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 performance, focusing on piston friction, scavenging, and pumping losses.
| Identifier | ExFiles\Box 54\4\ Scan031 | |
| Date | 12th July 1928 | |
| R.R. 493A (40 H) (SL 42 12-7-28). J.H., D. {John DeLooze - Company Secretary} -4- EXPERIMENTAL REPORT. Expl. No. REF: Hs {Lord Ernest Hives - Chair} /Rm {William Robotham - Chief Engineer} /LG5.9.24. piston friction is considerable. The test was repeated at 1000 r.p.m. when the losses were found to be 45.5 lbs/sq.in. M.E.P. The most noticeable feature of these figures is the amount of work required to draw in and expel the scavenging and working charge through the rotary valve. The scavenging, though only at 3 lbs/sq.in., absorbs almost 5 lbs/sq.in. M.E.P. While removing the valve caps only decreases the motoring losses by 2 lbs/sq.in. M.E.P., further removing the rotary valve makes a difference of 5½ lbs. M.E.P. On examining the Rotary Valve to account for these losses, it was observed that all the ports are necessarily restricted owing to the dimensions of the valve. In particular the transfer port for the supercharge is only .625" X .687" in area with irregular outline, while the scavenging is also restricted. We expect the pumping losses to be slightly increased when the engine is running under its own power. Increasing the scavenging pressure by operating the relief valve on the reservoir, augments the pumping losses very considerably, so much so that by raising the pressure from 3 lbs/sq.in. to 18 lbs.sq.in., the whole motoring loss is increased by over 30%. This is evidently sufficient to nullify any resultant gain in I.M.E.P. as the engine will not run under its own power with this scavenging pressure. As a summary of our impressions of the engine at the moment, we should say that by attention to the ignition and carburation, we may be able to improve the I.M.E.P. slightly. We believe that further improvement will be contd :- | ||