Patent Publication Number: US-2019170354-A1

Title: Fuel spray nozzle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Greek Patent Application No. GR20170100550, filed on 1 Dec. 2017, the contents of which are herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure concerns a fuel spray nozzle, also known as a prefilming airblast spray nozzle. 
     Description of the Related Art 
     In gas turbine combustion, prefilming airblast spray nozzles control the quantity and quality of mixing of air and fuel inside the combustor liner of gas turbine engines. To assist the mixing, a system of swirlers (axial or radial) and fuel circuits can be used. The swirlers spin air passing through them, and the fuel circuit can deliver fuel to the prefilming surfaces of the nozzle as a spinning film. When the fuel and air flows meet at the prefilming surface, the air flow shears the film towards the trailing edge of the prefilming surface causing the disintegration of the fuel film into fine droplets. 
     SUMMARY 
     The characteristics of the air/fuel flow on the prefilming surfaces and the subsequent atomisation at the prefilmer trailing edge affect the combustion performance. An ideal fuel spray nozzle system would be the one which achieves a uniform atomisation of the film into fine droplets around the periphery of the nozzle. To date, atomization improvements of pre-filming fuel spray nozzles have focused on changing the relative velocity between air and fuel circuits, either through streamlining or through co-/counter swirling the flows. 
     The present invention aims to improve the atomisation from a prefilming surface in a spray nozzle. 
     According to one aspect of the invention there is provided a spray nozzle, for atomising liquid in a gas, comprising: a gas passage; a liquid passage; a prefilming surface positioned downstream of the liquid passage and the gas passage, and configured to receive liquid from the liquid passage and to receive gas from the gas passage; wherein the liquid passage terminates at an exit orifice upstream of the prefilming surface; and wherein the gas passage contains a flow perturbator upstream of the liquid passage exit orifice, to increase the turbulence of gas passing from the gas passage to the prefilming surface. The provision of the flow perturbator increases the turbulence in the gas approaching the prefilming surface and thus improves the atomisation. 
     The flow perturbator can be a protrusion within the gas passage. Optionally, the flow perturbator is a bluff body on both upstream and downstream sides. Alternatively the flow perturbator is a streamlined body on its upstream side and a buff body on its downstream side. In both scenarios, an increase in turbulence of the gas passing the flow perturbator is achieved. 
     Optionally the prefilming surface has a length over which gas received from the gas passage and liquid received from the liquid passage passes, and the flow perturbator is positioned upstream of the liquid passage exit orifice by at least one length of the prefilming surface. Optionally the flow perturbator is positioned upstream of the liquid passage exit orifice by no more than ten lengths of the prefilming surface. Such positioning gives the optimal improvements in the atomisation performance. 
     Optionally the flow perturbator extends around an entire circumference of the gas passage. Optionally a height of projection of the flow perturbator into the gas passage varies around a circumference of the gas passage. Alternatively, a height of projection of the flow perturbator into the gas passage is substantially uniform around a circumference of the gas passage. 
     Optionally a height of the projection of the flow perturbator into the gas passage is between 0.1 and 10 times a length of the prefilming surface, preferably from 0.2 to 5 times the length of the prefilming surface. 
     Optionally two or more of said flow perturbators can be provided. The flow perturbators can be positioned at different distances from the prefilming surface. 
     Optionally the spray nozzle can be a fuel spray nozzle for atomising a fuel for combustion in air. The improved atomisation performance leads to improved combustion characteristics in a fuel spray nozzle such as a fuel injector. 
     According to another aspect of the invention there is provided a gas turbine engine incorporating such a fuel spray nozzle. 
     A swirler may be provided in the gas passage up stream of the flow perturbator. 
     The gas and liquid passages may be concentric. 
     The liquid passage may be arranged concentrically around the gas passage. 
     A second gas passage may be arranged concentrically around the liquid passage. 
     The second gas passage may have a swirler. 
     The liquid passage may be a pilot fuel passage of a lean burn fuel spray nozzle. 
     The liquid passage may be a main fuel passage of a lean burn fuel spray nozzle. 
     The liquid passage may be a fuel passage of a rich burn fuel spray nozzle. 
     According to another aspect of the invention there is provided a method of atomising liquid in gas, comprising the steps of: supplying gas to prefilming surface via a gas passage; and supplying liquid to the prefilming surface via an exit orifice upstream of the prefilming surface; wherein the gas passage contains a flow perturbator upstream of the liquid passage exit orifice, to increase the turbulence of gas passing from the gas passage to the prefilming surface. 
     The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described by way of example only, with reference to the Figures, in which: 
         FIG. 1  is a sectional side view of a gas turbine engine; 
         FIG. 2  is a section side view of a prior fuel injection arrangement suitable for a gas turbine engine; 
         FIG. 3  is a section side view of a fuel injection arrangement incorporating flow perturbators; 
         FIG. 4  is a section side view of different types of flow perturbators; 
         FIG. 5  depicts a flow perturbator; 
         FIG. 6  is a perspective view of the flow perturbator of  FIG. 5  in a fuel injection arrangement; 
         FIG. 7  illustrates gas phase velocity fluctuations for a fuel injection arrangement with and without a flow perturbator; and 
         FIG. 8  illustrates sooting in a fuel injection arrangement with and without a flow perturbator. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a gas turbine engine is generally indicated at  110 , having a principal and rotational axis  111 . The engine  110  comprises, in axial flow series, an air intake  112 , a propulsive fan  113 , an intermediate pressure compressor  114 , a high-pressure compressor  115 , combustion equipment  116 , a high-pressure turbine  117 , an intermediate pressure turbine  118 , a low-pressure turbine  119  and an exhaust nozzle  120 . A nacelle  121  generally surrounds the engine  110  and defines both the intake  112  and the exhaust nozzle  120 . 
     The gas turbine engine  110  works in the conventional manner so that air entering the intake  112  is accelerated by the fan  113  to produce two air flows: a first air flow into the intermediate pressure compressor  114  and a second air flow which passes through a bypass duct  122  to provide propulsive thrust. The intermediate pressure compressor  114  compresses the air flow directed into it before delivering that air to the high pressure compressor  115  where further compression takes place. 
     The compressed air exhausted from the high-pressure compressor  115  is directed into the combustion equipment  116  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines  117 ,  118 ,  119  before being exhausted through the nozzle  120  to provide additional propulsive thrust. The high  117 , intermediate  118  and low  119  pressure turbines drive respectively the high pressure compressor  115 , intermediate pressure compressor  114  and fan  113 , each by suitable interconnecting shaft. 
     Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan. 
     Referring now to  FIG. 2 , a fuel injection arrangement suitable for a gas turbine engine is generally indicated at  60 . The fuel injection arrangement  60  is a form of prefilming airblast spray nozzle. The fuel injection arrangement  60  is attached to the upstream end of a gas turbine engine combustion chamber  11 , part of which can be seen in  FIG. 2 . Throughout this specification, the terms “upstream” and “downstream” are used with respect to the general direction of a flow of liquid and gaseous materials through the fuel injection arrangement  60  and the combustion chamber  11  as shown by arrow A. Thus with regard to  FIGS. 1 to 4 , the upstream end is towards the left hand side of the drawing and the downstream end is towards the right hand side. The actual configuration of the combustion chamber  11  is conventional and will not, therefore, be described in detail. Suffice to say, however, that the combustion chamber  11  may be of the well known annular type or alternatively of the cannular type so that it is one of an annular array of similar individual combustion chambers or cans. In the case of a cannular combustion chamber, one fuel injection arrangement  60  would normally be provided for each combustion chamber  11 . However, in the case of an annular combustion chamber  11 , the single chamber would be provided with a plurality of fuel injection arrangement  60  arranged in an annular array at its upstream end. Moreover, more than one such annular array could be provided if so desired. For instance, there could be two coaxial arrays. 
       FIG. 2  shows a prior art piloted airblast lean direct fuel injector arrangement  60 , which is similar to that described in detail in U.S. Pat. No. 6,272,840, the teachings of which are incorporated herein by reference. However, the main features are briefly described where particularly relevant to the present invention. 
     The injector arrangement  60  is generally annular and symmetrical about an injector axis  62  and is disposed at the upstream end of the combustion chamber  11 . 
     The fuel injector arrangement  60  comprises a pilot or primary injector  12  and inner and outer pilot swirlers  13 ,  14  generally surrounding the pilot injector  12 . A main airblast fuel or secondary injector  16  is concentrically positioned around the pilot injector  12  and inner and outer main swirlers  18 ,  20  are concentrically disposed radially inwardly and outwardly respectively of the main airblast fuel injector  16 . 
     An annular air splitter  22  is located between the outer pilot swirler  14  and the inner main swirler  18 . The air splitter  22  comprises an air inlet  24  and downstream, an air outlet  26 . The air splitter  22 , in the direction of air flow, further comprises a generally cylindrical portion  28 , a radially inwardly tapered portion  30  and a downstream portion  32  that is tapered still further radially inwardly. 
     In use, fuel flows through galleries  64  and  66 , which are liquid passages, and exits through orifices  76 ,  78 , which are defined by annular and co-axial members  68 ,  70  and  72 ,  74 , of the main and pilot fuel injectors  16  and  12  respectively. The annular members  68  and  72  are fuel prefilmers having prefilming surfaces  80 ,  82  that the fuel flows over prior to being shed from downstream edges into the swirling airflows. As such, the exit orifices  76 ,  78  are upstream of their respective prefilming surfaces  80 ,  82 . At the same time as the fuel being supplied via the exit orifices  76 ,  78 , air is supplied to the prefilming surfaces  80 ,  82  from the inner pilot swirler  13  and inner main swirler  18  respectively. The air from the inner pilot swirler  13  passes along gas passage  21 , past the exit orifice  78 , to the prefilming surface  82 . Similarly, air from the inner main swirler  18  passes along gas passage  23 , past the exit orifice  76 , to the prefilming surface  80 . As such, the air passing over the prefilming surfaces assists with the atomisation of the liquid fuel from the prefilming surfaces  80 ,  82 . 
       FIG. 3  shows a fuel injector spray nozzle  60  similar to that of  FIG. 2  but provided with a flow perturbator  85  upstream of prefilming surface  82 , and a similar flow perturbator  86  provided upstream of prefilming surface  80 . Each flow perturbator  85 ,  86  is also provided upstream of the respective liquid passage exit orifice  78 ,  76 , corresponding to each prefilming surface  82 ,  80 . 
     The presence of the flow perturbators  85 ,  86  causes the gas supplied through the gas passages  21 ,  23  to increase in turbulence as it approaches the exit orifices  78 ,  76  and prefilming surfaces  80 ,  82 . The increase in turbulence assists with the atomization of the liquid fuel from the prefilming surfaces  80 ,  82  by decreasing the break-up length for atomizing the liquid from the prefilming surface. 
     The enlarged portion of  FIG. 3  illustrates a length/designating the distance of the flow protrusion from the start of the pre-filmer  82 . In some embodiments, the distance/is at least one pre-filmer length. In other words, the flow perturbator  85 ,  86  is positioned upstream of the liquid passage exit orifice  78 ,  76  by at least one length of the prefilming surface  80 ,  82 . In some embodiments, the distance/is no more than  10  pre-filmer lengths. In other words, the flow perturbators  85 ,  86  are positioned upstream of the respective liquid passage exit orifices  78 ,  76  by no more than 10 lengths of the respective prefilming surfaces  80 ,  82 . By providing the perturbators within one to ten pre-filmer lengths of the pre-filming surface, the optimum increase in atomisation is achieved. 
     The enlarged portion of  FIG. 3  also illustrates a height h. The height h of the flow perturbators  85 ,  86  in some embodiments is of the order of the respective pre-filmer length. In other words, the height of projection of the flow perturbators  85 ,  86  into their respective gas passages  21 ,  23  can be between 0.1 and 10 times the length of the respect prefilming surface  80 ,  82 , and preferably from 0.2 to 5 times the length of the prefilming surface. 
     As illustrated in  FIG. 3  the flow perturbators  85 ,  86  can be a protrusion into the respective gas passages  21 ,  23 . The protrusion may present a bluff body to the flow of gas through the gas passage. In other words, the protrusion may represent a step in the inner surface of the gas passage, with a substantially rectangular cross-section. Alternatively, the protrusion may be streamlined to the side facing the oncoming flow, with a bluff/abrupt shape on the downstream facing side. This is illustrated in  FIG. 4 , in which flow perturbator  85 A is of the bluff body type in both the upstream and downstream directions, whilst flow perturbator  85 B has a streamlined upstream face, with a bluff downstream face.  FIG. 4  also illustrates the possibility that more than one flow perturbator may be provided in each gas passage  21 ,  23 . The flow perturbators may be provided at different distances from the prefilming surface. 
     The flow perturbator can extend around the entire circumference of the gas passage  21 ,  23 . However, the height h of the flow perturbator may vary circumferentially. This is illustrated in  FIG. 5  which shows an example flow perturbator  85  that has a scalloped inner surface. As such, the height of the flow perturbator (which would be measured radially from the outer edge, as shown in  FIG. 5 , to the inner edge) varies radially around the flow perturbator  85 . In other alternatives, the height of the projection of the flow perturbator into the gas passage can be substantially uniform around the circumference of the gas passage.  FIG. 6  illustrates the positioning of the flow perturbator of  FIG. 5  in a fuel injector arrangement  60 . 
     Use of the flow perturbator  85 ,  86  as described above helps deliver a fuel-air mixture-fraction field of improved uniformity through improved liquid-sheet atomization from the prefilming surfaces  82 ,  80 . This also delivers an improvement in smoke/soot emissions. This is all achieved without requiring a drastic modification to the fuel spray nozzle or the technology required to manufacture one. 
     The improvements arise because, as the gas flow travels past the flow perturbator  85 ,  86 , the flow is ‘tripped’, generating increased turbulent regions in the gas near the surface of the gas passage. These locally increased turbulence levels in turn change the frequency/wavelength of the instability that arises at the interface of the liquid and gas sheet. A change in the interphase (liquid-gas) instability directly results in a change of the primary and secondary breakup lengths resulting in smaller droplets at the same measurement plane. 
     This is illustrated by  FIG. 7 , which depicts the increased gas phase velocity fluctuations (VelocityRMS, or VelRMS) for the fuel spray nozzle with the pre-filming steps. 
       FIG. 7  shows gas phase velocity fluctuations for a rich burn fuel nozzle. As such, it will be clear that the present invention is applicable to both rich burn fuel nozzles and lean burn fuel nozzles. The rich burn fuel nozzle shown in  FIG. 7  comprises concentric inner, intermediate and outer gas passages, each of which has a swirler. The fuel passage is provided between the inner and intermediate gas passages and supplies fuel through an exit orifice upstream of a prefilming surface on the inner gas passage. Thus the flow perturbator is positioned in the inner gas passage upstream of the exit orifice. 
     It will thus also be appreciated that although the fuel injector  60  of  FIG. 3  has a perturbator upstream of the prefilming surface of the pilot fuel injector  12  and a perturbator upstream of the prefilming surface of the main fuel injector  16  it is equally possible to only have a perturbator upstream of the prefilming surface of the pilot fuel injector  12  or to only have a perturbator upstream of the prefilming surface of the main fuel injector  16 . 
     For completeness, it is noted that some rich burn fuel nozzles, compared to what is shown in  FIG. 7 , only have the inner two gas passages and respective swirlers, and the present invention is also applicable to those arrangements. Also, some lean burn fuel injectors, compared to what is shown in  FIG. 3 , have an additional gas passage and associated air swirler between the outer gas passage of the pilot fuel injector  12  and the inner gas passage  23  of the main fuel injector  16 . 
       FIG. 7  shows VeIRMS for the gas phase in the streamwise (left-hand-side) and cross-stream (right-hand-side) directions, obtained from large eddy simulation (LES) calculations for a fuel spray nozzle both with the perturbator (top) and without (bottom). The increased velocity fluctuations are noticeable near the pre-filming surface in the stream-wise section on the left hand side of  FIG. 7 , within the dotted ellipse. 
     The presence of the flow perturbator slightly restricts the effective area (and thus discharge coefficient) of the whole fuel spray nozzle through subtle alteration of the shape of the precessing vortex core, and the introduction of a partial blockage in the gas passage (of the order ˜5-6%). However, this increased blockage may be offset by using a fuel spray nozzle with increased effective area thus maintaining the same overall air-to-fuel ratio. 
       FIG. 8  depicts in a qualitative sense the reduction in sooting predicted by employing a perturbator design on two fuel-spray nozzles operating at identical air-to-fuel ratios. The figure presents instantaneous fuel-to-air fields and soot fields with and without the perturbator (top and bottom, respectively) for two types of fuel spray nozzle seals (left and right hand sides, respectively, shown in different section). Red colours indicate regions of high variable value while blues indicate regions of little to no variable value, respectively. It should be noted here that the improvement (i.e. reduction in variability) shown is a conservative one as the fuel droplet diameter distribution has not been decreased within the model for the flow perturbator scenario as would be expected in reality. The illustrated improvement is achieved solely through the introduction of increased gas phase turbulence intensity near the injection location, and so an even greater improvement would be expected if the injected droplet size was also decreased. 
     The above discussion has focussed on the particular scenario of a fuel spray nozzle, and the improved combustion performance imparted. However, it will be appreciated that the improved atomisation from the prefilmer will also bring advantages in other scenarios where consistency of droplet size is important, such as emissions control. Thus, although the embodiments discussed above all relate to the use of a spray nozzle in the context of a turbine engine, the invention is applicable in other fields too. 
     It will thus be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.