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).
Review and comparison of fuel injection system designs and components for D.I combustion chambers.
| Identifier | ExFiles\Box 133\3\ scan0057 | |
| Date | 3rd March 1939 | |
| -4- Rm{William Robotham - Chief Engineer}/Edl/R.3.3.39. Fuel Injection. For D.1 combustion chambers, central injection was stated to be preferable, this being borne out by information obtained from A.E.C. With ante-chamber engines, the fuel jet should be arranged to spray down-stream, the best position being about quarter way across the chamber. Nozzles facing up-stream gave rise to dirty exhausts, soon carboned up and gave the engine a poor performance. Starting, however, was good. Pintle nozzles were stated to be very good, but suffered from disadvantages in that a cone angle of 60° was at present the best obtainable, though a 90° cone was being produced by Bosch. The Saurer "umbrella" nozzle is definitely better in this respect, but is very tied up with patents, and can only be obtained from the makers. Both these nozzles were upset, however, by corrosion on the seats upsetting the evenness of the spray. Penetration should be arranged to just reach the opposite wall, or the piston, as indicated by a slight smudge. Excessive deposit should, however, be avoided as this indicates over-penetration. The spray angle appeared relatively unimportant. Injection pressures of 1500 - 4500 lbs/sq.in. were usually employed, the higher figure being a "build-up" pressure at high speeds due to too small a time allowance to allow the fuel pressure to drop back to atmospheric. Fuel line capacity should be as small as possible, but symmetrical fuel pipes were rather a luxury though very nice to have if easily arranged. Too large a capacity allowed small injection quantities at, say, idling to be compressed into the fuel line without increasing the pressure sufficiently to raise the injector valve, the result was a double quantity of fuel on the next stroke of the pump. Injection advance remained constant on practically all types of engines throughout the speed range, as variable injection advance was not found to be justified by results obtained. Bosch fuel equipment appeared very reliable and quite up to modern engine requirements, and servicing was better than for other makers. Sims pumps were very good, and the American swash plate "Excello" pump had the big advantage of a master cam which could be ground to suit the volumetric efficiency curve of the individual engine, ensuring a smokeless exhaust at all speeds. | ||