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).
Ignition screening experiments for a 20/25 engine intended for a light tank.
| Identifier | ExFiles\Box 163\2\ img006 | |
| Date | 16th August 1932 | |
| To E.{Mr Elliott - Chief Engineer} & Ey. from Hs{Lord Ernest Hives - Chair}/Wst. c. R.{Sir Henry Royce} Sg.{Arthur F. Sidgreaves - MD} c. Nor. P. IGNITION SCREENING ON 20/25 ENGINE FOR LIGHT TANK We have now completeda series of experiments with our standard 20/25 battery ignition distributor and ignition coil fitted with metal screens round the coil and distributor and using metal braided aero type high tension cable earthed. First of all we tried the coil and distributor completely unscreened, then with the addition of a screen round the distributor with metal braided cables, and finally with a screen round the coil itself. We give below the results we obtained by actually measuring the voltage output from the coil under each condition of running, on our high tension volt measuring apparatus. (1) Coil unscreened, distributor screened with earthed metal braided cables. Primary voltage 12. Speed of distributor 800 R.P.M. Secondary high tension voltage 9800. At 8 volts on the supply voltage this high tension voltage was reduced to 5800. (2) Coil completely screened in addition to the distributor and the wires. With the same conditions of running, the high tension voltage available was 9200 at 12 volts and 5300 at 8 volts. (3) Coil, distributor and wires completely unscreened. Maximum voltage available was 12800 at 12 volts and 6800 at 8 volts. It will be seen, therefore, that a considerable reduction in the voltage available occurs due to the extra capacity inserted by the use of metal screening. These figures, of course, were taken without any appreciable leakage present on the high tension system. In conjunction with these experiments we also carried out tests on the sparking voltage of the K.L.G. type K.1 plugs which we use on the 20/25 in order to ascertain the correct gap for use with the screened ignition in view of such a big reduction in voltage due to the ignition screening. It was found that with a .020" gap such as is used on production the secondary voltage at the plug terminals when subjected to a pressure of 120 lbs/sq.in, which is approximately the compression pressure of the 20/25 | ||