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 head design, focusing on turbulence, detonation, volumetric efficiency, and comparing single vs multi-cylinder performance.
| Identifier | ExFiles\Box 133\2\ scan0098 | |
| Date | 13th November 1934 | |
| -3- HS{Lord Ernest Hives - Chair}/Smth.14/KW.13.11.34. By increasing the forced turbulence on the ramp head we have effected a considerable improvement in detonation. Would it be possible, or worth while, to try the effect of increasing the turbulence still further ? We feel that volumetric efficiency, and hence power, can be obtained readily enough by the adoption of some such head as the ramp, pent house or the "Power-head", and that when we have developed rubber engine mounting so as to eliminate roughness, detonation will be the main consideration which will determine which head we use. We notice on the drawing LeC.3871 that an increase in compression ratio of 0.44 lowers the head by 0.11 inch. It appears that the present design of the head precludes the use of a ratio higher than about 7.5 to 1 without some modification which will keep the inlet valve seat clear of the joint face. What modifications would be necessary for a compression ratio of, say, 9 to 1, which we can use on the standard head for competition work ? Would the modifications materially affect the performance of the head ? Regarding volumetric efficiency, we note that you record 86% on the standard head. We have recently measured the efficiency of a multi-cylinder engine and find that the maximum value is 75% (see attached curve). Our fuel consumption at 2500 R.P.M. was 43 pts/hour, or 7.17 pts/hour per cylinder. From sheet 4 of your report, the consumption on the single cylinder at 2500 r.p.m. was 8.22 pts/hr, which is about 86/75 x 7.17, thus confirming to a certain extent the accuracy of the air measurements. It would seem then either that the intake depression is less on the single than on the multi-engine, or that some ramming effect is present in the former case and not in the latter. It occurs to us that if the intake of the single cylinder was restricted to give the same volumetric efficiency with the standard head as on the multi, the improvement in power of the ramp head over the standard may be relatively less. It may be well worth while repeating some of the power curves under this condition to check the point. HS{Lord Ernest Hives - Chair}/F.Ll.Smith. | ||