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 erosion of different coated spark plug electrodes during tests in a Kestrel engine.
| Identifier | ExFiles\Box 58\2\ Scan167 | |
| Date | 1st November 1933 guessed | |
| 2. E&I.818. The amount of erosion of the electrodes during tests of 40 hours duration on each material was measured at frequent intervals and the results are shown on Fig.1. It will be seen that the platinum coating on pure nickel delays the onset of measurable erosion for a brief period (approximately 7 hours); beyond this point, however, erosion proceeds at approximately the same average rate as the pure nickel electrode. After 40 hours sparking the erosion of the two materials is roughly of the same order; the platinum coated electrode being slightly the better of the two. It is clear, however, from the shape of the curves that an extension of the test would eventually have produced equal amounts of erosion on both materials. 4. Tests in "Kestrel" engine. The Lodge A.2/1. 2 point plugs with platinum coated electrodes and two K.L.G. V.7 plugs with palladium and rhodium coated electrodes respectively were fitted in a "Kestrel" engine, one plug of each type in the inlet side and one of each in the exhaust side. The remainder of the plugs were standard Lodge A.2, single point. The engine was run at 2250 R.P.M., 90% power, on standard fuel D.T.D.134. Measurements of the erosion of the plug gaps of the two pairs of experimental plugs and one pair of standard plugs were made at 10 hour intervals during a test of 30 hours duration. The results are shown on Fig.2. The shape of the electrodes and number of gaps not being the same in all three sets of plugs tested, the results are not strictly comparable; they serve, however, to show that a coating of either of the 3 metals referred to delays erosion of the electrodes during the early life of the plug. This confirms the laboratory tests where microscopical examination showed that penetration of the coating occurred within 7 to 10 hours under a rate of sparking approximately 5 times as great as would occur in practice. Under engine conditions and a normal rate of sparking the effective life of the coating as an inhibitor of erosion does not appear to be widely different. The amount of erosion found on the V.7 plugs coated with palladium and rhodium was greater after 30 hours run than that of the A.2 plugs with non-coated electrodes. This is attributed in some measure to the different shape of the electrodes used in the two types, but at the same time it demonstrates the ineffective nature of the coating in relation to prolonged running. The Lodge A.2/1. plugs with platinum coated electrodes show, on the other hand, a smaller amount of erosion than the standard A.2. plugs. This is not unexpected since the latter have single point earth electrodes, whereas the former are of the twin point type. If allowance is made for this difference the amount of erosion in 30 hours would be approximately the same in each case. | ||