GB696757A - Apparatus for burning liquid fuel in a ducted gas stream - Google Patents

Abstract

696,757. Generating combustion products under pressure. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Feb. 13, 1951 [Feb. 14, 1950], No. 3798/50. Class 51(i) [Also in Groups XI and XXVI] Apparatus for burning liquid fuel in a ducted stream of combustionsupporting gas comprises at least one slender rod-like vaporizer body presenting a bluff unstreamlined profile to the oncoming gas, and means for continuously supplying fuel to wet the external surface of the vaporizer body, so that when such fuel supply is appropriately metered and gas is flowing in the duct, fuel evaporates from a wet film continuously maintained on the body, and when ignited burns only in the turbulent wake of the body. Liquid fuel is fed to the end 4 of a vaporizer rod, Fig. 1, and flows by gravity over the surface thereof, surplus fuel being collected in a return trough 5. The rod 3 may have a roughened surface, or may be coated or wound with an absorbent material such as asbestos string, and is of bluff cross-section to produce a flow reversal downstream thereof, being e.g. of triangular, semi-circular, or arrowhead section, and may be inclined to the air stream as indicated at 3a. The fuel may, alternatively, be forced under pressure into the interior of the rod 3 which is then perforated for distributing the fuel over the surface. The rod may be heated electrically to assist ignition of the fuel by known means. Instead of a single rod 3 a plurality of vaporizer rods may be provided, which may be arranged in one or more rows, which latter may be staggered, inclined, crossed, or interlaced. To control the rate of burning some or all of the rods may be slidable longitudinally or be provided with slidable sheaths to vary the areas of the rods exposed to the air stream, or, in the case of rods of non- circular cross-section, the rods may be turned about their longitudinal axes. Alternatively one or more rods may be moved to alter the pattern of the rod system, and to assist heating of some rods by the flames from others a lateral fin such as 13A, Fig. 8A, may be provided on such rods 13, which fin may be moved into or out of contact with the flame from an adjacent rod. As a further alternative, the number of rods' in the air stream may be varied as in the construction shown in Fig. 11 in which a cylindrical air duct 1 has a combustion zone of square cross-section provided by flat plates 22. The vaporizer rods are connected by flexible links to form a chain 23 which is mounted on rollers to enable the length of chain within the combustion zone to be adjusted. In an alternative construction the vaporizer rods may consist of flexible filaments such as wire or tape mounted for movement on rollers or pulleys for withdrawal from the duct for cleaning. In other constructions where the vaporizer rod is rigid it may be provided with a ring scraper, either the scraper or the rod being movable. An annular combustion chamber for a gas turbine engine may comprise an annular assembly of radially extending vaporizer rods 31, Fig. 16, rotatable on bearing means (not shown) and receiving fuel from an annular series of buckets 29, supplied by stationary radial spray pipes 28. The rods 31 are obliquely set so that air flow assists in spreading the films of fuel and the assembly of rods and buckets is rotated by swirl imparted to the air flow by stator vanes 32. In an alternative construction the rod and bucket assembly may be stationary while the fuel jet assembly is rotary. In a further embodiment for burning fuel in an annular combustion space fuel is supplied through radial fuel pipes 42, Fig. 21, which expel fuel substantially tangentially through jets 43 on to the trough-like inner surfaces of rings 40. A re-heat combustion system for a gas turbine propulsion duct may comprise a series of radial vaporizer rods 37, Fig. 17, pivotally mounted on an exhaust cone 36 or on the wall 35 of the duct, so that they may be moved into an inoperative position flush either with the cone 36 or with the wall 35. The fuel is supplied through a rotary jet assembly 38. As a further alternative the fuel may be introduced into the air duct as a spray upstream of the vaporizer body or bodies to be deposited on the latter as a film.