GB2091410A - Fuel nozzle for a gas turbine engine - Google Patents

Abstract

A fuel nozzle designed to reduce pollutant emissions and minimize the buildup of coke in the secondary fuel passage of a dual orifice fuel nozzle for the combustor of a gas turbine engine sizes the orifices and passages of the air and fuel so as to increase the pressure in the secondary passage during its inoperative mode and when the primary fuel passage is in the operative mode and having the air and fuel issuing from both the primary and secondary orifices swirl in the same direction. <IMAGE>

Description

SPECIFICATION Dual orifice fuel nozzle for gas turbine engine This invention reiates to fuel nozzles for turbine type of power plants and particularly to dual orifice nozzles and means for improving the quality of emissions.

In view of the ecological concern and the governmental requirements for the reduction of poliutants admitted in the atmosphere, there has been a concerted effort to improve the quality of the exhaust discharging from aircraft engines.

One of the major areas that is currently being explored is the engines combustor and its attendent fuel nozzle.

The purpose of this invention is to reduce the emissions from the gas turbine engines powering aircraft. In particular, we have found that by certain modifications to already existing fuel nozzles, it is possible to significantly reduce the pollutant emissions. To this end the swirl is selected so that both air and/or fuel when issuing to the combustion zone is in the same direction.

An essential feature of this invention to provide for a fuel nozzle of the type having primary and secondary fuel feed orifices for a combustor of a gas turbine engine means for imparting swirl to the fuel and air in the same direction.

A preferred feature of this invention is to judiciously select the value of the area ratio of air inlet and fuel/air outlet to produce a positive pressure inside the nozzle relative to the pressure in the burning zone in the combustor in combination with co-rotational fuel and air.

The co-rotational fuel and air egression into the combustion zone of the combustor reduces hydrocarbones, NOx, and carbon monoxide emissions.

It has been found that the essential teaching of this invention is also particularly advantageous in connection with fuel nozzle provided with water injection means. As it is well known, thrust of the engine can be increased by adding water to the burner section. In fuel nozzles for certain engines both the primary and secondary fuels are injected into the burner in conically radiating spray patterns that are in coaxial relationship. Such nozzles are, for example, utilized on the JT-9D engine manufactured by Pratt a Whitney Aircraft Group of United Technologies Corporation, the assignee of this patent application and the details of which are incorporated herein by reference. In this configuration, water is admitted upstream of the fuel spray and passes through the fuel support heat shields prior to being injected into the bruner section via the burner swirlers.The problem with this configuration is that a significant deterioration in burner performance was evidenced. Also, this type of water injection system manifested a high density, produced excessive hot spots at the turbine inlet as well as excessive distortions of the turbine inlet temperature radial profile.

It is also well known that fuel and air are injected into a burner with a tangential component so as to achieve a fast and complete mixing. Since water is admitted upstream of the juncture where it mixes with the fuel, it is carried in the airstream and assumes the same rotational direction. Hence, the fuel nozzle contains spin slots and vanes that are designed to impart a swirl to both the fuel and air. Further, the fuel nozzle is designed so that the fuel and air pattern in the burner combustion zone take the form of cones radiating from the apex as it leaves the fuel nozzle and flares into a cone as it propagates downstream in the burner.

In heretofore nozzle configurations it has been conventional to impart the swirl of the fuel in a direction that is counter to the direction of the swirl of the air.

By changing the relationship of the direction of the swirl so that the fuel and air/water mixture both swirl in the same direction we inhibit the tendency of the outer cone (air/water mixture) to collapse the inner cone (fuel spray) as is the case in counter rotation swirl patterns and improves the circumferential uniformity of burning and thus prevents localized hot spots that manifest into the turbine. The water in the airstream does not collapse the fuel pattern and does not tend to conglomerate in individualize streams. Actual tests have shown a remarkable reduction in smoke emission during wet performance as compared with wet performance of heretofore known water injection systems.

Other features and advantages will be apparent from the specification and claims and from the accompanying drawings which illustrate an embodiment of the invention.

In the drawings: Figure 1 is an enlarged view partly in section and partly in elevation illustrating the details of a first embodiment of this invention.

Figure 2 is an enlarged view partly in section and partly in elevation illustrating the details of a second embodiment of this invention.

In its preferred embodiment this invention has particular utility for pressure atomized fuel nozzles that include both the primary and secondary fuel systems. For details of this type of nozzles reference should be made to the fuel nozzles utilized in the JT-8D and JT-SD engines manufactured by Pratt a Whitney Aircraft Group of United Technologies Corporation, the assignee of this patent application. Inasmuch as the this invention only relates to the fuel nozzle the details of the engine and its combutor, fed by these nozzles, are eliminated herefrom for the sake of convenience and simplicity.Suffice it to say that the engines noted above utilize dual orifice fuel nozzles having pressure atomizing primary and pressure atomizing or air atomizing secondary nozzles where the primary nozzle is utilized for both low and high thrust engine operation and the secondary nozzle is operative only at the higher thrust regimes.

As shown in Figure 1 the nozzle comprises a primary fuel feed orifice 12 formed in the generally condically shaped primary nozzle 14 and a second fuel feed orifice 1 6 communicating with the annular passageway 1 8 defined between the spaced conical nozzle element 20 and the primary nozzle 14. Swirl ring 22 and swirl plug, 24 serve to impart a tangential velocity to the fuel before issuing into the combustion zone and produce the flow pattern illustrated.

A portion of air from the compressor is admitted internally in nozzle nut 26 through swirl slots 28 and likewise impart a tangential velocity to the air as it progresses into the combustion zone as shown by the flow pattern.

Air is also introduced around the fuel through the swirl cup 30 with an imparted tangential velocity by the swirl vanes 32. Splitter 34 may be employed as shown. As noted, the flow patten is as indicated.

As will be apparent to one skilled in the art, the direction of swirl and the tangential component is dictated by the vanes and swirl slots. According to this invention both air and fuel issuing into the combustion zone rotate in the same direction. The swirl 24 and the swirl ring 22 as well as the swirl slots 28 and the swirl vanes 32 impart swirling notion in a common direction.

The pressure inside the secondary fuel nozzle 20 upstream of orifice 1 6 is higher than the pressure downstream thereof when primary fuel only is flowing. Also in its preferred embodiment it was found that good emission results were achieved when the area of annular disdharge orifice area defined between the depending lip 36 of nozzle nut 26 and the fuel nozzle heat shield 50, and the area of orifice 36 were substantially equal.

To assure the proper pressure level the number of swirl slots 28 of the original nozzle nut was increased from 8 to 16 for an area of 0.206 square inch.

Actual engine test ran with these modifications in comparison with the heretofore used nozzles showed a substantial reduction in carbon monozide, hydrocarbons and NOx emissions.

The fuel nozzle shown in Fig. 2 is in all essential respects substantially identical to the fuel nozzle of Fig. 1. In both Figures 1 and 2 corresponding members are provided with the same reference numerals. The fuel nozzle of Fig. 2 only differs from the fuel nozzle of Fig. 1 in that orifice 36' has a greater area relative to the fuel nozzle heat shield 50 than in the embodiment of Fig. 1 and means are provided for admission of water into the airstream at a given location upstream of the swirling means shown as inlet 40 and is carried in the airstream and swirled therewith through nozzle nut 26 and cup 30.

As can be seen in Figure 2 the direction of swirl for both the fuel and air/water mixture streams are in the same direction. This co-rotational aspect serves to prevent the water droplets from coaiescing into a localized stream that would otherwise distort the temperature profile emanating from the combustor. From actual tests, it has been found that the co-rotational aspect has improved burner performance and reduced smoke emissions from the engine's exhaust during water injection modes.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit and scope of this novel concept as defined by the following claims.

Claims (7)

1. A dual orifice type fuel nozzle for a combustor of gas turbine engine having a compressor, said fuel nozzle having a generally conically shaped casing with a primary fuel passage centrally disposed therein, secondary fuel passage formed therein concentrically disposed relative to the primary fuel passage, both primary and secondary passages exiting fuel into said combustor through a substantially mutual transverse plane, means for imparting a swirl component to conipressor discharge air surrounding the fuel exiting from said primary and secondary passages, said primary fuel passage normally continuously operative throughout the engine operating envelope and said secondary fuel passage normally operative solely during the high thrust regimes and inoperative during the low thrust regimes of said engine operating envelope, first fuel swirl means in said primary passage for imparting a swirl motion to the fuel issuing therefrom, second fuel swirl means in said secondary passage for imparting a swirl motion to the fuel issuing therefrom, characterized in that said first fuel swirl means, said second fuel swirl means and said means for swirling the air impart swirling motion in a common direction.

2. A dual orifice type fuel nozzle as claimed in claim 1, comprising means for pressurizing the secondary passage when said primary passage is solely operative with said compressor discharge air whereby said secondary passage maintains a positive pressure for preventing fuel from said primary passage from migrating therein and coking the walls of said secondary passage.

3. A dual orifice type fuel nozzle as claimed in claim 2 wherein said means for imparting a swirl component to compressor discharge air includes a fuel nut mounted on the end of said conically shaped casing and having a central opening coaxially disposed relative to the axial axis of said primary passage, a dome shaped heat shield element having an apex attached to the apex of said conically shaped casing and a base end attached to the base of said conically shaped casing, annularly shaped wall means extending inwardly of said nozzle nut and defining a central opening coaxially disposed relative to said axial axis and being axially spaced from apex of said dome element, the central opening of said wall means and said space being dimensioned so that the compressor discharge air being swirled by passages formed in the base end of said nut and discharging through said central opening pressurizes said secondary passage when the primary passage is solely operative.

4. A dual orifice type fuel nozzle as in claim 2 including a first annular passage concentrically disposed between said secondary passage and said primary passage and a second annular passage concentrically mounted to and surrounding said secondary passage means for leading air discharging from said compressor into said first and second annular passages for commingling with the fuel emitted from said primary and secondary passages, means for imparting a swirl component to the air flowing in said first and second annular passages so that the air discharging therefrom swirls about said egressing fuel, said first and second annular passages being dimensioned so as to pressurize said secondary passage when the primary passage is solely operative.

5. A dual orifice type fuel nozzle according to any one of claims 1 to 4, wherein means are provided for injecting water just prior to said air swirling means.

6. A dual orifice fuel nozzle as in claim 5 including a nozzle nut disposed coaxially relative to the axes of said primary passageway and said secondary passageway, swirl slots in said nozzle nut for imparting a swirl motion to the air and water in the same direction as the swirl of the fuel issuing from said primary passage and said secondary passage.

7. A fuel nozzle as in claim 6 including an air swirl cup surrounding said nozzle nut having air swirl vanes disposed coaxially relative to said nozzle nut for imparting a swirl motion to the air and water in the same direction as the swirl of the fuel issuing from said primary passage and said secondary passage.