Combustion apparatus

Abstract

A combustor having an array of dilution holes it provided with an asymmetrically located trim port for injection a controlled volume of air into the combustor. The controlled volume mixes with fuel rich air near the combustor wall and improves the dilution of the combustion gases. The improved dilution reduces the formation of NO x .

1 . Combustion apparatus comprising
 a combustion envelope bounding a combustion volume the combustion volume having an upstream end and a downstream end,   the combustion envelope having a plurality of rows of dilution ports for the provision of dilution air which mixes in use in a midstream flow with hot combustion gas from a fuel injector,   wherein each row extends in a circumferential direction and is spaced from an adjacent upstream or downstream row, the ports of each row being offset circumferentially from the dilution ports of an adjacent row,   characterised in that at least one trim port is provided upstream of one or more of the rows of dilution ports for supplying in use a flow of trim cooling air into the combustion volume which mixes with hot combustion gas between the midstream flow and an envelope cooling film attached to a wall of the envelope.   
   
   
       2 . Combustion apparatus according to  claim 1 , wherein the trim port is sized to limit the degree of penetration of the trim cooling air into the combustion volume. 
   
   
       3 . Combustion apparatus according to  claim 2 , wherein the degree of penetration is less than one third of half the radial height of the combustion volume. 
   
   
       4 . Combustion apparatus according to  claim 1 , wherein the trim port is between 0.35 and 0.7 of the diameter of one of the dilution ports. 
   
   
       5 . Combustion apparatus according to  claim 1 , wherein the axis of the trim port is located downstream and circumferentially offset from a dilution port in one or more of the plurality of rows. 
   
   
       6 . Combustion apparatus according to  claim 1 , wherein the trim port is positioned to permit the flow of trim cooling air to be conveyed by swirl within the combustor to a location downstream and circumferentially aligned with a dilution port. 
   
   
       7 . Combustion apparatus according to  claim 1 , wherein the combustion volume is annular. 
   
   
       8 . Combustion apparatus according to  claim 1 , wherein the combustion envelope has a fuel injection location, wherein a dilution port in the most upstream row is circumferentially aligned with the fuel injection location and the trim port is associated with the circumferentially aligned trip port. 
   
   
       9 . Combustion apparatus according to  claim 8 , wherein the fuel injection location is in an upstream wall of the combustion envelope. 
   
   
       10 . Combustion apparatus according to  claim 8 , wherein the combustion apparatus has two rows of dilution ports. 
   
   
       11 . A method of improving combustion within a combustion envelope bounding a combustion volume the combustion volume having an upstream end and a downstream end and the combustion envelope having a plurality of rows of dilution ports, characterised in that the method comprises providing a trim port wherein dilution air is supplied through the dilution ports and mixed with hot combustion gas in a midstream flow, wherein trim cooling air is supplied through the trim ports and mixed with hot combustion gas upstream of one or the rows of dilution ports and outside the midstream flow. 
   
   
       12 . A method according to  claim 11 , wherein swirl within the combustor conveys the trim cooling air to a location downstream and circumferentially aligned with a dilution port.