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Evangelos G. Giakoumis - One of the best experts on this subject based on the ideXlab platform.

  • Irreversibility production during transient operation of a turbocharged diesel engine
    International Journal of Vehicle Design, 2007
    Co-Authors: Evangelos G. Giakoumis, Eleftherios C. Andritsakis
    Abstract:

    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.

  • Second-law analyses applied to internal combustion engines operation
    Progress in Energy and Combustion Science, 2006
    Co-Authors: C.d. Rakopoulos, Evangelos G. Giakoumis
    Abstract:

    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.

  • Availability analysis of a turbocharged diesel engine operating under transient load conditions
    Energy, 2004
    Co-Authors: Constantine D. Rakopoulos, Evangelos G. Giakoumis
    Abstract:

    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.

  • The Effect of Various Dynamic, Thermodynamic and Design Parameters on the Performance of a Turbocharged Diesel Engine Operating under Transient Load Conditions
    SAE Technical Paper Series, 2004
    Co-Authors: Constantine D. Rakopoulos, Evangelos G. Giakoumis, Dimitrios T. Hountalas, Dimitrios C. Rakopoulos
    Abstract:

    Thermodynamic, dynamic and design parameters have a significant and often conflicting impact on the transient response of a compression ignition engine. Knowing the contribution of each parameter on transient operation could direct the designer to the appropriate measures for better engine performance. To this aim an explicit simulation program developed is used to study the performance of a turbocharged diesel engine operating under transient load conditions. The simulation developed, based on the filling and emptying approach, provides various innovations as follows: Detailed analysis of thermodynamic and dynamic differential equations, on a degree crank angle basis, accounting for the continuously changing nature of transient operation, analysis of transient mechanical friction, and also a detailed mathematical simulation of the fuel pump. Each equation in the model is solved separately for every cylinder of the 6-cylinder diesel engine considered. The model is validated against experimental data for various load changes. The effect of several dynamic, thermodynamic and design parameters is studied, i.e. load schedule (type, and duration of load applied), turbocharger mass moment of inertia, exhaust manifold volume and configuration, cylinder wall temperature, aftercooler effectiveness as well as an interesting case of a malfunctioning fuel pump. Explicit diagrams are given to show how, after an increase in load, each parameter examined affects the engine speed response, as well as other properties of the engine and turbocharger such as fuel pump rack position, boost pressure and turbocharger speed. It is shown that certain parameters, such as the type of connected loading, the turbocharger inertia, a damaged fuel pump and the exhaust manifold volume, can have a significant effect on the engine and turbocharger transient performance. However others, such as the cylinder wall temperature, the aftercooler effectiveness and the exhaust manifold configuration have a less important effect as regards transient response and final equilibrium conditions.

  • Experimental and simulation analysis of the transient operation of a turbocharged multi-cylinder IDI diesel engine
    International Journal of Energy Research, 1998
    Co-Authors: C.d. Rakopoulos, Evangelos G. Giakoumis, Dimitrios T. Hountalas
    Abstract:

    SUMMARY An experimental and theoretical analysis is carried out to study the response of a multi-cylinder, turbocharged, IDI (indirect injection) compression ignition engine, under transient operating conditions. To this aim, a comprehensive digital computer model is developed which solves the governing di⁄erential equations individually for each cylinder, providing thus increased accuracy over previous ‘single-cylinder’ simulations. Special attention has been paid for diversifying the transient operation from the steady-state one, providing improved or even new relations concerning combustion, heat transfer to the cylinder walls, friction, turbocharger and aftercooler operation, and dynamic analysis for the transient case. An extended steady state and transient experimental work is conducted on a specially developed engine test bed configuration, located at the authors’ laboratory, which is connected to a high-speed data acquisition and processing system. The steady-state measurements are used for the calibration of the individual submodel constants. The transient investigation includes both speed and load changes operating schedules. During each transient test four major measurements are continuously made, i.e. engine speed, fuel pump rack position, main chamber pressure and turbocharger compressor boost pressure. The hydraulic brake coupled to the engine possesses a high mass moment of inertia and long nonlinear load-change times, which together with the indirect injection nature of the engine are important challenges for the simulation code. Explicit multiple diagrams are given to describe the engine and turbocharger transient behaviour including smoke predictions. The agreement between experimental and predicted responses is satisfactory, for all the cases examined, proving the validity of the simulation process, while providing useful information for the engine response under various transient operations. ( 1998 John Wiley & Sons, Ltd.

J.h. Horlock - One of the best experts on this subject based on the ideXlab platform.

  • Heat exchanger performance with water injection (with relevance to evaporative gas turbine (EGT) cycles)
    Energy Conversion and Management, 1998
    Co-Authors: J.h. Horlock
    Abstract:

    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.

  • The Evaporative Gas Turbine [EGT] Cycle
    Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 1998
    Co-Authors: J.h. Horlock
    Abstract:

    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

  • The Evaporative Gas Turbine [EGT] Cycle
    Volume 2: Coal Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations, 1997
    Co-Authors: J.h. Horlock
    Abstract:

    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.

  • multi objective optimization and exergetic analysis of a low grade waste heat recovery orc application on a brazilian fpso
    Energy Conversion and Management, 2018
    Co-Authors: Thiago Gotelip Correa Veloso, Cesar Adolfo Rodriguez Sotomonte, Christian J R Coronado, Marco A R Nascimento
    Abstract:

    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.

S. A. Sherif - One of the best experts on this subject based on the ideXlab platform.

  • Second law analysis of hydrogen liquefiers operating on the modified Collins cycle
    International Journal of Energy Research, 2001
    Co-Authors: M.t. Syed, S. A. Sherif, T.n. Veziroglu, John W. Sheffield
    Abstract:

    Hydrogen liquefaction systems have been the subject of intense investigations for many years. Some established gas liquefaction systems, such as the precooled Linde–Hampson systems, are not used for hydrogen liquefaction in part because of their relatively low efficiencies. Recently, more promising systems employing the modified Collins cycle have been introduced. This paper reports on second law analyses of a hydrogen liquefier operating on the modified Collins cycle. Two different modifications employing the cycle in question were attempted: (1) a helium-refrigerated hydrogen liquefaction system and (2) a hydrogen-refrigerated hydrogen liquefaction system. Analyses were carried out in order to identify potential areas of development and efficiency improvement. A computer code capable of computing system and component efficiencies; exergy losses; and optimum number and operating conditions of compressors, expanders, Aftercoolers, intercoolers, and Joule–Thomson valves was developed. Evaluation of the thermodynamic and transport properties of hydrogen at different temperature levels was achieved by employing a hydrogen property code developed by researchers at the National Bureau of Standards (currently NIST). A parametric analysis was carried out and optimal decision rules pertaining to system component selection and design were reached. Economic analyses were also reported for both systems and indicated that the helium-refrigerated hydrogen liquefier is more economically feasible than the hydrogen-refrigerated hydrogen liquefier. Copyright © 2001 John Wiley & Sons, Ltd.

  • Optimization of multistage vapour compression systems using genetic algorithms. Part 1: Vapour compression system model
    International Journal of Energy Research, 2001
    Co-Authors: A. C. West, S. A. Sherif
    Abstract:

    The vapour compression cycle is the most common type of refrigeration cycle in use today. Most vapour compression systems are simple, having only four major components: a compressor, a condenser, an expansion device and an evaporator. Multistage vapour compression systems are more complex with, for example, extra compressors, Aftercoolers, intercoolers, flash tanks and liquid-to-suction heat exchangers. The study performed here considers 121 different configurations operating at condensing and evaporating temperatures that range from −50 to 50°C. The refrigerants used are ammonia, R-22, R-134a, R-152a and R-123. The basis of comparison for the systems is multistage effectiveness. Multistage effectiveness is a novel term defined as the ratio of the coefficient of performance of a multistage system to the collective coefficient of performance of an equivalent group of basic single-stage systems operating at the same cooling capacities and evaporating and condensing temperatures. Equivalency here is defined on the basis of achieving the same cooling capacity at their respective temperatures as dictated by the multistage systems. The vapour compression system model presented here was put through genetic optimization with interesting results. Copyright © 2001 John Wiley & Sons, Ltd.

  • Thermoeconomics of hydrogen liquefiers operating on the modified Collins cycle
    Collection of Technical Papers. 35th Intersociety Energy Conversion Engineering Conference and Exhibit (IECEC) (Cat. No.00CH37022), 2000
    Co-Authors: M.t. Syed, S. A. Sherif, T.n. Veziroglu
    Abstract:

    Hydrogen liquefaction systems have been the subject of intense investigations for many years. Some established gas liquefaction systems, such as the precooled Linde-Hampson systems, are not used for hydrogen liquefaction in part because of their relatively low efficiencies. Recently, more promising systems employing the modified Collins cycle have been introduced. This paper reports on second law analyses of a hydrogen liquefier operating on the modified Collins cycle. Two different modifications employing the cycle in question were attempted: (1) a helium-refrigerated hydrogen liquefaction system; and (2) a hydrogen-refrigerated hydrogen liquefaction system. Analyses were carried out in order to identify potential areas of development and efficiency improvement. A computer code capable of computing system and component efficiencies; exergy losses; and optimum number and operating conditions of compressors, expanders, Aftercoolers, intercoolers and Joule-Thomson valves was developed. Evaluation of the thermodynamic and transport properties of hydrogen at different temperature levels was achieved by employing a hydrogen property code developed by researchers at the National Bureau of Standards (currently NIST). A parametric analysis was carried out and optimal decision rules pertaining to system component selection and design were reached. Economic analyses were also reported for both systems and indicated that the helium-refrigerated hydrogen liquefier is more economically feasible than the hydrogen-refrigerated hydrogen liquefier.

Constantine D. Rakopoulos - One of the best experts on this subject based on the ideXlab platform.

  • Availability analysis of a turbocharged diesel engine operating under transient load conditions
    Energy, 2004
    Co-Authors: Constantine D. Rakopoulos, Evangelos G. Giakoumis
    Abstract:

    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.

  • The Effect of Various Dynamic, Thermodynamic and Design Parameters on the Performance of a Turbocharged Diesel Engine Operating under Transient Load Conditions
    SAE Technical Paper Series, 2004
    Co-Authors: Constantine D. Rakopoulos, Evangelos G. Giakoumis, Dimitrios T. Hountalas, Dimitrios C. Rakopoulos
    Abstract:

    Thermodynamic, dynamic and design parameters have a significant and often conflicting impact on the transient response of a compression ignition engine. Knowing the contribution of each parameter on transient operation could direct the designer to the appropriate measures for better engine performance. To this aim an explicit simulation program developed is used to study the performance of a turbocharged diesel engine operating under transient load conditions. The simulation developed, based on the filling and emptying approach, provides various innovations as follows: Detailed analysis of thermodynamic and dynamic differential equations, on a degree crank angle basis, accounting for the continuously changing nature of transient operation, analysis of transient mechanical friction, and also a detailed mathematical simulation of the fuel pump. Each equation in the model is solved separately for every cylinder of the 6-cylinder diesel engine considered. The model is validated against experimental data for various load changes. The effect of several dynamic, thermodynamic and design parameters is studied, i.e. load schedule (type, and duration of load applied), turbocharger mass moment of inertia, exhaust manifold volume and configuration, cylinder wall temperature, aftercooler effectiveness as well as an interesting case of a malfunctioning fuel pump. Explicit diagrams are given to show how, after an increase in load, each parameter examined affects the engine speed response, as well as other properties of the engine and turbocharger such as fuel pump rack position, boost pressure and turbocharger speed. It is shown that certain parameters, such as the type of connected loading, the turbocharger inertia, a damaged fuel pump and the exhaust manifold volume, can have a significant effect on the engine and turbocharger transient performance. However others, such as the cylinder wall temperature, the aftercooler effectiveness and the exhaust manifold configuration have a less important effect as regards transient response and final equilibrium conditions.

  • Development of cumulative and availability rate balances in a multi-cylinder turbocharged indirect injection Diesel engine
    Energy Conversion and Management, 1997
    Co-Authors: Constantine D. Rakopoulos, Evangelos G. Giakoumis
    Abstract:

    Abstract A multi-cylinder turbocharged Diesel engine is analysed from a second law analysis point of view via a single-zone thermodynamic model. For this purpose, a comprehensive digital computer program is developed that incorporates subroutines to simulate, among other things, combustion, heat transfer, indirect fuel injection, mass flow through valves, turbocharger and aftercooler behaviour, and real multi-cylinder engine action. This is tested favourably against relevant data from an experimental investigation conducted at the authors' laboratory. A second law analysis is performed in all parts of the engine (cylinder, compressor, turbine, aftercooler, inlet and exhaust manifolds). The analysis describes explicitly all the availability terms existing, i.e. work, heat and mass transfer, availability accumulation in every control volume and fuel flow, thus providing the proper evaluation of every component's irreversibilities, which for the present study are compressor, turbine, inlet, exhaust and combustion. The model is applied to a six-cylinder, turbocharged and aftercooled, indirect injection, four-stroke, medium-high speed diesel engine, installed at the authors' laboratory. Availability rate and cumulative availability terms, with respect to crank angle, for all the processes encountered are presented in diagrams, which show the trends of the availability accumulation and destruction in every component during an engine cycle. Separate diagrams are presented for the main chamber and the prechamber and also for the closed and open parts of the cycle. Tabulation of all second law analysis terms is given for the full load-maximum speed operation and the differences against first law assessments are discussed. Special attention is paid to the correct determination and explanation of the irreversibility quantification and second law efficiencies for every component and for the whole plant. Thus, it is demonstrated that the second law analysis offers a more spherical and comprehensive insight into the processes occurring in a diesel engine that its traditional first law counterpart.