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01764 Part load performance analysis of recuperated gas turbines considering engine configuration and operation strategy
11 Engines (hybrid engine systems) important index concerning engine operation since engine conditions at the end of the compression stroke have a major effect on its overall performance. Such information is especially important for large-scale diesel engines used for stationary or marine applications. In these engines, it is important to develop non-catastrophic methods for estimating the cylinder compression condition without dismantling the engine cylinder. The outcome could be a serious reduction of maintenance costs, since unnecessary labour required for inspection could be avoided. When using measurement techniques, what is usually available is the cylinder pressure trace during the compression stroke. However, it is widely recognized that the compression stroke and peak compression pressure is strongly affected, beyond heat losses, by the initial pressure at the inlet valve closure, the compression ratio and the blowby rate. The last three parameters can vary significantly during engine operation, while the heat losses vary mainly due to engine operating conditions and their effect on the compression stroke can be considered. Thus, the knowledge of the peak compression pressure resulting from the cylinder compression pressure diagram is not adequate to define the cylinder compression condition. For this reason, an experimental investigation is conducted to examine the effect of the initial pressure at the inlet valve closure, the compression ratio and the blowby on the cylinder pressure trace. From analysis of the measured data, it is revealed that each parameter has a different effect on the different parts of the compression pressure trace, As revealed, it is possible to determine the compression condition of an engine cylinder based on the measured cylinder pressure trace.
calibration of the kinetics and for full transient cycle studies. In fact, if reactor tests are used to calibrate the kinetics, there is little difference between the compressible and incompressible formulations.
06101764 Part load performance analysis of recuperated gas turbines considering engine configuration and operation strategy Kim, T. S. and Hwang, S. H. Energy, 2006, 31. (2 3), 260-277, The purpose of this study is to analyse the performance characteristics of recuperated gas turbines operating at part load conditions. Differences in part load performance, due to various factors in design and operation, have been investigated. Various part load operation strategies including simple (fuel only control), variable speed and variable inlet guide vane operations for the single-shaft configuration as well as simple and variable area nozzle operations for the two-shaft configuration were considered. Maintaining high turbine exhaust temperature (and thus, the recuperator inlet gas temperature) enhances the part load efficiency considerably. In particular, the variable speed operation of the single-shaft configuration provides the most efficient part load operation. For operations using variable geometry, such as the variable inlet guide vane operation and the variable area nozzle operation, care must be given to minimize the component efficiency degradation in order to fully utilize the advantages offered by higher turbine exhaust temperature. As the design turbine inlet temperature increases, the relative part load efficiency becomes higher. A higher design pressure ratio exhibits better part load efficiency characteristics.
06101761 Flame structures and combustion efficiency computed for a Mach 6 scramjet engine Mitani, T. and Kouchi, T. Combustion and Flame, 2005, 142, (3), 187196. Our hydrogen-fuelled scramjet engines with a length of 2.1 m delivered net thrusts exceeding the engine drags and exhibited fuel specific impulses of about 10 km/s under Mach 4 to 8 flight conditions. A threedimensional, reactive CFD code using unstructured hybrid grids was developed to accelerate the engine studies. Combustion in the scramjet engine under the Mach 6 condition was simulated by using this code. In this paper, the engine testing and the CFD code were outlined first. Timewise progress of hydroxyl radicals was investigated to understand autoignition and upstream-wise developments of combustion in the eng!ne. Autoignition occurred from the cowl section at 0.1 ms after fuel mLxmg was completed. The reaction zones propagated upstream at speeds of about 500 m/s and reached the backward-facing steps in the combustor at 1 ms after the autoignition. Steady-state solutions showed small flames around individual fuel jets in the combustor and a largescale diffusion flame downstream in the engine. Sonic combustion was autonomously realized in the combustor, resulting in delivery of a maximum thrust of 2250 N in the stoichiometric condition. Variations of combustion efficiency indicated that combustion performance was determined in a narrow region with a length of 0.15 m in the combustor and that the combustion downstream of the engine was rate-controlled by a large diffusion flame. The results found by the CFD computations enable us to not only improve engine performances but also to optimize computations for scramjet engines.
06101762 Influence of unbalanced voltage supply on efficiency of three phase squirrel cage induction motor and economic analysis Faiz, J. et al. Energy Conversion and Management, 2006, 47, (3), 289302. The negative effect of unbalanced voltage upon the losses and efficiency of a three phase squirrel cage induction motor is investigated. The financial losses caused by unbalanced voltage of the power supply are determined using an analytical-statistical method. The analytical method is verified by experimental test.
06•01763
One-dimensional automotive catalyst modeling
Depcik, C. and Assanis, D. Progress in Energy and Combustion Science, 2005, 31, (4), 308 369. Classical one-dimensional (1D) models of automotive catalysts with simplified representation of the fluid flow through the device have proven their effectiveness in designing catalyst systems that have met emission standards to date. This paper reviews the history of 1D catalyst modelling to illustrate the physical phenomena that exist in the catalyst along with the corresponding numerical models. To further advance the state of the art, this paper proposes a promising approach where the bulk gas equations are reformulated based on the governing equations of inviscid flow, while retaining full transient capability. While a compressible formulation of the bulk gas equations will yield the most accurate results, it is rather impractical for kinetics calibration because of its long computational time. It can, however, be used to help calibrate the simpler models by determining the actual residence time within the catalyst. On the other hand, either the incompressible or the constant velocity and density formulations can be used for fast
Hybrid engine systems 06/01765 Design and control strategies of PV-diesel systems using genetic algorithms Dufo-L6pez, R. and Bernal-Agustin, J. L. Solar Energy, 2005.79, (1). 33-46. Hybrid photovoltaic systems (PV-hybrid) use photovoltaic energy combined with other sources of energy, like wind or diesel. If these hybrid systems are optimally designed, they can be more cost effective and reliable than PV-only systems. However, the design of hybrid systems is complex because of the uncertain renewable energy supplies, load demands and the non-linear characteristics of some components, so the design problem cannot be solved easily by classical optimization methods. When these methods are not capable of solving the problem satisfactorily, the use of heuristic techniques, such as the genetic algorithms, can give better results. The authors have developed the H O G A program (hybrid optimization by genetic algorithms), a program that uses a genetic algorithm to design a PV-diesel system (sizing and operation control of a PV-diesel system). The program has been developed in C + +. In this paper a PV-diesel system optimized by H O G A is compared with a stand-alone PV-only system that has been dimensioned using a classical design method based on the available energy under worst-case conditions. In both cases the demand and the solar irradiation are the same. The computational results show the economical advantages of the PV-hybrid system. H O G A is also compared with a commercial program for optimization of hybrid systems. Furthermore, the authors show a number of results and conclusions about hybrid systems optimized by HOGA.
06•01766 Energy, exergy and cost analysis of a microcogeneration system based on an Ericsson engine Bonnet, S. et al. International Journal of Thermal Sciences, 2005, 44, (12). 1161-1168. Hot air engines (Stiffing and Ericsson engines) are well suited for micro-cogeneration applications because they are noiseless, and they require very low maintenance. Ericsson engines (i.e. Joule cycle reciprocating engines with external heat supply) are especially interesting because their design is less constrained than Stirling engines, leading to potentially cheaper and energetically better systems. The authors studied the coupling of such an Ericsson engine with a system of natural gas combustion. In order to design this plant, the authors carried out classic energy, exergy and exergo-economic analyses. This study does not deal with a purely theoretical thermodynamic cycle. Instead, it is led with a special attempt to describe as accurately as possible what could be the design and the performance of a real engine. It allows us to balance energetic performance and heat exchanger sizes, to plot the exergy Grassmann diagram, and to evaluate the cost of the thermal and electric energy production. These simple analyses confirm the interest of such systems for micro-cogeneration purposes. The main result of this study is thus to draw the attention on Ericsson engines, unfortunately unfairly fallen into oblivion.
Fuel and Energy Abstracts
July 2006 269
calibration of the kinetics and for full transient cycle studies. In fact, if reactor tests are used to calibrate the kinetics, there is little difference between the compressible and incompressible formulations.
06101764 Part load performance analysis of recuperated gas turbines considering engine configuration and operation strategy Kim, T. S. and Hwang, S. H. Energy, 2006, 31. (2 3), 260-277, The purpose of this study is to analyse the performance characteristics of recuperated gas turbines operating at part load conditions. Differences in part load performance, due to various factors in design and operation, have been investigated. Various part load operation strategies including simple (fuel only control), variable speed and variable inlet guide vane operations for the single-shaft configuration as well as simple and variable area nozzle operations for the two-shaft configuration were considered. Maintaining high turbine exhaust temperature (and thus, the recuperator inlet gas temperature) enhances the part load efficiency considerably. In particular, the variable speed operation of the single-shaft configuration provides the most efficient part load operation. For operations using variable geometry, such as the variable inlet guide vane operation and the variable area nozzle operation, care must be given to minimize the component efficiency degradation in order to fully utilize the advantages offered by higher turbine exhaust temperature. As the design turbine inlet temperature increases, the relative part load efficiency becomes higher. A higher design pressure ratio exhibits better part load efficiency characteristics.
06101761 Flame structures and combustion efficiency computed for a Mach 6 scramjet engine Mitani, T. and Kouchi, T. Combustion and Flame, 2005, 142, (3), 187196. Our hydrogen-fuelled scramjet engines with a length of 2.1 m delivered net thrusts exceeding the engine drags and exhibited fuel specific impulses of about 10 km/s under Mach 4 to 8 flight conditions. A threedimensional, reactive CFD code using unstructured hybrid grids was developed to accelerate the engine studies. Combustion in the scramjet engine under the Mach 6 condition was simulated by using this code. In this paper, the engine testing and the CFD code were outlined first. Timewise progress of hydroxyl radicals was investigated to understand autoignition and upstream-wise developments of combustion in the eng!ne. Autoignition occurred from the cowl section at 0.1 ms after fuel mLxmg was completed. The reaction zones propagated upstream at speeds of about 500 m/s and reached the backward-facing steps in the combustor at 1 ms after the autoignition. Steady-state solutions showed small flames around individual fuel jets in the combustor and a largescale diffusion flame downstream in the engine. Sonic combustion was autonomously realized in the combustor, resulting in delivery of a maximum thrust of 2250 N in the stoichiometric condition. Variations of combustion efficiency indicated that combustion performance was determined in a narrow region with a length of 0.15 m in the combustor and that the combustion downstream of the engine was rate-controlled by a large diffusion flame. The results found by the CFD computations enable us to not only improve engine performances but also to optimize computations for scramjet engines.
06101762 Influence of unbalanced voltage supply on efficiency of three phase squirrel cage induction motor and economic analysis Faiz, J. et al. Energy Conversion and Management, 2006, 47, (3), 289302. The negative effect of unbalanced voltage upon the losses and efficiency of a three phase squirrel cage induction motor is investigated. The financial losses caused by unbalanced voltage of the power supply are determined using an analytical-statistical method. The analytical method is verified by experimental test.
06•01763
One-dimensional automotive catalyst modeling
Depcik, C. and Assanis, D. Progress in Energy and Combustion Science, 2005, 31, (4), 308 369. Classical one-dimensional (1D) models of automotive catalysts with simplified representation of the fluid flow through the device have proven their effectiveness in designing catalyst systems that have met emission standards to date. This paper reviews the history of 1D catalyst modelling to illustrate the physical phenomena that exist in the catalyst along with the corresponding numerical models. To further advance the state of the art, this paper proposes a promising approach where the bulk gas equations are reformulated based on the governing equations of inviscid flow, while retaining full transient capability. While a compressible formulation of the bulk gas equations will yield the most accurate results, it is rather impractical for kinetics calibration because of its long computational time. It can, however, be used to help calibrate the simpler models by determining the actual residence time within the catalyst. On the other hand, either the incompressible or the constant velocity and density formulations can be used for fast
Hybrid engine systems 06/01765 Design and control strategies of PV-diesel systems using genetic algorithms Dufo-L6pez, R. and Bernal-Agustin, J. L. Solar Energy, 2005.79, (1). 33-46. Hybrid photovoltaic systems (PV-hybrid) use photovoltaic energy combined with other sources of energy, like wind or diesel. If these hybrid systems are optimally designed, they can be more cost effective and reliable than PV-only systems. However, the design of hybrid systems is complex because of the uncertain renewable energy supplies, load demands and the non-linear characteristics of some components, so the design problem cannot be solved easily by classical optimization methods. When these methods are not capable of solving the problem satisfactorily, the use of heuristic techniques, such as the genetic algorithms, can give better results. The authors have developed the H O G A program (hybrid optimization by genetic algorithms), a program that uses a genetic algorithm to design a PV-diesel system (sizing and operation control of a PV-diesel system). The program has been developed in C + +. In this paper a PV-diesel system optimized by H O G A is compared with a stand-alone PV-only system that has been dimensioned using a classical design method based on the available energy under worst-case conditions. In both cases the demand and the solar irradiation are the same. The computational results show the economical advantages of the PV-hybrid system. H O G A is also compared with a commercial program for optimization of hybrid systems. Furthermore, the authors show a number of results and conclusions about hybrid systems optimized by HOGA.
06•01766 Energy, exergy and cost analysis of a microcogeneration system based on an Ericsson engine Bonnet, S. et al. International Journal of Thermal Sciences, 2005, 44, (12). 1161-1168. Hot air engines (Stiffing and Ericsson engines) are well suited for micro-cogeneration applications because they are noiseless, and they require very low maintenance. Ericsson engines (i.e. Joule cycle reciprocating engines with external heat supply) are especially interesting because their design is less constrained than Stirling engines, leading to potentially cheaper and energetically better systems. The authors studied the coupling of such an Ericsson engine with a system of natural gas combustion. In order to design this plant, the authors carried out classic energy, exergy and exergo-economic analyses. This study does not deal with a purely theoretical thermodynamic cycle. Instead, it is led with a special attempt to describe as accurately as possible what could be the design and the performance of a real engine. It allows us to balance energetic performance and heat exchanger sizes, to plot the exergy Grassmann diagram, and to evaluate the cost of the thermal and electric energy production. These simple analyses confirm the interest of such systems for micro-cogeneration purposes. The main result of this study is thus to draw the attention on Ericsson engines, unfortunately unfairly fallen into oblivion.
Fuel and Energy Abstracts
July 2006 269