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).
Comparison and analysis of different fuel injector and nozzle designs, including Bosch and R.A.E. types.
| Identifier | ExFiles\Box 133\3\ scan0064 | |
| Date | 6th March 1939 | |
| -4- dimensions were 7 holes of .010" dia. x .035" long and 130° cone angle. On inducing a specific swirl of 1.2 with the standard piston, a five hole R.A.E. nozzle .013" dia. x .050" long x 140° cone angle gave a power of 94.8 lbs/sq.in. It will be noted that less divergence is again required with swirl. Tests on an R.A.E. nozzle showed a differential ratio of .47 to be best, a BMEP of 99.2 being possible. This valve is only good for this type of injector, and has the disadvantage of giving a relatively low closing pressure. It is necessary due to the tendency of R.A.E. valves to be "sticky" in operation. With a Bosch integral construction nozzle, a ratio of .75 gives the best power of 101.6 lbs/sq.in. A flat top piston required a nozzle of normal size, but the cone angle had little effect between 140° and 160°. Comparison of Injectors. Bearing in mind the fact that these tests were carried out in 1932, it was found that the optimum performance was given by the Bosch nozzle. This appeared to be due to its integral valve and seat construction. The alignment being good and the valve action sensitive and rapid. The R.A.E. nozzle, however, had a detachable seat, and alignment of seat and valve could not be guaranteed under all conditions. Also to be leak-proof, clearances had to be finer and this increased friction and poor alignment robbed the valve of sensitivity and dropped the power output of the engine. A lighter valve coupled with a 25% quicker cam and a differential ratio of 0.47 brought the nozzle up to almost the same output as the Bosch. An "inverted" injector - valve opening outwards - has the advantage that the mechanism is totally enclosed in the fuel line and no leak path is presented. This requires less accurate workmanship and is cheaper to produce, but suffers from disadvantages in the way of increased capacity between the valve and spray holes, and increased fuel line capacity. | ||