FG Verbrennungskraftmaschinen und Flugantriebe
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An injection-ignition-system from an additive manufacturing process is presented with which gaseous fuels can be injected into the combustion chamber of an internal combustion engine under pressures of up to 80 bar and ignited. With the presented system, an improvement of the thermal efficiency can be achieved by a late fuel injection in the compression phase and with post-injection. With such a system, the engine becomes purely air-intake and a better filling level is achieved. Injection and ignition can take place simultaneously with this application. The system is designed with a high pressure stability for all components (200 bar) and can therefore also be used with higher compressions and combustion pressures. The spatial distribution of the fuel in the combustion chamber is achieved by angled fluid ports and also allows additional injections and ignitions in the power stroke and in the relief phase. This can improve thermal efficiency. A built-in annular channel also enables two different fuels to be injected as a mixing chamber. Finally, initial measurement results are shown for the use of hydrogen fuel in a single-cylinder engine. Indexing data and performance data of the engine indicate that the system can represent a significant increase in the efficiency of combustion engines with hydrogen fuel. Furthermore, the system can be used in conventional vehicle systems, whereby only fuel conditioning and control systems need to be adapted.
The TURBO fuel cell is a hybrid combination of a micro-gas turbine (MGT) and solid oxide fuel cells (SOFC). With its high electrical efficiency and low line losses, it will contribute to an environmentally friendly, reliable and affordable energy supply in residential areas. Thanks to its high efficiency, it enables greater independence from fossil fuels. Furthermore, by choosing a fuel cell type that is embedded in a turbomachinery process, hybrid technology maximises fuel flexibility and ultimately enables the transition from the existing fossil natural gas economy to a hydrogen economy. Power-to-X" products from renewable energies can be converted into electrical energy with maximum efficiency. In this way, it contributes to stopping CO2 emissions by 2050. The turbo fuel cell supplies energy in a decentralised manner and therefore exactly where it is needed. The waste heat generated by the principle can be used for building air conditioning (heating or cooling). Thanks to the condensing technology, an overall efficiency of over 96% can
be demonstrated. It also contributes to grid stability thanks to its high flexibility and cluster capability. When natural gas or green methane is used as a fuel gas in a TURBO fuel cell, a synthesis gas is produced from a CH4 partial flow via an integrated pre-reformer according to the principle of vapour reforming. This synthesis gas is fed to the high-temperature fuel cell for conversion into electricity. If a high proportion of hydrogen is added to this fuel gas, it is referred to as hythane. It is shown that when hythane is used in the turbo fuel cell up to a hydrogen content of 50 %, the very high efficiency of electricity generation by the TURBO fuel cell is maintained. The introduction of this technology can drive forward the decarbonisation of the energy industry. This demonstrates how important this technology is for the introduction of a hydrogen economy utilising existing infrastructures.
The turbo fuel cell is a hybrid combination of a micro-gas turbine (MGT) and solid oxide fuel cells (SOFC). It will contribute to an environmentally friendly, reliable and affordable energy supply due to its high electrical efficiency and low line losses in close proximity to residential districts. The turbo fuel cell (MGT-SOFC hybrid system) makes it possible to increase independence from fossil fuels by choosing a fuel cell type with maximum fuel flexibility embedded in a turbo machine process. This hybrid technology makes it possible to transform the existing fossil gas economy into a hydrogen economy. This technology converts products from "power-to-X-gas" conversions from renewable energies into electrical energy with the highest conversion efficiency and thus contributes to the goal of stopping CO2 emissions by 2050. The turbo fuel cell supplies energy exactly where it is needed. The principle-related waste heat can be used for building air conditioning (heating or cooling) systems. Thanks to the condensing technology, an overall efficiency of over 96% can thus be demonstrated. Additionally, it contributes to grid stability through high flexibility and cluster capability. For methane to be converted into electricity in a turbo fuel cell, a synthesis gas is generated from a CH4 partial flow via an integrated pre-reformer according to the principle of steam reforming. Through high-temperature separation after the pre- reformer, hydrogen can be extracted from the synthesis gas and discharged for use in other applications (e.g., hydrogen mobility). Hydrogen extraction does not lead to a deterioration of electrical efficiency, which is about 70% in the system under consideration. In the living spaces of tomorrow, hydrogen and electrical energy for mobility can thus be provided even before the realisation of a supra-regional hydrogen supply economy. Decarbonisation of the energy economy can be advanced through the introduction of this technology. In this publication, it is shown how important this technology is for the introduction of a hydrogen economy with the inclusion of existing infrastructure.
The system of hydrogen catalytic oxidation is applied in various industrial applications; for example, afterburning of fuel cell exhaust gases, removing of hydrogen residues from electrolysis gas, catalytic drying processes. Since the reaction rate is directly proportional to the surface area of the coating material, a number of small lattice slots is augmented. However, the slots also cause the increment of pressure losses on the system. In this study, CFD simulation is applied to investigate the physical and chemical phenomena in catalytic burners. Multiple slotted afterburners are modeled with slot densities of 1xC to 4xC cells per square inch (cpsi). The air mass flow rates vary from 20 to 100 g/s. The outlet velocities are validated using the experimental data. In parallel, the alternative simulation method using the porous media model is also employed. In order to simulate both homogeneous and heterogeneous oxidation, the chemical kinetics of hydrogen and carbon dioxide in Chemkin format are implemented. The calculated results are compared with the correlated experimental data. Furthermore, the variations of inlet pressure and temperature are also discussed.
In the present publication, a validation by means of the dimensionless ratios between the calculation of heat transfer coefficients and the experiment on an isothermally rotating device is performed. The investigations provide important insights into the design of internal cooling channels of turbine blades. It is shown that forced convection is dominant. For this reason, an isothermally rotating tube is chosen for the validation. This leads to further precision of the validation, since the buoyancy effect (described by the Archimedes-Number of rotations, Ar ≈ 0) in the axial direction is eliminated. The variation to determine the dimensionless heat transfer Nu-Number takes place in the ratio range Reynolds (Re)-Numbers = 8,500 to 52,000, Rotational (Ro)-Numbers = 0 to 0,2 and at a Prandtl (Pr)-Number of 2.5. In order to keep the isothermal conditions and to get an extremely high local resolution of the Nu-Numbers, experimental investigations were carried out with the Heat- and Mass- Transfer-Analogy. This is possible because the differential equations (energy / concentration) are the same at small Mach-Numbers (Ma ≈0) and the Stefan-current is negligible. By analogy with the Nu-Number, a dimensionless mass transfer Sh-Number could be chosen. The dimensionless Pr- Number then corresponds to the dimensionless Schmidt (Sc) -Number. Local Sh-Numbers (and thus the Nu-Numbers) could be determined with high resolution via the layer thickness loss of the sublimate (naphthalene /air system, Sc =2.5). The local Sh-Number and thus the Nu-Number are known. The Nu, Sh results are determined as a function of the Re- and Ro-Number (related to the pipe diameter), in the pipe circumferential direction φ and dimensionless length x/d (with and without hydraulic flow) for the Pr, Sc-number and compared with the numerical calculations and the correlation. It could be shown that the use of a sublimate results in the following advantages for the validation: no vagrant heat flows in the wall, exact compliance with the boundary condition, pipe wall temperature = const (since wall concentration is constant) and Ar ≈ 0. Thus, for the numerical investigation (with Pr, Sc = 2.5), the boundary conditions could be accurately reproduced and compared with the experimental results and correlation. The numerical flow problem was solved using the steady-state Reynolds-averaged Navier-Stokes (RANS) equations. For the closure problem, the Boussinesq approximation was used. The turbulent eddy viscosity of the Boussinesq approximation was calculated using turbulence models (Menter-SST model and the SST transition model). The SST- turbulence model was shown to be a very good fit. The experimental results including the laminar turbulent transition could be reproduced very well with a high precision. A high technical importance for the design of turbine cooling systems could be shown.
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.
The "Turbo Fuel Cell" represents a highly integrated and highly compact technology system of a micro gas turbine fuel cell cycle (MGT-SOFC). It provides the solution for a highly efficient reverse electricity generation with an electrical efficiency of at least 68% (status 2020-21) to approx. 75-80% (in the future). In the context of industrial research on such a hybrid process, adapted, dimensionless parameters should be used in the design and optimization of the overall system. As an example, simulations of thermally optimized solutions to improve the energy yield using various dimensionless key figures are presented. Above all, heat integration measures enable an increase in system efficiency and a reduction in primary energy input. On the basis of exergetic analyzes by use of a modified Heat Balance Factor Y, as presented at ETC12, and the consideration of the SOFC enthalpy spread j, as well as a highly integrative use of the High Temperature Heat Exchanger Function F, it is shown how the hybrid cycle process efficiency can be optimized through innovative coupling of the individual heat flows. Measures to change the hybrid process can be used to deliberately shift the useful energy from the predominant heat yield in order to optimize electrical efficiency. A developed system enables primary energy to be used with the highest possible efficiency. The primary fuel used here is gaseous primary energy in the form of methane (natural gas) and hydrogen from renewable sources. Treatment mechanisms, such as the reforming of the methane used, and the targeted use of modern heat insulation and recovery mechanisms also have been considered. For the optimized hybrid system, total electrical efficiencies of more than 68% could be demonstrated and additional thermal energy for heating purposes could be extracted. Ultimately, overall efficiencies for the utilization of the energy content of the primary energy of up to 97% can be achieved. Energy converters with a maximum system output of around 200-300kW were examined. In the near future, such plants can replace existing fossil power plants being part of decentralized network systems. By their flexibility, they can guarantee the necessary security of power supply.
Results from the measurement of SOFC fuel cell stacks under pressure conditions are presented. As part of a measurement campaign, the operation of a stack system is investigated, particularly under the operating conditions of a recuperated micro gas turbine. Above all, the performance and effectiveness of selected stack types at various operating pressures and operating temperatures are measured. With the test facility set up for such investigations, cell systems could be examined under atmospheric conditions and with pressures of up to 5 bar.
It is shown that in operating conditions under pressure, the output of the fuel cell systems are improving. From a gauge pressure of 4 bar, the performance curve is flattened and higher pressures only produced a marginal increase in performance. Furthermore, the cells tested at overpressure show a steady-state behavior more quickly under load change requirements than in atmospheric operation. This means that more flexible operating modes with faster response behavior can be realized. By choosing a suitable operating temperature, the efficiency of the system is further increasing. Care was taken to select the operating conditions of the cell systems so that coking can be prevented.
Finally, a statement can be made about the pressure dependence of the fuel conversion rate. Parasitic reactions at the anode can be related to the power output. The tests carried out have shown that the high-temperature fuel cell is a promising service provider of the future. A combination of SOFC high-temperature fuel cells and micro gas turbines in one machine could, in addition to the internal provision of the required pressure, also lead to better dynamics of the entire system and increase the energy yield from the primary energy source.
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.
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.