IL48019A - Combustor having staged premixing tubes - Google Patents

Description

·»-!¼ amy-Dt nnu. oy nyan COMBUSTOR HAVING STAGED PREMIXING TUBES COMBUSTOR HAVING STAGED PREMIXING TUBES Abstract of the Disclosure A gas turbine engine is shown having an annular burner with a plurality of staged premixing tubes extending from the forward end thereof. Each tube directs flow to the burner through two concentric flow passages. A movable tube section is arranged to direct all the air, through both flow passages or just through one passage. Fuel is directed into the staged premixing tube for mixing with air flowing therethrough. Swirl vanes are provided in each of the flo passages to provide for rotation of air passing therethrough. A centerbody is positioned within the inner flow passage providing a bluffbody to promote recirculatory flow in the general region rearwardly of the centerbody. Cooling is provided around the primary zone of the burner so as to provide a minimum of cooling flow into the primary zone .

The invention disclosed herein was made in the course of or under a contract with the Department of the Air Force .

This invention relates to the controlled formation of objectionable or harmful exhaust emissions, such as unburned hydrocarbons, oxides of nitrogen, and carbon monoxide , from a gas turbine engine burner to maintain said objectionable or harmful exhaust emissions at an acceptable level. A gas turbine engine burner ordinarily operates over a wide range of primary zone equivalence ratios while it is believed that the primary zone equivalence ratio should be maintained within a narrow range.

Prior devices have provided means for varying the distribution of airflow within a burner and means for providing atomization, premixing and substantial vaporization but these means have, not been set forth such as the device described herein.

Summary of the Invention A primary object of the present invention is to provide a burner with staged premixing tubes to control the formation of objectionable or harmful exhaust emissions in a gas turbine engine burner.

In accordance with the present invention, a staged premixing tube is provided which varies the distribution of airflow within the burner and provides fuel atomization, fuel-air premixing and substantial vaporization of the fuel prior to injection into the b-orner.

A further object of the invention is to provide a staged premixing tube that allows the dissemination of fuel into the two annular passages to be varied in terms the primary zone equivalence ratio is as low as possible ; to avoid the formation of large concentration levels of ; ΝΟχ" Brief Description of the Drawings Figure 1 is a view of a gas turbine engine showing the location of the burner having staged premixing tubes.

Figure 2 is an enlarged sectional view of the combustion section showing the burner and a staged premixing This positioning means places the exi of the burner 10 at the entrance to the turbine section for directing gas flow into turbine vanes 40.

The annular burner 12 is made having its forward portion which encloses the primary zone 22 formed of double-walled construction with a solid inner wall 25 and outer wall 29 having a plurality of cooling holes 44 to provide for impingement cooling of wall 25. The cooling air after it has completed its cooling function flows from between the double-walled construction over the inner wall of .the remainder of the burner 12 so as -not to enter the primary zone 22. The rear part of the burner 12 which encloses the dilution zone has its walls formed of conventional louver construction with dilution openings 46 located adjacent the rear of the double-walled construction and dilution holes 48 located rearwardly thereof towards the annular opening 27 at the rear of the burner. A cylindrical receptor 100 is mounted on the front of the annular burner 12 where each staged premixing tube 20 is desired. While the cylindrical receptor 100 is shown welded to the double-walled construction of the annular burner 12, it is to be understood the cylindrical receptor 100 may be connected by any other means. The cylindrical receptor 100 has an annular flange 102 mounted therearound for a purpose to be hereinafter described.

Air enters the annular burner case 10 of the combustion section 2 where it is distributed to various openings leading to the interior of the annular burner 12. These openings include cooling holes 44 , dilution openings 46 and 48 , and forward openings 50 of the staged premixing tubes 20.

Each staged premixing tube 20 comprises three main (see Figs. 3 .4) ' ' parts^ these are (1) an outer tube 52 , (2) a shorter inner tube 54 having a centerbody 55 , and (3) a movable bellmouth piece 56. The outer tube 52 has an enlarged inlet section 58 which is tapered inwardly as it extends rearwardly to a reduced area center section 59. This inlet section 58 directs incoming airflow from a forward opening 50 into the premixing tube 20. The inner tube 54 is located in the rear end portion of the outer tube 52 and with the centerbody 55 divides the tube into two concentric flow passages 60 and 62. The inner tube 54 is supported within the outer tube 52 by swirl vanes 64. The centerbody 55 is positioned in the inner tube 54 by swirl vanes 68 . The centerbody 55 , while spacing the inner ends of the vanes 68 , also serve as an aerodynamic bluff- body, promoting recirculatory flow in the general region just rearwardly of the centerbody. An opening 57 extends through the center of the centerbody 55 to aid in purging the region immediately adjacent to the centerbody of combusting flow. The swirl vanes 64 and swirl vanes 68 are placed in a manner so that airflow leaves the ; ference as possible with airflow passing thereby. The ; contour of the bellmouth piece 56 is such that in its ; rearward position the forward edge coacts with the inner wall of the inlet section 58 and the rearward end 70 · an acceptable aerodynamic contour to direct irllet flow into only the smaller diameter annular passage 62, and in its forward position it is positioned within the forward part of the outer tube 52 so that flow is directed smoothly into both of the concentric flow passages 60 and 62. The slidable engagement of the rearward end of the bellmouth piece 56 with the forward end of the inner tube 54 is of such a length that a small gap is permitted at A to permit airflow therethrough before the bellmouth piece 56 disen-gages the inner tube 54 as it moves KS^^s^d-ly.

Each staged premixing tube 20 has an annular flange 104 extending outwardly from the midportion of the outer tube 52. This flange 104 is positioned on the outer tube 52 so that when the rearward end of the staged premixing tube 20 reaches the end of the cylindrical receptor 100 adjacent the inner part of the burner 12, it will engage the cylindrical flange 102 of the cylindrical receptor 100. These flanges are fixed together to retain the staged premixing tube 20 in its proper operating position. The rearward end of the staged premixing tube 20 has a plurality- of radial projections 106 extending therefrom which- guide the end of the staged premixing tube 20 when it is' being inserted in the cylindrical receptor 100 and provides for any flow of cooling air which may pass thereby* If necessary, openings 108 can be provided in flange 104 to allow a minimum of cooling air to enter the space shown, dual nozzles can be used if desired. operated such as set forth in manner (1) or in manner (2) It is to be understood other types of operation can be used depending on power requirements for any specific engine.

Claims We claim: