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.
Stationary battery systems are becoming more prevalent around the world, with both the quantity and capacity of installations growing at the same time. Large battery installations and uninterruptible power supply can generate a significant amount of heat during operation; while this is widely understood, current thermal management methods have not kept up with the increase of stationary battery installations. Active cooling has long been the default approach of thermal management for stationary batteries; however, there is no academic research or comparative studies available for this technology. The present work presents assessment of different active cooling methods through an experimentally validated computational fluid dynamics simulation. Following model validation, several cooling system configurations were analyzed, including effects from implementing either a perforated vent plate or vortex generators. The vent plate was observed to greatly increase cooling performance while simultaneously promoting temperature uniformity between batteries. Vortex generators were shown to marginally increase cooling performance, yet, future research is recommended to study the effects and improvement of the design. The average battery temperature for the vented model is reduced by approximately 5.2 °C, while the average temperature differential among the batteries was only 2.7 °C, less than the recommend value (3 °C) by ASHRAE/IEEE Standards.
Micro gas turbines (MGT) provide a highly efficient, low-pollutant way to generate power and heat on-site. MGTs have also proven to be a versatile technology platform for recent developments like utilization of fuels with low specific heating values and solar thermal electricity generation. Moreover, they are the foundation to build novel cycles like the inverted Brayton cycle or fuel cell hybrid power plants. Numerical simulations of steady operation points are beneficial in various phases of MGT cycle development. They are used to determine and analyze the future potentials of innovative cycles for example by predicting the electrical efficiency and they support the thermodynamic design process (by providing mass flow, pressure and temperature data). Numerical Simulation allows to approximate off-design performance of known cycles e.g. power output at different ambient conditions. Additionally, numerical simulation is used to support cycle optimization efforts by analyzing the sensitivity of component performance on cycle performance. Numerical models of the MGT components have to be tuned and validated based on experimental data from MGT test rigs. At DLR institute of combustion technology a MGT steady-state cycle simulation tool has been used to analyze a variety of cycles and has been revised for several years. In this paper, the validation process is discussed in detail. Comparing simulation data with measurement data from the DLR Turbec T100 test rig has led to extensions of the numeric models, on the one hand, and to modifications of the test rig on the other. Newly implemented numerical models account for the generator heat release to the inlet air and the power electronic limitations. The test rig was modified to improve the temperature measurement at positions with uneven spatial temperature distribution such as the turbine outlet. Analyzing these temperature distributions also yields a possible explanation for the apparent strong recuperator efficiency drop at high load levels, which was also observed by other T100 users before.
Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. The first part focuses on the novel steam injecting and recovering aero engine concept. In the second part, the free-piston composite cycle engine concept is presented. Complementary to the two technical publications, this third part describes the cooperative project, which was initiated by an interdisciplinary consortium, aiming at the demonstration and the proof of concept of both aforementioned aero engine concepts. At the beginning of the project, simulations on propulsion, aircraft system, and test bench level will be conducted. On this basis, preliminary tests and fundamental experiments are planned in order to establish a solid basis for the demonstration. Finally, a system demonstration will be carried out at the laboratory level. Thus, the project allows for a final judgement on both the feasibility of the new concepts and the attainability of the requirements for future aircraft propulsion systems.
Micro gas turbine (MGT) technology is evolving toward a large variety of novel applications, such as weak gas electrification, inverted Brayton cycles, and fuel cell hybrid cycles; however, many of these systems show very different dynamic behaviors compared to conventional MGTs. In addition, some applications impose more stringent requirements on transient maneuvers, e.g., to limit temperature and pressure gradients in a fuel cell hybrid cycle. Besides providing operational safety, optimizing system dynamics to meet the variable power demand of modern energy markets is also of increasing significance. Numerical cycle simulation programs are crucial tools to analyze these dynamics without endangering the machines, and to meet the challenges of automatic control design. For these tasks, complete cycle simulations of transient maneuvers lasting several minutes need to be calculated. Moreover, sensitivity analysis and optimization of dynamic properties like automatic control systems require many simulation runs. To perform these calculations in an acceptable timeframe, simplified component models based on lumped volume or one-dimensional discretization schemes are necessary. The accuracy of these models can be further improved by parameter identification, as most novel applications are modifications of well-known MGT systems and rely on proven, characterized components. This paper introduces a modular in-house simulation tool written in fortran to simulate the dynamic behavior of conventional and novel gas turbine cycles. Thermodynamics, gas composition, heat transfer to the casing and surroundings, shaft rotation and control system dynamics as well as mass and heat storage are simulated together to account for their interactions. While the presented models preserve a high level of detail, they also enable calculation speeds up to five times faster than real-time. The simulation tool is explained in detail, including a description of all component models, coupling of the elements and the ODE solver. Finally, validation results of the simulator based on measurement data from the DLR Turbec T100 recuperated MGT test rig are presented, including cold start-up and shutdown maneuvers.
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