Investigation of Emission Characteristics for Diluted Flames and Renewable Fuels in Gas Turbine Combustors

Sammanfattning: Gas turbines have served as economically profitable and reliable generators of power for the past few decades, and have mainly been used in simple and combined cycles. The increased restrictions on hazardous emissions and the increased demand for profitability have created new prospects for innovative power cycles. The requirements for these new power cycles are substantially better emissions, higher thermal efficiency, fuel flexibility, continuously high reliability, and low cost. Some of the power systems that have been suggested are characterized by intensely dilute conditions, such as CO2 recirculation and humidification of the combustor air. Low calorific value gases, renewable fuels, and hydrogen-rich fuels are expected to be used increasingly in the next generation of power systems.In the foreseeable future, the aviation industry is expected to continue to rely on fossil fuels, but introduction of synthetic fuels has many advantages. Compared to conventional aviation fuel, a synthetic fuel can be produced from a great variety of raw materials such as renewable fuel, natural gas, coal, and oil. Moreover, synthetic fuels have the advantage of being less toxic, which would improve the quality of air in the vicinity of airports.In this thesis, the effects of dilution on the combustion characteristics, mainly on the emissions, have been investigated. The cases investigated are similar to the operating conditions that can be expected in the next generation of gas turbines, e.g. the evaporative gas turbine and the (semi-) closed gas turbine with CO2 recirculation. The combustion characteristics of a conventional aviation fuel and a synthetic fuel have also been compared.Two different methodologies have been used in this work: atmospheric and pressurized gas turbine combustor experiments and combustor reactor computation with detailed chemistry. The combustor rigs have been adapted to facilitate measurements of regulated emissions at the combustor outlet. When comparing a synthetic fuel with a commercial aviation fuel, also non-regulated emissions were measured. The rigs were designed to have a wide operation range, and with the option of diluting the inlet air stream with a high quantity of CO2 or water. The reactor models were mainly used to compute emission trends under diluted conditions.It has been shown in this thesis that the addition of diluents has a substantial potential to reduce the emission of NOX, even at constant combustion temperatures. A reduced combustion temperature causes an increase in emission of CO. Hence, the operation window approaches stoichiometric conditions when the dilution is increased. For CO2-diluted flames, the formation of CO increases due to the equilibrium forces between CO and CO2. From a comparative investigation of two liquid fuels, it was shown that regulated emission concentrations for the operating conditions investigated were almost identical. However, it was shown that emissions from the conventional aviation fuel were more toxic than those from the synthetic fuel. From the results, it can be concluded that the synthetic fuel has a potential future in the aviation industry. However, some modifications of the fuel may be required, and further tests will be required prior to commercialization.