Alcohol and Nitromethane
By
Craig S.
Walker
Gasoline is for washing parts, alcohol is for drinking and nitro is for racing. I saw that on the back of a fan’s shirt at New England Dragway. It seems some folks just don’t appreciate gasoline. What is so special about Alcohol and Nitromethane anyway? Well…..people don’t race funny cars; they race ALKY funnies or NITRO funnies. Gasoline has no real pizzazz in the racing world. Sure it powers Pro stock cars, trucks and bikes, but it just doesn’t have the same powerful intonation as Alcohol or Nitro. So where does this notoriety come from and why would someone want to use either of these fuels?
Alcohol is usually used in the form of Methyl alcohol or methanol for short. CH3OH is the chemical formula. Methanol when compared pound for pound to gasoline yields about half of the heat energy potential. Where alcohol offers 9000 BTU/lb. Gasoline offer 18000 BTU/lb. Basically methanol is a far less powerful fuel on a pound per pound basis. Gasoline however burns at a stoichiometric (scientifically correct) ratio of 14.7:1, and makes best power running slightly richer at 12.0 to 12.5:1, while methanol burns at 5.0 to 6.0:1. When the mixture is run in this fashion the result is a 5-11% increase in power.
The best part is, the above is not the only benefit. Methanol allows for much higher mechanical compression ratios far in excess of what even the best racing gasolines offer. Just a few years ago Pro stock (gasoline) bikes ran a max of 13:1 to 15:1 compression ratio, but alky bikes of the time could run 16 to 17:1. The extra compression allowed alcohol engines to gain a 15% advantage in power while normally aspirated. Now figure in the fact that methanol has a higher latent heat of evaporation (it absorbs or uses more heat in the evaporation process), and we have a fuel that can cool the intake charge better than gasoline. Can you think of a good use for this? How about supercharging or turbo charging?
Compressing air makes it get hot. Superchargers and turbochargers are not 100% efficient for several reasons, not the least of which is through lack of mechanical efficiency and compression of the intake charge itself the intake temp rises. Hot air is not good. 10 psi of hot air contains less oxygen for burning fuel than 10 psi of cold air. Think of it this way. If you blow up a child’s balloon and let it sit nothing happens. Put it in the freezer for 5 minutes and what does it look like? It comes out all shriveled up. Put it next to a warm bright light and not only does it return to its original size, it blows up even bigger as the air is heated. Now if we take that same hot compressed intake air and dump a little methanol into it, you guessed it, the temperature drops as the alcohol is evaporated. Alcohol is atomized and the mixture gets denser allowing for a whole lot of mixture to be shoved into the engine, much more so anyway than that of the turbo/gasoline mixture.
It is not unusual for supercharged alcohol motors to realize
a 20% improvement over their gasoline brethren.
Nitromethane works in a similar way. It is clear and very hard to light with a
match. If you are somehow successful at
lighting it, you’ll see it burn with a lazy blue flame. Smack a puddle of Nitromethane with a hammer
however and the head of the hammer will be come a projectile as the nitro
explodes in a violent blast.
Like methanol, Nitromethane does not have a lot going for it
in sheer power per pound.
·
Gasoline………….18,400 BTU/lb.
·
Benzol…………….17,500 BTU/lb.
·
TNT (trinitrotulene)..6,500 BTU/lb.
·
Ethyl Alcohol………11,500 BTU/lb.
·
Methanol…………..9,500 BTU/lb.
·
Nitromethane………5000 BTU/lb.
Nitromethane does contain a lot of oxygen, which makes it nearly a mono-propellant. Meaning, it requires almost no additional air (oxygen) for burning. Therefore it burns best when run at a very rich ratio of 2:1 to 1:1! Thus even though pound for pound nitro is less powerful than gasoline, nitro can make almost double the power of a gasoline engine of the same configuration.
Air Fuel ratio vs. Resulting Max BTU released
· Nitromethane:
o 1.3:1…………46,000 BTU
· Methanol:
o 5:1…………...23,000 BTU
· Gasoline:
o 12:1………….18,400 BTU
There may be more coming, you never know…………