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).
Downdraught carburetter tests on the Phantom II.
| Identifier | ExFiles\Box 182\M19\ img122 | |
| Date | 26th February 1931 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey} c. to Sg.{Arthur F. Sidgreaves - MD} Nor. c. to Da.{Bernard Day - Chassis Design} By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey}G/AT.26.2.31. X7080 DOWNDRAUGHT CARBURETTER ON PHANTOM II. We have carried out several tests with the Downdraught Carburetter on Phantom II. The carburetter functions as expected with regard to the extra air valve metering needle valve and diffuser but modifications to needle valve taper and diffuser are necessary to obtain the required metering. For the time being we have not worried about metering but adjusted the mixture for each condition. One of the chief trouble encountered is distribution. At full throttle and speeds above 1250 R.P.M. the distribution is reasonable but below that it becomes very erratic as the speed is decreased. Under throttled conditions the distribution is definitely bad, a whole characteristic changing with varying positions of the throttle. It seems that the throttle being so near the distributing pipe deflects the wet fuel and the extra air passing the centre choke in a cylindrical section does not mix intimately with the dense mixture from the centre choke. It is difficult to state any general tendency to the distribution as it fluctuates considerably - some cylinders receiving alternatively very rich and very weak. We have tried for expl. a distance piece 1.5" long between the carburetter flange and induction pipe but this has resulted in no improvement. Had this been successful it could not have been employed due to insufficient room under the bonnet. We have also tried a smaller outer choke - reduced to - dia. but this has not improved distribution. We think the throttle body diam. could be reduced with advantage and perhaps a continuation of this diam. in the form of a sleeve projecting into the induction pipe would assist distribution. This would be easy to test and could be made in the form of a sleeve containing a reduced throttle. Considering the good results we have obtained with the weir type induction system and the std. carb. it may be advantageous to try some such scheme with the Downdraught carb. | ||