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 report on the performance of a Bosch injector versus an in-house design, discussing differential ratios and valve settings.
| Identifier | ExFiles\Box 179\3\ img044 | |
| Date | 8th January 1932 | |
| -2- When fitted on to a test pump, the Bosch injector behaved in a faultless manner, in that the nozzle cannot be made to dribble however slowly the pressure is built up in the fuel line. Regarding the extra weight of the Bosch valve needle, we cannot see how this can be an asset, as our previous experience would suggest the opposite. The fact that a fairly large differential ratio is used on the Bosch nozzle, proves that a low value is not essential to good performance if the valve is working correctly. We are of the opinion that, in the case of our own valve, the low differential ratio is merely a means of achieving a more definite 'cut-off' with a comparatively poor valve. From these results we must accept the fact that the Bosch injector is far superior to our own in design or workmanship, and we think that we should make every effort to produce an article at least equal to the Bosch. As we shall soon have our combined pump and injector ready for test, it is highly important that we shall not be handicapped by inferior nozzles. It is worthy of mention that the Bosch nozzles are remarkably consistent in behaviour; three examples of the same dimensioned nozzle were found to vary in performance by no more than 1.5 lbs/sq.in. B.M.E.P. It will be noted that the Bosch nozzle requires a valve setting of but 3000 lbs/sq.in. to give the best performance; a higher pressure actually reduces the power output. In the case of our own nozzle a setting of 5000 lbs/sq.in. is necessary. This difference is probably controlled by several factors, but we think that the seating pressure of the valve is mainly responsible; thus the lower the differential ratio, the higher will be the lifting pressure for a given seating pressure. It is interesting to note that the performance obtained from a second Bosch nozzle, the spray holes of which were dimensioned to the Bosch company's specification for our combustion chamber, was considerably lower than that mentioned above, and only amounted to 73.5 lbs/sq.in. B.M.E.P. at a specific consumption of .300 lbs/HP/Hr. | ||