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).
Engine detonation concerning compression ratios, fuel mixtures, and ignition.
| Identifier | ExFiles\Box 42\4\ Scan046 | |
| Date | 21th September 1926 guessed | |
| Contd. -2a Hs{Lord Ernest Hives - Chair}/ACLL/T. The test was made with a 5.2 to 1 compression ratio which with ordinary commercial petrol detonated at low speeds and it was proved that under the above conditions the audible detonations became less severe as the speed increased and were quite inaudible when a speed of 1750 R.P.M. was reached. We think that the "fading away" of audible detonation with increase of speed is mostly due to the increase of turbulence. Keeping the I.M.E.P. constant seems to be an important point because for a given set of conditions the pressure appears to have considerable influence on detonation. With regard to the temp. of the ingoing air, we have not been able to experience any appreciable difference although naturally this affects the lower considerably. We have had air intake temperatures from 26°C. to 86°C. and no difference in detonation could be appreciated. (3) The Relative Tendency to Detonate with Weak and Rich Dry Mixtures:- It has always been our experience when running on ordinary commercial petrol with a compression ratio giving detonation and the spark adjusted in the most efficient position, that the most severe detonations were experienced with a mixture which gave the greatest B.M.E.P. at that particular speed. An efficient exhaust hot spot was in operation during some of these experiemts which remained at approx. a constant temperature and resulted in a fairly dry mixture. This would naturally be richer than the "chemically correct" mixture. Mixtures richer or weaker resulted in a decrease of the severity of the detonations. (4) At the present moment we have no information on this particular point regarding lead ethide dope. (5) The effect on the tendency to detonate with multiple ignition symmetrically and asymmetrically arranged:- With symmetrically arranged and synchronised dual ignition we found the tendency to detonate considerably reduced. The engine in question had the plugs facing each other on opposite sides of the cylinder bore. With ordinary (Contd.) | ||