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).
Investigation into the effects of increasing the bump on an Aerolite raised crown piston.
| Identifier | ExFiles\Box 148\1\ scan0160 | |
| Date | 9th June 1939 | |
| By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation} c. Da.{Bernard Day - Chassis Design} Da{Bernard Day - Chassis Design}/Jnr.{Charles L. Jenner} Da{Bernard Day - Chassis Design}/McS. Rm{William Robotham - Chief Engineer}/FD.{Frank Dodd - Bodies} Rm{William Robotham - Chief Engineer}/Wym.{G. Harold Whyman - Experimental Manager} Rm{William Robotham - Chief Engineer}/IMW.{Ivan M. Waller - Head of Chateauroux} Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}4/R.9.6.39. PISTONS. To investigate the effects of increasing the bump on the Aerolite raised crown piston, as compared with our normal flat top piston, as affecting - (a) Power (b) Detonation (c) Oil Temperature. Method of Test. The test unit was run with a dry sump; the oil being circulated through the engine from a separate tray beneath the sump. Procedure. Apart from normal power and detonation curves (a) and (b) above, our main interest in this test is the effect of increasing the size of the bump on the piston, on the oil temperature. It has to be remembered, that when the size of the bump is increased, the area of piston crown exposed to the combustion temperature is also increased; and in turn a considerable amount of oil is thrown up the bores, inside the piston. (a) Power. Graph No.S.8) shows the power developed when using pistons having different sizes of bumps. It should be pointed out that the section thickness of the crown has been kept the same for each piston tested. Starting with a normal flat top piston, the curves show that an increase in power is obtained from a raised crown. At high speeds, the increase is in about the same proportion as when raising the compression ratio by using a smaller combustion space on a flat top piston. But at low speeds the power increase is not in the same proportion. Actually, when using the largest bump (8:1 c.r.) less power is developed below 2000 R.P.M. than the intermediate bump (7:1.c.r.), although a proportionate increase is obtained at high speeds. | ||