|
Petrol
Petrol is what most of our cars came setup so it's usually what we
stick with.
Petrol is a mixture of hydrocarbons.
The petroleum
distillate fraction termed "Petrol" contains mostly saturated
hydrocarbons usually with a chemical formula of C8H18.
The air fuel
ratio, A/F Ratio, for complete combustion is 14.7:1, stoichiometric.
The A/F ratio for maximum power is approximately 12.5:1 - 12.8:1.
This
means that our engine at max power, 12.8:1, consumes 12.8 pounds of air
for 1 pound of fuel.
Petrol has approximately 18,400 BTU/lb .
Using an airflow calculator, we find a 355 cubic inch Small Block Chev consumes 567.53 cfm @
6500rpm which is 42.64 pounds of air and consumes 2.89 pounds of fuel.
Therefore if we are using Petrol our engine is producing 53,176 BTUs
of energy at 6500 rpm.
Alcohol (Methanol)
Alcohol is usually used in the form of Methyl alcohol or methanol.
CH3OH is the chemical formula.
Methanol burns at a much richer mixture
than Petrol does, between 5.0:1 - 6.0:1.
That's 5 lbs of air to one
pound of fuel.
Methanol has approximately 9,500 BTU/lb.
A 355 cubic inch Small Block Chev consumes 567.53 cfm @ 6500rpm which is 42.64 pounds
of air and now at 6.0:1 ratio for Methanol is 7.11 pounds of fuel.
Therefore if we are using Methanol fuel our engine is producing 67,545
BTUs of energy at 6500 rpm.
Nitromethane
Nitromethane is a fuel
that is used mostly in specialized drag racing classes, "nitro funny
cars" and "top fuel".
Nitromethane's chemical formula is CH3NO2.
The
oxygen in nitromethane's molecular structure means that nitromethane
does not need as much atmospheric oxygen to burn, part of the oxygen
needed to burn nitromethane is carried in the fuel itself.
Typical A/F
ratio for nitromethane is 1.7:1 and nitromethane has an energy content
of 5,000 BTU/lb.
A 355 cubic inch Small Block Chev consumes 567.53 cfm
@ 6500rpm which is 42.64 pounds of air and now at 1.7:1 ratio for
nitromethane is 25.08 pounds of fuel.
Therefore if we are using
Nitromethane fuel our engine is producing 125,412 BTUs of energy at
6500 rpm.
TABLE 1
Fuel |
Engine Air Flow (cfm) |
lbs of air (lbs) |
A/F Ratio |
Pounds of Fuel (lbs) |
Energy Content of Fuel (BTU/lb) |
Total Thermal Energy (BTU) |
Petrol |
567.53 |
42.64 |
12.8:1 |
2.89 |
18,500 |
53,176 |
Methanol |
567.53 |
42.64 |
6.0:1 |
7.11 |
9,500 |
67,545 |
Nitromethane |
567.53 |
42.64 |
1.7:1 |
25.08 |
5,000 |
125,412 |
Summary
As you can see
from table 1 above the clear winner is nitromethane.
But that doesn't
mean to go out and pour nitromethane in your car and see how it runs,
if you do your engine will surely blow up.
Nitromethane is very
expensive and dangerous to handle.
The interesting alternative to
Petrol is Methanol.
Methanol will make more power, typically around
20% more power than a similar engine running Petrol.
Some things to
consider in running methanol is your fuel system will have to be
completely changed / upgraded.
Based on the table above the fuel system
will have to flow approximately 2.5 times as much as the Petrol
engine.
I guess the old saying is true. "Petrol is for washing parts, alcohol is for drinking and nitro is for racing."
|
Home 
