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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Detonation tests comparing water and glycol coolants at various temperatures in a Bentley car.

Identifier  ExFiles\Box 131\5\  scan0118
Date  5th December 1938
  
-4-

We did a small amount of pressure cooled running on 39-EX Ph.III car and experienced no troubles whatsoever.

We have just carried out some detonation tests on a Bentley car - 3.S.IV operating with water and glycol respectively at various temperatures, as follows.

(a) 80°C (b) 100°C (c) 120°C - glycol only.

In the first case, detonation was appreciably worse, both in volume of sound and speed range, with glycol than with water, the speeds up to which detonation could be heard being 22 - 24 m.p.h. and 15-17 m.p.h respectively. The difference was particularly noticeable after the car had been driven hard for a mile or two.

In the second case (b), the difference in detonation between water and glycol was even more noticeable, (although the speed ranges were unaltered) - again particularly after hard driving.

With water at 100°C detonation was not seriously worse than standard, and did not worry one under normal driving conditions, whereas Glycol gave objectionable 'pinking' under normal conditions.

In case (c), the remarks about glycol are the same as (b) but the detonations are accentuated still further - also engine frequently continued to run after switching off. No test at this temperature was made with water.

SUMMARY.

In view of the above facts and the opinion universally agreed on by the Aero people (with whom I have discussed this matter) that pressure cooling will eventually be universally adopted for aero work, I think that if we decide to experiment seriously with a high temperature coolant system, we should commence with pressure cooling and concentrate on this system until we are satisfied that its disadvantages outweigh its advantages.
  
  


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