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).
Analysis of engine performance based on compression ratios, boost pressure, and the diameter of inlet valves.
| Identifier | ExFiles\Box 179b\3\ img202 | |
| Date | 4th February 1933 guessed | |
| -12- Hp/Td.1/AMA.2.SS.{S. Smith} contd. consumption will suffer. If the compression ratio is reduced then there will be a certain boost pressure at which the air motion is equivalent to naturally aspirated conditions at 14 : 1. This also accounts for the loss of power when the compression ratio is reduced under naturally aspirated conditions. Referring to Fig.2. it will be observed that, allowing 6 lbs/sq.in. B.M.E.P. for the blower drive, the performance supercharged with a compression ratio of 12 : 1 is much better than that under naturally aspirated conditions. If the injector had been satisfactorily cooled as in Tests Series 3 the performance would almost certainly have been still better. Even as it is the performance with 8 lbs/sq.in. boost is at least equal to the best naturally aspirated result so far obtained with C.1.2. Effect of diameter of inlet valves. Test 1c was run under normal conditions except that a larger inlet valve (2.060" dia.) was used in place of the standard "Buzzard" valve (1.250" dia.). The power was 79.5 lbs/sq.in. B.M.E.P. or 7.3 lbs/sq.in. below the figure with small valves. This result is in agreement with a test previously reported and is consistent with the theory of the power being dependent on a critical relative motion of air and oil since with C.1.1. the good performance was obtained with small inlet valves and the same injector and injection conditions as used in C.1.2. Volumetric efficiency with large and small inlet valves. To measure this quantity a sharp edged orifice was fixed in the end of a cylindrical tank which was connected in series with another similar tank and thence to the inlet ports of the engine. The depression over the orifice caused by the engine suction was measured from which the air flow through the orifice could be calculated. The volumetric efficiency is taken as the ratio of the volume of air at N.T.P. actually drawn into the cylinder per revolution to the swept volume. The engine was run under its own power during these measurements. The pipe connecting the engine to the air vessels may have an effect on the filling of the cylinder and hence the results of these tests may not be true for the engine running with a short breeches pipe on the inlet ports. For comparative purposes the tests are satisfactory. | ||