Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-02-05
2001-01-09
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
Reexamination Certificate
active
06170266
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a gas turbine engine. More particularly but not exclusively this invention relates to a gas turbine engine combustor and more particularly the wall structure of a gas turbine engine combustor.
BACKGROUND OF THE INVENTION
In order to improve thrust and fuel consumption of gas turbine engines i.e. the thermal efficiency, it is necessary to use high compressor pressures and higher combustion temperatures than have conventionally been used. Higher compressor pressures give rise to higher compressor outlet temperatures and higher pressures in the combustion chamber giving rise to the combustor chamber experiencing much higher temperatures.
There is, therefore, a need to provide effective cooling of the combustion chamber walls. Various cooling methods have been proposed including the provision of a double walled combustion chamber whereby cooling air is directed into the gap between the chamber walls thus cooling the inner wall. This air is then exhausted into the combustion chamber through apertures in the inner wall. The inner wall may also comprise a number of heat resistant tiles. Constructing the inner wall from tiles has the advantage of providing a simple low cost construction. Combustion chamber walls which comprise two or more layers whilst being advantageous in that they only require a relatively small flow of air to achieve adequate cooling are prone to some problems. These include the formation of hot spots in certain areas of the combustion chamber wall and the combustion chamber. Prior art proposals to alleviate this problem include the provision of raised lands or pedestals on the cold side of the wall tiles. Reference is hereby directed to GB Patent no. 2 087 065. These lands or pedestals serve to increase the surface area of the wall element thus increasing the cooling effect of the air flow between the combustor walls. Compressor delivery air is convected through pedestals on the ‘cold face’ of the tile and emerges as a film directed along the ‘hot’ surface of the following downstream tile.
The provision of such lands is also accompanied by inherent problems. For example localised overheating may occur behind obstructions such as mixing ports or adjacent to regions where near stoichiometric combustion gives rise to high gas temperatures (hot streaks). There is no provision for enhanced heat removal, either locally to remove hot spots or to alleviate more general overheating towards the downstream end of the tile. Overheating may occur downstream of the mixing ports since the protective wall cooling film is stripped away by the transverse mixing jets. Where design requirements have dictated a relatively long tile the cooling film quality towards the downstream edge of the tile may be poor and lead to overheating.
SUMMARY OF THE INVENTION
An object of this invention is, therefore, to provide an improved wall arrangement for a combustion chamber and/or to provide improvements generally.
According to the invention there is provided a wall structure for a gas turbine engine combustor which at least in part defines a combustion chamber, the wall structure comprising at least one outer wall and one inner wall which are spaced apart to define a space therebetween, the outer wall having a means for the ingress of air into the space between the outer and inner walls, the inner wall comprising a number of wall elements, each of said wall elements having a plurality of inclined apertures defined therein to facilitate the exhaustion of air into the combustion chamber, each wall element also comprising a plurality of raised lands, the raised lands arranged in staggered rows so that the lands of adjacent rows are offset from one another, and the inclined apertures are disposed between the raised lands, the arrangement of the raised lands providing in particular directions unobstructed channels between the raised lands, and the inclined apertures being orientated such that the axes of the inclined apertures lie along the unobstructed channels between the raised lands.
According to a second aspect of the invention there is also provided a wall structure for a gas turbine engine combustor which at least in part defines a combustion chamber which has a central axis, the wall structure comprising at least one outer wall and one inner wall which are spaced apart to define a space therebetween, the outer wall having a means for the ingress of air into the space between the outer and inner walls, the inner wall comprising a number of wall elements, each of said wall elements having a plurality of inclined apertures defined therein to facilitate the exhaustion of air into the combustion chamber, each wall element also comprising a plurality of raised lands, the raised lands arranged in staggered rows so that the lands of adjacent rows are offset from one another, and the inclined apertures each of which have an axis are orientated such that the angle defined between the aperture axis and the combustion chamber axis corresponds to an angular offset of the raised lands of adjacent rows.
Preferably said lands are arranged in an array and the offset of the lands of adjacent rows is at an angle to a central axis of the combustor.
Preferably the combustor is arranged to have a general direction of fluid flow therethrough and said apertures are angled at an angle of 30° to the general direction of fluid flow within the combustion chamber.
Preferably the wall elements comprise discrete tiles. The raises lands may comprise pedestals.
Mixing parts may be provided with the combustion chamber walls to provide air into the combustion chamber.
The downstream edges of each of the wall elements may be coated with a thermal barrier coating.
REFERENCES:
patent: 4653279 (1987-03-01), Reynolds
patent: 4695247 (1987-09-01), Ensaki et al.
patent: 2173891 (1986-10-01), None
Close Desmond
Pidcock Anthony
Spooner Michael P
Farkas & Manelli PLLC
Freay Charles G.
Gartenberg Ehud
Rolls-Royce plc
Taltavull W. Warren
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