Gas turbine engine fuel injectors

A gaseous fuel injector for a gas turbine engine, designed to burn gaseous fuels having a wide range of calorific values, includes a fuel nozzle attached to the engine casing and downstream fuel and air inlet means separate from the nozzle, attached to the head of the flame tube. The fuel and air inlet means comprise an outer annular passage containing a row of swirl vanes, through which compressed air from the engine compressor is arranged to flow, and an inner annular passage through which gaseous fuel and compressed air are arranged to flow, the inner annular passage decreasing in cross-sectional area in the direction of flow to prevent the flow of combustion products back into the injector. The nozzle and fuel and air inlet means, which is relatively large, are separate from each other so that the fuel nozzle can be removed and replaced through a relatively small opening in the engine casing.

This invention relates to gas turbine engine fuel injectors and is 
particularly concerned with fuel injectors which can burn gaseous fuels 
having a wide range of calorific values. For example the calorific value 
of the gas to be burnt may vary from 100 British Thermal Units/standard 
cubic foot (BTU/scf) in the case of a coal derived gas having a large 
proportion of inerts to propane (C.sub.3 H.sub.8) which has a calorific 
value of 2316 BTU/scf. In order to maintain a constant heat output/unit 
time over the whole range of fuels, the fuel injector must be able to cope 
with a wide range of mass flows. This will require a relatively large flow 
capacity fuel injector having correspondingly large swirler means and fuel 
and air inlet means in the flame tube or tubes of the air. With these 
requirements in mind, the fuel injector must also be readily removable 
from the in use position through an opening in the engine casing which is 
not excessively large, and be able to operate without the danger of 
combustion products from the flame tube or tubes flowing back into the 
fuel passage of the injector. 
The present invention provides a gas turbine engine fuel injector 
comprising a fuel nozzle and separate downstream fuel and air inlet means 
including an outer annular passage containing air swirling means and 
arranged to receive a flow of compressed air and an inner annular passage 
arranged to receive fuel from the fuel nozzle and a flow of compressed 
air, the inner annular passage decreasing in cross-sectional area in the 
direction of flow therethrough. 
The fuel nozzle can be removed from the engine separately from the fuel and 
air inlet means which can be attached to the upstream end of the or each 
flame tube. 
The fuel and air inlet means may comprise inner and outer rings between 
which a plurality of air swirl vanes are supported to define the outer 
annular passage, the inner annular passage being defined by a pintle 
supported centrally within the inner ring. 
The outlet of the inner annular passage may be aligned so that fuel and air 
issuing from the innular annular passage impinges upon the swirling mass 
of air issuing from the outer annular passage. 
The outlet of the fuel nozzle may be smaller in diameter than the outer 
diameter of the inner annular passage.

Referring to the drawings, a gas turbine engine fuel injector 10 comprises 
a gaseous fuel nozzle 12 attached to engine casing 14 and removable 
through an opening 16 in the casing and a fuel and air inlet means 18 
attached to the upstream end of a flame tube 20. 
The fuel and air inlet means 18 comprise inner and outer rings 22, 24 
respectively, between which are located a plurality of equispaced swirl 
vanes 26, the inner and outer rings defining an annular passage 28 
arranged to receive a flow of compressed air from the compressor of the 
engine. A pintle 30 is supported centrally in the inner ring 22 by radial 
arms 32 and with the ring defines an inner annular passage 34 decreases in 
the direction of flow and so acts as a venturi to prevent the reverse flow 
of combustion products from the flame tube 20 from entering the passage 34 
and nozzle 12. 
The outlet of the passage 34 is aligned so that the fuel and air which has 
already been at least partially mixed in the passage 34 is directed into 
the swirling mass of air issuing from the passage 28 to promote mixing 
between the fuel and air and to encourage re-circulation of the fuel and 
air in the primary zone of the flame tube. 
The nozzle 12 being separate from the fuel and air inlet means is readily 
removable from the in use position through the relatively small opening 16 
in the casing 14. If the nozzle and the fuel and air inlet means were an 
integral assembly an excessively large opening would be required for 
removal and replacement. Such large openings are undesirable in gas 
turbine engine casings as they adversely affect the casing strength.