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).
Engine cooling system performance, including pump pressure, road tests, and radiator modifications.
| Identifier | Morton\M21\ img084 | |
| Date | 12th April 1933 | |
| -4- and the pump pressure was found to vary exactly as the square of the engine RPM, being 2 lbs/sq.in. at 1000 RPM. or 1 lb. at 700 RPM. The water flow with these washers was only 10 galls/min. The size of the washers was therefore increased to .5" and the car was tested under load on the dynamometer, the complete system including the non-return valve and the injector being fitted. The system functioned very satisfactorily at engine speeds above 750 RPM. but below this speed the pump pressure was insufficient to work the injector against the high delivery head. It would be possible to overcome this by fitting a venturi of .750" throat dia. in the water pump suction pipe, which is of 1" bore, and to feed the injector delivery into the throat of the venturi as shewn in sketch No.2. It was not found possible to try this scheme in the time available, and so a restriction washer .875" dia. was placed in the circuit between the header tank and the injector. This reduced slightly the head on the pump inlet and enabled the injector to work down to a speed of 650 RPM. under load. Tests on Road. On road tests, including hills of 1 in 5 gradient, the system worked very satisfactorily, no trouble being experienced and no water being lost. Under normal conditions the car would never be driven for long periods at speeds below 650 engine RPM. (≈ 17.5 m.p.h. in top gear), but during the tests it was driven for over half a mile at its lowest top gear speed of 5 m.p.h., at the end of which the header tank was still full of water and the hotwell contained 2 pints. Under cruising conditions in top gear (35 m.p.h.) the temperature recorded in the top of the cylinder blocks was 103ºC. and the water pump pressure was 4 lbs/sq.in. The highest temperature measured was 108ºC. at 15 m.p.h. in 1st. gear near the top of a long hill, the corresponding pump pressure being 6 lbs/sq.in. A bi-metal element fitted in the radiator vent causes a warning light to appear whenever steam is being lost. The average air temperature during the tests was 18ºC. but even when driving with the radiator shutters closed, steam was only lost above 53 mph. in top gear or on steep hills. With the shutters open no steam was lost from the vent except occasionally for a few seconds at a time when changing from 1st. gear to 2nd., or 2nd. to 3rd. after a long hill climb, this being attributed to a combination of the effects of momentarily reduced air flow through the tube block and the continued rapid generation of steam in the cylinder blocks causing a puff of steam from the vent. This radiator would appear to be suitable for colonial conditions. | ||