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).
Comparison of calculated versus actual engine performance data, with an analysis of power loss and volumetric efficiency.
| Identifier | ExFiles\Box 134\1\ scan0064 | |
| Date | 21th December 1937 | |
| -5- results we have the following table:- RPM. 500 1000 1500 2000 2500 3000 3500 4000 Calculated. 107.5 119.0 122.5 120.0 116.0 108.5 96.5 76.5 Actual. 106.0 119.0 121.0 119.0 113.5 107.0 95.2 72.9 % Diff. 1.42 Nil. 1.24 0.840 2.20 1.40 1.37 4.95 In each case, it will be noted the calculated figures are slightly in excess of the actual figures, which may be accounted for by the extra piston loading slightly increasing mechanical friction. In no case, however, does the total variation exceed 5%. It would appear, therefore, that the power loss is due to a reduction in volumetric efficiency, which, as this affects the compression pressure in almost the same proportion as it affects the power, cannot be due to excessive temperatures, but must be put down to the shape of the piston crown. Considering this, it is thought that the shape of the crown may be giving the gas an organised swirl instead of mixing it up anyhow, and that the gas currents so induced are tending the bring the gas passing through the ports to rest long before the inlet valve closes, with a consequent reduction of volumetric efficiency. continued | ||