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 comparing a standard engine with a new head, and further experiments with smaller valves.
| Identifier | WestWitteringFiles\Q\December1926-January1927\ 42 | |
| Date | 1st December 1926 guessed | |
| contd :- -5- throttle down to 500 r.p.m. and see what time had to elapse at this speed before the engine could be switched off and give no self ignition. The standard engine required 28 seconds but with the new head self ignition would not occur after 5 seconds slow running and frequently we could switch off immediately after the two minutes at 2000 r.p.m. and still get no firing! Judging by the appearance of the exhaust valves when running - although this is only a rough estimate - it does not seem that the temperature is very much different between the two engines - standard and aluminium - and the difference in the self ignition tendency is credited to the increased turbulence preventing local heating of the charge up to ignition temperature by the hot exhaust valves. The improvement in this direction we think should be quite appreciable in practice and experience of this will be obtained from the running of car 14EX, fitted with the lighter engine. EXPERIMENTS WITH SMALLER VALVES. An alum. head of the original type was built up with smaller dia. valve seats so that the port dia. at the valve was reduced from the standard 1.75 ins. to 1.60 ins. The valve was also of smaller dia. to suit (see diagram 2 on page 1.) The object of these tests was to see how the resulting higher gas velocity would influence the spark advance and detonation. It was thought perhaps the smaller valves would keep cooler and give less trouble from self ignition contd :- | ||