A COMPUTATIONAL STUDY OF PRESSURE EFFECTS ON POLLUTANT GENERATION IN GAS-TURBINE COMBUSTORS

A numerical study of the effect of pressure on the formation of NOx an d soot in an axisymmetric 30 deg counterrotating axial swirler lean lo w-NOx gas turbine combustor has been conducted. This has previously be en studied experimentally and this CFD investigation was undertaken to explain the higher than expected NOx emissions. The combustion condit ions selected for the present study were 300 K inlet air, 0.4 overall equivalence ratio, and pressures of 1 and 10 bar. The numerical model used here involved the solution of time-averaged governing equations w ing an elliptic flow-field solver. The turbulence was modeled using al gebraic stress modeling (ASM). The thermochemical model was based on t he laminar flamelet formulation. The consented scalar/assumed pdf appr oach was used to model the turbulence chemistry interaction. The study was for two pressure cases at 1 and 10 bar. The turbulence-chemistry interaction is closed by assumption of a clipped Gaussian function for m for the fluctuations in the mixture function. The kinetic calculatio ns were done separately from the flowfield solver using an opposed lam inar diffusion flame code of SANDIA. The temperature and species profi les were made available to the computations through look-up tables. Th e pollutants studied in this work were soot and NO for which three mor e additional transport equations are required, namely: averaged soot m ass fraction, averaged soot particle number density, and finally avera ged NO mass fraction. Soot oxidation was modeled using molecular oxyge n only and a strong influence of pressure was predicted. Pressure was shown to have a major effect on soot formation.