ISBN 9783843935944

978-3-8439-3594-4, Reihe Energietechnik

Nicolai Stadlmair
Influence of Water Injection on the Thermoacoustic Stability of a Lean-Premixed Combustor

218 Seiten, Dissertation Technische Universität München (2018), Softcover, A5

Zusammenfassung / Abstract

Water injection at constant flame temperature is a promising option to achieve a short-term load increase of gas turbines without causing major drawbacks in pollutant formation. For this purpose, liquid water droplets are directly injected into the main combustion zone while simultaneously increasing the fuel mass flow rate. Commonly, combustors of modern gas turbines are operated with lean-premixed flames, which provide low emission levels but are often highly susceptible to thermoacoustic instabilities. Thermoacoustic phenomena occurring in gas turbine combustion chambers have been the subject of research for more than two decades, whereas water injection has not been included so far.

This work investigates the influence of water injection on the thermoacoustic stability of a single-burner test-rig under atmospheric conditions for water-to-fuel ratios of up to 2. The acoustic properties of the burner as well as the flame dynamics are characterized by measured scattering matrices and flame transfer functions over a broad range of operating conditions. It is shown that for water injection at constant flame temperature, the flame transfer function scales with the flame length over a wide frequency range. The acoustic properties of the burner are calculated based on linearized Euler equations and are successfully validated with measured scattering matrices.

%With a newly developed measuring technique, the influence of water injection on the stability margin, the acoustic dissipation and the flame driving are quantified.

Experimentally determined eigenfrequencies and damping rates are obtained to quantify the influence of the water-to-fuel ratio on the thermoacoustic stability. Measured damping rates show that an increasing water-to-fuel ratio decreases the stability of the Helmholtz mode and finally leads to self-sustained oscillations. Quantitatively accurate prediction of longitudinal eigenfrequencies, thermoacoustic damping, acoustic dissipation and flame driving is achieved using stability analyses on the basis of the scattering matrices and measured flame transfer functions. The accuracy of the numerical predictions are benchmarked quantitatively with measured eigenfrequencies and damping rates associated with the first longitudinal eigenmode of the combustor.