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).
Spark plug failures due to overheating and carbon, and the testing of various plug types.
| Identifier | ExFiles\Box 34\2\ Scan097 | |
| Date | 8th May 1918 | |
| Contd. -3- fixed in the end. This type of plug we could not by any means make the centre electrode red hot. We did get the bar which forms the earthed electrode red hot. Lately Mr. Ferranti brought some plugs for us to test; we were able to demonstrate to him that they would not stand up, the mica insulation was being destroyed by the heat. Sparking plugs are a very difficult problem. The two conditions which are the cause of failures, are over-heating and leakage due to carbon on the insulation. The failures due to leakage are not necessarily caused by over-oiling, they are usually caused by carbon formed due to variation in the conditions of running an engine. The carbon may be formed by excess petrol as much as oil, once carbon is formed on a part, the only chance of getting rid of it is to burn it off. I did think at one time a water cooled plug, would overcome all the troubles but I do not think so now, even if it is possible to make a water cooled plug so that it would keep at the same temperature as the combustion chamber it would still collect carbon similar to the walls of the combustion chamber. The best plug we have for general service, is the Lodge K.R. plug. This plug keeps very hot, it is just on the border line of pre-ignition, in fact, we cannot run them on the tests of new engines because of pre-ignition. It has a perforated plate for the earthed electrode, this place keeps very hot so that all carbon is burnt off. The cool est plug we have is the C.B. type K.L.G. It is useless in service because it soots up and leaks. Contd. | ||