چكيده به لاتين
The objective of the present thesis is to analyze the characteristics of liquid fuel spray during the reaction flow within an aero gas turbine model combustion chamber, with the aim of reducing the NOx emissions. An Eulerian −Lagrangian approach is applied to study spray of liquid fuel and identification of some phenomena such as distribution, break-up, and evaporation of droplets. At first, in order to investigate the phenomenon of spray of liquid fuel droplets, a non-reactive spray flow has been studied. The results show that the droplets collisions and secondary break-up events do not occur in the present numerical analysis and, considering their computations, do not affect the distributions of droplet diameter and velocity and merely increase the cost of computing. Nevertheless, the coupling between the gas and the droplet phases should be of the two-way type and the presence of droplets affects the gas phase flow. The results display that the conditions of the intake air causes a serious change in the distribution of the dynamic characteristics of the droplets. In order to investigate the spray reactive flow characteristics, the Reynolds Averaged Navier- Stokes (RANS), large eddy simulation (LES) and detached eddy simulation (DES) approaches, discrete ordinates radiation heat transfer model, Eddy dissipation, non-premixed equilibrium and flamelet combustion models as well as three different chemical reaction mechanisms for kerosene fuel have been applied. The NO_x simulation has been performed employing the finite rate model. The results indicate that the best outcomes are derived from the use of flamelet combustion model, the 26 reaction mechanism, and the LES turbulence approach. Due to considering the non-equilibrium reactive effects by the flamelet combustion model and owing to the different reaction steps numbers, combustion species and reactive activation energy of the selective mechanism, the temperature, velocity and concentrations are predicted accurately. In addition to the higher quality and accuracy of the LES and DES approaches in predicting the distributions of velocity, temperature and concentration of combustion species, the LES and DES approaches have superiority in terms of the quantity and variety of results (such as the detection of coherent structures, fluctuations of velocity, temperature and etc.) in comparison with the RANS approach. However, due to the higher computational costs of the LES and DES approaches and acceptable results of the RANS approach, the RANS approach and the realizable k-ε turbulence model have been applied to study the numerous parameters under the different conditions. In order to analyze the spray of liquid fuel and the amount of produced NOx pollutant, the spray relative flow has been investigated under the different conditions of fuel spray and intake air. So that the effects of each of these variable parameters of intake fuel and air on the temperature, droplet diameter, NOx pollutant etc. have been studied.
Keywords: Gas turbine model combustor, Liquid fuel spray, Reactive flow, NOx pollutant.
