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 head modifications to cure detonation, considering valve types, head angles, and materials.
| Identifier | ExFiles\Box 134\2\ scan0063 | |
| Date | 15th July 1935 guessed | |
| -3- On considering the subject, it would appear that, if the detonation trouble can be cured, the single inlet valve is the most suitable, as there will then only be one push rod, and automatic tappets are possible. The detonation is cured by fitting twin inlet valves, and a salt-cooled valve, and this latter helps to a certain extent on the single inlet valve, though it by no means cures it. Another method by which it was stopped was to fit an alum. head with twin inlet valves and a normal exhaust valve. Another point which arises is regarding the length of the engine, though this applies more to the twin than the single inlet valve head. The centre line of the combustion chamber is at present inclined to the plane of the inlet valves at about 23°. If this angle is persisted in, then the engine length becomes excessive, exceeding the present engine by about 4". If, however, the above angle be reduced to about 9°, we can arrange the cylinders to come within the existing engine length. It is thus fairly obvious that to obtain a head which will be suitable for main engines and is also likely to be free from this detonation characteristic, we should make a single inlet alum. head, with the 9° angle mentioned above, and employ a salt-cooled exhaust valve. There is, of course, the possibility with the new 9° head, that the rearrangement of the turbulence might do away with the detonation of itself, using a cast-iron head, though this is problematical. Another possibility which was not tried out is that by altering the plug position and reach to obtain satisfactory running on the exhaust valve plug, freedom from detonation might be obtained thus. Power. For a power comparison between the existing high power T.T. head, the standard head, and the turbulent high power head, curves have been drawn as in Fig.III, all valves being reduced to a C.R. of 6.5 and an approximate main engine depression. No allowance is made for the larger induction system of the T.T. engine or its higher mechanical efficiency, and this makes the gain of the high power head even more remarkable. | ||