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).
Continued tests of a Phantom II semi-expanding carburetter, focusing on acceleration and 'snap opening'.
| Identifier | ExFiles\Box 13\3\ 03-page400 | |
| Date | 19th March 1932 | |
| R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell} c. to Sd. H.Cr.{Mr Cra???ster / Mr Chichester} c. to E.{Mr Elliott - Chief Engineer} Oa. c. to Sy. 87080. Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}3/MA.19. 3. 32. PHANTOM II SEMI-EXPANDING CARBURETTER. We have continued our tests on the Semi-expanding carburetter Lec.2972 with the object of obtaining good "snap opening up" from idling speeds to high speeds full throttle. As mentioned in our previous report the difficulty encountered has been the initial jump of the suction piston when the throttle is sharply opened. This initial jump is created by the high induction pipe depression momentarily transferred to the suction piston. Immediately this happens air is taken through the large choke and a time lag occurs before the extra fuel permitted by the lifts of the taper needle valve is delivered from the diffuser, hence our flat spot where popping back occurs when the throttle is snapped open. Larger fixed chokes, one having a free area of .87 sq.in or 33% of the total, the other 1.02 sq.in., or 41.5% have been tried in order to overcome the poor opening up. They were tested on the principle that the percentage change of the fuel passing through the diffuser would not be so great when the suction piston starts to lift. These did not improve our acceleration when using a non damped piston and we began to experience trouble when changing over from the slow runner to the diffuser supply. Our conclusion is that the original small fixed choke which has a free area of .6 sq.in. or 28% of the total free area is preferable to the larger chokes on these grounds. (a) The small choke at speeds below the suction piston starting to lift develops a maximum power equal to that obtained with the larger chokes at the same speeds. (b) The acceleration up to these low speeds full power is better when running with the small choke. Good "snap opening" can be obtained by heavy damping of the suction piston that is using a small suction hole of .028 diameter. | ||