Quote:
Originally Posted by swift
how should something that was added to increase reliability increase the risk of overheating which would strongly reduce reliability? For me this is contradictory.
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The biggest problem with using pure ethylene glycol as a coolant is that it is less effective at conducting heat than water so, as it circulates around the engine, it is less effective at keeping engine components cool. While the high strength alloys and other metals developed by the likes of Rolls-Royce for use in aero engines were able to withstand higher temperatures than earlier metals, components such as gaskets and oil seals were more likely to fail - early Merlin engines were renowned for their oil leaks. Head gasket failure in the middle of combat ops is no fun.
A second problem is that in its pure form Ethylene glycol is flammable, thus it was a hazard to use 100% glycol in combat aircraft. The Merlin II and III series had a normal coolant temperature of 90°, and 120°C emergency maximum - close to the flash point of glycol
http://www.npi.gov.au/substances/eth...col/index.html Mixing glycol with water increases the flash point while preserving the anti-freeze, anti-corrosive properties of glycol.
Thus the Merlin XII and XX series (30% Glycol, 70% water) were able to run at higher temperatures 105° normal to 125° for climb, 1 hr maximum and 135° +12 lbs boost 5 minutes while the vulnerable gaskets and oil seals were less prone to failure.
I don't know why the British adopted 100% glycol, although I remember reading about it somewhere.