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Institute
BTU
Capable of high-speed and high-temperature operation, together with an "oil-free" technology concept, gas foil bearings are a perfect solution for a novel light weight (small scale) turbo machinery. While the gas film geometry and the pressure build-up are similar to other gas lubricated bearings, and as it has been well formulated
in the hydrodynamic lubrication theory, the compliant structure of the foil bearings have a variety of forms and characteristics. The cantilever-type of foil bearings are one sort of foil bearings that uses a pattern of small cantilever beams as support structure which is very robust and eases the manufacturing process. The aim of this paper is to present a measurement method and results of structural stiffness and damping characteristics of exemplary 50 mm tree-lobes radial foil bearings. Static structural test result shows that the bearing has a wide range of linear stiffness in the bearing's center area. The ramp of cartridge inner surface contour causes a cross coupling effect which may cause instability by a large rotor orbit. Increasing in bear - ing preload result in slightly increasing in static stiffness. In dynamic excitation test, the result shows that the dynamic stiffness is about three times higher than the static one. With a simple model of dry friction, the result shows that the dry friction coefficient is in a range of 0.4 to 0.7. The result also shows that the dynamic stiffness is more sensitive to vibration amplitude than frequency. While the damping decreases significantly with exciting frequency, especially at the vicinity of the rigid body resonance. The result evidence that the magnitude of displacement has a great effect on damping. As displacement amplitude decreases, the bearing is better in damping.
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.
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.
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.
Within the Framework of the "TurboFuelCell (TFC)" a highly integrated and compact energy conversion system based on Micro Gas Turbine Solid Oxide Fuel Cell (MGT-SOFC) hybrid process is being developed by the team at BTU-Cottbus Senftenberg. This work focuses on the extension of the pre-design process of a primary surface heat exchanger (PSHX), which is a key component for the coupling between MGT and SOFC, using an 1D/3D hybrid simulation method for the understanding of its behaviour under the influence of heat radiation. In a MGT-SOFC hybrid process the high temperature heat exchanger plays an important role in preheating the fresh air to a minimum operation temperature necessary for SOFC. Due to the special location of this PSHX in the TFC, it is constantly exposed to heat radiation from the SOFC module, which requires additional consideration of its influence for better model accuracy. A first design, which is later extended through an 1D Flow network model, based on 𝜖 − 𝑁𝑇𝑈 method is presented. A complete 3D-CFD simulation with consideration of heat radiation is initially employed for the whole flow process to examine the first design. However, this approach proves to be highly computationally expensive due to the large dimensional difference between the plenum for cathode exhaust air and the fine channels in the PSHX.
To reduce the computational effort, the flow and heat transfer in the PSHX is modelled by 1D elements. The flow in the plenum is simulated by 3D-CFD, which better accounts for convection and thermal radiation. A comparison between 3D-CFD and 1D/3D hybrid model is performed. A significant reduction of simulation time and computing resources can be achieved for well calibrated hybrid model without compromising on accuracy. In the talk, the effect of insulation layer thickness variations on the heat transfer on the plenum side due to heat radiation and their influence on the heat exchanger efficiency are discussed. Consequently, design improvements are realized based on the previous findings. Finally, the 1D/3D hybrid simulation method is evaluated and prepared for the general applications in thermal management of machines based on coupled MGT-SOFC process.
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.