Gas turbine engine combustion chambers

In a gas turbine engine having a can annular combustion system, the diffusion passage between the outlet annulus of the engine compressor and the inlets to the individual combustion chambers located in an annular housing, is partially defined by diffusion control housings, one of each of which is integral with the upstream end of a respective one of the combustion chambers. Each diffusion control housing is wedge-like in planform and increases in circumferential width and radial height in the downstream direction. An opening is provided to receive a fuel injector and an air outlet or inlets is located at the upstream end of each housing. The air inlet can be in the form of a single opening at the apex of the housing or in the form of an opening in each flank of the housing.

This invention relates to combustion systems of the can-annular type, for 
gas turbine engines and comprises a development of the combustion system 
described and claimed in co-pending United States patent application Ser. 
No. 163,481, filed June 27, 1980, and commonly assigned to Rolls-Royce 
Limited. In that application, some of the theoretical advantages of, and 
some of the practical problems associated with can-annular combustion 
systems were discussed. The solution to at least some of the difficulties 
proposed in that application was to control the rate of diffusion in the 
pre-combustor diffuser by the provision of radial struts of a wedge shape 
with the wedge apex facing upstream, the wedges being aligned with 
respective ones of the flame tubes of the combustion system. It was also 
proposed that the wedges could act as structural members and replace 
existing radial struts and that air scoops could be attached to the flame 
tubes to direct air to the combustion and dilution zones of the flame 
tubes. 
To accommodate these proposals in an existing combustion system would 
necessitate a major re-design. The present invention seeks to modify the 
basic proposals contained in the co-pending application and to apply these 
modified proposals to an existing combustion system, so that a minimum of 
re-design is required. In particular it is proposed that each flame tube 
is associated with a wedge, the wedge having an air inlet to feed air to 
the upstream end of the flame tube. 
Accordingly the present invention provides a gas turbine engine combustion 
system comprising a plurality of equi-spaced flame tubes located in an 
annular housing defined by inner and outer walls, the annular housing 
having an upstream diffuser casing providing a transition between an inlet 
arranged to receive compressed air and an outlet of larger cross-sectional 
area than the inlet, each flame tube, at its upstream end, having a 
diffusion control housing, the diffusion control housing having an inlet 
arranged to receive compressed air and an outlet arranged to deliver 
compressed air to the upstream end of the flame tube, each diffusion 
control housing extending between the inner and outer walls and increasing 
in cross-sectional area in the downstream direction, the diffuser control 
housings between them controlling the overall area ratio of the diffuser 
casing. 
Each housing in cross-section may be in the shape of a sector of an 
annulus, e.g. having inner and outer annular walls joined by or integral 
with two radially extending side walls. 
The inlet to the housing may be at its upstream end and may continue 
internally of the housing as a duct increasing in cross-sectional area in 
the downstream direction. Alternatively, the inlet to the housing may 
comprise openings in each of the side walls which may continue internally 
of the housing as further internal ducts. 
The air flowing through each housing may be arranged to flow through 
swirler vanes into the upstream end of the respective flame tube and some 
of the said air may also be used for cooling purposes. 
In plan, each diffuser control housing may appear as a wedge-like or 
truncated wedge-like shape with its apex or truncated apex facing upstream 
and its base facing downstream. 
Each diffusion control housing may be attached to or be integral with its 
respective flame tube.

Referring to FIGS. 1 to 3 inclusive a gas turbine engine 10 has a 
compressor 12 supplying compressed air to a known form of can-annular 
combustion system 14, the hot exhaust gases from which drive a turbine 16 
which in turn drives the compressor 12. 
The combustion system 14, comprises an annular housing 18 having inner and 
outer walls 20, 22 and a plurality of circumferentially arranged 
equi-spaced flame tubes 24. A load carrying strut 28 located between 
adjacent flame tubes extends between the walls 20 and 22 and may extend to 
an inner structural part of the engine. The upstream ends of the walls 20, 
22 define a diffusion passage for the combustion system supply air from 
the compressor 12. 
Referring now to FIGS. 4 to 9 inclusive, attached to the upstream end of 
each flame tube 24 is a diffuser control housing 32 analogous to the wedge 
32 in the aforementioned patent application Ser. No. 163,481, which 
extends between the walls 20, 22 and which is in cross-section 
substantially the shape of a sector of an annulus (see FIG. 7). Each 
housing 32 has an external wall comprising inner and outer annular walls 
34, 36 joined to or integral with two radially extending walls 38. Each 
housing also has internal walls defining a duct 40 having an inlet 42 for 
compressed air from the compressor 12 and an outlet 44 to discharge the 
compressed air to the upstream end of the respective flame tube 24. 
The wall 20 and the housing 32 have an opening 46 for the fuel injector 26, 
the end of which is located in an opening in a ring of swirl vanes 48. The 
swirl vanes are secured in central opening in the upstream end of the 
flame tube, which also has apertures 50 for the throughflow of cooling 
air. 
The external shape of each housing 32 is such that while the diffusion 
passage 30 is increasing in radial height, it is also decreasing in 
circumferential width, because each housing increases in cross-sectional 
area in the downstream direction and the radial height between the walls 
20, 22 increases in the downstream direction. Thus in FIG. 4, the 
diffusion passage increases in height from dimension B to dimension C and 
decreases in circumferential width from dimension D to dimension E. 
The internal duct 40 of each housing 32 is designed to be a continuation of 
the diffusion passage 30 and both the external shape of the housing and 
the shape of the duct 40 are designed to the aerodynamic requirements of 
the diffusion passage 30 and the duct 40 causing them to have a lower area 
ratio than would otherwise be the case, without incurring unacceptable 
pressure losses. 
Referring now to FIGS. 10, 11 and 12, which shows a modified form of 
diffuser control housing 32 particularly adapted to accept a gas burner 52 
(nozzle not shown) for burning low calorific value gas fuel. When burning 
such a fuel larger quantities of air are required and each housing 32 is 
provided with two diffusion ducts 54 having inlets 56 and outlets 58 
arranged to receive compressor delivery air from the diffusion passage 30 
and to discharge the compressor to the swirl vanes 48 and the upstream end 
of the flame tube 24 respectively. As will be seen more clearly in FIGS. 
11 and 12, the ducts 54 are formed on the side walls of the housing 32 and 
leave a central upstream facing apex 60, similar to the upstream ends of 
the wedges 32 in the copending application Ser. No. 163,481.