am not sure the specifics, but gas companies in N. America and Europe use different methods of attaining the Octane numbers (hence the bigger number availability and owners manual requirements in Europe).
I own a motorcycle chassis dyno (Dynojet 200) and I have done fuel comparisons in the past. The big difference in fuels that you have no control over, other than weather you buy it or not, is ethanol/ethanol blended gas. I never got as good numbers as this fuel doesn't contain as much potential energy. I can't remember the specifics as to why, maybe one of the members in the petroleum industry can shed some light on this.
Anyway, what you can control is to buy your gas from a busy station as their tanks will be emptied more often providing fresher fuel. Yes it does make a difference. If you have ever opened a bloated gas can and had it hiss as you open it, that is all the high end volatiles (read: the "premium" part of the fuel) checking out. You then have mid grade or worse. put that stuff in your lawn mower.
Unless of course you milled the deck and flowed the head, did a three angle valve job and bored the carb on your mower, but nobody else has done that, right?
OK, I'll bite
Propane has about an octane of 110 when used in blending, Butane has about a 107 octane for blending, as you get heavier in hydrocarbons, the octane gets less, but the amount of energy increases. then there is the branch Hydrocarbon stuff, (this post is too short to get into! :barf: )
Diesels get better gas mileage because it's a denser fuel, it has more energy per kilo, but the octane is lower, for diesels you blend on cetane, anyway
Ethanol, is supposed to be better for the environment because it is an oxygenator, i.e. it has oxygen in the chemical formula, and therefore relys less on the combustion chamber mixing properties to enhance combustion, top fuel dragsters would use alchohol!, more oxygenates, burns cleaner, more octane, burns faster as well, so you can rev the engine faster, that is also an issue, most diesels are limited in rpm, because of the flame velocity, that is sometime over come with better mixing with the injection assembly.
that stuff pissing out of your fuel can is based on the vapour pressure, it is based on the time of year you buy the gas. In winter you have a higher vapour pressure, and consequently the gasoline has more butane blended in the gas to increase the vapour pressure of the cold fuel. If you buy gas in the winter, and save it for the summer, you'll vapour lock most cars, as the butane will try to escape into the vapour phase (engineer speak:bow: ).
summer blend gas has the lowest amount of butane in the blend, and therefore has to make the octane for high blended gas from denser blending stock, typically from alkylates and reformates, iso octanes etc. (read more expensive to make):thumbsup:
so ethanol gas burns faster, but because it's a less dense blend of gas, it has less energy per kilo, and therefore gives lower gas mileage.
What is debated by many is whether the benefits of the ethanol blend out weighs the increase in fuel consumption:eyebulge:
We don't have to worry, because our GTI's don't like too much ethanol blend in our gas!:thumbup:
