James D. Gounder

PHASE RESOLVED ANALYSIS OF FLAME STRUCTURE IN LEAN PREMIXED SWIRL FLAMES OF A FUEL STAGED GAS TURBINE MODEL COMBUSTOR

A scaled model of a gas turbine (GT) burner with coaxially mounted swirlers has been used to study the effects of fuel staging on the behavior of lean premixed methane air flames. Lean flames are known to be susceptible to instabilities that can lead to unsteady operation, flame extinction, and thermo-acoustic oscillations. High speed (10 kHz) laser and optical diagnostic techniques have been used to investigate the fuel staging effect on the mechanisms involved in such instabilities. Methane air flames at atmospheric pressure have been investigated at a constant thermal power of 58 kW. The global equivalence ratio was kept constant, while the fuel staging was varied. The bulk flow velocity at the exit plane was kept constant at 20 m/s. Simultaneous high speed OH PLIF, OH* CL, and acoustic measurements were performed at kHz repetition rate to characterize the flames and determine the operability limits of the combustor. The characterization measurements reveal significant changes in flame shape for various staging ratios as well as onset of self-excited thermo-acoustics in flames with more than 55% fuel injection in the outer swirler. The phase resolved analysis of the OH* CL revealed pulsation in the heat release due to acoustics in flames with higher percentage of fuel in the outer swirler. Comparison of the pressure oscillation in the combustion chamber with the heat release yielded a clear picture regarding the feedback mechanism that sustains the self-excited thermo-acoustic pulsations. The variation of local equivalence ratio of the mixture seems to be the driving force that initiates the onset of acoustics pulsations.

Experimental and numerical investigation of spray characteristics in a new FLOX® based combustor for liquid fuels for Micro Gas Turbine Range Extender (MGT-REX)

A liquid fuel combustor based on the FLOX ® gas turbine burner concept has been developed for application in a Micro Gas Turbine (MGT) Range Extender (REX) for next generation cars. The characterization of this combustor was performed at the High Pressure Optical Test rig (HIPOT) at DLR Stuttgart. Spray characteristics were measured using droplet mie scattering and phase Doppler interferometry in flames of a stable burner operation point (BOP) at a pressure, preheat temperature, global lambda (λG), and jet velocity of 3.5 bars, 300 °C, 1.45 and 120 m/s respectively. The experimental results showed long flames with deep penetration of the spray into the combustion chamber. A comprehensive data set of the spray characteristic with well-defined boundary condition was made available for CFD simulations. The CFD simulation of the two-phase flow was performed by coupling the DLR liquid phase simulation code SPRAYSIM with the commercial CFD-code ANSYS CFX-16.1. The comparison of axial and radial velocity profiles between simulation and experiment clearly showed that the turbulence model used in the numerical simulation was unable to predict the measured turbulence appropriately. The calculated and measured spray behavior in the combustion chamber showed satisfying agreement. The observed differences were mainly due to the simple 1-step global combustion model, which predicted an early onset of the heat release. The simulation showed that even though a large portion of the evaporation happened already inside the nozzle, the remaining spray droplets penetrate deep into the combustion chamber.