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).
Vehicle cooling system tests and conclusions drawn from the results.
| Identifier | ExFiles\Box 155\1\ scan0296 | |
| Date | 24th June 1937 | |
| -2- Tests were carried out on 37-MX.{John H Maddocks - Chief Proving Officer} car and the method of testing was to thoroughly warm the car up by driving it hard and then idle the engine at its minimum idling speed with the car stationary in a spot sheltered from direct winds. All the radiators tested were fitted with steam valves set to blow at 2½ lbs/sq.in. The top and bottom water temperatures and outside air temperatures were noted at fixed time intervals, as well as underbonnet temperatures, petrol feed temperatures etc. CONCLUSIONS FROM TESTS. Sheet No.1. shows(attached) the results of the tests and indicates that we can gain considerably in low speed cooling by adopting the 5 blade fan and also by increasing its speed. However, the speed ratios above 1/1 were too noisy to be desirable. These results also indicate that we gain in low speed cooling by opening the bonnet shutters and still more by fitting a louvred bonnet - a small gain is obtained by fitting the ring surrounding the fan, but certainly not sufficient to justify the difficulty and expense of fitting this item, particularly as later tests show no gain with it under high speed conditions. The only matrix which gave as good results as the Std. Mk.VI. one, was that with air slots at the side to admit cool air under the bonnet (made in std. Mk.VI. construction). When idling with the car stationary, these slots actually served to permit air to escape forward past the matrix from under the bonnet and in these circumstances gave a better cooling figure than the standard matrix. As can be seen from the times to reach 100°C. and also to lose water given on Sheet (1), these tests represented more severe conditions than would be met with in the most dense of traffic. To illustrate this point we give on Sheet (2) the results of some runs in the most dense London traffic which we could find - it will be seen that although the atmospheric temperature was well above the critical air temperature for the car 100°C. was not reached under these traffic conditions. Of course, if the stationary blocks are long enough and the moving intervals between short enough, loss of water would occur whenever the atmospheric temperature was 3°C. or more above the idling critical air temperature (steam valve blow off pressure 2½ lbs/sq.in. equivalent to a boiling point of 105°C.) From these figures, which show that the average temperature drop across the radiator while idling is approximately 6°C, we see that we shall not be able to raise the critical air temperature much by decreasing this temperature drop, owing to the law of diminishing returns, however, we shall carry out experiments to determine the effect of increasing the water flow on the heat transmission. | ||