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).
Investigation into carburetter flooding and fuel starvation issues on a Phantom II during cornering.
| Identifier | Morton\M19\ img146 | |
| Date | 17th April 1931 | |
| ORIGINAL To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey} c. to SG.{Arthur F. Sidgreaves - MD} Nor. c. to E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} c. to HY.{Tom Haldenby - Plant Engineer} PHANTOM II. TWIN CHOKE CARBURETTERS. X7080. We pointed out in a previous report that we had experienced trouble with flooding when making sharp or fast left hand turns, and symptoms of fuel starvation when taking right hand turns. We have further investigated this trouble by observing the carburetter with an open bonnet and found excessive flooding on left hand turns. If the car is driven round in a circle on full lock, petrol pours out of the top of the accelerator pump and continues to do so far in excess of the amount contained in the float chamber. The flooding is so excessive that by following behind in another car the petrol can be seen running out from under the car on corners. A simple test was made to determine the approx. magnitude of the outward acceleration during fast cornering by hanging a plumb line inside the car and noting the angle taken up on a corner. It was found that 30° inclination could be easily recorded which represents about .58g. We then made a static test by tilting the carburetter 30° when coupled up to a petrol feed and found the fuel ran straight past the needle valve. On removing the fuel feed and caps above the needle valves, it was found on reaching an angle of 14° - with a normally filled float chamber - the needle valve opened. Further examination with the top half of the carburetter removed shewed that at 14° the fuel rises in the one half of the float chamber and completely submerges one float, while it recedes from the other half leaving that float practically high and dry. This means that there is not sufficient reserve buoyancy on the float in the filled half of the float chamber to compensate for the falling level in the other, and support the weight of floats and hold the needle valve against the fuel head. Appended diagram shows the observed effect. It will be noticed that the floats are not symmetrical above and below the normal fuel level - the top portions being removed in order to provide a compact float chamber. Our Kestrel and Buzzard engines have symmetrical floats, but the R.{Sir Henry Royce} engine has similar floats to P.II. The conditions are | ||