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).
Technical analysis of engine ignition timing and spark generation.
| Identifier | ExFiles\Box 54\5\ Scan309 | |
| Date | 30th October 1928 guessed | |
| -2- Contd. Further, the fully advanced make will occur R + 120r - d degrees before dead point. It is clear that in moving the ignition lever from full retard to full advance a make will occur if the stopping position S degrees of the engine lies somewhere between 120r -d degrees and R + 120r -d degrees. Also that on the reverse motion of the lever, i.e. retarding the lever through its whole range, a break will occur, in the same circumstances, at the same point. Such a break causes an igniting spark with which to start the engine, if the ignition is switched on. (The spark does not go to the cylinder under consideration but to the one next in advance of this). The difficulty that may prevent the realisation of this spark is that the engine stopping postion may lie outside this range on the retard side; or algebraically that S may be less than 120r -d. {John DeLooze - Company Secretary} The condition therefore that such a spark may be realised is that S > 120r -d e.g. if d = 6° and r = .55, in accordance with the production setting, then S must be > 66° - 6°, i.e. > 60°. With equally good compressions and engine quite free, S has been found to be 65° within 1° or 2° each way. The reason for this not being exactly 60° is that the compression angle is somewhat longer than the expansion angle. Contd. | ||