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).
Preliminary test results and modifications for the Phantom II Expanding Carburetter.
| Identifier | ExFiles\Box 179\2\ img240 | |
| Date | 12th February 1932 | |
| To R.{Sir Henry Royce} From Ha/Sdl. ORIGINAL c. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to R.{Sir Henry Royce} Ds. c. to Hy.{Tom Haldenby - Plant Engineer} R.R. Phantom ll Expanding Carburetter. We have carried out preliminary tests on the Phantom ll expanding carburetter to LeC.2972. The first tests were made with the object of determining the power output capacity of the carburetter without attention being paid to the metering, the mixture strength being independently adjusted by hand for each speed. It was found that the air valve permitted full lift at 750 RPM. full throttle. From the consideration of the metering, which point would be tackled later, it would be necessary for the air valve and the jet operating needle to attain full lift only at the maximum output of the engine which occurs at approximately 3000 RPM. Consequently a spring exerting a pressure which together with the weight of the valve amounted to 10 lbs. when at maximum lift was employed and gave full air valve lift at 3000 RPM. The jet orifice had to be increased from .125 diameter to .15 diameter, also the holes in the diffuser head were increased from .375 diam. to 1.25 dia. to permit sufficient fuel flow for maximum power. The power curve obtained is shown on (Y.1304) compared with the 2.500 bore S.U. and shows a maximum B.H.P of 150 or only 7.1% lower than the single 2.5", 13° above standard. The combined free area of the small and large chokes in the carburetter is 2.98 sq.ins. as against 4.98 sq.ins. the free area of the S.U. carburetter. The low speed torque is quite good and a little better than the S.U., the depression of the R.R., however, is greater than the S.U. at speeds above 1750 RPM. The distribution at all speeds full throttle is good but it is very susceptible to throttle position, especially at low speeds. A test was made with the suction passage to the top of the air valve position blanked off and the upper side of the piston open to atmosphere. It was then found that the piston was then lifted by the pressure difference on each side of the air valve diaphragm and would attain maximum lift at 2500 RPM. full throttle. By fitting a spring on the air valve exerting a pressure of (11 ozs) together with the weight of the air valve (9 ozs.) the max. lift was obtained at 3000 RPM. full throttle The valve commences to lift at 650 RPM. full throttle. | ||