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).
Effects of high altitude on Autovac fuel systems and engine performance.
| Identifier | ExFiles\Box 40\4\ Scan055 | |
| Date | 6th March 1923 | |
| Hs.{Lord Ernest Hives - Chair} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} X3579 6.3.23. AUTOVAC SYSTEMS AFFECTED BY ALTITUDE. At 15,000 ft. the atmospheric pressure is only 53% of that at sea level. We should therefore say that the height at any engine revs. to which the induction manifold vacuum will raise the petrol at 15,000 ft. will be reduced to 53% of the normal. On the other hand, owing to the decrease of air density and pressure at the altitude in question, the volumetric efficiency of the engine will be so reduced that the B.H.P. will only be about 55% of that at sea level. Of course, being unable to draw in a normal weight of air will correspondingly reduce the weight of petrol consumed, i.e., an apparently weaker mixture will be needed. This means that at high altitudes, it will take longer to exhaust the reserve supply of petrol collected by the autovac when not running at full throttle and slow engine speed. Probably this advantage will be anulled by the fact that, owing to the drop in B.H.P. there will be considerably more full throttle work at these altitudes than there would be at sea level, consequently reducing the opportunities of recuperation. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||