Reduction Of Methane/Air Mechanism And Spatial Distribution Of Combustor Pollutants

With the increasing awareness of environmental protection,people have increasingly strict requirements on the emission of gas turbine pollutants.How to realize the low pollution emission of gas turbine has become a major problem that needs to be solved urgently by the academia and industry.Numerical simulation is a powerful tool in the process of combustion chamber design.Because of the large computation and "stiff" problem of the detailed mechanism,it is very important to develop a reduced mechanism suitable for the numerical simulation of combustor.Although many reduced mechanisms of methane combustion have been developed by previous researchers,these mechanisms are often used for specific operating conditions or not containing NOx mechanism,and not suitable for numerical simulation in a wide range of operating conditions in the combustor.Therefore,it is of great engineering significance to develop a reduced mechanism applicable to a wide range of operating conditions and clarify the generation mechanism and spatial distribution of pollutants in the combustor based on the reduced mechanism.Based on the research subject of a model combustor,this paper developed a reduced methane/air nitrogen-containing combustion mechanism suitable for the gas turbine combustor,and then studied the pollutant generation mechanism and spatial distribution in the model combusor,and proposed the pollutant control strategy accordingly.The specific work is as follows:(1)Aiming at balancing the simulation accuracy and the calculation consumption caused by mechanism selection in the numerical simulation process,the detailed methane kinetic mechanism GRI-mech 3.0 was taken as the research object,and the Direct Relation Graph method and Sensitivity Analysis method were used to reduce it.The three parameters of ignition delay time,CO and NO pollutant mole fraction were taken into account in the process of the reduction.Finally,a reduced mechanism of methane/air nitrogen-containing combustion with 29 species and 74 steps was obtained.Furthermore,the reduced mechanism was verified by the calculation of 0-dimensional and 1-dimensional ideal reactors.The results show that the reduced mechanism is in good agreement with the detailed mechanism in a wide range of operating conditions,and it is suitable for the numerical simulation of combustion process and pollutant generation process in combustion chamber.(2)Taking Sandia Flame D and an industrial gas turbine combustor as the object of verification,the combustion process and pollutant generation characteristics were simulated based on the obtained 74-step reaction mechanism,the accuracy and applicability of the reduced mechanism to predict the combustion field and pollutants’ spatial distribution in the numerical simulation were analyzed,and the pollutants’ generation mechanism and spatial distribution in the combustion process were explored.(3)Taking a model combustor as the research object,based on the obtained reduced mechanism,numerical simulation work is carried out for three typical working conditions of the model combustor,and the combustion characteristics,NO generation characteristics and different NO generation mechanisms’ contributions to NO emission at the outlet under different working conditions are analyzed.The results show that the Zeldovich mechanism plays a dominant role in NO formation under three operating conditions,and the prompt mechanism mainly contributes to the outlet NO by accelerating the kinetic reaction rates of N+O2=NO+O and N+OH=NO+H.(4)In order to solve the problems of excessive discharge of NO at the outlet of the combustor and ablation of the central body of the swirler and the head wall of the combustor under rated working conditions,the method of blowing air into the central blunt body of the swirler and arranging asymmetrically distributed cooling holes on the head wall of the combustor was adopted,then the fuel distribution scheme was changed,and finally the concentration of NO emission at the outlet was reduced to meet the requirements of low pollution emission.