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The novel combustor design also has an impact on the ignitor arrangement. The conventional ignitor system cannot guarantee optimal ignition performance in the usual radial position. The difficult ignitability of gaseous fuels was the main challenge for the ignitor system improvement. One way to improve the ignition performance significantly is a torch ignitor system in which the gaseous fuel is directly mixed with a large amount of the combustor air. To reach this goal, the ignition process was investigated in detail. The micro gas turbine (MGT) ignition was optimised considering three main procedures: torch ignitor operation, burner ignition and flame propagation between the neighbour injectors. A successful final result of the chain of ignition procedures depends on multiple aspects of the combustor design. Performed development work shows an important step towards designing modern high-efficiency lowemission combustors.
Solid oxide fuel cells convert chemical energy in electrical energy and are highly suitable for the conversion of hydrocarbon based fuels and products from PowerToGas conversions. Embedded in a micro gas turbine-cycle instead of the combustion chamber the heat energy of the injected fuel, released in the SOFC-Stack, can additionally converted into work and by a turbine-generator into electricity. In a compact system, SOFC stacks are designed to realize a direct steam-reforming process inside. In such direct-reforming fuel cell systems the SOFC operating temperature due to the heat demand for reforming, can be reduced to a value in the range of the outlet temperature of the downstream flow (650°C). If the cycle uses a recuperating system, the operating conditions of the SOFC can be realized without additional high-temperature heat exchanger systems. The system with an uncooled turbine, described in [1], just can reach the operating temperature with an additional high-temperature heat exchange. The system described in this publication does not require an additional high-temperature heat exchanger, because the X-value, as the ratio between the exchanged heat quantity and the required amount of heat to complete the MGT-cycle [2] due to the referring process, is nearly zero and can be realized via the inner container wall (of the MLC). The cycle is completed (between the SOFC and the turbine entry) by the heat input of an afterburner. Here the unreacted fuel of the SOFC fuel-stream is used to provide the necessary heat energy for the downstream turbo-generator-system.
In this paper the in-house technique mesh moving function based on AVL-FIRE has been developed as a simulation tool to investigate the in-chamber flow phenomena of the Wankel rotary engine. The meshes from the starting rotor position at 165° BTDC until the ending rotor position at top dead center (TDC) have been created and connected together. The numerical simulations between an intake stroke and the end of a compression stroke have been successively performed. The results are validated with the selected publication on various engine speeds, at 675 rpm and 1170 rpm. In parallel three refinements of meshes have been carried out, in order to optimize the suitable meshes' elements for the calculation of this engine type. In addition, the turbulence models, which are standard k-ε and Large Eddy Simulations (LES), have been varied for detailed investigation of their predictive capabilities. The simulation results show that the flow phenomena are well corresponding to the experimental data in both engine speeds, especially with the LES. It could be also identified that the LES model performs better on predicting the flow field both in directions and characteristics. Moreover, there is no evidently difference on the results between the medium (c.a. 100,000 elements) and fine (c.a. 1,000,000 elements) meshes comparing to the experimental results.
Hybrid combinations of solid oxide fuel cell and recuperated micro gas turbines can convert the chemical energy of hydrocarbon-based fuels in electrical energy with high electrical efficiency. With an integrated and improved cycle management, more than 70% of the energy content of the fuel could be converted. Therefore, the systems are highly suitable for the Power-To-Gas conversion. In particular, a pressure charging of the SOFC fuel cell leads to an increase in stack performance. By a downstream turbo set, after residual fuels are intentionally oxidized with an afterburner, additional electrical energy can be gained from the expansion of the hot exhaust gas stream and the overall efficiency can be increased. In order to increase the electrical efficiency of the system, it is proposed, to ensure the required compression of the process air in particular by a-two-staged turbo compressor with an intermediate cooling system. By thus achievable reduction of the dissipation of the compressor and by targeted condensation of finest drops in front of the second compressor stage affected by intermediate cooling, an increase in efficiency of the system is possible. This is achieved by targeted cooling of the process air behind a low pressure compression, so that it is saturated over 100% relative air humidity. As a result, a slightly supersaturated airflow is available for the second compressor stage, which enters the compressor after heat removal via an intermediate cooling having a small number of microdroplets. Therefore, the condensed water evaporates again by the heat of compression in the second stage and the compressed flow ultimately enters the recuperation at a lower temperature than during normal compression. Thus, more heat can be recovered within the recuperation system. Therefore, the electrical energy of the system can be produced having higher efficiency, because the heat dissipation of the overall system decreases. In this article it is presented, how such a process is thermodynamically modelled and how a technical realization can be built after optimization by simulations. Finally, in this study, the process-influencing factors are analyzed to show the highest possible electrical yield of such a system.
Brennverfahrensentwicklung für eine neuartige Kreiskolbenmotorenfamilie, Wankelmotorenentwicklung
(2008)
The improvement of decentralised energy supply systems has received an important role in the recent years. One option is the combination of SOFC with recuperated MGT. Here, a new strategy for selecting the system parameters, such as the operating temperature of the SOFC, turbine inlet temperature and the pressure ratio of the hybrid system, is presented. By introducing the heat ratio between the heat required to increase the process gas to the SOFC operating temperature and the heat required to raise the SOCF exhaust gas to the TIT, it was found that high efficiency (approx. 68%) is realisable in a compact hybrid system today. Analysis also shows that the HEX-technology is needed to improve the system effectiveness. Also, high recirculation rates with lower TIT can be considered as the future development direction. In addition, a sample configuration of an oil-free MGT rotor unit with high speed foil bearings is presented.
The improvement of decentralised energy supply systems has received an important role in the recent years. One option therefore is the combination of SOFC with a recuperated MGT. Here, a new strategy for selecting the system parameters, such as the operating temperature of the SOFC, the turbine inlet temperature and the pressure ratio of the hybrid system, is presented. By introducing the heat ratio between the heat required to increase the process gas to the SOFC operating temperature and the heat required to raise the SOCF exhaust gas to the TIT, it was found that high efficiency (approx. 68%) is realisable in a compact hybrid system today. Analysis also shows that the HEX-technology is needed to improve the system effectiveness. Also, high recirculation rates with lower TIT can be considered as the future development direction. In addition, a sample configuration of an oil-free MGT rotor unit with high speed foil bearings is presented.
Der Weg zum elektrischen Fliegen ist abhängig von der Entwicklung hochleistungsfähiger, kompakter und vor allem leichter Energiespeicher. Als mittelfristige, umweltschonende Überganglösung bieten sich, insbesondere für Flugtriebwerke mittlerer Leistungsklassen, Hybridsysteme aus Turbo-Compound-Kreiskolbenmotoren und Elektromaschinen für die Start- und Steigphasen an. Vorgestellt werden auf dem HSD-Konzept (HSD=Hybrid Super-Drive, vgl. [1]) beruhende luftfahrtechnische Anwendungen für unterschiedliche parallelhybride Flugantriebe. Die Basistechnologie stützt sich auf eine in der Produktion befindliche, vielstofffähige Wankeltriebwerksfamilie. Das HSD-Konzept legt hierbei ein Kammervolumen von 650ccm zu Grunde. Der Leistungsbereich (0,8 bis 1,36MW) wird mit einem innovativen elektrischen parallel-hybriden Turbo-Compound-Konzept abgedeckt. Hierbei kommt zur Aufladung der Kreiskolben-Verbrennungsmaschine eine neuartige luftgelagerte Turbomaschine mit integrierter E-Maschine zum Einsatz. Als Vortriebstechnologie trägt das Counter-Rotating-Fan (CRF)-Konzept, welches am Beispiel eines Flugzeugtechnologieträgers (Light-Jet) dargestellt wird, zur weiteren Steigerung der Wirtschaftlichkeit des Gesamtsystems bei. Der vorliegende Artikel basiert auf den in [1] beschrieben Grundlagen und stellt eine weiterführende Diskussion im Rahmen des DLRK dar.