[Amc-list] MW50 / MW30

[Brien Tourville <hh7x@xxxxxxxxxxxxx>]

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*MW 50* was a 50-50 mixture of methanol 
<http://en.wikipedia.org/wiki/Methanol> and water 
<http://en.wikipedia.org/wiki/Water> (thus the name) that was sprayed 
into the supercharger <http://en.wikipedia.org/wiki/Supercharger> of 
German <http://en.wikipedia.org/wiki/Germany> aircraft engines 
<http://en.wikipedia.org/wiki/Aircraft_engines> primarily for its 
anti-detonant <http://en.wikipedia.org/wiki/Engine_knocking> effect, 
allowing the use of increased boost pressures. Secondary effects were 
cooling of the engine and charge cooling. Higher boost was only 
effective at altitudes below the full throttle height, where the 
supercharger could still provide additional boost pressure that was 
otherwise wasted, while the smaller secondary effects were useful even 
above that altitude.

MW 50 is something of a misnomer, as it is actually a mixture of three 
fluids; 50% methanol acting primarily to achieve optimum anti-detonant 
effect, secondarily as an anti-freeze, 49.5% water, and 0.5% Schutzöl 
39, an oil-based anti-corrosion additive. The similar MW 30 increased 
the water to 69.5 and decreased methanol to 30%. This increased the 
cooling performance but made it easier to freeze, intended to be used 
for lower-altitude missions.

The effect of MW 50 injection could be dramatic. Simply turning on the 
system allowed the engine to pull in more air due to the charge cooling 
effect, boosting performance by about 100 hp on the BMW 801 
<http://en.wikipedia.org/wiki/BMW_801>. However the MW 50 also allowed 
the supercharger to be run at much higher boost levels as well, for a 
combined increase of 500 hp. At sea level 
<http://en.wikipedia.org/wiki/Sea_level> this allowed the 1,600 hp 
engine to run at over 2,000 hp. MW 50 was fully effective up to about 
6,000 m, above which it added only about 4% extra power, due largely to 
charge cooling.

Aircraft generally carried enough MW 50 for about 10 minutes of use, 
allowing them to increase their climb rate for interception 
<http://en.wikipedia.org/wiki/Interceptor_aircraft> missions. Fittings 
for MW 50 first appeared on the BMW 801D in 1942, but it never went into 
production for this engine because the cylinder heads developed 
micro-cracks when MW 50 was used. Instead, the DB 605-engined 
Messerschmitt Bf 109 <http://en.wikipedia.org/wiki/Messerschmitt_Bf_109> 
was fitted with an MW 50 injection system. Later engines designs all 
included the fittings as well, notably the Junkers Jumo 213 
<http://en.wikipedia.org/wiki/Junkers_Jumo_213>, which relied on it in 
order to reduce non-boosted performance and tune the supercharger for 
higher altitudes.

MW 50 was not the only charge cooling system to be used by the Germans. 
Some engines dedicated to high altitude included an intercooler instead, 
as they would be needing the cooling for longer periods of time. The 
801D also included the ability to spray gasoline into the supercharger, 
in place of the MW 50 (the erhöhte notleistung system), and while this 
was not as effective it did increase boost without the complexity of the 
additional tanking and plumbing. Additionally many of the late-war 
engines also included a system for high-altitude boost, GM 1 
<http://en.wikipedia.org/wiki/GM_1>, which was intended to add oxygen 
instead of improve boost levels.

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