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).
Investigation into poor slow running performance caused by the supercharger and various attempts to improve it.
| Identifier | ExFiles\Box 140\1\ scan0192 | |
| Date | 30th October 1935 | |
| -3- Slow Running. We have attempted to improve the slow running with the blower on the induction side of the engine, feeding downwards into the manifold. We fitted a transparent window at the Tee joint of the manifold, and it was immediately apparent that one of the causes of poor slow running was that wet petrol drained from the supercharger, ran down the inside of the intermediate pipe bend, and fell into the manifold in large drops which were drawn into one or other of the branch pipes. The collecting device shown in Ms.2211 improved this state of affairs considerably by ensuring that only vaporised fuel was allowed to enter the branch pipes. With this arrangement the slow running was no worse than when the blower fed over the rocker cover with a long jacketted intermediate pipe. We have again gone over the question of heating the supercharger casing, and have decided that better slow running is obtained by doing so. We lose about 5 M.L.P. however at F.T. by heating the casing (see curve D.V.62 attached to Hs{Lord Ernest Hives - Chair}/Wms.1/KW.21.12.34). A possible scheme would be to have a small capacity jacket round the supercharger with an arrangement whereby the water supply is automatically turned off when the throttle is more than say one eighth open. As a matter of interest we tried the supercharger mounted on the exhaust side, feeding into a 4-port induction pipe with an exhaust hot-spot, similar to the downdraught carburetter system developed for the 25 HP. engine. The slow running was no better than the best we have obtained with a six port pipe. We have arrived at a position where we think we can make the slow running passable for a Bentley engine, but we have never had a system which compares with the best we know for an unsupercharged 25 HP. engine. | ||