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 spark advance, ignition, and compression ratios between Hispano, Lorraine, and 20 HP engines.
| Identifier | WestWitteringFiles\S\March1928-May1928\ Scan016 | |
| Date | 1st August 1923 guessed | |
| contd :- -2- way as the system used on the Hispano. An interesting feature observed was the small spark advance required when using dual ignition, to give maximum power. With one ignition appreciably more advance was necessary and if the optimum advance were used the engine was found more prone to detonate at low speeds than when operating on the best ignition advance with the synchronised ignition. Considering the high compression ratio of 5.9 to 1 and the low grade fuel employed for these tests, the engine seemed particularly good for not detonating. Detonations were more severe on our 20 HP. when tested with a 5.4 to 1 compression ratio. A print is appended which shews the minimum advance required to give maximum power on the Lorraine with one and two ignitions, also for comparison is a similar curve for the 20 HP. We see the 20 HP. single ignition curve requires considerably more advance than the single advance on the Lorraine. There are several factors which could account for this. The induction pipe depression on the 20 HP. is higher than on the Lorraine and we know more advance is required with a high induction pipe depression due to the greater dilution by the exhaust gas which is drawn back to mingle with the fresh charge. This is clearly demonstrated by the greater advance that can be given when an engine is throttled. Another factor is the higher compression ratio of the Lorraine and we have found that a high ratio requires less advance than a low ratio [redacted] which is probably due to the smaller amount of residuals left in the combustion chamber, and the higher temperature of compression. An article on 'Spark Advance' in Internal Combustion Engines' is given in contd:- | ||