Investigation On Emission And Combustion Stability For Coaxial Staged Model Combustor

As the environmental regulations become more and more stringent,advanced lowemission combustion technology has become one of the key technology for the further development of gas turbine combustor.The application of lean premixed low emission combustion technology can avoid excessive combustion temperature,thus reducing the thermal NOx.Coaxial staged technology is a promising and widely used low emission combustion technology.Compared with other lean premixed staged combustors,coaxial staged combustor has the advantages of compact structure and stable off-design operation conditions.However,there are still some problems should be solved in design and application of the coaxial staged combustor.It is difficult to select coaxial staged swirler parameters range,due to the complex influence mechanism of numerous parameters on combustion characteristics.While considering the influence of various parameters on combustion efficiency,emissions and total pressure loss,it is also necessary to take combustion stability into account.However,the combustion stability optimization is difficult because of the lack of numerical judgment methods.In order to obtain a high-efficiency,low-resistance,low-emission and stable coaxial staged combustor,this paper first explores the influence law of various parameters on the combustion fields by numerical simulation,and gradually narrows the geometric parameters range.After determining the swirler geometric parameters,the emission performance boundary of the combustor is obtained by adjusting the fuel spilt strategy.On this basis,combined with flame dynamics analysis,dynamic mode decomposition and flame transfer function,the current paper gives a numerical judgment method for combustion stability.Then,the high stability low emission operation range of this combustor is widened by adding lobes in the swirler.The main research contents of this paper are as follows:(1)In order to reveal the complex influence mechanism of numerous parameters on combustion characteristics,design of experiment(DOE)orthogonal experiment method is used to narrow the swirler geometric parameter range.The effects of swirl number,oblique radial angle and hub spanwise angle on the combustion performance are explored.The main stage air split ratio is determined by off-design operation conditions.After determining the swirler geometric parameters,the emission performance boundary at rated conditions is given by adjusting the fuel supply schemes.These above researchs provide swirler structure and working condition range for subsequent combustion stability study.(2)Within the working condition range for excellent static performance(combustion efficiency,emission and total pressure loss),this paper explores the influence of fuel spilt strategy on combustion stability by large eddy simulation(LES).Then,defines the high stability low emission operation range of the combustor.The results show that the unsteady circumferential vortex will induce combustion instability,and the circumferential vortex scale is about 5 mm.In this paper,a numerical judgment method for combustion instability is given by flame dynamics analysis,dynamic mode decomposition and flame transfer function.When stratified ratio of this model combustor is 1,the pilot equivalent ratio needs to be controlled above 0.8 to achieve stable combustion.In the stable combustion range,NOx and CO can be controlled at about 15 ppm and 10 ppm respectively.(3)In order to optimize the combustion stability without affecting the static performance of the combustor,lobe structures are added at different positions of the swirler.In this paper,PIV experiment and non-reacting LES study are carried out successively,and the influences of lobes on the instantaneous flow field and instantaneous component transport field are analyzed.The influence mechanism of the lobes on combustion stability is explored by decoupling flow,mass transfer with combustion process.The results show that adding lobes to the first main stage hub and vanes can improve the instantaneous vorticity field stability and component transport field stability respectively,then optimize the combustion stability.Compared with the original combustor,the heat release rate fluctuation amplitude of the 1J-YB combustor decreased by about 80%.When stratified ratio is 1 for 1J-YB combustor,stable combustion can be achieved by controlling the pilot equivalence ratio at about 0.6.In the stable combustion range,NOx and CO can be controlled at about 5ppm and 10 ppm respectively.