Lean Gas Turbine Combustor Research Articles

Effects of Swirl Number and Central Rod on Flow in a Lean Premixed Swirl Combustor

ABSTRACT In most modern-day lean gas turbine combustors, flame is stabilized by swirl flows. A central toroidal recirculation zone (CTRZ), developed by these swirl flows, helps to stabilize the flame. The current study is focused on the effects of swirl number and a central rod on the flow behavior in a lean premixed swirl-stabilized combustor. Turbulence is modeled using the two-equation, realizable k-ϵ model of Reynolds-Averaged Navier–Stokes (RANS), and flamelet generated manifold (FGM) technique is used to model combustion. Both swirl number and central rod have a very significant effect on the flow and the flame in the combustor. The CTRZ moves upstream along with the flame, creating a flashback, with an increase in the swirl number. Also, the presence of a central rod accelerates the flame flashback at high swirl numbers. Higher turbulence is observed in inner shear layers, especially at high swirl numbers. emissions are higher in the regions of high temperature, especially in the CTRZ. These emissions decrease with the increase in the swirl intensities. At low swirl numbers, the case with the central rod exhibits lower production, and at high swirl numbers, the case without the central rod yields better results in the mitigation.

Impact of H2 addition on flame stability and pollutant emissions for an atmospheric kerosene/air swirled flame of laboratory scaled gas turbine

Abstract The purposes of this study are to compare the stability domains and the pollutant emissions when combustion occurs with and without addition of H2 to a kerosene (Jet A1)/air premixed prevaporised mixture injected in a lean gas turbine combustor. Chemiluminescence of CH*, pollutant emissions (NOx and CO) and pressure fluctuations data are simultaneously collected in order to determine the effects of H2 addition on the stability of the combustion and on the flame structure for an inlet temperature of 473 K, atmospheric pressure and for a large range of equivalence ratio (from 0.3 to 1). Addition of hydrogen enables keeping stable combustion conditions when, for the same kerosene mass flow, the flame becomes lifted and very unstable. As for pollutant emissions, results show that the equivalence ratio is the key parameter to control NOx emission even in the situation where the combustion power is increased due to H2 addition. As H2 addition strongly increases the flammability limits and the combustion stability domain, stable combustion can occur at leaner equivalence ratio and then decreases CO and NOx emissions. This is an important fact since no substitution effect takes place in the reduction of NOx and CO emissions. Study at constant combustion power and equivalence ratio by adjusting hydrogen and kerosene mass flow shows again a decrease in the pollutant emissions. Hydrogen injection in power generation systems using combustion seems to be a promising way in combustion research since due to the combined effects of enlarging combustion stability domain and reducing NOx emissions by substituting kerosene to the benefit of H2.

Fitting nonlinear low-order models for combustion instability control

Abstract Tools for fitting low-complexity nonlinear models based on experimental data are examined through the example problem of finding a reduced-order model suitable for control of a combustion instability operating in a limit cycle. This proceeds in four parts; physical modeling, linear system identification, nonlinear analysis, and validation test design. It is shown how the nonlinear tools of describing functions, bifurcation methods and manifold analysis assist in developing a simple nonlinear model capable of describing the data and consistent with physical understanding. The system being modeled is a lean gas turbine combustor which exhibits a sustained mid-range (100– 1000 Hz ) limit cycle instability. The closed-loop experimental data does not contain a sufficiently rich spectrum for confident modeling in the first linear system identification phase. Despite the paucity of information quality, a grey-box nonlinear model is created and parametrized which provides an explanation both of the limit-cycle fundamental oscillation and of a high frequency nonharmonic signal also present. The model structure is explored and various operating conditions simulated to understand the model better. The validation and/or refinement of this model is then considered. The model validation problem is important because of the poor information content of the periodic limit cycle data. The challenge is to provide a practically feasible, small excitation to the loop to improve identifiability and to provide qualitative tests of model performance. We examine this problem by considering the nonlinear dynamics of the model class and feasible excitation mechanisms.