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).
The effects of different valve timings on engine firing and cylinder pressure.
| Identifier | WestWitteringFiles\K\September1923\ Scan52 | |
| Date | 20th September 1923 | |
| -2- R.R. 493A (40 H) (SL 42 12-7-23). J.H., D.{John DeLooze - Company Secretary} EXPERIMENTAL REPORT. Expt. No. 4229 REF: Hs{Lord Ernest Hives - Chair}3/LG20.9.23. engine firing, and that it could be accentuated by advancing the valve timing, or eliminated by retarding it. Indicator cards were therefore first taken with the engine roaring slightly at 2000 r.p.m. - standard timing. The valve timing was then advanced two teeth and diagrams again taken; the roaring being worse. Finally the timing was retarded two teeth and cards taken with no engine roar. The results of these plotted on a P.V. basis are given in Fig. G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 11. It will be observed that the positive pressure is present in the cylinder under all three conditions but in a slightly different form. There is, however, little difference between the maximum positive pressure obtained in each case. At first sight therefore, it would appear that there should be much the same roar for each condition. In the advanced timing, however, the inlet valve opens 10° before T.D.C. and so gets the full benefit of the bump. With the standard timing it opens 6° after T.D.C. and by that time the pressure in the cyl. is less. With the late timing, the inlet valve opens 22° after T.D.C. and the pressure has fallen to atmospheric. The exact pressure at the points in question are much clearer on the pressure time cards than on those transformed to pressure volume, as the point where the valve opens can be determined more exactly. The figures obtained are :- Valve timing. Inlet opens. pressure in cyl. at moment of opening. 2 teeth early. 10° B.T.D.C. 10.2 lbs./sq.in. Standard. 6° A.T.D.C. 5 " " 2 teeth late. 22° A.T.D.C. Atmospheric. contd:- | ||