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).
Report analyzing carburettor performance and the effects of turbulent air flow on induction pipe depression.
| Identifier | WestWitteringFiles\Q\2-July1927-September1927\ 117 | |
| Date | 19th September 1927 guessed | |
| contd :- -3- could be reduced by using a 'straight through' type of carb. on the existing std. induction systems. On the Phantom an old type horizontal Claudel was attached to the hot spot bend and a Zenith triple diffuser used on the 20 HP. The Claudel reduced the depression from 3.2 to 1.5 in. of mercury on the Phantom, and on the Goshawk with two Zeniths, a depression as low as .5" was obtained at 3000 r.p.m. Appended are curves shewing the gain in power when working with the lower depression. We think these tests prove conclusively that the major cause of the high induction pipe depression is not the chokes and size of the air ports but the turbulent air flow through the carburetter. The 'straight through' type of carb. restores pressure to a certain extent as the air velocity decreases after passing the choke with the result that good volumetric efficiency is obtainable. There appears little chance of restoring pressure in the Phantom or Goshawk carburetters as the air must suddenly fall in velocity after its passage through the chokes and air ports, or where it enters the body. It would be imagined a considerable amount of 'eddying' takes place here and the two air streams through the ports and high speed choke somewhat oppose each other. The relatively low velocity in the body of the carb. would be very favourable for the precipitation of fuel, particularly in cold weather and would consequently not assist in promoting good distribution. When the Zenith and Stromberg carbs. were tested on the 20 HP., we got contd :- | ||