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).
Fuel mixture fault related to unvaporised fuel suspension in the engine's centre chamber.
| Identifier | ExFiles\Box 93\2\ scan0057 | |
| Date | 8th July 1935 | |
| -8- certain amount was now being deposited on the walls of the chamber. In view of this, shields were placed over the ends of the pipe which protruded into the centre chamber. The result of this was another slight improvement in tick-over. There was no further gain by extending these shields more than as shown in Fig. 15. Also there was no apparent advantage in further altering the ceiling as shown in Fig. 16. Figs. 14, 15 & 16. At this stage there is another serious fault to contend with on this latest type of pipe, which can best be described in the following way. Engine run at full throttle at 1,000 r.p.m. for 5 minutes. During this period, a certain amount of the unvaporised fuel is held in suspension, and literally tossed about in the centre chamber before entering the main bore of the pipe. This means that of the mixture leaving the carburetter, a certain amount of the petrol present is delayed in the centre chamber, resulting in temporarily weak combustion until such time as this centre chamber has a certain maximum quantity in suspension. At this point, the surplus over and above this certain quantity in suspension goes into the engine in small gulps, and is shown up externally by intermittent richness from the exhaust ports. This phenomenon, however, is not as serious in itself as that which results from it. As the throttle is gradually closed from the condition previously explained, the depression is gradually increased in the centre chamber, and normal flow takes place from the carb. through the pipe. In the meantime, the petrol previously held in suspension has had to be cleared, causing a temporarily rich mixture to enter the cylinders. This effect soon clears itself, but can be felt very distinctly on the road, after climbing a steep hill at the equivalent engine speed mentioned (1000 R.p.m.) full throttle, and gradually releasing the throttle as the car gains speed on the other side of the hill. | ||