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).
Ignition plug temperature, pre-ignition, and cooling issues on a 20 HP engine.
| Identifier | ExFiles\Box 19\7\ Scan131 | |
| Date | 10th April 1929 | |
| R.{Sir Henry Royce} from E.{Mr Elliott - Chief Engineer} c. to SG.{Arthur F. Sidgreaves - MD} Hs.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} X790 E1/M10.4.29. INDIA 4. - COMPRESSION RATIO & PREIGNITION. X.790 X.1812 Hs{Lord Ernest Hives - Chair}/ACL1/LG28.3.29. X.5970 X.5050 (1) HIGHER TEMPERATURE OF IGNITION PLUGS. Regarding the tendency to pre-ignite on the 20 HP. aluminium head there are reasons why the ignition plugs may be hotter than on the old high comp: 20 HP. iron head as follows : (1) The use of an inserted seat for carrying the plug in the alum. is an obstacle to cooling. (2) The presence of turoulence in the burning charge should heat up the plug more. (2) The ignition plug is more buried in the aluminium head reducing air cooling effects. Regarding (1) although we have arranged on the R.{Sir Henry Royce} racing engine to carry the ignition plugs direct in the alum. for the sake of the improved thermal contact this is not the practice we could recommend as std., as the alum. thread is too liable to be damaged by small faults in the sparking plug thread. Regarding items (2) and (3) we believe the plug could be withdrawn a little from the head with no loss in ignition efficiency and with less turbulent heating, better air and water cooling, and freer passage-ways round the boss. (2) WATER COOLING AROUND IGNITION PLUG BOSS. The sample turbulent head cut up by Mr. Lovesey is not up to the usual standard as regards coring. The actual section as designed is shewn in fig.1. Lec.2689 (print attc.) from which it will be seen that the passage-way beneath the plug is reasonably good. We believe nevertheless that the stud bosses on either side do join up to and from an undesirably large mass with the plug boss, and from our early experience on the dry liner F.{Mr Friese} engine cyl. blocks we know that alum. cannot take the place of water for cooling purposes. On the cyl. head tested by ACL. we have very little doubt that there is a hot spot immediately underneath the plug where a large portion of the internal heating surface of the combustion chamber is not served by water due to the casting being below standard. contd :- | ||