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).
Analysis of fuel pump discharge and spill characteristics, with supplementary oscilloscope observations of the fuel jet.
| Identifier | ExFiles\Box 179b\3\ img104 | |
| Date | 1st February 1933 | |
| Hg/Ud.6/AIR.2.33 contd. -14- Referring to Table 4, in which are set out the discharge and spill at normal and maximum injection for the full speed range, it will be noted that at maximum injection the sum of the discharge and spill is practically constant at all speeds. It is consistently greater than the theoretical discharge and this difference is attributed to direct leakage from the suction chamber to the spill chamber. Considering now the sum of the discharge and spill at normal injection, it is seen that this decreases from .479 ccs/cycle at 1000 R.P.M. to .392 ccs/cycle at 336 R.P.M. This falling off is made up of .028 ccs decrease in discharge and .059 ccs decrease in spill. From an examination of the pump, neglecting the compressibility of the fuel and the possible variations in volumetric efficiency, the pump chamber will be full and sealed off at the instant the pump plunger passes the edge of the suction chamber annulus. After the pump cam has passed through 19° (normal injection) the relief ports open and the remainder of the oil in the pump chamber passes to spill. Hence the spill plus the discharge should equal the volume displaced by the plunger during its effective stroke. From Table 4 this is seen to be approximately so for maximum injection when the spill ports are never opened. This suggests that the cause of the falling off in the sum of the discharge and spill may be connected with the spill port design. Without further experiment it is not possible to determine precisely the cause of this effect but so far as the delivery characteristics of the pump are concerned the matter does not appear of great importance. It is hoped to investigate the matter again at a future date. SUBSIDIARY OSCILLOSCOPE OBSERVATIONS. After some preliminary experiments the Elverson oscilloscope was adapted and adjusted to give a very clear view of the jet. Commencing at the first appearance of the jet and advancing the phase gear, the development of the jet throughout the injection period could be studied. Viewed under the oscilloscope the spray appeared like a jet of steam showing that the drops were extremely small. At the beginning of injection a small wisp of atomised oil issued from the nozzle, this spread in a fine cone across the field of view, growing denser and broader as injection progressed until it thinned out rapidly at the nozzle and then abruptly terminated. | ||