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WE are now at the stage where you have come to the end of what one might term the usual fuels and enter the area of the additives, that is to say where you be come part chemist, part engineer, and full-time optimist.

The main object in the use of an additive is to obtain out of the existing fuel a further increase in power output at the engine shaft.

Other uses are to alter the tendency of the fuel to pre-ignite and/or detonate, to obtain easier starting, particularly under cold climatic conditions, to reduce running temperature, or as a means of obtaining better mixing of the fuels, that is to say to act as blending agents, not of course all of these attributes at the same time.

Before we go any further let it be made quite clear that when you commence handling chemicals, liquids or fuels, call them what you will, it is essential to maintain a very high standard of cleanliness personally and with regard to containers used in the operation, also to mark the contents of each container with its known contents since you are now in the realm of chemical mixing, which under certain conditions could become dangerous.


Accuracy of measurement is paramount and attention to detail essential, and if you are not sure of what you are doing then leave it alone, and in no circumstances experiment with mixtures of fuels unless you really know what you are doing as the result could be poisonous or explosive, and the explosion could well occur long before the mixture gets placed in the tank.

Any containers used must be clean internally, and made of a suitable material to resist the fuel chemically (see the Basic Fuel Characteristics page). They should be marked clearly with the nature of the contents, and re-marked when any changes are made.

Many engines have been wrecked due to not marking containers correctly so make this one of the essential items to be done without fail.


In general it is safer to obtain fuel, plus any required additives, already pre-mixed by the supplier who will do this and mark the container in such a manner there is no doubt at all of the contents, the proportions of the mixture being clearly marked.

It also pays to keep a complete and very accurate record of all fuels and mixtures used, together with carburetor or injector system settings, and the results obtained for future reference, plus, of course, ignition data and type of plugs and so on.

Having, we hope, given due warning, let us now consider which additives we can use, taking in turn the basic fuels we have so far discussed and the use of additives with them, with the objective use of the additive stated.

In connection with this we have regarded the use of up to 10 percent as an additive, and over that amount we consider to be a major component of the fuel.


Since almost our major requirement is that of getting more power out of the engine let us see what can be done taking our basic fuels in turn, starting with Petrol.

Additives are:-

Nitromethane. This increases power, measured at the engine shaft, in proportion to the percentage used, limited by mechanical considerations such as compression ratio, rate of fuel flow possible in existing system.

If the engine is on the maximum compression ratio usable with petrol, this ratio will have to be dropped by a figure of one ratio if 10 percent additive used, and by half a ratio if 5 percent additive is decided upon.

With regard to the fuel flow the jet diameter will have to be increased by a figure of 1.125 for use with 10 percent, and in proportion less for the 5 percent.

Methanol. The use of Methanol enables a power increase to be obtained by the simple act of using a higher compression ratio and in fact with 10 percent the ratio can be increased by 1.5.

That is to say an engine running on 10 to 1 on petrol can now, by the use of 10 percent Methanol, run on a ratio of 11.5 to 1 provided, and we stress this point, steps are taken to enable the fuel rate of flow to be increased by a figure of 1.125 minimum, or put another way, the jet diameter increased by that amount on the diameter.

In each case, that is either Nitromethane or Methanol used as an additive, the mixture should be premixed and not just supplied to the tank relying on mixing taking place by accident as it were.

Before we leave petrol it might be pointed out while other additives are sometimes used, they do not as a result of being mixed increase the power output potential of the total fuel.


We must now consider Methanol as the basic fuel.

To obtain power increase additives are:-

Nitromethane. Bearing in mind we are, as an additive only considering a maximum amount of 10 percent, although we know in fact up to 100 percent can be used as has already been explained, the power increase at the engine shaft will be in proportion to the amount of additive used, provide' and once again we stress this, the fuel flow and jet diameter is increased by 1.125.

The compression ratio will have to be modified, on the maximum for Methanol before the additive was introduced and for 10 percent will have to be lowered by a ratio of 1.

Propylene Oxide. This fuel additive in general is safe to handle except for two possible conditions, which under certain circumstances could well be dangerous these are the effects cause by the fuel coming in contact with copper/alloy containers, fuel tanks, etc., or by rust particles getting in the fuel by accident, for example from a rusty container, or from rust from damaged can top cap.

To avoid this possibility this fuel is better kept in, and used from, a plastic container of the pure polythene type.

If rust particles are introduced they can do two things. One is to Polymerize slowly, or put another way, change its chemical state, in this particular case to form slowly a nasty waxy solid akin to polythene.

The second condition is where the polymerization process takes place quickly due to external heat on the container, say for example from strong sunlight, which causes the speed up, resulting in a possible explosion.

The remedy is of course obvious so take steps to keep it cool, bearing in mind the boiling point of this fuel is 93 degrees F. Or as we now tend to regard temperature, 34 degrees C.

The best increase in power is obtained by some 5 percent as additive, as above this figure the gain does not increase in proportion, like the other additives, but in fact tends to decline, so stay at the 5 percent mark.

This fact is known and although reasons can be given for this behavior, at this moment of time there is a lot of experimental work to be done with this additive when used with pure methanol, but anyone carrying out such work must be very much out on their own.


We now come to our last basic fuel, that being Nitromethane, assumed pure, and undiluted, and again our object in using the additive is to obtain a power gain at the engine shaft.

The additive is:-

Propylene Oxide. We have a slight change here in that this can be used up to a figure of 30 percent rather than our previous 10 percent.

Increase in power output will not be proportional to the amount used, but varies from engine to engine, and also with the use of other additives with the total fuel, water being a good example.

In general terms one may well expect an increase of some 10 percent at the shaft for the addition of 10 percent additive, but over this figure it is almost impossible to give an estimate as so many factors will influence the result.

Due to the oxygen provided by the Nitromethane, the usual air-fuel ratios no longer hold good and from that fact alone, it is very difficult to state what the actual power increase will be.

It has been very clearly stated before that care should be taken when using Nitromethane, but this be-comes even more necessary when dealing with this fuel plus propylene oxide additive.

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