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).
The development and testing of fuel injector nozzles under various conditions.
| Identifier | ExFiles\Box 133\3\ scan0042 | |
| Date | 28th February 1939 | |
| -3- Nozzle Development. Nozzles were developed for two major conditions of no swirl and a specific swirl of 2.0, obtained by masking the seats. Alternative methods of inducing swirl such as vaned valve seats and diagonally opposite inlet valves only produced slight swirl, and nozzles were not developed for these conditions. Most of the development was carried out under no swirl conditions, where it was found that the best conditions were obtained with an eight hole nozzle, each hole being .010" diam. x .025" long, 140° cone angle at 5000 lbs/sq.in. injection pressure. A slight improvement was effected by increasing the pressure to 6000 lbs/sq.in., but wear and tear on the valve was too severe. Altering the length of the holes, dropped the power from 94.8 BMEP to 85.3 BMEP for holes .035" long, and 91.3 for .015" long. A second critical factor appears to be the cone angle, an alteration of only 5° dropping the power to 81.8 BMEP. The number of holes, however, did not appear to make much difference. It would appear from these nozzle tests that a condition of pure turbulence requires a very fine spray, with considerable divergence. The trouble which then arises appears to be lack of penetration, and any further increase in injection pressure leads to excessive pump and injector wear. The differential ratio of the injector valve is the ratio Area exposed to fuel with valve shut / Area exposed with valve open, appears critical as too large a valve gives sluggish operation with consequent reduction in power. An average figure of 0.7 appears best for the above conditions. When swirl is introduced, a nozzle with 5 holes, .017" dia. x .100" long x 140° angle gives the best power of 92.6 BMEP with a differential ratio of 0.87. This MEP could possibly have been improved if a smaller capacity fuel line had been employed. For this condition of swirl, due presumably to the "sweeping" action of the air as the jets penetrate it, coarser jets of greater penetrating power are required, the necessary atomisation being accomplished by the air. It is considered that for the condition of no swirl, a pintle nozzle - not tried before - would quite possibly give good results. | ||