In gasoline engines, as with any intercooler, this suppresses detonation so more power producing boost and timing can be utilized. Water, with its high latent heat of vaporization cools the intake charge and combustion. Methanol cools the charge and combustion but also acts like an extremely high octane fuel (some researchers claim as high as 120 octane) as well as adding more oxygen to combustion.
In diesels, the effect is three fold: 1. The intercooling effect provides for more available air and all the benefits of a higher positive pressure ratio (more power giving fuel can be utilized safely without high combustion temperatures). 2. The combustion of water provides for more power on the power stroke. 3. Methanol acts as an additional fuel for more power.
A brief History:
Water injection was evaluated scientifically in the 1930.s by H. Ricardo who demonstrated that one can basically double the power output of an engine using water/methanol. The first widespread use was during WWII on supercharged and turbocharged aircraft. In 1942, the German Luftwaffe increased the horsepower of the Focke-Wulf 190D-9 fighter aircraft from 1776HP to 2240HP using 50/50% water/methanol injection. The allies soon followed by fitting the P51 Mustang and other high performance aircraft with water/methanol injection. Following the war, the turboprop aircraft industry used water/methanol injection and called it the "automatic power reserve system (APR)" for use in hot or high altitude take off. It surfaced again in the 60's when GM used a system on the OEM turbo Corvair. It was used effectively in Formula 1 before being banned for adding too much power.
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