Numerical Study On The Influence Of Different Chemical Reaction Mechanisms On Combustion In A Heavy Duty Gas Turbine

In this paper,a three-dimensional numerical simulation of a heavy gas turbine combustor developed in China was conducted to study the influence of different chemical reaction mechanisms on the flow characteristics and the emission of pollutants from the combustion chamber.The gas turbine combustor was reconstructed by Pro-E software and the grids were generated using Gambit software.Finer girds are located in the primary zone where strong reaction is expected,as well as the air entrances where the physical properties change more dramatically.Total amount of 36 million grids were used,and grid quality has been checked.The mathematical equations are based on the conservations of mass,momentum,and energy with other equations for the turbulence and combustion.The simulations were performed with standard k-?turbulent flow model and EDC turbulent combustion model for chemical reaction.Gas mixtures radiation is considered in the model and computed by DO model.The SIMPLE algorithm is used to handle the pressure and velocity coupling.Firstly,methane-air single step chemical reaction mechanism provided by Fluent was used to calculate the flow,heat transfer and combustion in the combustion chamber at a relative power of 0.7.The calculated results were compared with the experimental values.The results show that the velocity field,temperature field,the profiles of the reactant,product can better reflect the actual burning situations of the gas turbine combustor,and the calculated outlet temperature distribution agreed well with the experimental data.Then,combustion characteristics and pollutants emission in the combustor are conducted using five reaction mechanisms for methane-air mixture,namely,simplified mechanism of DRM19 and DRM22,and the detailed chemical reaction mechanisms of GRI1.2,GRI2.11 and GRI3.0,the predicted results are compared with these results by the one-step mechanism.It is shown that the maximum temperature,the maximum velocity of the axial center section predicted by the one-step reaction mechanism are 2500K and 120m/s,respectively,both greater than the prediction value of the simplified mechanism and the detailed mechanisms.The flame predicted by the single-step mechanism is close to the nozzle.However,the predicited temperature,the flow fields and species distributions by the simplified mechanism and detailed mechanisms show small difference.The outlet temperature quality is poor predicted by six kinds of mechanisms.The NOx emissions predicted by the six mechanisms are seriously beyond the design standards of the gas turbine,but the NOx emissions predicted by the detailed chemical reaction mechanism GRI3.0 was 116.53 mg/m~3,which is in line with the experimental value of the gas turbine.In addition to the single-step mechanism,the CO emissions predicted by the other five mechanisms are greater than these of design standards of the gas turbine,and the chemical reaction mechanism has little effect on the prediction of CO emission.