Showing papers on "Thermal efficiency published in 1999"

A thermoacoustic Stirling heat engine

Abstract: Electrical and mechanical power, together with other forms of useful work, are generated worldwide at a rate of about 1012 watts, mostly using heat engines. The efficiency of such engines is limited by the laws of thermodynamics and by practical considerations such as the cost of building and operating them. Engines with high efficiency help to conserve fossil fuels and other natural resources, reducing global-warming emissions and pollutants. In practice, the highest efficiencies are obtained only in the most expensive, sophisticated engines, such as the turbines in central utility electrical plants. Here we demonstrate an inexpensive thermoacoustic engine that employs the inherently efficient Stirling cycle1. The design is based on a simple acoustic apparatus with no moving parts. Our first small laboratory prototype, constructed using inexpensive hardware (steel pipes), achieves an efficiency of 0.30, which exceeds the values of 0.10–0.25 attained in other heat engines5,6 with no moving parts. Moreover, the efficiency of our prototype is comparable to that of the common internal combustion engine2 (0.25–0.40) and piston-driven Stirling engines3,4 (0.20–0.38).

Experimental study of some performance parameters of a constant speed stationary diesel engine using ethanol--diesel blends as fuel

Abstract: The performance of a constant speed, stationary diesel engine using ethanol–diesel blends as fuel has been evaluated experimentally. The experiments were performed using 5, 10, 15 and 20% ethanol–diesel blends. Diesel fuel was used as a basis for comparison. The effect of using different blends of ethanol–diesel on engine horsepower, brake specific fuel consumption, brake thermal efficiency, the exhaust gas temperature and lubricating oil temperature were studied. The results indicate no significant power reduction in the engine operation on ethanol–diesel blends (up to 20%) at a 5% level of significance. Brake specific fuel consumption increased by up to 9% with an increase of ethanol up to 20% in the blends as compared to diesel alone. The exhaust gas temperature, lubricating oil temperatures and exhaust emissions (CO and Nox) were lower with operations on ethanol–diesel blends as compared to operation on diesel.

Thermodynamic based comparison of sorption systems for cooling and heat pumping

Abstract: A comparison of thermodynamic performances of sorption systems (liquid absorption, adsorption, ammonia salts and metal hydrides) is carried out for typical applications (deep-freezing, ice making, air-conditioning and heat pumping) with either air-cooled or water-cooled heat sink. The results are given in terms of cooling coefficient of performance (COP) (heating COP or coefficient of amplification (COA) for the heat pump), cooling (heating) power versus reactor volume or weight and thermodynamic efficiency. LiBr–water systems show the best results for air-conditioning except when small units are required (metal hydride systems lead to more compact units). Other systems, however, show better results for other applications (chemical reaction with ammonia salts for deep-freezing, adsorption for heat pumping).

A numerical study of a free piston ic engine operating on homogeneous charge compression ignition combustion

Abstract: A free piston, internal combustion (IC) engine, operating at high compression ratio (~30:1) and low equivalence ratio (φ~0.35), and utilizing homogeneous charge compression ignition combustion, has been proposed by Sandia National Laboratories as a means of significantly improving the IC engine’s cycle thermal efficiency and exhaust emissions. A zero-dimensional, thermodynamic model with detailed chemical kinetics, and empirical scavenging, heat transfer, and friction component models has been used to analyze the steady-state operating characteristics of this engine. The cycle simulations using hydrogen as the fuel, have indicated the critical factors affecting the engine’s performance, and suggest the limits of improvement possible relative to conventional IC engine technologies.

Thermodynamic Optimization of Complex Energy Systems

Abstract: Preface. Acknowledgements. Presentation of the foundations of thermodynamics in about twelve one-hour lectures E.P. Gyftopoulos. Pictorial visualization of the entropy of thermodynamics E.P. Gyftopoulos. Thermodynamic optimization of inanimate and animate flow systems A. Bejan. Constructyal flow geometry optimization A. Bejan. Fundamentals of exergy analysis and exergy-aided thermal systems design M.J. Moran. Strengths and limitations of exergy analysis G. Tsatsaronis. Design optimization using exergoeconomics G. Tsatsaronis. On-line thermoeconomic diagnosis of thermal power plants A. Valero, et al. Exergy in thermal systems analysis J. Szargut. Allocation of finite energetic resources via an exergetic costing method E. Sciubba. Optimisation of turbomachinery components by constrained minimisation of the local entropy production rate E. Sciubba. Available energy versus entropy A. Ozturk. Exergy analysis in the process industry R.L. Cornelissen, G.G. Hirs. Exergetic life cycle analysis of components in a system R.L. Cornelissen, G.G. Hirs. The intimate connection between exergy and the environment I. Dincer, M.A. Rosen. Effect of variation of environmental conditions on exergy and on power conversion Y.A. Gogammaus, O.E. Ataer. Bonds graphs and influence coefficients applications Y.A. Gogammaus. Repowering options for existing power plants P.F. Mathieu. Cogeneration based on gas turbines, gas engines and fuel cells P.F. Mathieu. Gas dynamics cycles of thermal and refrigerating machines A.I. Leontiev. Energy saving techniques in distillation: thermodynamic efficiency and energy conservation Z. Fonyo, E. Rev. Second law based optimization of systems withthermomechanial dissipative processes E. Mamut. Solar energy conversion into work: simple upper bound efficiencies V. Badescu. Thermodynamic approach to the optimization of central solar energy systems A. Segal. Thermodynamic optimization in ocean thermal energy conversion Y. Ikegami, H. Uehara. How to unify solar energy converters and Carnot engines A. de Vos. Optimal control for multistage endoreversible engines with heat and mass transfer S. Sieniutycz. Thermodynamics and optimization of reverse cycle machines M.L. Feidt. Synthesis on Stirling engine optimization M. Costea, et al. Minimizing losses -- tools of finite-time thermodynamics B. Andresen. Physics versus engineering of finite-time thermodynamic models and optimizations P. Salamon. Optimization and simulation of time dependent heat driven refrigerators with continuous temperature control J.V.C. Vargas. Intelligent computer aided design, analysis, optimization and improvement of thermodynamic systems C. Wu. A study of the large oscillations of the thermodynamic pendulum by the method of cubication G. Stanescu. Author Index. Subject Index.

Effect of heat transfer law on the performance of a generalized irreversible Carnot engine

Abstract: In a classical endoreversible Carnot engine model, irreversibility in the form of heat resistance between the reversible Carnot cycle and its heat reservoirs is taken into account. This paper presents a generalized irreversible Carnot engine model that incorporates several internal irreversibilities, such as heat leak, friction, turbulence etc. These added irreversibilities are characterized by a constant parameter and a constant coefficient. The relation between optimal power output and efficiency is derived based on a generalized heat transfer law . The effect of heat leakage, internal irreversibility and heat transfer law on the optimal performance of the generalized irreversible heat engine is investigated.

Zero-Emission MATIANT Cycle

Abstract: In this paper, a novel technology based on the zero CO{sub 2} emission MATIANT (contraction of the names of the two designers MAThieu and IANTovski) cycle is presented. This latter is basically a gas cycle and consists of a supercritical CO{sub 2} Rankine-like cycle on top of regenerative CO{sub 2} Brayton cycle. CO{sub 2} is the working fluid and O{sub 2} is the fuel oxidizer in the combustion chambers. The cycle uses the highest temperatures and pressures compatible with the most advanced materials in the steam and gas turbines. In addition, a reheat and a staged compression with intercooling are used. Therefore, the optimized cycle efficiency rises up to around 45% when operating on natural gas. A big asset of the system is its ability to remove the CO{sub 2} produced in the combustion process in liquid state and at high pressure, making it ready for transportation, for reuse or for final storage. The assets of the cycle are mentioned. The technical issues for the predesign of a prototype plant are reviewed.

Ecological optimization of an irreversible Brayton heat engine

Abstract: Finite-time thermodynamics is used to determine the maximum ecological function, its corresponding thermal efficiency and power output of an irreversible Brayton heat engine. The ecological function of a heat engine is defined as the power output minus the loss power, which is equal to the product of the environmental temperature and the entropy production rate. The ecological function is optimized with respect to the thermal conductance ratio and the adiabatic temperature ratio. The optimum values of adiabatic temperature ratios and thermal conductance ratios of irreversible Brayton heat engines are presented. To obtain a higher ecological function, the thermal conductance of the cold-side heat exchanger should be larger than that of the hot-side heat exchanger. The effects of the total number of transfer units of heat exchangers, turbine and compressor isentropic efficiencies, thermal reservoir temperature ratios and heat leaks on the maximum ecological function and its corresponding parameters are studied and discussed. Results can be used as important criteria in the design of Brayton heat engines.

Small-scale cogeneration system for producing heat and electrical power

Abstract: A self-powered heating system includes a boiler (102) for generating steam, an expander (114) for extracting mechanical and electrical energy from the steam and a heat exchanger (116) for transferring heat energy from the steam to room air. A fan (122) mounted adjacent to the heat exchanger forces room air to be heated past the heat exchanger and through the space being heated. An electric pump (120) returns condensate from the heat exchanger to the boiler. The mechanical and electrical power for operating the fan and pump are provided by the expander. In particular, the expander extracts mechanical energy from the low pressure steam supplied by the boiler to power the fan and includes a magneto for generating an alternating current which may be converted to a direct current for powering the pump. The electrical power generated by the magneto is also sufficient to power a steam valve (154) to the expander and a fuel valve (109) regulating fuel flow to the burner. In another embodiment, the system includes a high pressure water heater (404) for small-scale cogeneration of heat and electrical power. The high pressure hot water is expanded (420) to obtain mechanical energy for driving a generator and, thereby, producing a supply of electrical power. Hot water and steam from the expander are passed through a condenser (426) to transfer heat to a supply of secondary water. The heated secondary water may then be used for space heating purposes.

System for cooling drive units and for heating the inner space of a hybrid vehicle

Abstract: A combined system for cooling drive units and for heating the inner space of a hybrid vehicle comprises a cooling circuit, in which are connected in series an internal combustion engine, a thermostat valve, a cooler and an electrovalve. The system comprises a cooler bypass in which are arranged an electric heater and a heat exchanger for heating the inner space of the vehicle. According to the mode of operation of the hybrid vehicle, the heat exchanger (68) may take up heat from the internal combustion engine or from the electric heater (80), wherein, in the electric operating mode, i.e. with the internal combustion engine not running, for the purpose of keeping the heat losses low, an uncoupling of the internal combustion engine and cooler (26) from the heat exchanger (68) is made possible by means of the thermostat valve and electrovalve.

High power density combined cycle power plant

Abstract: A system and method for increasing the specific output of a combined cycle power plant and providing flexibility in the power plant rating, both without a commensurate increase in the plant heat rate, is disclosed. The present invention demonstrates that the process of upgrading thermal efficiencies of combined cycles can often be accomplished through the strategic use of additional fuel and/or heat input. In particular, gas turbines that exhaust into HRSGs, can be supplemental fired to obtain much higher steam turbine outputs and greater overall plant ratings, but without a penalty on efficiency. This system and method by in large defines a high efficiency combined cycle power plant that is predominantly a Rankine (bottoming) cycle. Exemplary embodiments of the present invention include a load driven by a topping cycle engine (TCE), powered by a topping cycle fluid (TCF) which exhausts into a heat recovery device (HRD). The HRD is fired with a supplementary fuel or provided an additional heat source to produce more energetic and/or a larger quantity of the bottoming cycle fluid (BCF) which is used to power a bottoming cycle engine, (BCE) which drives a load (potentially the same load as the topping cycle engine). Energy contained in either the TCF or BCF is used to power the TCE and BCE respectively, but these fluids, and/or their respective engine exhausts, may also be used to support a wide variety of cogeneration applications.

Effects of intensive evaporative cooling on performance characteristics of land-based gas turbine

Abstract: Injection of finely-atomized water droplets at inlet to compressor is demonstrated to increase the power and augment the efficiency of gas turbine using a 115MW simple cycle commercial power plant. Power-up mechanism of the present system is identified to be a composite of three existing methods. Design requirement on droplet diameter is discussed in view of blade erosion as well as evaporation efficiency within the compressor. Special spray nozzle to generate water droplets with sauter mean diameter of 10 {micro} m is developed and applied to demonstration test. Experiments show that injection of spray water of 1% to air mass ratio would increase power output by about 10% and thermal efficiency by 3% (relative) respectively. A newly introduced incremental efficiency defined as the ratio of incremental power to additional fuel energy is found to be in excess of 10% (absolute) over thermal efficiency in case without water injection and to be independent of spray amount. It is also revealed that the operation of water spraying suppresses dust deposition on compressor blades under proper control of water quality, which mitigates the deterioration of compressor adiabatic efficiency.

Design of Thermal Oxidation Systems for Volatile Organic Compounds

Abstract: INTRODUCTION Combustion History of Air Pollution Thermal Oxidation's Wide Applicability Air Pollutant Emissions in the United States Industrial Sources of Air Pollution ENVIRONMENTAL REGULATIONS Federal Law - State Implementation 1990 Clean Air Act Titles VOC DESTRUCTION EFFICIENCY Operating Parameters Destruction Efficiency EPA Incinerability Ranking Environmental Regulations Halogenated Compounds COMBUSTION CHEMISTRY Generalized Oxidation Reactions Highly Halogenated VOCs Chemical Equilibrium Dewpoint Products of Incomplete Combustion (PICs) Substoichiometric Combustion Emission Correction Factors MASS AND ENERGY BALANCE Fundamentals Energy Balance Lower and Higher Heating Values Auxiliary Fuels Mass-to-Volume Heat Release Conversions Mixture Heating Values VOC Heating Value Approximations Heat of Formation Water Quench Auxiliary Fuel Addition Adiabatic Flame Temperature Excess Air Wet vs Dry Combustion Products Simplified Calculational Procedures WASTE CHARACTERIZATION AND CLASSIFICATION Waste Stream Characterization Waste Stream Variability Minor Contaminants - Major Problems Classifications Liquid Waste Streams THERMAL OXIDIZER DESIGN Burners Residence Chamber Refractory Insulation Thermal Conductivity Heat Loss Mixing Plenums and Nozzles Typical Arrangements HEAT RECOVERY Heat Exchangers Waste Heat Boilers (WHB) Heat Transfer Fluids Water Heating Drying Regenerative Heat Recovery CATALYTIC OXIDATION Applications Theory Basic Equipment and Operation Gas Hourly Space Velocity (GHSV) Catalyst Design Operation Halogens Catalytic vs. Thermal Oxidation Waste Gas Heating Value Effects Catalyst Deactivation Deactivation Indicators Regeneration Performance Comparison Pilot Testing Summary REGENERATIVE SYSTEMS Evolution of the RTO Basic Concept Thermal Efficiency Number of Heat Sink (Regenerator) Beds Purge System Bed Orientation Thermal Efficiency vs Cycle Time Heat Sink Materials Flow Diverter Valve Single-Chamber Design Auxiliary Fuel Injection Pollutant Emissions Effect of Waste Stream Component on Design and Operation Exhaust Temperature Control Waste Stream Motive Force Regenerative Catalytic Oxidizers (RCO) Retrofit of RTO COMBUSTION NOx CONTROL Characterizing/Converting NOx Emission Levels NOx Formation Mechanisms Thermal NOx Equilibrium/Kinetics Parametric Affects Fuel Type Affects NOx Prediction Low NOx Burners Vitiated Air Flue Gas Recirculation (FGR) Fuel-Induced Recirculation (FIR) Water/Stream Injection Air/Fuel Staging Staged Air Oxidation for Chemically Bound Nitrogen Effect of Sulfur POST-COMBUSTION NOx CONTROL Selective Noncatalytic Reduction (SNCR) Chemistry Effect of Temperature Normalized Stoichiometric Ratio NOx Inlet Loading Effect of Residence Time Effect of POC Carbon Monoxide Concentration Practical Reduction Levels Injection Methods Computational Fluid Dynamic Modeling Ammonia Slip Reagent By-Products Selective Catalytic Reduction (SCR) GAS SCRUBBING SYSTEMS Wet Scrubbers Dry Systems Hybrid Systems SAFETY SYSTEMS Lower Explosive Limit (LEL) Minimum Oxygen Concentration Flashback Velocity Flashback Prevention Techniques Combustion Safeguards Typical Natural Gas Fuel Train Start-Up Sequence Interlocks Lead/Lag Temperature Control Electrical Hazard Classifications DESIGN CHECKLIST Primary Objectives Scope of Supply Process Conditions Design Requirements Performance Requirements Auxiliary Equipment Utilities Available Environment Preferred Equipment/Approved Vendors Start-Up Assistance Spare Parts Design Documentation Appendix A - Incinerability Ranking Appendix B - Table of the Elements Appendix C - Heats of Combustion of Organic Compounds Appendix D - Abbreviated Steam Tables Appendix E - Explosive Limits of VOCs References Bibliography Index

Modified bottoming cycle for cooling inlet air to a gas turbine combined cycle plant

Abstract: A method for improving the overall power rating and thermodynamic efficiency of a steam and gas turbine combined cycle plant having a conventional heat recovery steam generator (“HRSG”) as part of the bottoming cycle by cooling the inlet air to the gas turbine (particularly under circumstances when the ambient inlet air temperature to the gas turbine exceeds about 60° F.) using an external chiller subsystem. The preferred method includes the steps of initially heating a multi-component working fluid consisting of higher and lower boiling components (such as ammonia and water) by exposing the working fluid to the gas turbine combustion gases inside the HRSG, evaporating part of the working fluid to generate a vapor fraction enriched in the lower boiling point component, separating the enriched vapor fraction from the multi-component working fluid in a vapor-liquid separator, condensing the vapor into an enriched liquid, subcooling a portion of the enriched liquid, and then cooling the inlet air to the gas turbine through heat exchange with a portion of the subcooled and enriched liquid.

Integrated coal gasification combined cycle power generator

Abstract: Embodiments of the invention provide an IGCC which achieves improved plant thermal efficiency by using a cooling steam supply system that cools the high-temperature sections of the gas turbine 34 . Embodiments of the invention further provide and IGCC in which the cooling steam recovery system recovers steam after cooling the gas-turbine high-temperature section and makes practical re-use of the energy and substances within the system. Therefore, embodiments of the invention can reduce or eliminate the degradation of certain equipment by cooling the high-temperature sections. Methods are provided for increasing the thermal efficiency o an IGCC.

Engine provided with energy recovering device

Abstract: PROBLEM TO BE SOLVED: To reduce generation of NOX in such a way that thermal energy of exhaust gas recovered by a heat exchanger is recovered by driving a turbine so as to improve thermal efficiency, and a part of the exhaust gas is supplied to a combustion chamber as EGR gas, in an engine provided with an energy recovery device. SOLUTION: The engine is provided with a heat exchanger 4 disposed on a trail pf the turbine 20 of a turbocharger 3 driven by the exhaust gas, an EGR control valve 7 for supplying a part of the exhaust gas cooled by the heat exchange 4 into the combustion chamber 2 as the EGR gas, the heat exchanger 5 for cooling intake air delivered from a compressor 21 by water, and a confluent control valve 7 for supplying steam generated by exhaust gas energy of the heat exchanger to the turbine 20. Water heated by the heat exchanger 5 is converted into high temperature steam by the heat exchanger 4, and heat energy of exhaust gas is recovered by driving the turbine 20 with the high temperature steam. COPYRIGHT: (C)2001,JPO

An experimental investigation of steam ejectors for applications in jet-pump refrigerators powered by low-grade heat:

Abstract: The jet-pump refrigerator cycle offers a low-capital-cost solution for utilizing low-grade waste heat in the production of cooling for buildings and process refrigeration. The heart of the jet-pump refrigerator is an ejector, the performance of which strongly determines the thermal efficiency of the cycle. This paper describes and evaluates the results of an experimental investigation into the operation of ejectors primarily for use in jet-pump refrigerators. The construction of a steam-steam ejector test facility and experimental method are described. Experimental results are provided concerning the effects of primary nozzle exit position within the mixing-entrainment section, primary nozzle exit and diffuser throat areas. The causes and effects of flow instability under conditions of high secondary pressure ratio are also discussed and methods of increasing the critical condenser pressure are identified and rated in order of effect.

Hybrid fuel-cell electric-combustion power system using complete pyrolysis

Abstract: This is a procedure for producing mechanical power and a hybrid power generation unit for practicing such a process. In particular, the procedure uses a thermal or catalytic cracker to crack or to pyrolyze (partially or completely) a liquid or gaseous petroleum fuel to produce a primary gaseous stream primarily containing hydrogen (and likely methane or other short-chain hydrocarbons). The hydrogen may be used in a fuel cell to produce electricity, which electricity is used in a linear or rotary electric motor. In the preferred procedure, the residuum of the pyrolyzed feedstock is laid down in the reactor. A regeneration step is used to remove that residuum and produce a carbon monoxide-rich gas which then may be introduced to an internal or external combustion engine for further production of mechanical power. Most preferred of the combustion engines is one having high thermal efficiency. This combination of pyrolysis, fuel cell, and high efficiency heat engine results in a procedure and device which is significantly more efficient in terms of utilizing the energy present in the feedstock hydrocarbon fuel. Additionally, under high temperature operation when the fuel to the engine is a carbon monoxide-rich gas, the emissions from the system will be substantially lower than for conventional power systems. Finally, when some portion of the process heat required by the pyrolysis and de-coking operations is obtained from waste heat from the engine, an increase in the total thermal content of the fuel can be realized, further increasing the overall fuel economy of the hybrid system.

Thermal Barrier Coatings for Low Emission, High Efficiency Diesel Engine Applications

Abstract: Thermal efficiencies of 54% have been demonstrated by single cylinder engine testing of advanced diesel engine concepts developed under Department of Energy funding. In order for these concept engines to be commercially viable, cost effective and durable systems for insulating the piston, head, ports and exhaust manifolds will be required. The application and development of new materials such as thick thermal barrier coating systems will be key to insulating these components. Development of test methods to rapidly evaluate the durability of coating systems without expensive engine testing is a major objective of current work. In addition, a novel, low cost method for producing thermal barrier coated pistons without final machining of the coating has been developed.

An Assessment of the Performance of Closed Cycles With and Without Heat Rejection at Cryogenic Temperatures

Abstract: This paper presents optimized cycle performance that can be obtained with systems including a closed cycle gas turbine (CCGT). The influence of maximum temperature, minimum temperature, and recuperator effectiveness on cycle performance is illustrated. Several power-plant arrangements are analyzed and compared based on thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term of future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing liquid hydrogen (LH{sub 2}) or liquefied natural gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for closed gas-cycle systems.