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Evangelos G. Giakoumis – One of the best experts on this subject based on the ideXlab platform.
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Irreversibility production during transient operation of a turbocharged diesel engine
International Journal of Vehicle Design, 2007Co-Authors: Evangelos G. Giakoumis, Eleftherios C. AndritsakisAbstract:A computer model has been developed for studying the first- and second-law balances of a turbocharged diesel engine under transient conditions. Special attention is paid to the identification and quantification of the irreversibilities of all processes and devices after a ramp increase in load. The model includes a detailed analysis of mechanical friction, a separate consideration for the processes in each cylinder during a cycle (‘multi-cylinder’ model) and a mathematical simulation of the fuel pump. Experimental data taken from a turbocharged diesel engine are used for the evaluation of the model’s predictive capabilities. The contribution of combustion, manifolds, aftercooler and turbocharger irreversibility production is analysed using detailed diagrams. It is revealed that transient in-cylinder irreversibilities develop in a different manner compared to the respective steady-state. Combustion has always a dominant contribution but the exhaust manifold irreversibilities cannot be ignored, whereas those attributed to the inlet manifold, turbocharger and aftercooler are always of lesser importance.
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Second-law analyses applied to internal combustion engines operation
Progress in Energy and Combustion Science, 2006Co-Authors: C.d. Rakopoulos, Evangelos G. GiakoumisAbstract:This paper surveys the publications available in the literature concerning the application of the second-law of thermodynamics to internal combustion engines. The availability (exergy) balance equations of the engine cylinder and subsystems are reviewed in detail providing also relations concerning the definition of state properties, chemical availability, flow and fuel availability, and dead state. Special attention is given to identification and quantification of second-law efficiencies and the irreversibilities of various processes and subsystems. The latter being particularly important since they are not identified in traditional first-law analysis. In identifying these processes and subsystems, the main differences between second- and first-law analyses are also highlighted. A detailed reference is made to the findings of various researchers in the field over the last 40 years concerning all types of internal combustion engines, i.e. spark ignition, compression ignition (direct or indirect injection), turbocharged or naturally aspirated, during steady-state and transient operation. All of the subsystems (compressor, aftercooler, inlet manifold, cylinder, exhaust manifold, turbine), are also covered. Explicit comparative diagrams, as well as tabulation of typical energy and exergy balances, are presented. The survey extends to the various parametric studies conducted, including among other aspects the very interesting cases of low heat rejection engines, the use of alternative fuels and transient operation. Thus, the main differences between the results of second- and first-law analyses are highlighted and discussed.
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Availability analysis of a turbocharged diesel engine operating under transient load conditions
Energy, 2004Co-Authors: Constantine D. Rakopoulos, Evangelos G. GiakoumisAbstract:A computer analysis is developed for studying the energy and availability performance of a turbocharged diesel engine, operating under transient load conditions. The model incorporates many novel features for the simulation of transient operation, such as detailed analysis of mechanical friction, separate consideration for the processes of each cylinder during a cycle (“multi-cylinder” model) and mathematical modeling of the fuel pump. This model has been validated against experimental data taken from a turbocharged diesel engine, located at the authors’ laboratory and operated under transient conditions. The availability terms for the diesel engine and its subsystems are analyzed, i.e. cylinder for both the open and closed parts of the cycle, inlet and exhaust manifolds, turbocharger and aftercooler. The present analysis reveals, via multiple diagrams, how the availability properties of the diesel engine and its subsystems develop during the evolution of the engine cycles, assessing the importance of each property. In particular the irreversibilities term, which is absent from any analysis based solely on the first-law of thermodynamics, is given in detail as regards transient response as well as the rate and cumulative terms during a cycle, revealing the magnitude of contribution of all the subsystems to the total availability destruction.
J.h. Horlock – One of the best experts on this subject based on the ideXlab platform.
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Heat exchanger performance with water injection (with relevance to evaporative gas turbine (EGT) cycles)
Energy Conversion and Management, 1998Co-Authors: J.h. HorlockAbstract:Abstract Humidification of the flow through a gas turbine has been proposed in a variety of forms. These include the so-called evaporative gas turbine (EGT) cycle, in which water is injected in the compressor discharge in what is essentially a regenerative gas turbine cycle. In another variation water is also added downstream of the evaporative aftercooler, continuously in the heat exchanger. The operation of heat exchangers under these conditions (of “cold stream” water injection) is discussed: work on heat exchanger effectiveness is first briefly reviewed; and previous analysis of how the thermal capacity of the cold gas stream can be increased by water injection is developed, for both reversible and irreversible flows. It is shown how heat exchanger performance is modified, and the amount of water to be injected is determined. Finally the thermal and rational efficiencies of evaporative gas turbine cycles are discussed, using both first and second law analysis, with relevance to the results on heat exchangers described earlier.
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The Evaporative Gas Turbine [EGT] Cycle
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 1998Co-Authors: J.h. HorlockAbstract:Humidification of the flow through a gas turbine has been proposed in a variety of forms. The STIG plant involves the generation of steam by the gas turbine exhaust in a heat recovery steam generator (HRSG), and its injection into or downstream of the combustion chamber. This increases the mass flow through the turbine and the power output from the plant, with a small increase in efficiency. In the evaporative gas turbine (or EGT) cycle, water is injected in the compressor discharge in a regenerative gas turbine cycle (a so-called CBTX plant–compressor [C], burner [B], turbine [T], heat exchanger [X]); the air is evaporatively cooled before it enters the heat exchanger. While the addition of water increases the turbine mass flow and power output, there is also apparent benefit in reducing the temperature drop in the exhaust stack. In one variation of the basic EGT cycle, water is also added downstream of the evaporative aftercooler, even continuously in the heat exchanger. There are several other variations on the basic cycle (e.g., the cascaded humidified advanced turbine [CHAT]). The present paper analyzes the performance of the EGT cycle. The basic thermodynamics are first discussed, and related to the cycle analysis ofmore » a dry regenerative gas turbine plant. Subsequently some detailed calculations of EGT cycles are presented. The main purpose of the work is to seek the optimum pressure ratio in the EGT cycle for given constraints (e.g., fixed maximum to minimum temperature). It is argued that this optimum has a relatively low value.« less
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The Evaporative Gas Turbine [EGT] Cycle
Volume 2: Coal Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations, 1997Co-Authors: J.h. HorlockAbstract:Humidification of the flow through a gas turbine has been proposed in a variety of forms. The STIG plant involves the generation of steam by the gas turbine exhaust in a heat recovery steam generator [HRSG], and its injection into or downstream of the combustion chamber. This increases the mass flow through the turbine and the power output from the plant, with a small increase in efficiency. In the evaporative gas turbine [or EGT] cycle, water is injected in the compressor discharge in a regenerative gas turbine cycle [a so-called CBTX plant-compressor [C], burner [B], turbine [T], heat exchanger [X]]; the air is evaporatively cooled before it enters the heat exchanger. While the addition of water increases the turbine mass flow and power output, there is also apparent benefit in reducing the temperature drop in the exhaust stack. In one variation of the basic EGT cycle, water is also added downstream of the evaporative aftercooler, even continuously in the heat exchanger. There are several other variations on the basic cycle [e.g. the cascaded humidified advanced turbine (CHAT)].The present paper analyses the performance of the EGT cycle. The basic thermodynamics are first discussed, and related to the cycle analysis of a dry regenerative gas turbine plant. Subsequently some detailed calculations of EGT cycles are presented. The main purpose of the work is to seek the optimum pressure ratio in the EGT cycle for given constraints [e.g. fixed maximum to minimum temperature]. It is argued that this optimum has a relatively low value.Copyright © 1997 by ASME
Marco A R Nascimento – One of the best experts on this subject based on the ideXlab platform.
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multi objective optimization and exergetic analysis of a low grade waste heat recovery orc application on a brazilian fpso
Energy Conversion and Management, 2018Co-Authors: Thiago Gotelip Correa Veloso, Cesar Adolfo Rodriguez Sotomonte, Christian J R Coronado, Marco A R NascimentoAbstract:Abstract This paper presents an analysis of the application of an Organic Rankine cycle (ORC) for power generation of a Brazilian FPSO (Floating Product Storage Offload). The peculiarity of this analysis is the investigation of power generation using low-temperature waste heat sources. Low-grade sources represent a significant amount of heat rejected on the platform. The primary production in the platform processes was evaluated using ASPEN-HYSYS® software v.8.6. The main sources of low-temperature residual heat were preliminarily identified, and the highest potential for energy recovery was: the heat rejected in the intercoolers and Aftercoolers of the compression processes in the Main Compression Unit and the CO2 Compression Unit. For the development of this study, a computational tool was elaborated in MATLAB® to evaluate the thermodynamic performance and to predict the design of the heat exchanger of the ORC. A multi-objective optimization was conducted to verify the ORC application at the established sources. The higher net power was obtained at Main Compression Unit heat recovery, operating with R245CB2 as working fluid. This application allows to generate up to 2063 kW with a heat transfer area of 2997 m2, providing a 23.6% increase in exergy efficiency of the system. The results of this study suggest that the application of ORC cycles on FPSO platforms for heat recovery from low-temperature sources allows an essential increase in the energy and exergetic efficiency of the production processes of the platform. Although the ORC doesn’t give a substantial increase in the supply of electricity, they contribute to less gas consumption in gas turbines. In this way, contributing to a significant reduction of GHG emissions.