Fuel Ratings

To determine a fuel’s rating, two things must be taken into consideration.
The first is heat content (Btu’s/lb). The higher the figure the more heat will be produced by combustion to produce power. With just this consideration it would appear that Methanol (near enough 10000 Btu/lb) is twice as good a fuel as Nitro (5000).

However, we know this can’t be right.

Now look at their respective Air/Fuel ratios. Methanol, at its richest figure, is 4.5:1 whereas Nitro is .5:1. This indicates that 9 times as much mass of Nitro is needed for the correct A/F ratio than Methanol. So, theoretically, Nitro could provide 4.5 times as much power as Methanol at the expense of horrific fuel consumption. This is why the needle valve must be opened more as Nitro content increases and also why the needle is less sensitive.

In the column headed “Fuel Rating” I have divided each fuel’s Btu content by its richest A/F ratio to get a comparative figure. This shows that (other than Nitro) Methanol is the best fuel.

With this in mind I have rated Methanol as 1 and then compared all other fuels to get the figure in brackets which gives a clearer indication of how each fuel rates against Methanol.

Brian Hampton

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