11/05/2003

Serious thoughts for those who are contemplating fuels and radical
performance.

A.  Why leaded fuels are different than unleaded.  
    Tetraethyl Lead  (C2H5)4PB  Mole wght 323  Boiling 396f
    Ethylene Dibromide C2H4BR2  Mole wght 188  Boiling 269f

    Lead and its normal scavenger - both have to be present in about the
    right amounts for lead to work increasing octane.  This is the main 
    ingredients in liquid fuel in the manifold

B.  iso-octane ( approximately the average of fuels data for gasoline
    C8H18  Mole wght 114.22 Boiling 211f Autoigntion 837f 7.3 Crit Comp

C.  benzenes
    benzene C6H6 Mole wght 78.108 Boiling 176f Auto 1097 xxx Crit Comp
    toluene C7H8 Mole wght 92.134 Boiling 231f Auto 1054 15 Crit Comp
    xylene C8H10 Mole wght 106.16 Boiling 282f Auto 1045 15.5 Crit Comp

Now for thimking.
    benzene requires 15 oxygen atom or 7.5 moles of oxygen for stoic
    toluene requires 18 oxygen atoms or 9 moles of oxygen for stoic
    xylene requires 21 oxygen atoms of 10.5 moles of oxygen for stoic.

The more slow and late burning benzene in the mixture, at stoic, the
more excess oxygen there will be at the start of combustion.  Fuels that
scission early such as alcohols and acetone, will burn at stoic with an
increase of speed because of the excess oxygen.  

There are two ways to increase the effective octane - speed the burn
rate so is it is consumed before detonating, and increase the resistance
of the fuel to detonation.

Since the benzene do not burn early, this leaves excess oxygen for the
remaining fuel.  Fuels burns fastest with about 10% excess oxygen
because the fuel particle has the shortest statistical distance to an
oxygen particle.

The more benzene/toluene/xylene in the mixture, the later the fuel will
burn and conversely, the more oxygen will be available early in
combustion.

In a high output engine, you are normally running near peak pressure and
adding fuel and air may take you over the top.  However, if the fuel is
a benzene ring, you can burn it later in the cycle, just like in a
supercharged cycle.  Benzene rings like supercharging and add
significantly to the power available supercharged.

Now if you were truly sick, you would have some kickapoo joy juice aka
model boat fuel with 40% nitromethane.  Nitromethane breaks an NO2
radical out which combines with an OH radical and forms Nitric Acid -
HNO3.  It eventually breaks down into oxygen, hydrogen and nitrogen much
later in the cycle.

Toluene likes nitric acid.  Ummmm Good rocket fuel.  Lots of expansion
and lots of energy release.

Xylene works well too.  So if we add toluene or xylene to the base fuel,
we lean up the intial mixture and raise its temperature and we got lots
of later burning high pressure high lever arm combustion i.e. more power
yet.