| Wide stable working boundary and high combustion efficiency are key design performances of combustor,which is one of the three major components of aero-engine.Fuel-air ratio and air mass flow rate of combustor climb with the increase of thrust-to-weight ratio.The above make the stable working boundary of combustor insufficient,which restricts the development of aero-engine.Traditional combustors can no longer meet the need to widen working boundary,for which fuel-staged partially premixed air-blast atomizers are widely used in new combustors.The pilot stage of fuel-staged partially premixed air-blast atomizer adopts fuel-rich diffusion combustion to improve ignition and flameout performance and widen working boundary.The main stage of fuel-staged partially premixed air-blast atomizer adopts lean premixed combustion to enhance fuel-air mixing and improve combustion efficiency.The complex structure of fuel-staged partially premixed air-blast atomizer leads to strong interactions between sub-components,and increasingly air mass flow rate leads to strong interactions between sectors,which make the flow field organization and spray field organization complicated.In addition,dual-orifice pressure atomizer is widely used in pilot stage with the increase of thrust,interaction between liquid films of which are strong.As we all know,flow field and spray field play an important role in determining the combustion performance.Thus,there is an urgent need to study flow field and spray field organization to provide support for the design and optimization of new combustor.In order to gain a deeper understanding of flow field and spray field organization,the method of breaking up the whole into parts is used to divide the fuel-staged partially premixed air-blast atomizer into pressure-swirl atomizer,pilot stage and main stage to research separately.Firstly,atomization characteristics of single-orifice pressure-swirl atomizer and dual-orifice pressure-swirl atomizer are investigated using experiments.Secondly,interactions between sub-components of fuel-staged partially premixed air-blast atomizer and interactions between sectors are investigated using experiments and numerical simulations.The research work mainly contains four parts:investigation on relationship between liquid film breakup phenomena,atomization characteristics and liquid film breakup mechanism of single-orifice pressure-swirl atomizer,investigation on atomization characteristics of dual-orifice pressure-swirl atomizer and optimization method,investigation on interactions between sub-components of fuel-staged partially premixed air-blast atomizer,investigation on interactions between sectors of fuel-staged partially premixed air-blast atomizer.The main contents and conclusions are as follows:(1)In the first part,breakup phenomena of liquid film,liquid film cone angle,droplet size,liquid film breakup length and liquid film breakup mechanism of single-orifice pressure-swirl atomizer are investigated under different pressure drops.The relationship between liquid film breakup phenomena,atomization characteristics and liquid film breakup mechanism are established.It is found that onion-shaped liquid film,tulip-shaped liquid film,wave cone-shaped liquid film,perforation cone-shaped liquid film and fully developed cone-shaped liquid film appear in sequence with the increase of pressure drop.Droplet size becomes smaller,liquid film cone angle becomes larger first and then smaller,liquid film breakup frequency becomes larger with the increase of pressure drop.Breakup of onion-shaped liquid film is dominated by impact breakup mode and perforation breakup mode,and liquid film breakup length becomes larger with the increase of pressure drop.Breakup of tulip-shaped liquid film and wave cone-shaped liquid film are dominated by surface wave breakup mode,liquid film breakup length becomes smaller first and then remains stable with the increase of pressure drop.Surface wave average velocity becomes larger with the increase of pressure drop.Breakup of perforation cone-shaped liquid film is dominated by perforation breakup mode,which is determined by turbulent kinetic energy and surface wave.Liquid film breakup length becomes smaller with the increase of pressure drop.Breakup of fully developed cone-shaped liquid film is dominated by turbulent kinetic energy breakup mode,and liquid film breakup length is small and changes little with the increase of pressure drop.(2)In the second part,influences of structure parameters on mass flow rate and atomization characteristics(spray cone angle,droplet size,interactions between liquid films)of dual-orifice pressure-swirl atomizer are investigated,secondary separation pressure and contraction amplitude of main stage spray cone angle are defined.Mechanism of interaction between liquid films is clarified,optimization method is obtained and it is further supplemented during engineering application.It is found that mass flow rate of main atomizer is sensitive to main nozzle diameter,main convergent angle,main swirling groove depth and main swirling angle.Spray cone angle of main atomizer is sensitive to round structure and main nozzle diameter.Droplet size of main atomizer is sensitive to main nozzle diameter and main convergent angle.Mass flow rate of pilot atomizer is sensitive to pilot nozzle diameter,pilot swirling groove depth and pilot nozzle length.Spray cone angle of pilot atomizer is sensitive to pilot nozzle diameter,pilot nozzle length and pilot swirling groove depth.Droplet size of pilot atomizer is sensitive to pilot nozzle diameter and pilot swirling groove depth.Expansion angle of pilot nozzle can be used to adjust spray cone angle of pilot atomizer when pilot nozzle diameter is too small,whereas too large expansion angle will induce liquid film oscillation.Pilot swirling groove depth and expansion angle are key parameters that influence liquid film oscillation.Three patterns(separation-fusion-secondary separation)of main liquid film and pilot liquid film appear with the increase of pressure drop.Liquid film fusion makes droplet size larger,and there is a delay in liquid film separation when reduce pressure drop after liquid film fusion.Liquid film fusion pressure,secondary separation pressure and contraction amplitude of main stage spray cone angle after secondary separation are mainly influenced by mass flow rate and spray cone angle of main atomizer and pilot atomizer.In general,mass flow rate,spray cone angle of main atomizer and pilot atomizer should be allocated reasonably during the design and optimization process of dual-orifice pressure-swirl atomizer.Droplet size should be as small as possible.Liquid film fusion and liquid film oscillation should be avoided when main atomizer and pilot atomizer work at the same time.Contraction amplitude of main stage spray cone angle should be smaller than 10°.In addition,machining and structure coordination of main atomizer and pilot atomizer should also be considered.(3)In the third part,influences of structure parameters on interactions between sub-components of fuel-staged partially premixed air-blast atomizer are investigated to gain a deeper understanding of flow field and spray field organization,pilot stage of which is a swirl-cup air-blast atomizer,main stage of which is a cross-jet air-blast atomizer.Mechanism of interactions between sub-components of fuel-staged partially premixed air-blast atomizer is clarified.Effectiveness of venturi and effectiveness of sleeve are defined.It is found that there are strong interactions between sub-components of swirl-cup air-blast atomizer(pilot stage).The first-stage swirler improves atomization characteristics of pressure-swirl atomizer,and enhances the mixing of fuel and air.The mixture of fuel and air flow downstream along the venturi expansion wall.Venturi throat diameter and venturi expansion angle are key factors to control spray cone angle downstream of venturi,whereas cannot control atomization characteristics.There are ligaments and big droplets at outlet of venturi.The second-stage counter swirler improves atomization characteristics downstream of venturi,whereas cannot control spray cone angle.Sleeve length and sleeve expansion angle are key factors to control spray cone angle downstream of sleeve,and there are less ligaments and smaller droplets at outlet of sleeve than these at outlet of venturi.In addition,there are strong interactions between main stage and pilot stage of fuel-staged partially premixed air-blast atomizer.The strong entrainment of main stage swirling air makes the mixing of pilot stage swirling air and main stage swirling air.Part of pilot stage fuel follow the swirling air into main combustion zone,and be transported to ignition zone by main stage swirling air.Main stage swirling air make the fuel distribution area and spray cone angle be larger.The spray cone angle is a key performance parameter of fuel-staged partially premixed air-blast atomizer when fuel is only supplied at pilot stage.There is a best main stage vane angle that make the spray cone angle biggest.(4)In the fourth part,influences of working conditions(pressure drop,fuel-air ratio)and structure parameters(main stage velocity,main stage swirl intensity)on interactions between sectors are investigated using an optical three-sector combustor test rig.Mechanism of interactions between sectors is clarified.It is found that interactions between sectors are mainly determined by velocity and expansion angle of high-speed jet when the sector spacing is constant.When the expansion angle of high-speed jet is larger than a certain value,interactions between sectors will become stronger with the increase of velocity and expansion angle of high-speed jet.In addition,the axial velocity at interaction plane will rise,and even the phenomenon of jet merging will occur.The enhancement of interactions between sectors will further reduce the expansion angle of high-speed jet and recirculation zone area.When the expansion angle of high-speed jet is smaller than a certain value,axial velocity at interaction plane is small,and interactions between sectors will further make the expansion angle of high-speed jet rise.In general,atomization characteristics,interactions between sub-components of atomizers and interactions between sectors are investigated in this paper.All conclusions can provide support for the design and optimization of new combustors. |
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