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).
Suspicion that 'Mercury' plugs are causing pre-ignition due to the design of their porcelain.
| Identifier | ExFiles\Box 35\3\ scan 141 | |
| Date | 8th March 1921 | |
| X.4196 To Hs.{Lord Ernest Hives - Chair} from R.{Sir Henry Royce} c. to CJ. c. to EFC. R4/G8.3.21. X.4295 - RE "MERCURY" PLUGS. X.4196. X.1812. I have a suspicion that one of these on the small pump engine here was causing pre-ignitions after being in use many hours. Kindly beware of this, and if you confirm this, it is probably due to the wall of the pocelain being too thin, and too large in diameter, or too high, and so giving a very large heating surface for its cooling condicticity. So far the Champion has not shewn the same fault. It is possible, however, that the Mercury has partly cracked its porcelain in such a way that the walls are more isolated than when new. If my suspicions are correct, it is highly advisable that we ask the makers to alter the proportions of the porcelain for those that they are supplying to us. This matter could easily be tested by running the plugs hard in one of our aero engines, but this probably is too severe a test. One could therefore bring the severity of the test about right by comparing the Mercury plug with some other porcelain plugs which are satisfactory, including in the list of the Champion, which may have a very lucky proportion in the design of the porcelain. R.{Sir Henry Royce} | ||