Showing papers on "Thermal efficiency published in 1984"

Combined-Cycle System With Novel Bottoming Cycle

Abstract: A new thermodynamic energy cycle has been developed using a multicomponent working agent. This cycle is designed to replace the currently used Rankine Cycle as a bottoming cycle for a combined-cycle energy system as well as for generating electricity using low-temperature heat sources. Several combined power systems based on this cycle have been designed and cost-estimated. The efficiency of this cycle is from 1.6 to 1.9 times higher than that of the Rankine Cycle system, at the same border conditions. The investment cost per unit of power output for this cycle is lower than that for the Rankine Cycle system in approximately direct proportion to the energy advantage. The application of this cycle as a bottoming cycle in combined-cycle systems involves the use of an energy system which utilizes heat from the exhaust of a gas turbine, resulting in an increase in overall efficiency of up to 20 percent above the efficiency of the combined systems using the Rankine bottoming cycle. As a result, a thermal efficiency in the range of 50–52 percent can be achieved using a conventional gas turbine. The project to build the first experimental installation is now in progress. This installation is to become operational at the end of 1984.

A quantum mechanical open system as a model of a heat engine

Abstract: A quantum model of a heat engine is analyzed This engine is constructed from two coupled oscillators in interaction with a warm and cold reservoir Power is extracted by an external periodic driving force As a function of control parameters a maximum in power is obtained, and a decline of thermodynamic efficiency below the ideal Carnot value This irreversibility is a consequence of the mechanism devised to extract power in its perturbing the energy level structure of the engine In the limit of weak coupling to the driving force the efficiency at maximum power obtains the value of η=1−((Ta/Tb))1/2

Method and apparatus for gas separation and synthesis

Abstract: @ Pressure swing adsorption gas separations are conducted inside an open loop Stirling cycle apparatus which may operate as an engine, refrigerator or heat pump. Adsorbent surfaces are associated with the thermal regenerators of the Stirling cycle apparatus, so that a preferentially adsorbed gas fraction is concentrated by parametric pumping into a colder end of an engine or into a warmer end of a refrigerator or heat pump, while a less readily adsorbed gas fraction is concentrated into warmer end of an engine or into colder end of a refrigerator or heat pump. Flow control means are provided to introduce the feed gas into the working space of the apparatus and to remove separated product fractions. Feed gases may be chemically reactive within a portion of the working space, with reactant and product species of the reaction separated by the apparatus to drive the reaction off equilibrium. Engine embodiments of the invention may then convert the heat of an exothermic reaction to mechanical power, while heat pump embodiments may supply heat to an endothermic reaction.

Physics Considerations of Solar Energy Conversion

Abstract: A comparative analysis is presented of the conversion of radiant energy to useful work by thermal and quantum processes. The operation of thermal and quantum converters and the thermodynamic conversion efficiency of each are developed in terms of the mechanism of radiation-matter interaction in thermal and quantum systems. From the analysis the maximum conversion efficiency of a single-collector thermal converter with unconcentrated solar radiation and an ambient (reservoir) temperature of 300 K is 0.540; for the same conditions the maximum conversion efficiency of a single-collector quantum system is 0.309. The analysis is extended to consider the effects on the conversion efficiency of heat reject temperature, cascaded operation, in which the reject heat of the quantum converter is used as the input to a thermal bottoming cycle, and of concentration of the solar radiation. The results obtained represent the thermodynamic limits for radiant energy conversion by thermal and quantum processes, and calculations with solar input serve as a reference against which to judge the performance and capabilities of prospective solar energy conversion systems.

Cummins/TACOM Advanced Adiabatic Engine

Abstract: Cummins Engine Company, Inc. and the U.S. Army have been jointly developing an adiabatic turbocompound engine during the last nine years. Although progress in the early years was slow, recent developments in the field of advanced ceramics have made it possible to make steady progress. It is now possible to reconsider the temperature limitation imposed on current heat engines and its subsequent influence on higher engine efficiency when using an exhaust energy utilization system. This paper presents an adiabatic turbocompound diesel engine concept in which high-performance ceramics are used in its design. The adiabatic turbocompound engine will enable higher operating temperatures, reduced heat loss, and higher exhaust energy recovery, resulting in higher thermal engine efficiency. This paper indicates that the careful selection of ceramics in engine design is essential. Adiabatic engine materials requirements are defined and the possible ceramic materials which will satisfy these requirements are identified. Examples in design considerations of engine components are illustrated. In addition to these important points, the use of ceramic coatings in the design of engine components. The first generation adiabatic engine with ceramic coatings is described. The advanced adiabatic engine with minimum friction features utilizaing ceramics is also presented. The advanced ceramic turbochargermore » turbine rotor as well as the oilless ceramic bearing design is described. Finally, the current status of the advanced adiabatic engine program culminating in the AA750 V-8 adiabatic engine is presented.« less

Solar-powered/fuel-assisted rankine cycle power and cooling system: sensitivity analysis

Abstract: The subject of this analysis is a solar power/cooling system based on a novel hybrid steam Rankine cycle. Steam is generated by the use of solar energy collected at about 100/sup 0/C, and it is then superheated to about 600/sup 0/C in a fossil-fuel-fired superheater. The addition of about 20-26 percent of energy as fuel doubles the power cycle's efficiency as compared to organic fluid Rankine cycles operating at similar collector temperatures. A sensitivity analysis of the system's performance to the size and type of its components was performed by a transient (hourly) computer simulation over the month of August in two representative climatic regions (Washington, D.C. and Phoenix, Ariz.), and led to the description of a system configuration which provides optimal energy performance. The newly designed turbine's predicted efficiency is seen to be essentially invariant with system configuration, and has a monthly average value of about 73 percent.

Fluid injection gas turbine engine and method for operating

Abstract: A gas turbine including at least a compressor, a combustor, and a turbine is constructed to operate at a preferred thermal efficiency in predetermined compressor and turbine flow pressure ratios. A fluid, such as steam, for example produced by waste heat and pressurized as water, and characterized as having a higher specific heat at constant pressure than effluent from the combustor is introduced into such effluent to provide a turbine operating medium of improved potential to transfer energy downstream of the combustor. Such injection provides effective variable geometry to the system. This injection system maintains such pressure flow ratios substantially independent of engine power output.

Heating arrangement for electrically driven vehicles

Abstract: A heating system for a dual-mode vehicle, such as a bus equipped with both electrical and internal combustion engine drive systems, is provided with an electrically powered heat exchanger and an auxiliary fuel heater serially connected in the engine cooling water flow line. The electric heat exchanger provides a non-polluting source of heat for the vehicle's interior within electrified portions of the drive route. The auxiliary heater supplies heat when the vehicle is standing (i.e., parked) with the engine shut off in non-electrified portions of the route. An electric water pump is also connected in series with the electric and fuel heaters. During periods of electric drive operation, the electric heater is activated when the engine cooling water temperature falls below a predetermined level even if no heat is required for the vehicle interior. The electric heater prevents the engine from cooling off and, thus, improves exhaust gas characteristics, from an environmental viewpoint, when the engine is re-started.

High efficiency boiler

Abstract: The thermal efficiency of a boiler is increased by actively causing condensation of water vapour in the flame gas and transferring the latent heat of condensation to water being fed to the boiler. A heat pump system incorporating an evaporator (32) and a condensor (30) is used to provide a controllable heat sink which causes the active condensation. The condensor (30) is preferably included in a heat exchanger (20) so that the water being fed to the boiler is heat by both the flame gases from the boiler and by the condensor.

Duplex Stirling machines

Abstract: The duplex Stirling concept - in which a Stirling engine drives a Stirling cycle heat pump - presents a major technological advantage over other types of heat pumps. The free-piston free-displacer device has nominally three moving parts in a single pressure enclosure, the same working fluid in both the engine and heat pump sections, freedom from halogenated hydrocarbons, all this in a highly efficient, well matched system. Over the past five years Sunpower has successfully developed and demonstrated various forms of duplex Stirling devices, ranging from gas fired refrigerator systems having 50W capacity to a residential heat pump having a 10kW capacity. This paper describes some of these projects, and presents an update of this new and very promising technology.

Comparison of ethanol fumigation systems for a diesel engine

Abstract: Ethanol is a fuel which can be effectively fumigated, but the major limitation in most systems is in getting the ethanol uniformly distributed among the cylinders. Thermal efficiency, air flow to the engine inlet, fuel distribution and exhaust smoke density were measured, using a 6 cylinder engine of 6.62 liter displacement and 100 kw capacity. Several nozzle arrangements were tried. Four combinations of load and speed were tested. Results showed that the size of the nozzles is significant, the multiple nozzle systems being superior to the single nozzle system, but impractical due to manifold and head design. A constant-flow alcohol system, replacing a varying amount of diesel fuel would be the simplest to build and install.

Maximum efficiency steam temperature control system

Abstract: A system is disclosed for increasing the main steam temperature in a boiler/turbine installation to the maximum level consistent with safe operation of the installation. The difference between the main steam temperature and a system parameter is determined and used as an index to adjust the main steam temperature set point upward or downward. The system parameter selected for comparison with the main steam temperature may be the allowable variance between the main steam temperature and the main steam temperature set point or may be a "safety margin" temperature selected so as to be below the maximum allowable temperature for the installation.

Fuel cell power generating plant

Abstract: PURPOSE: To make turbine inlet temperature go up as well as to improve thermal efficiency in the whole lot of a plant, by installing a combustor in a pipe line leading cathode exhaust gas into a turbine, while leading a part of anode exhaust gas into this combustor, and making it into combustion together with the cathode exhaust gas. CONSTITUTION: The cathode exhaust gas branched off from cathode circulating gas 78 in cathode exhaust gas 76 is fed to a combustor 170 installed in a pipe line leading the cathode exhaust gas 76 into an expansion turbine 84 as combustion air 168. In addition a part of combustion gas 64 to be fed to a combustion part 62 of a modifier 24 is fed to this combustor 170 as combustion gas 172. The combustor 170 uses the combustion gas 172 for fuel and burns a part of the cathode exhaust gas 76 as the combustion air 168, feeding the expansion turbine 84 with combustion exhaust gas as turbine inlet ags 174. With this constitution, thermal efficiency in the expansion turbine 84 is raised and, what is more, the efficiency of an exhaust heat recovery system 92 is raisable. COPYRIGHT: (C)1986,JPO&Japio

Combined gas turbine/steam turbine plant

Abstract: Supercharged vortex furnaces have the advantage that fine-grained refuse coal with very high ash contents can be burnt in them and that it is possible, by adding lime dust or dolomite dust to achieve high retention of the sulphur dioxide arising in the burning of the coal There are plans for using supercharged vortex furnaces as heating devices for combined gas turbine/steam turbine plants, which can achieve a particularly high thermal efficiency However, such combined plants generally require high-temperature flue-gas filters which filter the flue gases emerging from the vortex furnace at temperatures of 800-900 DEG C Such high-temperature flue-gas filters are not available at present (although they will probably be available in future) The invention relates to a further increase in the efficiency of these combined gas turbine/steam turbine plants with a vortex furnace by the use of hot-air turbines, air heaters and/or additional low-temperature gas turbines, this increase being achieved both when they are employed without a high-temperature flue-gas filter and when they are employed with such a filter

Water-Ethanol-Gasoline Blends—Physical Properties, Power, and Pollution Characteristics

Abstract: Factors relevant to the utilization of nonanhydrous ethanol as a blending component with gasoline for use in current on-the-road spark ignition engines are investigated. Miscibility limits are determined and key physical properties important for proper engine operation are measured. Dynamometer tests on an unmodified production engine with hydrated ethanol-gasoline blends containing varying percentages of water show potential for increased thermal efficiency and reduced oxides of nitrogen emissions.

Liquid fuel combustion with porous fiber burner

Abstract: Improved combustion of liquid fuel is achieved with a porous fiber burner by forming a mixture of the vaporized fuel and all of the desired combustion air sufficiently heated to prevent condensation of the vaporized fuel, and introducing the heated mixture into the porous fiber burner to effect flameless combustion on the outer surface of the burner. The resulting surface combustion produces a high proportions of radiant heat and increased thermal efficiency while suppressing the formation of nitrogen oxides and other pollutants in the flue gas. Periodically, fuel gas may be supplied to the same porous fiber burner.

Energy release rates from hybrid fuels

Abstract: HEAT release patterns of hybrid fuels containing diesel fuel and soybean oil in a microemulsion with ethanol were compared to those of straight diesel fuel. A naturally-aspirated direct-injection diesel engine was used. The hybrid fuels were found to burn faster with higher levels of premixed burning and lower levels of diffusion flame burning than diesel fuel, resulting in higher brake thermal efficiencies, cylinder pressures and rates of pressure rise.

Analysis of combustion patterns effective in improving anti-knock performance of a spark ignition engine

Abstract: Measures to improve specific fuel consumption of a spark-ignition engine have been taken by improving indicated thermal efficiency and reducing engine friction loss. In this work higher compression ratios have been used as a means of improving thermal efficiency and so improve specific fuel consumption. Higher compression ratios result in the phenomenon of knocking under full load and is studied in the article. The studies described evaluated the mechanism of knocking, and its relationship with combustion pattern, using a knocking-prediction mathematical model. The purpose of the study involved a need to control the knocking caused by a higher compression ratio, by means of modifying the pressure rise during combustion. (TRRL)

A comparison of engine performance using methanol or dissociated methanol as the fuel

Abstract: Methanol will react in the presence of a catalyst and decompose into hydrogen and carbon monoxide. This is an endothermic reaction in which the lower heating value of the reformed gas is about 20% greater than liquid methanol. Since the reformed gas is hydrogen rich it has the potential to increase the engines brake thermal efficiency and reduce exhaust emission compared to liquid methanol. To explore this possibility a series of dynamometer engine test were conducted to compare the performance of a 100% dissociated methanol fueled engine to a liquid methanol fueled engine. The combustion characteristics of dissociated methanol are similar to pure hydrogen. The low ignition energy requirements resulted in pre-ignition and severe backfires at the mid and high speed--load test points. Data obtained at the low speed-low load points, the area of greatest interest, show some reduction in exhaust emissions and improvements in brake thermal efficiency. Additional testing and/or theoretical analysis is required to determine if the improvements in fuel economy and reduction in exhaust emissions offset the potential problems, complexity and costs of a dissociation reactor system.

Internal combustion closed rankine cycle steam engine

Abstract: Disclosed is a steam engine which is used to propel underwater vehicles without exhausting combustion products to the surrounding water. A solid metallic fuel reacts in a first chamber with water to produce hydrogen which is subsequently reacted in a second chamber with oxygen to produce heat and water. The amount of water produced in the second chamber is equal to the amount of water used in the first chamber. Consequently, no excess water is produced.

Polyurethane-urea elastomers as working substances in rubber heat engines

Abstract: The possibility of using synthetic elastomers as working substances in a rubber heat engine was investigated at the laboratory and pilot scale. Two polyurethane–urea elastomers were subjected to expermental heat engine cycles at a variety of strains and temperature differences. It was found that optimum power and thermal efficiency were obtained at small strain perturbations where the elastomers were close to mechanical equilibrium. Crystallization of the rubbery phase during large strain perturbations is a nonequilibrium process which should be avoided. Quasi-ideal rubber behavior is approached in the pilot-scale heat engine which supports these conclusions.

Energy system for environmentally friendly refuse degassing or coal-refuse degassing with following fluidised bed furnace and integrated low temperature carbonisation gas combustion chamber and heat exchanger

Abstract: The invention relates to a process and an apparatus for the environmentally friendly utilisation of refuse with or without additions of e.g. coal or coal-like solids. According to the invention, in order make it possible to cover current peaks which arise suddenly, the combination and integration is proposed of assemblies connected in series, consisting of a refuse degassing reactor (A) and also a following fluidised bed furnace system (B), consisting of a fluidised bed furnace (6) and a following low temperature carbonisation gas combustion chamber system (5) and, connected following these units, a boiler part (C) with a heat exchanger (7), characterised in that the refuse can be continuously eliminated, i.e. degassed, in order to produce low temperature carbonisation gases and a low temperature carbonisation coke which can be stored, and according to the invention the low temperature carbonisation gas (3) is burnt above and in the fluidised bed furnace (6) with little NOx and SO2, in order to use it in the low load phase to the greatest extent in the following heat exchanger surfaces (7), and in the peak load firing, by taking up the low temperature carbonization coke (4) in the fluidised bed furnace region (6) to burn it such that the coal-containing ash particles liberated by the fluidised bed are recombusted so that the greatest possible thermal efficiency can be utilized via the following heat exchanger surfaces (7) in the boiler region (C) and ... to a following power station boiler as low-SO2 and -NOx flue gas (8) ... Original abstract incomplete.

Overview of NASA Lewis Research Center free-piston Stirling engine activities

Abstract: A generic free-piston Stirling technology project is being conducted to develop technologies generic to both space power and terrestrial heat pump applications in a cooperative, cost-shared effort The generic technology effort includes extensive parametric testing of a 1 kW free-piston Stirling engine (RE-1000), development of a free-piston Stirling performance computer code, design and fabrication under contract of a hydraulic output modification for RE-1000 engine tests, and a 1000-hour endurance test, under contract, of a 3 kWe free-piston Stirling/alternator engine A newly initiated space power technology feasibility demonstration effort addresses the capability of scaling a free-piston Stirling/alternator system to about 25 kWe; developing thermodynamic cycle efficiency or equal to 70 percent of Carnot at temperature ratios in the order of 15 to 20; achieving a power conversion unit specific weight of 6 kg/kWe; operating with noncontacting gas bearings; and dynamically balancing the system Planned engine and component design and test efforts are described