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).
Results of spark plug measurements at atmospheric temperature, including a table of values and analysis.
| Identifier | ExFiles\Box 35\4\ scan 005 | |
| Date | 17th March 1928 guessed | |
| E.E.311. 3. Table I. Results of Measurements at Atmospheric Temperature. | Plug No. | Gap Inches. | Sparking Characteristics under air Pressure. | Insulation Resistance 1,000 volt Megger Ohms. | Effective Resistance by Magneto Ohms. | |---|---|---|---|---| | 1 | 0.011 | No spark between electrodes at any pressure. Shorting over surface of insulator. | 20,000 | 25,000 | | 2 | 0.015 | ditto. | 11,000 | 15,000 | | 3 | 0.009 | Sparking at electrodes up to 200 lb.per sq/in | Infinity | 2 Megohms | | 4 | 0.020 | No spark between electrodes at any pressure Shorting over insulator | 30,000 | 35,000 | | 5 | 0.010 | Sparking at electrodes up to 200 lb.per sq/in. | Infinity | > 2 Megohms | | 6 | 0.018 | Sparking at electrodes up to 15 lb.per sq/in. Shorting across insulator. | 40,000 | 45,000 | It will be seen from the above table that four of the plugs, Nos. 1,2,4 and 6 have exceptionally low insulation resistances and as it is known that any plug whose insulation resistance is lower than about 0.2 megohms will cause mis-firing, it is clear that these particular plugs would cause complete failure of ignition in the cylinders of any engine in which they were fitted. Previous investigations (R.A.E. Reports Nos. E.E.276 and E.E.280) have shown that where the percentage of T.E.L. dope in the fuel is high, as in this case, the deposit formed on the plug insulator is of a highly conducting nature. There is therefore little reason to doubt that the failure of the four plugs in this instance was due to this cause. 5. Measurements of Effective Insulation Resistance at Various Temperatures. Following the above tests it was decided to measure the effective insulation resistance of the plugs at temperatures of the order of those reached under actual | ||