Study On Combustion Stability Of Natural Gas Coaxial Staged Combustion Chamber

With the increase in industrial demand,the thermal capacity of combustion chamber of modern gas turbine is increasing,and the temperature rise is increasing.But higher combustion temperature will produce heavy NO_X.The research shows that lean premixed combustion can lower the combustion temperature and reduce NO_Xemission significantly.However,the problems of combustion instability and lean blowout exist on the natural gas coaxial staged combustion chamber with lean premixed combustion.Both of them restrict the stable combustion performance of combustor.Therefore,it is necessary to study two aspects of combustion stability:dynamic stability of combustion and stability of lean blowout.Ensure stable operation of gas turbine and build the foundation for broadening the stability boundary.In this thesis,the dynamic stability of combustion and lean blowout stability of a coaxial staged combustor are studied by experiment and numerical simulation.The variation rules of the combustion stability with the fuel stratification ratio,the flow ratio,and the swirl ratio was obtained.Therefore,this thesis has carried out the following works:(1)The dynamic stability of combustion is measured by experiment.As the fuel stratification ratio increases in 0 to 3,the dynamic stability of combustion goes through three states:low frequency and low amplitude oscillation combustion,stable combustion and high frequency and high amplitude oscillation combustion.The dynamic stability of combustion is related to the flow ratio,the swirl ratio and the reaction zone.And the influence is variable at different stages.(2)The typical conditions of the experiment are simulated.The reaction zone and tempering match well with the experiment result,which proves the feasibility of numerical simulation.The dynamic stability of combustion of the two operating conditions with fuel stratification ratios of 1 and 3 is very different.The periodic disturbances of axial velocity,CO mass fraction and flame index obtained by the precession vortex core are captured by time series.The internal mechanism of dynamic stability of combustion is revealed.The pressure pulsation,heat release rate pulsation and coherent structure in the combustion chamber were studied when the inlet pulsation is imposed.The response mechanism of combustion to inlet disturbance is obtained.(3)The stability of lean blowout is studied by experiment and numerical simulation.The stability of lean blowout with various parameters is obtained,which are equivalence ratio of first stage,flow ratio swirl ratio,inlet temperature,pressure,mass flow,central stage and mixing performance.The change of parameters in the process of reducing the equivalent ratio of second stage is analyzed by numerical simulation,which are velocity field,temperature field,combustion efficiency,characteristic temperature and flame volume.The applicability of the existing prediction method of lean blowout limit to coaxial staged combustion chamber of natural gas was studied.