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 self-ignition tests, focusing on the relationship between valve temperature, engine speed, and charge ignition.
| Identifier | WestWitteringFiles\O\2April1926-June1926\ Scan215 | |
| Date | 8th June 1926 guessed | |
| contd :- -2- 800 r.p.m. This simple test shows us that for a particular valve temperature the engine speed has to be below a certain value in order to obtain self ignition and that the lower the valve temperature the lower has to be the speed. It is reasonable to suppose that the influence of speed is two-fold - firstly, the lower the speed the longer is the time during which the charge can pick up heat from the hot valve and - secondly, low speed would give little or no turbulence with the result that the stagnant gas in contact with the hot valve may rapidly reach its ignition temperature and inflame the whole charge. One would imagine at all times the exhaust valve to be the hottest part in the cylinder, except perhaps at times the sparking plug points, but the heating area of these would be much less. In another test we proved conclusively that if the exhaust valve remained cool we could experience no signs of self ignition. The cooling was accomplished by directing a fine jet of water on to the valve by a pipe leading in through the port. The engine was run at full throttle until all the valves were a bright red heat and then the one valve was cooled by the water jet until it had lost all redness. Upon switching off this cylinder would not fire but the others would continue to e ignite regularly. Therefore considering the phenomenon due to local ignition of the compressed charge by the heated exhaust valve, a reasonable supposition is that the readiness of the charge to self ignite will be further influenced by the nature contd:- | ||