Numerical Simulation Of Flashback And Blowout Of Lean Premixed Burner

Lean-burn premixed combustion can reduce the flame peak temperature and effectively reduce the generation of thermal NOx,thus it is a low-pollution combustion technology commonly used in modern gas turbines.However,because the lean-burn premixed combustion process deviates from the proper equivalence ratio,combustion instability is likely to occur.This thesis focuses on two unstable combustion phenomena: flashback and blowout of lean premixed swirl burners,aiming to establish numerical simulation methods for quickly predicting flashback and blowout limits.The methods are applied to analyze and predict the flashback and blowout limits and stable combustion conditions of actual burners,in order to provide an analysis method for the design and operation optimization of the combustion chamber.Taking the lean premixed swirl burner in the literature as the object,the steady-state computational fluid dynamics simulation method was adopted to obtain the flashback and blowout limits by changing the conditions gradually to approach the occurrence of flashback and blowout.The turbulence models of Realizable k-? and RSM were compared and analyzed to obtain the flashback and blowout limits of the burner under different premixed gas compositions,and the RSM turbulence model showed better prediction,thus it was used in subsequent CFD simulation.A large amount of data in the process of simulating flashback and blowout were analyzed,and the relationship between the average Damk?hler(Da)number of the characteristic position of the combustion chamber and the mixing fraction of the inlet premixed gas was obtained.The results showed that the 1/Da of the critical flashback point and the Da of the critical blowout point have certain linear correlation with the mixing fraction under different gas velocities.Subsequently,under the condition of fixed inlet swirl number,the effects of three swirl inlet structure sizes on the flashback and blowout limits and the flow field were analyzed,and it was shown that there exists optimal inlet structure size combination to obtain the maximum stable combustion range of the burner.Based on the limits of flashback and blowout obtained by steady-state simulation,the typical conditions were selected for transient CFD simulation to obtain the dynamic process of flashback and blowout,as well as a comparative verification of the steady-state simulation method.Extracting the flow field and temperature distribution of the combustion chamber at different moments obtained by transient simulation,the lean blow-off(LBO)analysis were performed to show more intuitively the transient blowout results.Based on the steady-state CFD simulation data,the chemical reactor network(CRN)models of the burner was established to predict the blowout limits.The blowout boundary close to the steady-state simulation result was obtained,but the calculation time can be shortened to realize faster prediction of blowout limits.The steady-state CFD simulation method was applied to the prediction of flashback and blowout limits of the DLN lean premixed swirl burner.The effects of hydrogen addition and humidification on the flashback and blowout limits were analyzed.At the same time,the CRN models of the lean premixed swirl burner were established to predict the blowout limits,and a similar conclusion was obtained.It also showed that there is a room for further mining and improvement of this CFD-CRN method for rapid blowout prediction.