FG Verbrennungskraftmaschinen und Flugantriebe
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This work introduces a new approach of analyzing convective heat transfer in porous medium by considering the foam structure as a type of fin. It provides the resulting heat transfer characteristics for the design of a longitudinally flowed tube bundle reformer used for the Micro Gas Turbine Solid Oxide Fuel Cell (MGT-SOFC) hybrid process. Owing to a limited experimental database available in literature for the above-mentioned situation, a physical model is initially introduced for a channel flow configuration between two large flat plates using a commercial PDE solver. This model is then validated with experimental results available in literature. A comparison with theoretical solutions is also conducted. Later, this model is modified/adapted for a pipe flow configuration. The physical model for a channel with representative cross-section shape of a longitudinally flowed tube bundle is more complex and is therefore built in a commercial CFD-Solver. A comparative study of the heat transfer behavior in channels of different cross-sections is performed based on a new dimensionless correlation, whose physical coherence with fin efficiency is explained and mathematically proved. The applicability of the heat transfer correlation from one cross-sectional shape to the other are discussed. The proposed new treatment of the porous medium as a fin structure considerably simplifies the heat transfer analysis in porous medium by the clear physical meaning behind fin efficiency and Biot number. This relationship contributes to a better understanding of the heat heat transfer characteristics in porous media in contrast to the correlation between Nusselt number and Reynolds number. Furthermore, this correlation enables a direct comparison between foam structures of different parameters because the fin efficiency is always between 0 and 1. The strong physical background of new correlations also enhances the reliability and plausibility at characterizing and designing the metal foam for heat transfer enhancement.
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.
In this study, the AVL Cruise is implemented to simulate driving parameters including the driving path, the power loss on engine accessories, the gear-shifting scheme and the engine's fuel cut-off strategy influencing the bus fuel efficiency and emission. The Mercedes Conecto LF city bus using a diesel engine with Standardised On-Road Test Cycles was firstly simulated and compared with available literature. The application of hydrogen fuel was then examined and its result was compared with the diesel fuel on the specific fuel consumption. In addition, the driving cycles in Bangkok were simulated. The results show the pattern on both driving cycles with different fuel are similar, however, the fuel consumption of H2 is significantly less than in the case of Diesel. Moreover, it is also evident that the SORT driving cycle cannot represent the heavy traffic of Bangkok.
The path to electric propulsion systems depends on the development of powerful, compact and very light energy storage system with a high storage density. In order to create an environment-friendly intermediate solution in the medium term, especially for aircraft engines of medium power classes, it makes sense to use an innovative, electrically parallel hybrid unit based on rotary engines and electric boosters for start and climb phases as a propulsion system. An aero-engine application, based on the HSD concept (HSD = hybrid super-drive – hybrid Wankel rotary engine) for different hybrid-parallel propulsion systems is presented. In this article, the introduced technology is based on a currently produced family of multi-component Wankel rotary engines. The proposed HSD concept uses a chamber volume of 650ccm per rotor. The projected power range (0.8 to 1.36 MW) is covered by an innovative hybrid electric parallel turbo compound concept together with 2x4 rotary engine units. A novel, airbearing turbo engine with integrated electric drive is used as a turbocharger for charging the rotary engine. For the aero-engine technology, the counter-rotating fan (CRF) concept shown as an example for an aircraft technolo¬gy carrier (light jet) leads to a further increase in the efficiency of a complete system.
The present study focuses on performance and emission characteristics of three emulsion fuels with different additives on a single cylinder CI engine. Each of these emulsified fuels is distinctively engineered to be an alternative fuel for diesel engines. The test fuels are diesel, biodiesel, an emulsion fuel with 86% biodiesel, 5% DEE, 3% Ethanol, 50 ppm CNT, 2% Water, 2% Tween 80 and 2% Span 80 (BD.CNT.DEE.E), an emulsion fuel with 86% biodiesel, 5% EHN, 3% Methanol, 50 ppm Al2O3, 2% Water, 2% Tween 80 and 2% Span 80 (BD.ALO.EHN.M) and an emulsion fuel with 86% biodiesel, 5% Glycerine, 3% Butanol, 50 ppm TiO2, 2% Water, 2% Tween 80 and 2% Span 80 (BD.TIO.GLC.B). Experimental results revealed that BD.CNT.DEE.E has significant improvement compared to diesel and biodiesel in every aspect of performance such as enhanced brake power and brake thermal efficiency by 8.1% and 4.5%, respectively along with the most BSFC reduction by 4%. It also shows exceptional reduction in all emissions compared to biodiesel by 26%, 7.5%, 9.2% and 36% in CO, UHC, NOx and smoke, respectively. BD.ALO.EHN.M also shows considerable improvement in performance including the highest brake thermal efficiency with 6% increment and decline in all emissions except UHC, compared to biodiesel. Finally, BD.TIO.GLC.B shows a slight drop in performance with 6.6% drop in brake thermal efficiency, but on the other hand it has the lowest smoke opacity by a plummet of 74.3%, 20% decline in CO and 10.7% reduction in NOx compared to biodiesel. Therefore, it can be deducted that the emulsion fuels with the proper additives including oxygenated fuels, nano metals, stabilizers, cetane improvers and mixture emulsifiers could ensure clean and renewable alternatives for diesel engines.
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.
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.
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 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.
The “Turbo-Fuel-Cell-Technology” has been described as a MGT-SOFC hybrid system consisting of a recuperated micro gas turbine (MGT) process with an embedded solid oxide fuel cell (SOFC) subsystem. SOFC stacks are connected to “SOFC stack grapes” and are equipped with the so called HEXAR-Module. This module is composed of a high-temperature heat exchanger (HEX), an afterburner (A) and a steam reformer (R). The MGT-concept is based on a generator driven directly by the turbomachine and a recuperator, which returns the exhaust heat to the pressurized compressor outlet air. This provides the necessary base for a highly effective, pure MGT process and the “MGT-SOFC-high-efficiency process”. This paper describes the concept and the thermodynamic background of a highly effective and compact design of the “Turbo-Fuel-Cell 1.0-Family” in the electrical performance class from 100 to 500kW. The technological state of the system is shown and a rating of the system with comparative parameters is discussed. It becomes visible that all necessary basic technologies should be available and that the technology (for stationary applications) can have the “entry into services (E.I.S.)” in the next 10 years. The MGT-SOFC performance map under different operation conditions is discussed. This article also provides an overview of the research on MGT-SOFC-Systems and the scenario of an energy supply network and a mobile energy conversion of the future introduction.