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).
Supercharged engine's performance, detailing issues with temperature increases, detonation, and the lack of an inter-cooler.
| Identifier | ExFiles\Box 22\5\ Scan131 | |
| Date | 18th November 1924 | |
| R.R. 408A (20H) (D.A. 622 20-2-24) z.r.m. -2- EXPERIMENTAL REPORT. Exptl. No. REF: Ha/Rml/Lg18.11.24. It is brought into action when required by means of a multiple plate clutch. It is completely cut off when not in use by a spring loaded piston valve. The carburetter is supplied with a safety valve which opens at a pressure of 10 lbs/sq.in. The normal air intake is cut off by a butterfly valve when supercharging. The blower cannot be used at engine speeds below 1800 r.p.m. as it will be seen from the power curves that it actually reduces the engine efficiency when under these conditions. The distribution is very bad at low speeds. Temperatures of the charge were taken in the induction pipe. When running normally - this is about 58°C - upon supercharging the temperature rises in a few moments to 100°C due to the fact that there is no provision whatever for cooling the air after it has been compressed by the blower. The lack of some sort of inter-cooler is a very serious defect in this system as it largely cancels the main benefit to be derived from forced induction i.e., that the temperature at the end of the compression stroke shall be the same as normally. The net result is that the engine behaves as if it was being run on far too high a compression ratio - violent detonation occurring at speeds below 2000 r.p.m. when supercharging, and pre-ignition commencing with consequent falling off in power after a very short time. The super-charged power curve was obtained by running the engine for a few moments only with the blower in action contd :- | ||