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).
Technical report on the development and operation of carburetter systems, including slow running and altitude compensation.
| Identifier | ExFiles\Box 31\5\ Scan278 | |
| Date | 20th December 1934 | |
| -2- These are distinct features which we have proved by experience to be unobtainable with automatic units adapted to operate our own carburetters. DEVELOPMENT. ( Engine was run under Standard Kestrel Vl.{V. Lewis / Mr Valentine} conditions) In its initial state it was found that some development was necessary to improve the slow running range up to the change over position. Two slow running systems are employed and consist of fixed jet and air bleed orifices and fixed jetted orifices at the throttle edge. See Sketch Hs.{Lord Ernest Hives - Chair}1654 Attached. The throttle edge system is interesting and very effective and consists of three orifices, one central to the throttle edge and one each above and below vertically to the central orifice the spacing allowing all three orifices to be above the throttle edge at the changeover allowing a large quantity of rich mixture at this position. When throttled back to slow running the lowest orifice acts as an air bleed and the quantities can be adjusted to perfection by variation of the jet sizes. When the correct combination of the jets were obtained the slow running range and changeover could not be improved. After the slow running range was completed, the main jet orifices and needle shapes were fixed, the richening aneroid was connected to the boost pressure side of the blower and the needle shape fixed. The results are shewn on appended Curve No.1. It will be seen that the mixture increases progressively from the rated boost pressure right up to full throttle power at ground level and the delivery is such that the engine is well out of the detonation range at any boost pressure. The altitude needle was calibrated by reducing the air intake pressure when running at a fixed throttle opening and adjusting the mixture at each equivalent altitude by manually operating a tapered needle of known dimensions and measuring the position. The action of the altitude needle is to reduce the jet orifice at altitude to compensate for reduced density to the extent that the cruising throttle curve is maintained constantly parallel to the ground level curve. This was found to hold good up to a point but the whole altitude correction fails when simulating a constant rated boost climb up to full throttle height, in which the throttle is adjusted to maintain the rated boost. | ||