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 how pressure drop at engine inlet valves reduces power.
| Identifier | ExFiles\Box 134\2\ scan0055 | |
| Date | 30th October 1935 | |
| - 4 - Hs{Lord Ernest Hives - Chair}/Wd.{Mr Wood/Mr Whitehead}1/GB.30.10.35. APPLICATION OF RESULTS. The pressure drop at the inlet valves of an engine reduces the power in four ways. - (a) The friction of the air passing through the valves during the suction stroke increases the entropy so that the temperature at the end of the stroke is raised, decreasing the charge density. This rise in temperature also increases the tendency to detonation. (b) The pressure drop at the valve causes the cylinder pressure to lag behind the induction pipe pressure although these pressures are nearly equalised at the end of the stroke when the piston is moving slowly. This loss of pressure may be reduced slightly by closing the inlet valve after bottom dead centre and so allowing the pressure a little more time to equalise. (c) Ramming always exists in an induction system and any pressure drop at the valves causes a reduction in ramming efficiency. This effect was clearly marked with the Kestrel and ramp type inlet valves on the old single cylinder beds where a large ramming effect existed. (d) Valve friction increases pumping losses and so reduces B.M.E.P. The importance of these factors at any speed may be calculated from the curves given in this report together with the valve lift diagrams and a knowledge of the induction system, the process being simple though tedious. Roughly the effects are as follows at a speed of 3000 R.P.M. (a) 1 lb. M.E.P. suction loss increases the charge temperature by 6°C. reducing power by 1½% and lowering detonation point by about 2%. The suction loss is about 3 M.E.P. with the Kestrel and 1½ M.E.P. with the Ramp. The Ramp head thus has an advantage of 2% in power and 3% in detonation owing to this effect alone. (b) Valve timing influences this effect in so many ways that no figures can be given but it should not exceed 2% | ||