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).
Analysis of engine valve expansion and temperature differences between sodium-cooled and non-sodium valves.
| Identifier | ExFiles\Box 113\5\ scan0185 | |
| Date | 28th January 1937 guessed | |
| -4- The engine is then run at 4000 R.P.M. full throttle, with the micrometer maintaining a consistent contact with the top valve spring washer every time the valve closes. This indicates the time at which the maximum expansion is reached. The throttle is then closed to give a light running speed of 1000 R.P.M. and the mike reading taken every 15 seconds (giving contraction against time). This test was carried out on the sodium cooled valve in No.5 cylinder, and on completion the sodium was removed from the valve and the test immediately repeated. The result showed that this particular valve expanded half as much with the sodium removed. The expansion of a similar valve in No.6 cylinder was checked in the same way, and the result on Graph No.S.18 shows a max. expansion less than the valve in No.5. while the max. temperatures are quoted as being the same. We should point out, however, that the temperatures were arrived at by the use of the Cambridge Cn{Mr Chamberain}/con instrument, and it is practically impossible to determine temperatures below 700 C. The figure of 740 C for the non-sodium cooled valve can be taken as reliable. But the figure of 680 C is only a very approximate figure, the colour of the valve being almost indistinguishable. The standard exhaust valve temperature is 750 to 775 C. There might, therefore, be a difference in temperature of 10-20 C. between the sodium cooled valve in No.5 cylinder, and the one in No.6 which would then account for the difference in expansion between the two valves. At the time the test was being taken, No.6 cylinder was burning noticeably more oil than No.5. The differences in the temperatures quoted do explain the difference in expansion, with and without sodium however. In the case of the sodium cooled valve, the heat is conducted up the stem by the sodium. This means that the stem is running much hotter than when the sodium is removed. In the latter case, although the valve head is hotter in comparison, the expansion is more likely to follow the grain flow in the valve head. Cylinder Head. (a) Power Output. Considering graph No.S.20, it is interesting to note, when comparing the performance of the O.H.C. unit with the standard 4 1/4 litre unit, that the power lost to a given exhaust silencing system, is not proportional to the open exhaust power of the two engines. A considerable amount of work is required to get a satisfactory explanation for this phenomenon. | ||