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, comparing spark advance, detonation, and cylinder head design with Hispano and other models.
| Identifier | WestWitteringFiles\Q\February1927-March1927\ 111 | |
| Date | 28th November 1928 guessed | |
| (?|contd :-) -7- contact makers in the same way as on the Hispano. One particularly interesting feature is the small spark advance required to give maximum power at full load. This advance is even less than required by the Hispano which we have always considered small compared with our own engines and also less than the best results we have obtained with the new alum: Phantom. The cylinder is of course smaller than these above mentioned engines and would therefore have less distance for flame travel from the points of propogation. We are not in possession of the corresponding ignition curves for the 20 HP. but are arranging to obtain these. The engine seems particularly sensetive to the ignition control, the power rising rapidly as the ignition is advanced to the values given on print 7. and falling rapidly when these values are exceeded. With one ignition appreciably more advance is necessary and the engine is slightly more prone to detonate at low speeds than when the two are employed. Slight audible detonations are evident up to about 1250 r.p.m. but considering the high compression ratio of 5.9 to 1 and the low grade fuel used for testing, the engine seems extremely good in this respect. Detonation was more severe on the 20 HP. when we tested it with a compression of 5.4 to 1. The combustion head has rather a peculiar shape, the only reason being apparently to accommodate the valves. The cylinder head is not detachable and it therefore becomes necessary in order to remove the inlet valve, to carry the guide in a form contd :- | ||