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).
Engine detonation theory, particularly the impact of engine size and the use of dual ignition systems.
| Identifier | ExFiles\Box 65\1\ scan0177 | |
| Date | 29th September 1926 | |
| contd :- -2- Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}/LG29.9.26 ------------------ the tendency to detonate is largely proportional to the distance from the sparking plug to the remotest point on the surface of the combustion chamber. This conforms with what one would expect from the theory of detonation previously enunciated. It is therefore a fact that if two engines are identical in design, but one is double the size of the other, the large engine will detonate very much more easily than the small one for a given compression ratio. The only method of freeing the big engine from this defect is to provide two ignition points, so reducing the effective distance through which the wave of compression has to travel by starting it in two positions. The important point, however, is that the spark must occur at the two places absolutely simultaneously, otherwise little benefit is derived. R-R employ two separate ignition systems - magneto and coil. These ensure that should the battery fail, the car will not be out of action. In order to ensure perfect synchronisation of the two ignitions and at the same time to obtain an automatic advance to provide maximum power output for the whole range of engine speed, a governor is employed in conjunction with an oil relay. A single governor to operate two ignition systems which are linked together, would have to be a very massive unit of altogether unwieldy proportions to deal with all conditions of stiffness likely to be encountered. contd :- | ||