Michael Cerkowski said:
If he drives mainly on level ground and doesn't need all the power
the engine can give with premium, he should get better fuel economy on
regular, not worse. Regular vaporizes more completely, which can cause
knocking if the knock sensor isn't working, but under normal driving
conditions fuel economy should go up about 2mpg. Regular grade is also
better for cold starting in Winter, for the same reason.
You are saying the level ground bit because you are expecting the
regular fuel to knock or ping. It doesn't. I have used regular gas in
all my Volvos for 41 years with no ping or knock. They go up hills and
accelerate great on regular.
The fuel economy is better with premium in cars that are tuned for
premium, but usually it is a complete wash as to how much you pay in
$/mile in such vehicles.
What you are trying to say is that regular fuel is more explosive, not
vaporized more completely. The explosive nature can cause a knock or
ping if the timing is not right and the piston has not yet started its
down stroke. Premium fuel burns more uniformly and less explosively and
will tolerate being detonated before the piston has started its down
stroke.
There are not nearly as many different fuels as their are different
brands. They fill up a just a couple of different fuel terminals and
then add their own additives. So most of the gasoline is the same and
the only difference is the additives.
Both premium and regular fuel are both more volatile in the winter and
less in the summer to prevent vapour lock. Most brands use the same
fuel for both regular and premium and just change the additives. The
most popular additives include aromatic hydrocarbons, ethers and alcohol
(usually ethanol or methanol).
Oxygenate blending adds oxygen to the fuel in oxygen-bearing compounds
such as MTBE, ethanol and ETBE, and so reduces the amount of carbon
monoxide and unburned fuel in the exhaust gas, thus reducing smog.
Methylcyclopentadienyl manganese tricarbonyl (MMT) has been used for
many years in Canada and recently in Australia to boost octane. It also
helps old cars designed for leaded fuel run on unleaded fuel without
need for additives to prevent valve problems. However, US Federal
sources state that MMT is suspected to be a powerful neurotoxin and
respiratory toxin.