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).
Technical report on the performance of various spark plugs, observing their temperature characteristics and pre-ignition points.
| Identifier | ExFiles\Box 34\2\ Scan096 | |
| Date | 8th May 1918 | |
| -2- Contd. We shall be sending a report on this. One can only distinguish the plug when some portion of it becomes red hot. So as to be able to know where to look in the cylinder, we can time one magneto to give a spark on the exhaust stroke. We found that all the sparking plugs we tested did get red hot. The fact of the plugs being red hot does not cause pre-ignition, in the same way the exhaust valve does not. Pre-ignition only takes place when the over-heated plug reaches the temperature of 900°C or 950°C judging by colour. We have observed in the cylinder the following plugs - Lodge Plugs -- various types. K.L.G. " -- various types. Bosch " -- various types. Pognon " -- C.C. " It is noticeable on all plugs fitted with pot insulators that the insulators themselves when the engine is working are red hot, for instance the Pognon Plug, the porcelain is the hottest part, it gets hotter much quicker than the metal points. All the types of "Bosch" plugs work with porcelain red hot, even these have been found in "Gotha" engines brought down. The old type 4 point Bosch plugs will not stand up on an Eagle engine. The only plug we found in which the insulated electrode did not get red hot, was C.B. type K.L.G. plug. This is the type with the copper electrode and small piece of nickel Contd. | ||