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).
Comparison of various fuel grades and their detonation characteristics for the Tourist Trophy race.
| Identifier | ExFiles\Box 82\4\ scan0382 | |
| Date | 1st October 1936 | |
| -5- Hs{Lord Ernest Hives - Chair}/CTS.{C. Trot Salt - Carburation}16/KW.1.10.36. PART 3. Having taken the cylinder head development to this stage, various grades of petrol were compared with a view to making a final choice for the fuel to be used in the Tourist Trophy race. We give them in order of efficiency with attendant characteristics :- (1) 50% Benzol 30% Methanol } Tested at 9 : 1 Comp. Ratio. 20% Aviation "680" No audible detonation anywhere in the speed range. This is the best fuel for power holding, general running, etc. (2) 50% Benzol 50% Shell No.1 } Tested at 9 : 1 Comp. Ratio. Not quite as good as 50/30/20. Slight detonations at very low speeds, full throttle. This is a similar combination to the fuel used in the 1935 T.T. race, except that Ethyl was substituted for Shell No.1. (3) "Esso" Ethyl. Tested at 8.5:1 Comp. Ratio. Very good for power holding at high speeds, full throttle. Detonation fades out at 2650 R.P.M. (F.T.) (i.e., no detonation can be heard above this speed) with ignition advance and mixture set for ideal running. With detonation so far up the speed range, it becomes possible to notice the difference between maximum and minimum combustion chamber temperatures. This is explained as follows :- With the brake set for, say, 2000 R.P.M. full throttle; when the engine is opened up to full throttle from tick-over, detonation is not at first too pronounced, but gradually increases to a certain maximum degree. After immediately throttling back from this condition, and straight away snap accelerating again, the detonation is very pronounced indeed, as the engine revs. increase, but as the throttle is opened and closed in this manner (snap accelerating) the degree of detonation decreases gradually to nil. NOTE: The circulating water temperature is maintained constant throughout this procedure. | ||