1. Field of Endeavor
The present invention relates to the field of combustion technology, especially in connection with gas turbines. It relates to an injection nozzle and to a method for operating such an injection nozzle.
2. Brief Description of the Related Art
For the atomizing injection of liquid fuel into the combustion chamber of a gas turbine, a multiplicity of various injection nozzles, which differ with respect to their internal construction and the type of spray cone which is generated, are known from the prior art.
A fuel nozzle with swirl passage, which includes a sleeve and a pin, is known, for example, from WO 2009/095100. The pin is arranged in the sleeve so that the inner surface of the sleeve is connected in a positive manner to the outer generated surface of the pin. Along the outer generated surface of the pin extends a swirl passage in the form of a recess which winds in a helical manner around the center axis of the pin on the outer generated surface. As a result of the arrangement of the pin in the sleeve, a swirl passage is covered or delimited radially with regard to the center axis of the pin by the inner surface of the sleeve. The sleeve has a discharge orifice in the flow direction of the fuel which leaves the fuel nozzle. The pin is arranged in the sleeve so that the cover surface of the pin is recessed towards the discharge orifice of the sleeve. As a result, a swirl chamber is formed. In the swirl chamber, a mixing of the fuel—that is to say, of the oil in the present exemplary embodiment—with air takes place. As a result of the recessing, a film atomization instead of a jet atomization is furthermore enabled. It is also possible for the cover surface to align with the discharge orifice. In the case of the swirl chamber, the spray cone can only be adjusted with difficulty. If the cover surface aligns with the discharge orifice, the fuel only discharges at the ends of the swirl passages, that is to say is localized to a high degree. Furthermore, the production of the swirl passages is comparatively costly.
A liquid fuel nozzle for the combustion chamber of a gas turbine, which includes a nozzle cap 100, a nozzle insert 101, a pilot insert 102, and a nozzle body 103, is known from EP 1 793 165 (FIG. 1 there). The pilot insert 102 is arranged inside the nozzle insert 101. The nozzle insert 101 is, in turn, arranged inside the nozzle cap 100. The nozzle has a pilot passage 105 which supplies the pilot insert 102 with fuel. The pilot insert 102 has a swirl chamber 110 into which a pilot swirl orifice 107 tangentially leads. Pilot fuel 32 flows via the pilot passage 105 from the vicinity of the pilot insert 102 through the pilot swirl orifice 107 and maintains a swirl there, by which it moves in the swirl chamber 110. The pilot fuel 32 forms a film on the inner wall of the swirl chamber 110 and shoots from the pilot injection orifice 108 in fine droplets.
The construction and function of the pilot arrangement of EP 1 793 165 are comparable with a simplex swirl atomizer which has been described in an article by D. B. Kulshreshtha et al., Variations of Spray Cone Angle and Penetration Length of Pressure Swirl Atomizer Designed for Micro Gas Turbine Engine, Int. J. Dynamics of Fluids, Vol. 5, Number 2, pp. 165-172 (2009). In both cases, the fuel which is pressurized and provided with a swirl discharges from a circular hole. The swirl chamber, into which the fuel flows tangentially and perpendicularly to the nozzle axis, is formed as a simple chamber without devices which promote swirl. Both lead to a non-optimized design of the spray cone which, moreover, has a limited cone angle.