GB125687A - Improvements in and relating to Carburetters. - Google Patents

Abstract

125,687. Dodson, E. Feb. 12, 1918. Spray carburettors.-A carburettor, particularly for use on aircraft, in which normally the fuel supply would be over-corrected, has two air passages, one, of relatively small dimensions, referred to a.s a secondary air passage, and another of larger dimensions and always in action and referred to as a primary air passage. Fuel is fed from the float chamber to primary fuel orifices in the secondary passage by a pipe, a branch from which, or from a separate supply. leads to a nozzle in the main passage at or near its point of maximum constriction or, in the case of a mixed-flow type of carburettor, the branch may be merely an air pipe connecting the constricted part of the primary air passage with the fuel space of the main orifices. The secondary air passage supplies the engine with an efficient mixture for cruising speeds, and the fuel supply leading into the main air passage is brought into action when additional power is required irrespective of efficiency. In the construction shown in Fig. 1, the seconday air passage is in the form of a Venturi tube 8 co-axial with and enclosed by the main air passage 5. Fuel is fed to orifices 13 by a pipe 11, and a pipe 14 supplies a nozzle 15 located at or about the constricted portion of the main passage 5. As the engine speed increases, the air flow through the secondary passage, owing to friction, ultimately reaches a maximum and the mixture strength from this point, due to air flowing through the main passage, would become weaker but for the nozzle 15, which then begins to discharge fuel which keeps the mixture strength constant. In a modification, the auxiliary air passage enters the main passage at right-angles at about the point of maximum constriction. In the mixed-flow type of carburettor shown in Fig. 3, a pipe 36, with valve 37, connects the maximum constriction portion with a space 34 around the spraying orifices 31. At low speeds, sufficient air is drawn through pipe 36 to keep down the flow of fuel, but, at higher speeds, this air flow ceases and in fact may reverse its direction and convey. additional fuel to the nozzle 35. In a modification of this construction, the pipe corresponding to 36 leads to a fuel well fed from the float chamber through a restricted orifice and is also in communication with the constricted portion of the primary air passage and with a pipe in the main air inlet 5 from which a pressure-balance pipe may lead to the top of the float chamber. The nozzles such as 15, Fig. 1, and the constrictions in the various pipes may be replaced by others of different bores.