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).
Description of fuel flow and consumption testing apparatus, including carburetter air-fuel ratio control.
| Identifier | ExFiles\Box 140\1\ scan0208 | |
| Date | 28th March 1938 guessed | |
| -4- Figure 7 is a photograph of the special pressure float bowl, and Figure 8 shows the fuel weighing tank and a portion of the electrical wiring between the scales and the electric clock used to time the fuel flow. It can be seen that if the pressure on the fuel in the high pressure float bowl had not been at least equal to the pressure of the air surrounding the carburetter, fuel could not have been pumped into the carburetter flow bowl by the electrically-operated engine fuel pump because of the excessive differential pressure. Figure 9 is a wiring diagram of the electrical system for timing the fuel flow. When determinations were to be made, the fuel supply valves were so regulated that the engine received fuel from the weighing tank only. The scale beam rider was set slightly lighter than the load on the scale and the three-way switch was turned to the 'down' position. As the fuel was used from the weighing tank, the load on the scales was correspondingly reduced and the scale beam dropped. This closed the electrical circuit through the mercury wells, which in turn closed the two pole relay and started the electric clock. If the length of time to burn one pound of fuel was desired, the beam rider was moved back a division equivalent to one pound. after the clock had started. After the scale beam rose, breaking the contact at the mercury well, the three-way switch was turned to the 'up' position. As the load was reduced on the scales, the beam dropped a second time and contact was made again at the mercury wells. This closed the circuit through the telegraph-type relay and thus broke the circuit through the two-pole relay, causing the electric clock to stop. With the time indicated on the clock necessary to burn one pound of fuel, it was possible to calculate the fuel consumption in pounds per hour. Figure 10 is a schematic diagram of the equipment for varying the carburetter air-fuel ratio by controlling the pressure on the carburetter float bowl. The water manometer showed the differential pressure between the carburetter float bowl and the carburetter box. The pressure line leading from the 'bleed tank' was connected to the air line from the first air receiver, hence the pressure in the 'bleed tank', if the 'bleed valve' was closed, was essentially the same as that in the carburetter box. Since the 'bleed tank' was also connected to the float bowl of the carburetter, the differential pressure between the float bowl and carburetter box could be varied by regulating the 'bleed valve'. This controlled the pressure head on the fuel in the carburetter, changing the amount of fuel that flowed through the jets, and correspondingly the air-fuel ratio. | ||