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).
Page discussing the operation of the Phantom carburettor, focusing on low-speed performance and acceleration.
| Identifier | ExFiles\Box 66a\1\ scan0216 | |
| Date | 28th January 1929 guessed | |
| contd :- -8- vigorously - or keeps pace better with the throttle opening - and a high velocity quickly results in the choke being sufficient to prevent a break down in the fuel supply like in the previous case cited. In our Phantom carburetter we get over the low speed and acceleration trouble by having the low speed operation carried on by a separate choke and jet which accurately performs its metering duty by the compensation of the suction controlled air valve. We therefore get automatic operation at the low speed range independent of the position of the throttle. Now if the throttle is opened suddenly the suction cannot break down on the low speed choke because the air valve governs the admission of further air and this will only respond at a certain rate due to it being damped. Further, the air valve operating under suction and being controlled by a spring, ensures that the low speed supply jet supplies the demands of the engine until such time that the velocity in the high speed choke becomes sufficient to draw fuel from the main jet. The acceleration of the car depends upon the torque available at the road wheels, and comparing a static carburetter with an expanding carburetter there should be no difference assuming that each resulted in the same BMEP. - this is of course assuming the absence of 'flat spots'. The fact contd :- [Text from diagram] DILUTING AIR ONLY FOR LOW SPEED JET ENTERS THRO' HIGH SPEED CHOKE. FIG.4. SUDDEN OPENING OF THROTTLE DOES NOT BREAK DOWN SUCTION ON IDLE JET DUE TO AUTOMATIC AIR VALVE. | ||