GB1519031A - Lasers - Google Patents

Abstract

1519031 Lasers ROLLS ROYCE Ltd 27 Jan 1976 [28 Jan 1975] 3585/75 Addition to 1390919 Heading H1C In a CO 2 gas dynamic laser, either combustion gas or compressed air is tapped off an air breathing gas turbine engine, and a laserable gas mixture is produced by burning one or more hydrocarbon fuels in the tapped off gas, the laserable gas being aerodynamically expanded in a supersonic nozzle to produce lasing in an optical resonator. It is a requirement that the total amount of fuel added to the tapped off gas is such as to produce a gas fuelair mixture, before burning, having a ratio of between 0À35 and 0À85 to its stoichiometric mixture. A gas turbine 1 is shown in Fig. 1 having a compressor section 2, combustion equipment 3, a turbine section 4 and a jet pipe 5, a portion of the combustion gas being taken off at the outlet end of the combustor 6 and passed to a reservoir/combustion chamber 8 where fuel injected at 9 is burned. The laserable gas mixture so produced is passed through convergent-divergent nozzles 10 developing supersonic flow, and lasing takes place in an expansion chamber 11 bounded by an optical resonator C to produce an output beam 12. The exhausted gases are removed from chamber 11 by a compressor 13 so as to pass through a duct 14 into the jet pipe 5. Alternatively a diffuser unit may be used. A parallel line of converging-diverging nozzles may be used, Fig. 3 (not shown), or alternatively a system of flow turning axi-symmetric nozzles 18, 19, may be used, Fig. 5, for both supersonic expansion and diffusion. An embodiment using tapped-off compressed air is described, Fig. 2 (not shown), this embodiment differing from Fig. 1 only by the inclusion of a further supply duct used to supply additional substances as needed to the reservoir 8, and by the engine tapping point at the compressor section. The hydrocarbon fuel or fuels used is/are selected to give a gaseous H 2 O : CO 2 ratio in the combustion gases in the range between 1 : 2 and 2 : 1, a suitable fuel mixture being of two different hydrocarbon fuels of carbon to hydrogen content of 1 : 2 or more and less than 1 : 2, respectively. The main hydrocarbon fuel may be aviation kerosene or benzene, but examples of other fuels are given. The additional fuel, if used, may be carbon monoxide, carbon disulphide, cyanogen or finely divided carbon. Other gases may also be added to the combustion gases before expansion such as air, nitrogen or carbon dioxide. The additional fuel may supply a pilot burner for a main burner through which the main fuel is passed.