posted September 04, 2001 10:45 AM
ANTI PRE-IGNITION ADDITIVES
WE now come to the use of additives for reasons other than power increase. In this chapter we will deal only with additives that can be of assistance to us in connection with Pre-ignition and the other problem of Detonation.
We again go through our three basic fuels in the same order.
WHEN USING PETROL . . .
We have three additives in Methanol, Acetone and Benzole (Benzene) and all of them are introduced with the main object of reducing Detonation by increasing in effect the Octane rating of the total fuel. Pre-ignition in general should not present a problem when using as basic fuel petrol.
Methanol in Petrol. This is the best from the point of view of reducing Detonation, followed by Acetone and then Benzole in that order.
Methanol can be added in all proportions up to 100 percent, but as an additive limited to 10 percent will give an Octane increase of about 5 points. For example 98 Octane can be increased to 103, or looking at it another way, cheap fuel of say 91 Octane can, by the use of 10 percent Methanol, or approximately three quarters of a pint per gallon, will produce fuel of 96 Octane.
Acetone in Petrol. Can be used up to 100 percent but with the nominal 10 percent will give an increase of 3 points rather than 5.
The major difference from Methanol being that due to the higher calorific value of Acetone, the consumption does not increase so much, but still provides a higher octane rating.
Benzole (Benzene) in Petrol. Again can be used up to 100 percent but with the 10 percent amount will provide in points a rise of 2.
In many cases this additive is used to counteract detonation since some 10 percent will, in certain cases, provide enough rise in octane rating to do just that.
WHEN USING METHANOL .
Now we come to Methanol as the main fuel, and as additives to reduce Preignition and/or Detonation we have two.
Acetone in Methanol. Here we are concerned only with Pre-ignition since Methanol has itself a very high octane rating, and is therefore to be regarded as almost free from detonation problems.
Once again our figure of 10 percent is the most advantageous use of the additive, as over that figure has a declining effect in proportion to the amount used.
The effect of using this additive is to move the auto-ignition point upwards, and this was fully explained as will be remembered.
Water in Methanol. Up to 5 percent or a maximum of 10 percent with the object of increasing the octane rating even higher, to reduce detonation under very high supercharge conditions.
WHEN USING NITROMETHANE
Last of all now we have Nitromethane as our main fuel. Here we have three additives to help with preignition and or detonation.
Methanol in Nitromethane. Since Nitromethane has itself a tendency to pre-ignite and detonate, the sole object of up to 10 percent Methanol as an additive is to reduce this tendency to detonate while having only a minor effect on pre-ignition.
Water in Nitromethane. Up to a maximum of 2.5 percent as this is the maximum amount that will mix without separation taking place. It reduces both preignition and detonation due to the internal cooling effect alone.
In practice a combination of Methanol and Water is the better use of the two additives, the proportions being 2.5 percent water and 7.5 percent Methanol giving a good safe usable blend of Nitromethane, with almost the full power capability of undiluted Nitromethane.
Acetone in Nitromethane. Up to a maximum of 5 percent. This reduces preignition by raising the auto-ignition point and any small decrease in detonation is incidental.