This document was typeset using L A T E X.Cover image: Structure of a water spray produced by a pressure-swirl atomizer. SummaryThe combustion of liquid biofuels in gas turbines is an efficient way of generating heat and power from biomass. Gas turbines play a major role in the global energy supply and are suitable for a wide range of applications. However, biofuels generally have different properties compared to the conventional fossil fuels. This can lead to various problems when biofuels are directly used in existing installations.This thesis aims to provide better insights into the combustion of biomass-derived pyrolysis oil in gas turbines. Pyrolysis oil can be produced from non-edible biomass via the fast pyrolysis process. In this process, the organic matter is thermally decomposed under mild conditions (~500 • C, 1 atm) through rapid heating in an oxygenfree environment. The vapors formed in the reactor are subsequently condensed to obtain a combustible liquid as the main product. In comparison to the most common biofuels of the first generation, i.e. bioethanol and biodiesel, pyrolysis oil has advantages regarding cost and environmental benefits. From a technical point of view, however, it is a less favorable fuel due properties such as a low heating value, high water content, high acidity, high viscosity, increased surface tension and poor stability. Gas turbines therefore need to be modified before they can successfully operate on pyrolysis oil in pure form. One of the essential tasks is to develop a suitable burner for liquid fuels of such low quality. In this thesis, two research objectives have been formulated to support the development of pyrolysis oil combustion technology.The first objective is to describe the evaporation and flame characteristics of pyrolysis oil. This objective has been addressed by developing a CFD model based on the Euler-Lagrange method in ANSYS Fluent. The modeling approach was first applied to simulate the combustion of ethanol in a modified, downscaled diesel burner of the OPRA OP16 gas turbine rated at 1.9 MW e . This part of the numerical work can be regarded as a first step to validate the model against experiments and literature. Ethanol is a suitable replacement of pyrolysis oil for this purpose, since it is a singlecomponent, nonviscous, volatile and clean burning biofuel that has been studied more extensively in the past. In the next step, the model was further developed to simulate the full-scale combustion of pyrolysis oil in a burner that was recently designed by OPRA for biofuel applications. The complex composition of pyrolysis oil has been approximated by means of a surrogate fuel containing seven components: methanol, water, acetic acid, acetol, phenol, eugenol and levoglucosan. Each comv ponent is known to be present in pyrolysis oil and is used to represent a group of constituents with similar properties. The initial mass fractions of the seven components are chosen such that the surrogate fuel matches the volatility, water content, elemental composition...