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).
The characteristics and effects of the initial spark versus the arc discharge in an ignition system.
| Identifier | ExFiles\Box 4\5\ 05-page087 | |
| Date | 10th April 1929 guessed | |
| -18- Contd. of the initial oscillatory spark is small, but the arc discharge is of relatively great volume. Conversely if the high tension gap is only just broken down it means that practically all the redistribution of flux has to take place in the first period, so that the initial oscillatory spark is of greater amplitude and voltage and the succeeding arc effect is of comparatively small volume. These remarks apply also to the operation of an induction coil, there being only this difference, that in the magneto case some portion of the arc discharge is due to subsequent rotation of the secondary winding in the field due to the permanent magnets. It is generally considered that a truly gaseous explosive mixture is fired by the initial oscillatory spark and that the arc discharge plays no part. If, however, the explosive mixture consists of little liquid globules in suspension instead of being truly gaseous, it may be the case that the arc discharge causes the explosion, the initial oscillatory spark being too quick and disruptive for this purpose. It is probable that in most cases that the amount of heat energy in the arc component is very much larger than in the initial spark component, but that the actual temperature of the initial spark is very much greater than the arc owing to the fact that the energy constituting this is released in a very much quicker time. It may therefore be that for starting an engine from cold the arc effect is useful, but it appears unnecessary for running the engine under warmed up conditions. ...Contd. | ||