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 engine pre-ignition, its effect on exhaust valves, and ongoing tests on various engines.
| Identifier | WestWitteringFiles\J\December1922\ Scan97 | |
| Date | 27th December 1922 guessed | |
| contd:- -2-NACXXXXXXXXX We know from past experience that it is necessary for the pre-ignition to start at a certain point on the compression stroke in order to produce the worst results, for instance, it frequently happens with a bad pre-ignition the incoming charge is fired and blows back through the carburetter - this type of pre-ignition of course, would never injure the exhaust valve. On the other hand, it is possible to get a pre-ignition which fires only slightly in advance of the normal ignition. This would not cause any harm. From our work in connection with aero engines, we found that the pre-ignition which destroys the exhaust valve is one which ignites the charge approximately at the point at which the inlet valve closes so that the burning charge is compressed during the whole of the compression stroke. Once pre-ignitions take place at that critical point, the valve will burn in a few minutes. Once it has arrived at the temperature which will fuse the exhaust valve steel, we have never been able to notice that there was any difference between Stainless, Quickstep or Tungsten steels. We are continuing our tests on the 20 HP. engine until we can reproduce exhaust valve failures. We are arranging to have battery and magneto ignitions fitted and using one to fire a plug at any point of the stroke. We consider our tests so far on the 20 HP. are satisfactory inasmuch that they prove that there is nothing seriously wrong or any cause for alarm. We still get exhaust valves burn out on the 40/50. contd | ||