The increasing importance of decentralized energy production based on renewable resources requires gas turbine systems due to their low emissions and flexible energy conversion. Therefore, a suitable hybrid power plant demonstrator consisting of an SOFC (solid oxide fuel cell) coupled to an MGT (micro gas turbine) is being set up at the German Aerospace Center (DLR). This facility requires a burner concept for low calorific gases capable of combusting the exhaust products of the fuel cell system anode side, here referred to as SOFC off-gas. The combustor behavior for the demonstrator system is investigated using an atmospheric combustor test rig at DLR. The main aspect of this work is the combustor operation inside the power plant system with varying power demands and also varying methane contents, representing biogas operation. This is leading to operating points with very low heating values (LHV) which require a flame stabilization strategy via direct addition of natural gas / biogas into the SOFC off-gas before entering the combustor. This is tested in view of expected impacts on electrical system efficiency and other critical system parameters. The combustion system is furthermore investigated in view of CO emissions in various significant operating points.

Numerical studies discussing micro gas turbines (MGTs) as a basis for automotive range extenders can be found in literature. A comprehensive set of experimental measurement data for an MGT of adequate size, however, is currently not available. In this work, a test rig and demonstrator based on a 30 kWel liquid fueled MGT is built up. Its major components’ performance is characterized by measuring temperature and pressure at inlet and outlet, as well as corresponding fuel and air flows and the exhaust gas composition. A compressor bleed air tapping is installed to characterize the turbo components’ off-design behavior. Stationary load points and transient maneuvers are investigated. The presented data provide coherent information on the operational behavior and cycle parameters. This can be used to validate existing numerical investigations. It further provides a foundation to identify the optimization potential of MGT components and will serve as design baseline for subsequent optimization measures to meet the requirements of mobile applications.

Hybrid Power plants (HyPP) combining a micro gas turbine with a solid oxide fuel cell are projected to reach very high electric efficiency values. Powered by biogas, they have the potential to become an important pillar for a future CO 2-neutral energy mix. However, to compensate the fluctuating energy yield of wind turbines and photovoltaic power plants they should also provide a wide operating range. While previous numerical studies show that this is the case for natural gas powered HyPP, the impact of biogas utilization on the operating range was still unknown. In the present study, a detailed numeric model of the HyPP being constructed at DLR is presented. The model is used for an in-depth investigation of the operating limits using biogases with various methane contents. The influence of fuel cell operating limits, like the stack temperature, minimal cell voltage and maximal fuel utilization rate, on the HyPP operation range are discussed. While the results show a strong correlation between methane content and operation range, a power output reduction of 33 % is still feasible for methane contents as low as 60 vol%. Knowing the operating range of the HyPP is also crucial for the design of the plants components. Hence, in a final step the operating conditions for the fuel cell off-gas combustor are derived for the respective operating ranges.

Steady state simulations are an important method to investigate thermodynamic processes. This is especially true for innovative micro gas turbine (MGT) based cycles as the complexity of such systems grows. Therefore, steady state simulation tools are required which ensure large flexibility and computation robustness. As the increased system complexity result often in more extensive parameter studies also a fast computation speed is required. While a number of steady state simulation tools for micro gas turbine based systems are described and applied in literature, the solving process of such tools is rarely explained. However, this solving process is crucial to achieve a robust and fast computation within a physically meaningful range. Therefore, a new solver routine for a steady state simulation tool developed at the DLR Institute of Combustion Technology is presented in detail in this paper. The solver routine is based on Broyden’s method. It considers boundaries during the solving process to maintain a physically and technically meaningful solution process. Supplementary methods are implemented and described which improve the computation robustness and speed. Furthermore, some features of the resulting steady state simulation tool are presented. Exemplary applications of a hybrid power plant, an inverted Brayton cycle and an aircraft auxiliary power unit show the capabilities of the presented solver routine and the steady state simulation tool. It is shown that the new solver routine is superior to the standard Simulink algebraic solver in terms of system evaluation and robustness for the given applications.

Renewable energy sources such as wind turbines and photovoltaics are the key to an environmentally friendly energy supply. However, their volatile power output is challenging in regard to supply security. Therefore, flexible energy systems with storage capabilities are crucial for the expansion of renewable energy sources since they allow storing off-demand produced power and reconverting and supplying it on-demand. For this purpose, a novel power plant concept is presented where high-temperature energy storage (HTES) is integrated between the recuperator and the combustor of a conventional micro gas turbine (MGT). It is used to store renewable energy in times of oversupply, which is later used to reduce fuel demand during MGT operation. Hereby, pollutant emissions are reduced significantly, while the power grid is stabilized. This paper presents a numerical process simulation study, aiming to examine the influence of different storage temperatures and load profiles of HTES on the MGT performance (e.g., fuel consumption, efficiency). Furthermore, relevant operating points and their process parameters such as pressures, temperatures, and mass-flow rates are derived. As operation conditions for the combustor are strongly influenced by the HTES, the paper contains a detailed theoretical analysis of the impact on combustor operability and includes an experimental investigation of the first combustor design adapted for the compound and tested under higher inlet temperatures conditions.