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).
Test report comparing the performance of three different types of spark plugs in a supercharged F.X. engine.
| Identifier | ExFiles\Box 35\3\ scan 173 | |
| Date | 22th August 1927 | |
| X4196 Hs{Lord Ernest Hives - Chair}/VH/LG22.8.27. F.X. WITH SUPERCHARGER. X4196 (16.6.27) X4550 X2410 Sparking plugs. During our tests with the supercharged engine on a mixture of aviation spirit + 20% benzol we tried three different types of sparking plugs :- Champion R.12. Detachable centres. Pot insulator. 'Salamanite'. Good under oily conditions. Max: HP.430. Champion R.1. Detachable centres. Pot insulator. 'Salamanite'. Fairly good under oily conditions. Max: HP.490. B.G. mould 1XB. Detachable centres. Mica insulator. Oils up readily. Max: HP. 480 The R.12s, which had been in use during tests with this engine on 100% benzol became very hot and shewed signs of cracking up when the 20% benzol mixture was used. The max. power figure on these plugs was roughly 430 HP. and a change was made to R.1s. On these (champion R.1.) plugs the maximum appeared to be in the neighbourhood of 480 HP. Pre-ignition first set in on A.1. cyl. and the exhaust plugs was removed for examination. It was found that a cracked insulator had resulted. B.G.mould 1XB. plugs were then fitted, 18 only, were available and these were fitted to the exhaust side and to inlet cyls. shewing the most pronounced signs of heat. The max. power was approx. the same as with the R.1. plugs - 480 HP. Pre-ignition first set in on B.1. cyl. The exhaust plug (a BG.1XB) was found to have the mica insulation broken away from the centre electrode, which shewed signs of excessive heat. The central electrode of the BG.1XB. plug consists of a short length of nickel alloy held in a rather heavy steel body. It is thought that ultimately pre-ignition is set up by this rather large and insulated body of metal becoming hot and heating the gas in the immediate vicinity. In the case of the Champion plug, the central electrode is of small section and in one piece, passing right through the Salamanite insulator and rivetted over the brass cap, which is threaded to take the terminal. The small annular space between this central electrode wire and the insulator is fitted with a cement which contd :- | ||