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).
Description of tests on reduced compression ratios and supercharging performance.
| Identifier | ExFiles\Box 179b\3\ img201 | |
| Date | 4th February 1933 | |
| -11- He/14.1/AM.4.2.33 contd. DESCRIPTION OF TESTS. Series 1. In all the tests run in this series the sleeve shown in Fig.1 was removed and water circulated in the annulus thus formed. On account of the restricted space and the difficulty in inducing a satisfactory flow of water, the injector was not so efficiently cooled as in Series 3 & 4 and the performance of the engine in this series suffered in consequence. Effect of Reduced Compression Ratio. For the supercharging tests the compression ratio was reduced to 12.0 : 1 by inserting a washer under the cylinder block as done in the case of C.I.1. A test under naturally aspirated conditions with this compression ratio was first run (test 1a) and a power figure of 83.2 lbs/sq.in. obtained at normal injection which is 3.6 lbs lower than the power with the normal compression ratio of 14 : 1. Supercharging. Supercharged consumption loops were now taken with boost pressures of 5, 8 and 10.1 lbs/sq.in. and these are plotted on Fig.2 from which it will be seen that the best performance is obtained with 8 lbs/sq.in. boost. This is in accordance with the results in C.I.1. It appears that for a given compression ration there is a critical boost pressure at which the highest power is obtained for a given injection quantity. In a systematic investigation of supercharging a series of tests should be run in which the power at normal injection is measured for a range of boost pressures for various compression ratios. By plotting B.M.E.P. against boost pressure for each compression ratio a series of pecked curves would be obtained from which it would be possible to determine the best conditions for supercharging. It is suggested that the fact that for a given compression ratio there is a critical boost pressure is consistent with the theory frequently advocated by the writer that in the direct injection engine with open type cylinder a high B.M.E.P. and a low specific consumption is dependent on a critical relationship between air and oil motion within the cylinder being obtained and maintained. If a good performance is obtained under naturally aspirated conditions with a compression ratio of 14 : 1 then supercharging the engine at this ratio will disturb the relative air and oil motion and the | ||