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).
Piston performance concerning engine detonation and oil temperature.
Identifier | ExFiles\Box 148\1\ scan0161 | |
Date | 9th June 1939 | |
-2- (b) Detonation. Graph No.S.84 shows the power lost at low speeds in avoiding detonation with the various pistons, and the results agree with the power figures shown on Graph No.S.83. Road experience is showing that tendency to detonate becomes more sensitive on the raised crown piston as carbon deposit accumulates. For comparative purposes, the pistons used in these tests have been kept free of carbon. Briefly, therefore, in their present form the pistons with the large bump (.470) giving a compression ratio of 8:1 would only be suitable for a continental unit where power at the high speeds is appreciated, but in the meantime a careful study should be made of the effects of accumulated carbon on detonation. On the test bed, if full throttle is employed beyond a certain proportion to part throttle, the carbon does not accumulate beyond a certain degree as it is burnt off as fast as it collects. For the purpose of a special test, it would be useful to obtain a set of "carboned up" pistons out of a car, and straight away carry out a low speed detonation curve on the bed. Then clean the pistons and repeat the test. In this way we would be able to obtain a more accurate figure of merit for road requirements. We consider also that further development work is worth while on these raised crown pistons to further improve that factor which causes them to have some detonation control (at least when they are clean). (c) Oil Temperature. Graph No.S.85 shows heat carried away to the oil when running with the various pistons. To obtain these figures the engine was run over prolonged periods, to obtain the constant temperatures. Oil cooling was done by an external cooler, the oil being forced through by a separate oil pump which maintained circulation in the separate tray mentioned earlier. | ||