[Richard L]

If the chart is correct, it appears that all you need is 3% water/fuel will replace two points of afr (10-12.5).

I'd better explain how the chart was calculated:

Without water:
10Kg air + 0.95kg fuel = 10.5 afr
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10Kg air + 0.80kg fuel - 12.5 afr



With water
10kg air + 0.95kg fuel + 0.00475kg = 10.5 afr + 5% wfr
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10kg air + 0.95kg fuel + 0.095kg = 10.5 afr + 10% wfr

Substitude the latent heat of each liquid and plot the result with excel.

Latent heat of fuel = 350KJ/kg
Latent heat of Methanol = 1109 Kg/kJ
Latent heat of water 2256KJ/kg