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).
The insulation resistance of spark plugs at various temperatures, detailing the effects of lead deposits and comparing different plug insulator materials.
| Identifier | ExFiles\Box 162\4\ img168 | |
| Date | 7th September 1936 | |
| -2- test at various temperatures, obtained by inserting the plug in a small electric furnace and measuring the insulation resistance at various temperatures. The curves attached show the increase in electrical conductance as the plugs heat up and the increase when the plugs are covered with lead deposit. For comparison a leaded aero plug and also a plug cleaned are also shewn The initial loop on the curves is probably due to moisture drying out. Referring to the dotted line on these curves, which indicates the leakage after the plug is well heated, it will be seen that the worst plug had a resistance of 70 megohms at 600°C. as compared with 400 megohms after cleaning and 480 megohms when new. In the actual engine these figures are likely to be much worse due to the presence of moisture and oil deposit on the inlet and compression stroke, but the curves serve to indicate the measure of the reduction in resistance caused by the deposits. It is thought that Ceramic insulated plugs are less prone to the formation of conductive deposits than Mica in view of the almost universal use of such plugs in the U.S.A. where Ethyl is firmly established and tests are being carried out with Lodge, Champion, and A.C. plugs to ascertain this. In the case of the A.C. plugs the insulators are made in the New Aluminium Oxide insulator known as "Intercorund" which is claimed to have special heat resistance and thermal conductivity exceeding that of any other known Ceramic. It is also claimed to be impervious to lead attack. Tests are also being made with mico plugs of different heat values and construction. Hs{Lord Ernest Hives - Chair}/E.E.West. | ||