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).
Report comparing the performance of sodium-filled versus solid exhaust valves on B.80 and B.60 engines.
| Identifier | ExFiles\Box 124\1\ scan0072 | |
| Date | 21th April 1939 | |
| 104H To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} c. Hs.{Lord Ernest Hives - Chair} c. Da.{Bernard Day - Chassis Design} c. Da{Bernard Day - Chassis Design}/Jnr.{Charles L. Jenner} c. Da{Bernard Day - Chassis Design}/McS. Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}2/MH.{M. Huckerby}21.4.39. EXHAUST VALVES AND THEIR COOLING ON B.80 AND B.60 ENGINES. As stated in our original report on the B.60 engine, very bad detonation and preignition was experienced when the combustion chamber throat area was reduced by machining off the cylinder head face to obtain a higher compression ratio. In this condition the exhaust valve temperatures were very high and though no actual temperatures were recorded they were approaching "white heat". It was at this time that sodium filled exhaust valves were fitted and an appreciable improvement was effected. Since that time the throat area was increased as much as possible and the heads not machined on the face so that the throat area was left as a maximum figure on this type of head. In this, the best condition sodium filled exhaust valves were compared with solid valves, both having the same .375 stem diameter which incidentally compares with .343 stem diameter of the original solid valves, which may also attribute to the cooling of the valves. The result of the tests is slightly in favour of the sodium filled valves, but insufficient to warrant using them on account of the considerable increase in cost compared with the solid valves, therefore we propose in future to use only the latter. Regarding the actual temperatures as taken by means of an optical pyrometer, the average of several runs and all cylinders at 4000 R.P.M. is 785°C with the sodium filled valves and 774°C with solid valves. At 3000 R.P.M. the temperatures are practically the same at 705°C, likewise the stopping time on switching off at full throttle. Through-out the full throttle speed range the ignition advance to avoid detonations with the solid valves is approx. 3° retarded compared with the advance figure for the sodium filled valves. | ||