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 characteristics, air consumption, and motoring losses.
| Identifier | ExFiles\Box 133\1\ scan0111 | |
| Date | 17th September 1936 | |
| -7- A power curve at a C.R. of 8:1 is shown on Fig.VIII, and needs no comment. Detonation. Detonation characteristics are rather interesting, though investigation was somewhat limited, due to the fact that with the Rudge and Bentley camshafts, the engine would not run below 3,000 R.P.M. and 2,500 R.P.M. respectively, though it would go to 2,000 R.P.M. with the modification No.1 camshaft. On a C.R. of 7.3 : 1 it was impossible to obtain detonation with Shell No.1 fuel down to the speeds mentioned above. When, however, the C.R. was raised to 8 : 1, rather a different story was told. On D.T.D.230, and a 50/50 mixture of Benzole and Shell No.1, no detonation was present, but on Shell No.1 alone, detonation set in at about 3,500 R.P.M. - on Bentley cams - and once started, it increased in intensity until pre-ignition began with consequent overheating, culminating in one instance in slight piston seizure. The rise in temperature was clearly shown by a thermo-couple in the plug which, once detonation had started, sent the galvanometer reading streaking up. Under these conditions it was obviously impossible to obtain the usual speed/detonation curve, and the attempt was abandoned. Air Consumptions. Air consumptions for the penthouse and hemispherical heads are shown on Fig.VI using Bentley cams, when a maximum volumetric efficiency of 88.5% is obtained for the penthouse head, and 86.5% for the hemispherical. It is almost certain that these values would be considerably higher if Rudge cams had been used, probably being about 94% and 92% respectively. Motoring Losses. These were carried out on a 40 HP. Laurence Scott electric dynamometer, and are very susceptible to slight errors in readings, as the M.E.P. factor is 10.4. This means that an error in reading of .05 lb. is equivalent to about .5 lbs/in.2 or nearly 3% of the result. As it is almost impossible to read the brake to even this accuracy, from this source alone a 5% error may be expected. | ||