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).
Analysing engine performance from indicator cards, focusing on compression, ignition, and external factors.
| Identifier | ExFiles\Box 54\4\ Scan048 | |
| Date | 25th September 1924 | |
| R.R. 493A (50m) (D.B. 175 25-9-24) J.H.D. EXPERIMENTAL REPORT. Expl. No. REF: Hs {Lord Ernest Hives - Chair} /Rm {William Robotham - Chief Engineer} /LGS.9.24. COPY. INDICATOR CARDS. It will be observed from the indicator cards that the cylinder fills up very well, the compression pressure being about 85 lbs/sq.in. The conventional compression ratio of the engine being 3.45 - 1, this corresponds to a volumetric efficiency of over 100% due to the supercharge. We are of the opinion that this is a flattering figure, as the charge is bound to have undergone a considerable amount of pre-heating before it reaches the cylinder. The best ignition point is 14° B.T.D.C. and the charge ignites very slowly, the peak pressure being delayed until 30° A.T.D.C. The peak pressure is very low, the resultant I.M.P. being 54¼ lbs/sq.in. This figure agrees very well with that of 53¼ lbs/sq.in. obtained by motoring and brake tests. There are two external factors which may influence this :- (a) Position of the plug. At present we have only been able to use the plug in the transfer port. (b) Carburation. This does not seem to be very satisfactory - we are trying another carburetter. In addition to these we have the fact that the scavenging port opens when the pressure in the cylinder is 80 lbs/sq.in. The scavenging pressure for the test was 3 lbs/sq.in., contd :- | ||