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 performance relating to exhaust valves, ignition timing, pressure rise, and spark plug position.
| Identifier | ExFiles\Box 134\2\ scan0019 | |
| Date | 27th June 1935 | |
| - 6 - SODIUM COOLED EXHAUST VALVES. When reference is made to the above, a valve in which the stem only is sodium filled is indicated. Tests have been carried out with a fully cooled valve but as the performance was impaired, these tests were not continued. IGNITION ADVANCE. The ignition advance curves given on sheet 11 show that the high power heads require quite a small ignition advance for the development of maximum power (see centre curve). The lower curve shows the figure to which the point of ignition may be retarded before a 5% power drop results. Similarly the top curve shows the point to which the ignition may be advanced before a similar loss of power is experienced. The curves given on sheet 11 were actually taken with the twin inlet valve head but the figures hold good also for the single inlet valve head. Both heads are very sensitive to ignition timing in that a small advance over that which is necessary for maximum power will bring up detonation to an alarming degree. This does not apply when the sodium cooled exhaust valve is fitted. RATE OF PRESSURE RISE. Several indicator cards have been taken with the high power heads at 2000 and 3000 R.P.M. They all show an exceptionally high rate of pressure rise, which appears to be insensitive to changes in fuel. The shape of the indicator diagram at the point where the compression line merges into the explosion line denotes rough running. A typical card is reproduced on sheet 12 of the curves. This and the other diagrams were taken at the sparking plug position immediately above the exhaust valve. ALTERNATIVE PLUG POSITION. Two positions for the sparking plug are provided in the high power heads; one roughly in the centre of the combustion space and one directly over the exhaust valve. Maximum power is obtained by the use of the former position; when the latter position is used, however, the engine will not run smoothly | ||