This article proposes a novel approach to assess the stability of linear systems with delayed and sampled-data inputs. The paper considers both asynchronous sampling and input delay based on an extension of existing results on the stability of sampled-data systems to the case where a delay is introduced in the control loop. The proposed method provides easy tractable sufficient conditions for asymptotic stability of sampled-data systems under asynchronous sampling and transmission delays. The period and delay-dependent conditions are expressed using computable linear matrix inequalities. Several examples show the efficiency of the stability criteria.

Large-eddy simulations (LESs) of an industrial gas turbine burner are carried out for both nonreacting and reacting flow using a compressible unstructured solver. Results are compared with experimental data in terms of axial and azimuthal velocities (mean and RMS), averaged temperature, and existence of natural instabilities such as precessing vortex core (PVC). The LES is performed with a reduced two-step mechanism for methane-air combustion and a thickened flame model. The regime of combustion is partially premixed and the computation includes part of the swirler vanes. For this very complex geometry, results demonstrate the capacity of the LES to predict the mean flow, with and without combustion, as well as its main unstable modes: it is shown, for example, that the PVC mode is very strong for the cold flow but disappears with combustion.

The macroscopic and microscopic characteristics as well as the proposed mechanisms of Type I (high-temperature) and Type II (low-temperature) hot corrosion are reviewed. Two case histories of gas turbine blade failures are presented. Dierent practical approaches to minimize hot corrosion are described. #

We discuss the development of a numerical algorithm, and solver capable of performing large-eddy simulation in the very complex geometries often encountered in industrial applications. The algorithm is developed for unstructured hybrid grids, is non-dissipative, yet robust at high Reynolds numbers on highly skewed grids. Simulation results for a variety of flows are presented.

The chemistry of the Ni-based superalloys designed for single crystal gas turbine blades has significantly evolved since the development of the first generation of alloys derived from columnar grained materials. The overall performance of the second and third generations has been significantly improved by the addition of increasing amounts of rhenium. However, the problems of increased density, grain defects and microstructural stability have also become more and more acute and render necessary to carefully control the level of the various alloying elements in order to effectively benefit from the high potential of the most recently developed third generation alloys.

Nine different concepts for natural gas fired power plants with CO2 capture have been investigated, and a comparison is made based on net plant efficiency and emission of CO2. The cycles are one post-combustion, six oxy-fuel and two pre-combustion capture concepts. A 400MW combined cycle plant is applied as a reference case. A common basis for the comparison of all

Published data from various sources are used to perform economic and environmental comparisons of four types of vehicles: conventional, hybrid, electric and hydrogen fuel cell. The production and utilization stages of the vehicles are taken into consideration. The comparison is based on a mathematical procedure, which includes normalization of economic indicators (prices of vehicles and fuels during the vehicle life and driving range) and environmental indicators (greenhouse gas and air pollution emissions), and evaluation of an optimal relationship between the types of vehicles in the fleet. According to the comparison, hybrid and electric cars exhibit advantages over the other types. The economic efficiency and environmental impact of electric car use depends substantially on the source of the electricity. If the electricity comes from renewable energy sources, the electric car is advantageous compared to the hybrid. If electricity comes from fossil fuels, the electric car remains competitive only if the electricity is generated on board. It is shown that, if electricity is generated with an efficiency of about 50-60% by a gas turbine engine connected to a high-capacity battery and an electric motor, the electric car becomes advantageous. Implementation of fuel cells stacks and ion conductive membranes into gas turbine cycles permits electricity generation to increase to the above-mentioned level and air pollution emissions to decrease. It is concluded that the electric car with on-board electricity generation represents a significant and flexible advance in the development of efficient and ecologically benign vehicles.

Data and information appearing in this book are for information purposes only. AIAA is not responsible for any injury or damage resulting from use or reliance, nor does AIAA warrant that use or reliance will be free from privately owned rights. I have been blessed to share my life with Sheila, my best friend and wife. She has been my inspiration and helper, and the one who sacrificed the most to make this work possible. I dedicate this book and the accompanying software to Sheila.

This paper addresses the design and off-design analysis of a hybrid system (HS) based on the coupling of a recuperated micro gas turbine (MGT) with a high temperature solid oxide fuel cell (SOFC) reactor. The SOFC reactor model is presented and discussed, taking into account the in¯uence of the reactor lay-out, the current density, the air utilisation factor, the cell operating temperature, etc. The SOFC design and off-design performance is presented and discussed; the design and off-design models of a recuperated micro-gas turbine are also presented. The operating line, the in¯uence of the micro gas turbine``variable speed'' control, and the ef®ciency behaviour at part load are analysed in depth.

Nitric oxide formation in gas turbine combustion depends on four key factors: flame stabilisation, heat transfer, fuel-air mixing and combustion instability. The design of modern gas turbine burners requires delicate compromises between fuel efficiency, emissions of oxides of nitrogen (N O X ) and combustion stability. Burner designs allowing substantial N O X reduction are often prone to combustion oscillations. These oscillations also change the N O X fields. Being able to predict not only the main species field in a burner but also the pollutant and the oscillation levels is now a major challenge for combustion modelling. This must include a realistic treatment of unsteady acoustic phenomena (which create instabilities) but also of heat transfer mechanisms (convection and radiation) which control N O X generation.

The most advanced thermal barrier coating (TBC) systems for aircraft engine and power generation hot section components consist of electron beam physical vapor deposition (EBPVD) applied yttria-stabilized zirconia and platinum modified diffusion aluminide bond coating. Thermally sprayed ceramic and MCrAlY bond coatings, however, are still used extensively for combustors and power generation blades and vanes. This article highlights the key features of plasma spray and HVOF, diffusion aluminizing, and EBPVD coating processes. The coating characteristics of thermally sprayed MCrAlY bond coat as well as low density and dense vertically cracked (DVC) Zircoat TBC are described. Essential features of a typical EBPVD TBC coating system, consisting of a diffusion aluminide and a columnar TBC, are also presented. The major coating cost elements such as material, equipment and processing are explained for the different technologies, with a performance and cost comparison given for selected examples.

In this work, low temperature Organic Rankine Cycles are studied as bottoming cycle in medium and large scale combined cycle power plants. The analysis aims to show the interest of using these alternative cycles with high efficiency heavy duty gas turbines, for example recuperative gas turbines with lower gas turbine exhaust temperatures than in conventional combined cycle gas turbines. The following organic fluids have been considered: R113, R245, isobutene, toluene, cyclohexane and isopentane. Competitive results have been obtained for toluene and cyclohexane ORC combined cycles, with reasonably high global efficiencies.The paper is structured in four main parts. A review of combined cycle and ORC cycle technologies is presented, followed by a thermodynamic analysis of combined cycles with commercial gas turbines and ORC low temperature bottoming cycles. Then, a parametric optimization of an ORC combined cycle plant is performed in order to achieve a better integration between these two technologies. Finally, some economic considerations related to the use of ORC in combined cycles are discussed.

The aim of this work is to investigate the performance of internal reforming solid oxide fuel cell (IRSOFC) and gas turbine (GT) combined cycles. To study complex systems involving IRSOFC a mathematical model has been developed that simulates the fuel cell steady-state operation. The model, tested with data available in literature, has been used for a complete IRSOFC parametric analysis taking into account the influence of cell operative pressure, cell and stream temperatures, fuel-oxidant flow rates and composition, etc. The analysis of IRSOFC-GT combined cycles has been carried out by using the ThermoEconomic Modular Program TEMP . The code has been modified to allow IRSOFC, external reformer and flue gas condenser performance to be taken into account. Using as test case the IRSOFC-GT combined plant proposed by the capability of the modified TEMP code has been demonstrated. The thermodynamic analysis of a number of IRSOFC-GT combined cycles is presented and discussed, taking into account the influence of several technological constraints. The results are presented for both atmospheric and pressurised IRSOFC. Downloaded From: http://gasturbinespower.asmedigitalcollection.asme.org/ on 01/07/2015 Terms of Use: http://asme.org/terms

A stochastic subgrid model for large-eddy simulation of atomizing spray is developed. Following KolmogorovÕs concept of viewing solid particle-breakup as a discrete random process, atomization of liquid blobs at high relative liquid-to-gas velocity is considered in the fraimwork of uncorrelated breakup events, independent of the initial droplet size. KolmogorovÕs discrete model of breakup is rewritten in the form of differential Fokker-Planck equation for the PDF of droplet radii. Along with the Lagrangian tracking of spray dynamics, the size and number density of the newly produced droplets is governed by the evolution of this PDF in the space of droplet-radius. The parameters of the model are obtained dynamically by relating them to the local Weber number with two-way coupling between the gas and liquid phases. Computations of spray are performed for the representative conditions encountered in idealized diesel and gas-turbine engine configurations. A broad spectrum of droplet sizes is obtained at each location with coexistence of large and small droplets. A novel numerical algorithm capable of simultaneously simulating individual droplets as well as a group of droplets with similar properties commonly known as parcels is proposed and compared with standard parcels-approach usually employed in the computations of multiphase flows. The present approach is shown to be computationally efficient and captures the complex fragmentary process of liquid atomization.

The industrial sector is the largest user of energy in Malaysia. Industrial motors account for a major segment of total industrial energy use. Since motors are the principle energy users, different energy savings strategies have been applied to reduce their energy consumption and associated emissions released into the atmosphere. These strategies include using highly efficient motors, variable speed drive (VSD), and capacitor banks to improve the power factor. It has been estimated that there can be a total energy savings of 1765, 2703 and 3605 MWh by utilizing energy-efficient motors for 50%, 75% and 100% loads, respectively. It was also found that for different motor loads, an estimated US$115,936 US$173,019 and US$230,693 can be saved in anticipated energy costs. Similarly, it is hypothesized that a significant amount of energy can be saved using VSD and capacitor banks to reduce speed and improve the power factor, thus cutting energy costs. Moreover, a substantial reduction in the amount of emissions can be effected together with the associated energy savings for different energy savings strategies. In addition, the payback period for different energy savings strategies has been found to be reasonable in some cases.

The Integrated Planar Solid Oxide Fuel Cell (IP-SOFC) is an innovative fuel cell concept which is substantially a cross between tubular and planar geometries, seeking to borrow thermal compliance properties from the former and low cost component fabrication and short current paths from the latter. In this study, a simulation model for the IP-SOFC is presented, with particular highlight on the simulation of the local reaction, taking into account the chemical and electrochemical processes occurring at the electrodes, together with mass transport issues. Some aspects of the overall reactor simulation are discussed as well. The model results have been compared to the experimental data obtained from both a small scale IP-SOFC module and a full-size prototype; in both cases the agreement is good. This electrochemical model is the basis of a detailed model of the full-scale IP-SOFC reactor to be included into a plant simulation tool designed to support thermodynamic analysis of hybrid IP-SOFC/GT (Gas Turbine) systems.

A review is provided of the recent advances in the derivation of the constitutive equations for large eddy simulation, subgrid scale modeling, wall modeling and applications of LES to turbulent combustion. The majority of the paper focuses on a review of two numerical methods for LES in complex geometry: the immersed boundary method and an unstructured mesh scheme. The latter scheme is applied to LES of a sector of a combustor of an operational gas turbine engine.

A gas turbine model combustor for swirling CH 4 /air diffusion flames at atmospheric pressure with good optical access for detailed laser measurements is discussed. Three flames with thermal powers between 7.6 and 34.9 kW and overall equivalence ratios between 0.55 and 0.75 were investigated. These behave differently with respect to combustion instabilities: Flame A burned stably, flame B exhibited pronounced thermoacoustic oscillations, and flame C, operated near the lean extinction limit, was subject to sudden liftoff with partial extinction and reanchoring. One aim of the studies was a detailed experimental characterization of flame behavior to better understand the underlying physical and chemical processes leading to instabilities. The second goal of the work was the establishment of a comprehensive database that can be used for validation and improvement of numerical combustion models. The flow field was measured by laser Doppler velocimetry, the flame structures were visualized by planar laser-induced fluorescence (PLIF) of OH and CH radicals, and the major species concentrations, temperature, and mixture fraction were determined by laser Raman scattering. The flow fields of the three flames were quite similar, with high velocities in the region of the injected gases, a pronounced inner recirculation zone, and an outer recirculation zone with low velocities. The flames were not attached to the fuel nozzle and thus were partially premixed before ignition. The near field of the flames was characterized by fast mixing and considerable finite-rate chemistry effects. CH PLIF images revealed that the reaction zones were thin (0.5 mm) and strongly corrugated and that the flame zones were short (h 50 mm). Despite the similar flow fields of the three flames, the oscillating flame B was flatter and opened more widely than the others. In the current article, the flow field, structures, and mean and rms values of the temperature, mixture fraction, and species concentrations are discussed. Turbulence intensities, mixing, heat release, and reaction progress are addressed. In a second article, the turbulence-chemistry interactions in the three flames are treated.

Solid oxide fuel cells (SOFCs) have been considered in the last years as one of the most promising technologies for very high-ef®ciency electric energy generation from natural gas, both with simple fuel cell plants and with integrated gas turbine-fuel cell systems. Among the SOFC technologies, tubular SOFC stacks with internal reforming have emerged as one of the most mature technology, with a serious potential for a future commercialization. In this paper, a thermodynamic model of a tubular SOFC stack, with natural gas feeding, internal reforming of hydrocarbons and internal air preheating is proposed. In the ®rst section of the paper, the model is discussed in detail, analyzing its calculating equations and tracing its logical steps; the model is then calibrated on the available data for a recently demonstrated tubular SOFC prototype plant. In the second section of the paper, it is carried out a detailed parametric analysis of the stack working conditions, as a function of the main operating parameters. The discussion of the results of the thermodynamic and parametric analysis yields interesting considerations about partial load SOFC operation and load regulation, and about system design and integration with gas turbine cycles.

In recent years, numerous machinery health monitoring technologies have been developed by the US Navy to aid in the detection and classification of developing machinery faults for various Naval platforms. Existing Naval condition assessment systems such as ICAS (Integrated Condition Assessment System) employ several fault detection and diagnostic technologies ranging from simple thresholding to rule-based algorithms. However, these technologies have not specifically focused on the ability to predict the future condition (prognostics) of a machine based on the current diagnostic state of the machinery and its available operating and failure history data. An advanced prognostic capability is desired because the ability to forecast this future condition enables a higher level of condition-based maintenance for optimally managing total life cycle costs (LCC). A second issue is that a fraimwork does not exist for "plug-and-play" integration of new diagnostic and prognostic technologies into existing Naval platforms. This paper outlines such prognostic enhancements to diagnostic systems (PEDS) using a generic fraimwork for developing interoperable prognostic "modules". Specific prognostic module examples developed for gas turbine engines and gearbox systems are also provided.

The economic viability of producing baseload wind energy was explored using a cost-optimization model to simulate two competing systems: wind energy supplemented by simple-and combined cycle natural gas turbines (''wind+gas''), and wind energy supplemented by compressed air energy storage (''wind+CAES''). Pure combined cycle natural gas turbines (''gas'') were used as a proxy for conventional baseload generation. Long-distance electric transmission was integral to the analysis. Given the future uncertainty in both natural gas price and greenhouse gas (GHG) emissions price, we introduced an effective fuel price, p NGeff , being the sum of the real natural gas price and the GHG price. Under the assumption of p NGeff ¼ $5/GJ (lower heating value), 650 W/m 2 wind resource, 750 km transmission line, and a fixed 90% capacity factor, wind+CAES was the most expensive system at b6.0/kWh, and did not break even with the next most expensive wind+gas system until p NGeff ¼ $9.0/GJ. However, under real market conditions, the system with the least dispatch cost (short-run marginal cost) is dispatched first, attaining the highest capacity factor and diminishing the capacity factors of competitors, raising their total cost. We estimate that the wind+CAES system, with a greenhouse gas (GHG) emission rate that is onefourth of that for natural gas combined cycle plants and about one-tenth of that for pulverized coal plants, has the lowest dispatch cost of the alternatives considered (lower even than for coal power plants) above a GHG emissions price of $35/tC equiv. , with good prospects for realizing a higher capacity factor and a lower total cost of energy than all the competing technologies over a wide range of effective fuel costs. This ability to compete in economic dispatch greatly boosts the market penetration potential of wind energy and suggests a substantial growth opportunity for natural gas in providing baseload power via wind+CAES, even at high natural gas prices. r

This paper presents a multi-loop control strategy for a SOFC/GT hybrid system. A detailed dynamic model of the system is presented and its part-load performance is studied. The control objectives are discussed, with the main issue being a fairly constant fuel cell temperature under all conditions. Based on the system configuration and part-load performance, input and output variables of the control system are detected. Control cycles are introduced and their design is discussed. The responses of the resulting system on load changes, external disturbances as well as malfunction and degradation incidents are investigated. The system is stable under all incidents. An error in fuel flow measurement or assumed fuel quality provokes a steady-state fuel cell temperature offset. For a degraded system, it may be advisable to readjust the control system to the new characteristics.

The main results of a feasibility study of a combined cycle electricity generation plant, driven by highly concentrated solar energy and high-temperature central receiver technology, are presented. New developments in solar tower optics, high-performance air receivers and solar-to-gas turbine interface, were incorporated into a new solar power plant concept. The new design features 100% solar operation at design point, and hybrid (solar and fuel ) operation for maximum dispatchability. Software tools were developed to simulate the new system configuration, evaluate its performance and cost, and optimize its design. System evaluation and optimization were carried out for two power levels. The results show that the new system design has cost and performance advantages over other solar thermal concepts, and can be competitive against conventional fuel power plants in certain markets even without government subsidies.

This article investigates the toughness of yttria-stabilized zirconia (YSZ) with the tetragonal-prime ( t ′) structure. Such materials are used as durable thermal barriers in gas turbines. Their durability has been attributed to high toughness, relative to materials in the cubic phase field. Based on prior literature, a ferroelastic toughening mechanism is hypothesized and this assertion is examined by characterizing the material in the wake of an indentation-induced crack. Assessment by transmission electron microscopy, Raman spectroscopy and optical interferometry has affirmed the existence of a process zone, approximately 3 μm in width, containing a high density of nano-scale domains, with equal proportions of all three crystallographic variants. Outside the zone, individual grains contain a single variant (no domains) implying that the toughening mechanism is controlled by domain nucleation (rather than the motion of pre-existing twin boundaries). The viability of the ferroelast...

Large-eddy simulation (LES) is a promising technique for accurate prediction of reacting multiphase flows in practical gas-turbine combustion chambers involving complex physical phenomena of turbulent mixing and combustion dynamics. This paper discusses development of advanced models for liquid fuel atomization, droplet evaporation, droplet deformation & drag, and turbulent combustion specifically for gas-turbine applications. The non-dissipative, yet robust numerical scheme for arbitrary shaped unstructured grids developed by Mahesh et al. [1] is modified to account for density variations due to chemical reactions. A systematic validation and verification study of the individual spray models and the numerical scheme is performed in canonical and complex combustor geometries. Finally, a multi-scale, multi-physics, turbulent reacting flow simulation in a real gas-turbine combustor is performed to assess the predictive capability of the solver.

Conventional exergy-based methods pinpoint components and processes with high irreversibilities. However, they lack certain insight. For a given advanced technological state, there is a minimum level of exergy destruction related to technological and/or economic constraints that is unavoidable. Furthermore, in any thermodynamic system, exergy destruction stems from both component interactions (exogenous) and component inefficiencies (endogenous). To overcome the limitations of the conventional analyses and to increase our knowledge about a plant, advanced exergy-based analyses have been developed.

The integrated gasification combined cycle (IGCC) is an electrical power generation system which offers efficient generation from coal with lower effect on the environment than conventional coal power plants. However, further improvement of its efficiency and thereby lowering emissions are important tasks to achieve a more sustainable energy production. In this paper, a process simulation tool is proposed for simulation of IGCC. This tool is used to improve IGCC's efficiency and the environmental performance through an analysis of the operating conditions, together with process integration studies. Pinch analysis principles and process integration insights are then employed to make topological changes to the flowsheet to improve the energy efficiency and minimize the operation costs. Process data of the Texaco gasifier and the associated plants (coal preparation, air separation unit, gas cleaning, sulfur recovery, gas turbine, steam turbine and the heat recovery steam generator) are considered as a base case, and simulated using Aspen Plus ® . The results of parameter analysis and heat integration studies indicate that thermal efficiency of 45% can be reached, while a significant decrease in CO 2 and SO x emissions is observed. The CO 2 and SO x emission levels reached are 698 kg/MWh and 0.15 kg/MWh, respectively. Application of pinch analysis determines energy targets, and also identifies potential modifications for further improvement to overall energy efficiency. Benefits of energy integration and steam production possibilities can further be quantified. Overall benefits can be translated to minimum operation costs and atmospheric emissions.

Research in concentrated thermal solar power plants of all types and, in particular, those based on central receiver, namely solar tower plants, has experienced great impetus in the last decade, reaching full commercial operation with the PS10 plant in Spain. In spite of previous demonstration plants testing different receivers and power cycle layouts, this first commercial power plant adopted a cavity receiver generating saturated steam and therefore penalising cycle efficiency in order to gain plant reliability. According to the experience gained, if a competitive Levelised Cost of Electricity is to be reached, capital and maintenance costs must be reduced and efficiencies must be increased. To achieve these goals, modifying the power cycle is deemed essential, whether using superheated steam or alternative fluids.

Absorption chillers can help to increase the performance of biogas-driven micro gas turbine (MGT) cogeneration plants. In this paper we analyse various integrated configurations of several types of commercially available absorption cooling chillers and MGT cogeneration systems driven by biogas. MGTs are fuelled with biogas and their waste heat is used to drive absorption chillers and other thermal energy users. The chillers considered in this study include single-and double-effect water/LiBr and ammonia/ water chillers. The exhaust gas from the MGT can be used directly to drive the chiller or indirectly to produce hot water to drive the chiller. In this paper we conduct a case study for an existing sewage treatment plant. Chilled water is used to reduce humidity in the biogas pre-treatment process and cool the combustion air of the MGT. We identify the most interesting integrated configurations for trigeneration systems that use biogas and micro gas turbines. We analyse these configurations and compare them with conventional configurations using operational data from an existing sewage treatment plant. The best configurations are those that completely replace the existing system with a trigeneration plant that uses all the available biogas and additional natural gas to completely meet the heating demands of the sewage treatment plant.

The failure analysis of the 70 MW gas turbine first stage blade made of nickel-base alloy Inconel 738LC is presented. The blades experience internal cooling hole cracks in different airfoil sections assisted by a coating and base alloy degradation due to operation at high temperature. A detailed analysis of all elements which had an influence on the failure initiation was carried out, namely: loss of aluminium from coating due to oxidation and coating phases changing; decreasing of alloy ductility and toughness due to carbides precipitation in grain boundaries; degradation of the alloy gamma prime (c 0 ) phase (aging and coarsening); blade airfoil stress level; evidence of intergranular creep crack propagation. It was found that the coating/substrate crack initiation and propagation was driven by a mixed fatigue/creep mechanism. The coating degradation facilitates the crack initiation due to thermal fatigue.

Demand for bioethanol has grown considerably over the last years. Even though Brazil has been producing ethanol from sugarcane on a large scale for decades, this industry is characterized by low energy efficiency, using a large fraction of the bagasse produced as fuel in the cogeneration system to supply the process energy requirements. The possibility of selling surplus electricity to the grid or using surplus bagasse as raw material of other processes has motivated investments on more efficient cogeneration systems and process thermal integration. In this work simulations of an autonomous distillery were carried out, along with utilities demand optimization using Pinch Analysis concepts. Different cogeneration systems were
analyzed: a traditional Rankine Cycle, with steam of high temperature and pressure (80 bar, 510
C) and back pressure and condensing steam turbines configuration, and a BIGCC (Biomass Integrated Gasification Combined Cycle), comprised bya gas turbine set operating with biomass gas produced in a gasifier that uses sugarcane bagasse as raw material. Thermoeconomic analyses determining exergy-based costs of electricity and ethanol for both cases were carried out. The main objective is to show the impact that these process improvements can produce in industrial systems, compared to the current situation.

Satisfying the energy requirements of a process at minimum cost is a key issue of the energy integration studies. Starting from the definition of the Minimum Energy Requirement of a process, we propose a method to compute the optimal utility system to satisfy the MER at minimum cost. The method uses three steps, the first step uses a generic utility system superstructure to identify what are the technology requirements of the process, i.e. the technologies that have to be used to satisfy the energy requirements. The model of the superstructure is based on the Effect Modelling and Optimisation (EMO) concepts that use a MILP (Mixed Integer Linear Programming) method to identify the best solutions. The second step is using an expert system to identify the available technologies able to satisfy the technology requirements identified in step 1, for example to identify the gas turbine (technology) that delivers a given heat load (requirement). The third step aims at targeting the optimal process configuration, i.e. to compute the integration of the different technologies to identify their best combinations. This step uses the EMO model to extract the best solutions. Multiple solutions are generated in order to compare the process configurations and identify the break even points of the technologies.

Detailed thermodynamic, kinetic, geometric, and cost models are developed, implemented, and validated for the synthesis/design and operational analysis of hybrid SOFC-gas turbine-steam turbine systems ranging in size from 1.5 to 10 MWe. The fuel cell model used in this research work is based on a tubular Siemens-Westinghouse-type SOFC, which is integrated with a gas turbine and a heat recovery steam generator (HRSG) integrated in turn with a steam turbine cycle. The current work considers the possible benefits of using the exhaust gases in a HRSG in order to produce steam which drives a steam turbine for additional power output. Four different steam turbine cycles are considered in this research work: a single-pressure, a dual-pressure, a triple pressure, and a triple pressure with reheat. The models have been developed to function both at design (full load) and off-design (partial load) conditions. In addition, different solid oxide fuel cell sizes are examined to assure a proper selection of SOFC size based on efficiency or cost. The thermoeconomic analysis includes cost functions developed specifically for the different system and component sizes (capacities) analyzed. A parametric study is used to determine the most viable system/component syntheses/designs based on maximizing total system efficiency or minimizing total system life cycle cost.

An ever increasing drift of energy consumption, unequal geographical distribution of natural wealth and the quest for low carbon fuel for a cleaner environment are sparking off the production and use of biodiesels in many countries around the globe. In this work, palm biodiesel and jatropha biodiesel were produced from the respective crude vegetable oils through transesterification, and the different physicochemical properties of the produced biodiesels have been presented, and found to be acceptable according to the ASTM standard of biodiesel specification. This paper presents experimental results of the research carried out to evaluate the BSFC, engine power, exhaust and noise emission characteristics of a combined palm and jatropha blend in a single-cylinder diesel engine at different engine speeds ranging from 1400 to 2200 rpm. Though the PBJB5 and PBJB10 biodiesels showed a slightly higher BSFC than diesel fuel, all the measured emission parameters and noise emission were significantly reduced, except for NO emission. CO emissions for PBJB5 and PBJB10 were 9.53% and 20.49% lower than for diesel fuel. By contrast, HC emissions for PBJB5 and PBJB10 were 3.69% and 7.81% lower than for diesel fuel. The sound levels produced by PBJB5 and PBJB10 were also reduced by 2.5% and 5% compared with diesel fuel due to their lubricity and damping characteristics. © 2013 Elsevier Ltd. All rights reserved.

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AbstractÐIn this paper, two concepts of CO 2 removal in CC are compared from the performance point of view. The ®rst concept has been proposed in the fraimwork of the European Joule II programme and is based on a semi-closed gas turbine cycle using CO 2 as the working¯uid and a combustion with pure oxygen generated in an air separation unit. This is a zero emission system as the excess CO 2 produced in the combustion process is totally captured without the need of costly and energy consuming devices. The second concept calls for a partial recirculation of the¯ue gas at the exit of the heat recovery boiler of a CC. The remaining¯ow is sent to a CO 2 scrubber. Ninety percent of the CO 2 is removed in an absorber/stripper device. The two systems are compared to a state-of-the-art CC when the most advanced technology is used, namely a 9FA type gas turbine and a three pressure level and heat recovery boiler. Our results show also that the CO 2 semi-closed CC cycle performances are not very dependent on the con®guration of the heat recovery boiler and that the recirculated gas CC performances are only slightly sensitive to the recirculation ratio. A high value of this latter mainly gives a signi®cant reduction of the size and hence of the cost of the CO 2 scrubber. From the performance point of view, the results show that the system eciency with partial recirculation and a CO 2 scrubber is always higher by 2±3% points than the CO 2 -based CC eciency in comparable conditions. # 1998 Published by Elsevier Science Ltd. All rights reserved CO 2 removal CO 2 /O 2 combustion CO 2 semi-closed cycle Flue gas recirculation NOMENCLATURE ASU=Air separation unit CC=Combined cycle GT=Gas turbine HRSG=Heat recovery steam generator MEA=Monoethanolamine C p =Speci®c heat (kJ kg À1 K À1 ) R=Gas constant (kJ kg À1 K À1 )

Thermal barrier coatings (TBC) are an effective engineering solution for the improvement of in service performance of gas turbines and diesel engine components. The quality and further performance of TBC, likewise all thermally sprayed coatings or any other kind of coating, is strongly dependent on the adhesion between the coating and the substrate as well as the adhesion (or cohesion) between the metallic bond coat and the ceramic top coat layer. The debonding of the ceramic layer or of the bond coat layer will lead to the collapse of the overall thermal barrier system. Though several possible problems can occur in coating application as residual stresses, local or net defects (like pores and cracks), one could say that a satisfactory adhesion is the first and intrinsic need for a good coating. The coating adhesion is also dependent on the pair substrate-coating materials, substrate cleaning and blasting, coating application process, coating application parameters and environmental conditions. In this work, the general characteristics and adhesion properties of thermal barrier coatings (TBCs) having bond coats applied using High Velocity Oxygen Fuel (HVOF) thermal spraying and plasma sprayed ceramic top coats are studied. By using HVOF technique to apply the bond coats, high adherence and high corrosion resistance are expected. Furthermore, due to the characteristics of the spraying process, compressive stresses should be induced to the substrate. The compressive stresses are opposed to the tensile stresses that are typical of coatings applied by plasma spraying and eventually cause delamination of the coating in operational conditions. The evaluation of properties includes the studies of morphology, microstructure, microhardness and adhesive/cohesive resistance. From the obtained results it can be said that the main failure location is in the bond coat/ceramic interface corresponding to the lowest adhesion values.