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).
Analysis of ignition plug overheating issues and proposed design modifications to improve water cooling.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan066 | |
| Date | 10th April 1929 | |
| R.{Sir Henry Royce} FROM E.{Mr Elliott - Chief Engineer} C. to HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} INDIA 4. - COMPRESSION RATIO & PREIGNITION- HS{Lord Ernest Hives - Chair}/ACL1/LG28329 (1) HIGHER TEMPERATURE OF IGNITION PLUGS. Regarding the tendency to pre-ignite on the 20HP. aluminium head there are reasons why the ignition plugs may be hotter than on the old high compression 20HP. iron head as follows: (1) The use of an inserted seat for carrying the plug in the aluminium is an obstacle to cooling. (2) The presence of turbulence in the burning charge should heat up the plug more. (3) The ignition plug is more buried in the aluminium head reducing air cooling effects. Regarding item (1) although we have arranged on the R.{Sir Henry Royce} racing engine to carry the ignition plugs direct in the aluminium for the sake of the improved thermal contact this is not a practice we could recommend as standard, as the aluminium 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 Regarding items (2) and (3) we believe the plug could be withdrawn a little from the head with no loss in ignition efficiency and with less turbulent heating, better air and water cooling, and freer passage-ways round the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 attached) 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 form 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 aluminium cannot take the place of water for cooling purposes. On the cyl. head tested by Mr. Lovesey 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 With the proposed reduction in the India 4. compression ratio however there is a distinct opportunity of considerably improving the water cooling of the plug. We propose to add .125" approximately to the height of the head to reduce the ratio from 5.5 to 5.1 and to put this all into the water space under the plug to ensure the complete penetration of the water into the large area shewn in plan - fig. 3. LeC. 2689. We also propose to withdraw the plug boss about .200" from the combustion space for reasons given elsewhere, and this allows of two water ways passing up, one on each side of the plug boss close to the surface of the cyl. head, which passages can be inspected, and if (1) | ||