Showing papers on "Thermal efficiency published in 1992"

High efficiency hybrid car with gasoline engine, and electric battery powered motor

Abstract: A hybrid-propulsion car system having one axle driven by an internal combustion engine and another axis driven by an electric motor. The waste heat of the internal combustion engine is absorbed by the engine cooling fluid, and is then heat exchanged with an evaporative fluid in a closed circuit. The evaporative fluid is vaporized by the heat of the engine cooling fluid in order to drive an expander which in turn drives an electric generator. The electric generator supplies current to a storage battery and to the electric motor.

General performance characteristics of real heat engines

Abstract: Realistic upper bounds can be placed on the power and efficiency of real heat engines via a relatively simple analytic treatment of primary sources of irreversibility. Generalized curves for heat engine performance, their universal nature, and quantitative evaluation of upper bounds for power and efficiency are derived for several engine types, specifically: Brayton cycle (gas turbines), Rankine cycle (steam turbines), and cycles with sizable heat leaks, such as thermoelectric generators. The key irreversibility sources include fluid friction, the constraint of the equation of state of the engine’s working fluid, and heat leak. It is demonstrated that maximum power and maximum efficiency operating points are usually relatively close, with the associated implications for the selection of optimal heat engine operating conditions. The limitations of past analyses of endoreversible cycles as models for real heat engines will be discussed and the fortuitous nature of agreement between their predictions and actual heat engine performance will be explained.

Method and apparatus for improved operation of internal combustion engines

Abstract: A process for operating an internal combustion heat engine which comprises the steps of thermochemically regenerating waste heat rejected by the heat engine by reacting at least one conventional fuel compound containing hydrogen and carbon with an oxygen donor using substantial quantities of the waste heat to produce a mixture of engine-fuel containing substantial quantities of hydrogen and carbon monoxide and utilizing the mixture of engine-fuel to operate an internal combustion engine.

High efficiency natural gas engine driven cooling system

Abstract: A method for recovering and utilizing residual waste heat energy normally rejected into the atmosphere from a combined direct expansion refrigeration system driven by a natural gas or internal combustion engine, wherein the waste heat energy rejected from the condenser of the refrigeration system is combined with the heat energy rejected from the engine block cooling fluid and the exhaust gas stream and recovered by a refrigerant power fluid to drive a vapor power expander and co-generate auxiliary electric power.

Optimization of a solar‐driven heat engine

Abstract: The optimum performance of the solar‐driven heat engine consisting of a solar collector and a heat engine is investigated, based on the linear heat‐loss model of solar collectors and the endoreversible Carnot cycle model of heat engines. Some new results such as the optimum operating temperature of the solar collector, the maximum overall efficiency of the system, the optimum operating temperatures of the working fluid in two isothermal heat exchange processes of the heat engine, and so on, are derived. It is expounded that these results have more realistic meaning than the previous relative theoretics for the optimum design of practical solar‐driven heat engine systems.

Hybrid electric power generation

Abstract: A new hybrid electric power production cycle is revealed, which utilizes hot, dry-rock, geothermal energy to produce dry, saturated steam, and utilizes natural gas or other fossil fuel to superheat the produced steam to a desired temperature. The superheated steam would then be used in a conventional Rankine cycle to produce large-scale electric power and energy. For a preferred steam pressure of 1800 pounds per square inch and a temperature of 1000 degrees Fahrenheit, the total energy consumed in the hybrid cycle would be 78% geothermal and 22% fossil-fuel.

Apparatus for combustion, pollution and chemical process control

Abstract: Disclosed is a system for regulating the efficiency of a combustion process by detecting radiant energy emitted from ash particles entrained in the gas stream exiting the combustion chamber of a boiler or incinerator. The intensity of selected wavelengths of light emitted from the particles is indicative of the temperature of the particles. The change in the intensities of the selected wavelengths of light, and thus of the temperature of the gas stream at the furnace exit, is monitored, and a feedback control mechanism is used to regulate one or more combustion, pollution control, or heat transfer parameters thereby maximizing the thermal efficiency of the combustion process in the boiler or incinerator.

Management of heat generated by aircraft gas turbine installations

Abstract: A program-controlled heat management system for an aircraft's bypass gas turbine (turbofan) engine installation, in which the engine's fuel system is put into direct heat exchange relationship with the engine's own oil system, and with an engine-driven electrical generator's oil system, by means of respective fuel/oil heat exchangers and also into selective indirect heat exchange relationship with a variable proportion of the engine's bypass air means of an engine oil/air heat exchanger. The fuel system is switchable between four different fuel flow configurations in order to vary the heat flows between the fuel system and the oil systems, two of the fuel flow configurations also involving recirculation of fuel from the engine's fuel system to a fuel tank in the aircraft wing in order to put the fuel system into selective heat exchange relationship with the tank and hence with the airstream passing over the wing. Temperatures in the oil and fuel systems are monitored and kept within predetermined limits by selecting the appropriate fuel flow configuration and selectively dumping heat to the environment through the engine oil/heat exchanger and the aircraft wing in a way which maximizes the fuel efficiency of the engine.

Direct Cycle Light Water Reactor Operating at Supercritical Pressure.

Abstract: The concept of a direct cycle light water reactor (LWR) operating at supercritical pressure is presented. It is attractive for improving the thermal efficiency of LWRs and for simplifying the reactor system(1). The critical pressure of water is 22.1 MPa (221 bars). The density of water changes continuously above it and the concept of boiling does not exist. The system is conceptually depicted in Fig. 1. The water coolant which flows into the core is heated up and can be directly fed to turbines. Compared with the current BWRs, the recirculation system and steam separators and dryers will be eliminated. The vessel size will be greatly reduced. This will reduce the capital cost. The thermal efficiency will be also revolutionally improved. The feasibility of the system was studied through the conceptual design of the core.The axial temperature and density distribution of the coolant in the core were calculated at 25 MPa (250 bars) using a single channel model of a fuel and coolant. The density decreases continuously from the inlet (0.725 g/cm3) to the outlet (0.137 g/cm3) and the temperature increases from 583 K (310°C) to 689 K (416°C). The heat is efficiently removed due to the high specific heat of water around 658 K (385°C). The density change is mild at 250 bars than 225 bars which is close to the critical pressure. It is desirable to choose 250 bars for the stability of the flow in the core.

Method for fuel flow determination and improving thermal efficiency in a fossil-fired power plant

Abstract: A method for determining fuel flow rate, pollutant flow rates, and boiler efficiency for a fossil-fired steam generator system from an analysis of the composition of the dry fuel base and composition of the combustion effluents.

Hydrogen assisted jet ignition for near elimination of NOx and cyclic variability in the S.I. Engine

Abstract: The performance of a combustion initiation system for the Otto cycle engine is described which uses a pre-chamber of 1.5% main chamber clearance volume, fuelled with minute quantities of hydrogen. The order of magnitude faster flame kernel growth, obtained with hydrogen mixtures compared with hydrocarbon fuels, provides enhanced jet momentum from a small proportion of the total charge energy, and active radicals and intermediate species which assist in initiating combustion in mixtures significantly leaner than the lean flammability limit with normal ignition. The performance results demonstrate the ASTM CFR engine working at up to 70% maximum torque with NO x emissions close to ambient levels. The hydrogen assisted jet ignition, HAJI, use to achieve this also confers extremely stable combustion with coefficients of variation of peak cylinder pressure and specific work per engine cycle reduced by 50 to 80% from those normally achieved with this engine. This allows increased thermal efficiency at ultra lean operation, at relative air/fuel ratios of around 2, and about two numbers increase in the highest useful compression ratio. There is no lean limit of combustion within the range of usable engine torque. Operation with relative air/fuel ratios of 5 have been achieved. With methanol as the main chamber fuel, the results presented here demonstrate an improvement in maximum indicated thermal efficiency of 15 per cent simultaneously with the low NO x emissions. The hydrocarbon emissions remain high which is a characteristics of this research engine.

Economic power generation from low-temperature geothermal resources using organic rankine cycle combined with vapour absorption chiller

Abstract: Power generation with low temperature geothermal resources is not economically viable due to the poor thermal efficiency of organic Rankine cycles (ORC). A novel idea is proposed where a vapour absorption chiller (VAC) can be employed to lower the ORC condensing temperature, thus increasing its power output. This paper presents detailed analysis of a VAC that operates with water-lithium bromide to extract heat from the geothermal brine leaving the ORC vaporizer. The evaporator of the VAC serves as the ORC condenser. A computer program is coded to simulate the combined ORC-VAC performance and compare it with that of the conventional ORC. The results indicate that the ORC-VAC option would render power generation more economical. The organic fluid flow rate in the ORC per unit power output is cut by at least 50% in this case, thus reducing the ORC size and turbine cost. Moreover, even though the ORC-VAC includes more components, the total heat exchange area requirement per unit power output remains practically unchanged.

Effects of Irreversibility and Economics on the Performance of a Heat Engine

Abstract: In this paper, optimization of the power output of an internally irreversible heat engine is considered for finite capacitance rates of the external fluid streams. The method of Lagrange multipliers is used to solve for working fluid temperatures which yield maximum power. Analytical expressions for the maximum power and the cycle efficiency at miximum power are obtained. The effects of irreversibility and economics on the performance of a heat engine are investigated. A relationship between the maximum power point and economically optimum design is identified. It is demonstrated that, with certain reasonable economic assumptions, the maximum power point of a heat engine corresponds to a point of minimum life-cycle costs.

Method and apparatus for increasing the efficiency of internal combustion engines

Abstract: This invention relates generally to a system for increasing the thermodynamic efficiency of internal combustion engines. In the system of the invention, the unused heat generated during normal engine operation in the exhaust gases, lubricating oil and engine coolant is utilized to compress air which produces additional energy that performs additional work in the engine system by means of a modified Rankine cycle. This same system used to maximize efficiency and increase power also acts to reduce pollutants in the exhaust emissions.

On the efficiencies of absorption heat transformers

Abstract: Although commonly used, the coefficient of performance (COP) is not always an adequate measure to describe the effectiveness of a sorption heat pump. Equations for four different efficiencies are derived, discussed and compared for absorption heat transformers. A flow-sheeting computer program, developed for both design and evaluation simulations of arbitrarily complex absorption cycles, is used to exemplify the derived equations. The working pair H2ONaOH is used in two heat transformer systems. The given examples clearly show that the COP can only be used to compare different heat transformers operated at the same circulation ratio. The COP can be considered as an indicator of the effectiveness of heat exchange within and thermal insulation of a heat transformer operated at a fixed circulation ratio. The thermodynamic efficiency, E th , is shown to be a more logical measure of the heat transformer efficiency, since it takes into account both heat losses, heat exchange and the temperature lift. The exergetic efficiency, E ex , is an alternative to E th since both are mathematically compatible. The possibility of taking into consideration the temperature level, at which heat energy may be considered economically worthless, is demonstrated to be a major advantage of the exergetic efficiency. However, its numerical value does not provide a clear interpretation of the importance of exergetic losses in the system. The exergetic index, I ex , is directly related to the exergetic efficiency but its numerical value is more significant for evaluating the performance of the heat transformer system.

Clean power generation using IGCC process

Abstract: An integrated gasification combined cycle (IGCC) process and plant are provided in which an improvement in overall thermodynamic efficiency can be achieved by increasing the proportion of power generated by gas turbine(s) to that generated by steam turbine(s). This is achieved by placing an exothermic catalytic reactor downstream of the gasifier to pre-heat the gas turbine fuel gas which is supplemented by the addition of non-combustible gas.

Triple-effect absorption refrigeration system with double-condenser coupling

Abstract: A triple-effect absorption refrigeration system is provided with a double-condenser coupling (22) and a parallel or series circuit for feeding the refrigerant-containing absorbent solution through the high (14), medium (16) and low (18) temperature generators utilized in the triple-effect system. The high temperature condenser (134) receiving vaporous refrigerant from the high temperature generator (14) is double coupled to both the medium temperature generator (16) and the low temperature generator (18) to enhance the internal recovery of heat within the system and thereby increase the thermal efficiency thereof.

Application of SEM Techniques to the Characterization of Coal and Coal Ash Products

Abstract: Coal is a major source of fuel for generating electrical power in the United States.(1) The last decade has seen a significant increase in the use of coal for power generation. The increased demand for coal and the tendency to use a variety of coals to meet economic and environmental restrictions has required a more detailed understanding of boiler operations. Ash species produced from inorganic impurities in coal during combustion can be a major operational problem.(2) These ash species can produce deposits on heat transfer surfaces (thereby reducing thermal efficiency), cause corrosion/ erosion of structural material, and lead to particulate emissions in excess of current standards. Industry is finding that a more detailed knowledge of ash behavior is valuable in the efficient and environmentally acceptable operation of coal-fired power plants. The inorganic impurities in coal are important with respect to fuel selection, the design and size of a boiler, and how the boiler is operated. Extensive research at the University of North Dakota Energy and Environmental Research Center (EERC) has focused on methods to determine inorganic components in coals, mechanisms of ash formation, and the factors that influence the formation of ash deposits on heat transfer surfaces.

On the efficiencies of absorption heat pumps

Abstract: Although commonly used, the coefficient of performance COP is not always an adequate measure to describe the effectiveness of a sorption heat pump. Equations for four different efficiencies are derived, discussed and compared for absorption heat pumps (AHP). A flow-sheeting computer program, developed for both design and evaluation simulations of arbitrarily complex absorption cycles, is used to exemplify the derived equations. The working fluid pair H 2 OLiBr has been used in two different AHP configurations. The examples given clearly show that the COP can only be used to compare different AHPs operated at the same circulation ratio. The COP can be considered as an indicator of the effectiveness of heat exchange within and thermal insulation of a heat pump operated at a fixed circulation ratio. Nevertheless, it is an insufficient measure to compare different AHPs, even when they are operated at the same circulation ratio. On the other hand, the coefficient of performance for cooling Q e / Q g is better in this respect since it takes into account the real heat flow to the generator. The Carnot efficiency COP rev takes into consideration both the real heat outputs from the absorber and condenser, and the temperature of heat sources and heat sinks. The thermodynamic efficiency E th is shown to be a more logical measure of the heat pump efficiency, since it takes into account the real heat input the generator. The exergetic efficiency E ex can be considered as an alternative to the thermodyanamic efficiency E th but it offers a possibility to take into account any temperature level where heat energy may be considered worthless. However, both E ex and E th are not conventionally used since their numerical values are always less than 1.0. On the other hand, the exergetic index I ex is directly related to E ex but its numerical value shoul be considered as a more significant measure for evaluating the performance of AHP systems, since it properly takes into account the exergy losses which inevitably occur in the system. It may however be stressed that exergy analysis should be used as a compliment to the First Law analysis.

Combined geothermal and fossil fuel power plant

Abstract: A power production process integrates geothermal steam and fossil fuel energy sources to give a higher energy efficiency than is normally obtained when using these energy sources individually. Geothermal steam is partially diverted from a steam turbine and injected into a combustion turbine. Although the steam turbine output is reduced by the diversion of steam, the plant efficiency and total plant output are improved.

Heat recovery ventilator

Abstract: A heat recovery ventilator having a rotary wheel heat exchanger includes a unique configuration for driving both the rotary wheel heat exchanger and impellers to provide an inexpensive, compact and light-weight ventilator unit adaptable for use across a wide range of residential, commercial and industrial applications. A random matrix media is also used to provide high thermal efficiency in exchanging heat and moisture between inlet and exhaust air streams.

Azeotrope assisted power system

Abstract: The azeotrope assisted power system is a double cycle engine with condenser at an available low temperature and which uses a refrigerant of low boiling point as working fluid, with its boiler held at an elevated constant temperature for good operating efficiency by thermal contact between the boiler and the condenser of an efficient azeotrope assisted heat pump. The efficiency of the heat pump cycle is increased by the use of an azeotrope mixture of two refrigerants which shows a vapor pressure versus temperature less steep than the similar curves for the separate component refrigerants. These are closed cycles with no mixing of fluids between the cycles. The heat pump compressor draws its required power from the engine cycle, leaving some useable energy. The efficiency of the engine cycle is helped by having a stable temperature in the boiler, and the over all efficiency is maintained by preheating the working fluid fed to the boiler by heat exchange with condensate leaving the condenser of the heat pump. The combined system allows the use of lower temperature heat to produce power.

Absorption chillers improve cogeneration energy efficiency

Abstract: When power is being generated from fossil fuel and used as shaft horsepower or electrical energy, the process is only 20% to 35% thermally efficient if the waste heat from the prime mover is not effectively utilized Although there are new gas turbine engines that boast 40% thermal efficiency, they are not only on the market yet Fortunately, there are many ways to capture and utilize most of the 65% to 80% of the energy wasted in the conventional utility generation of electric energy This article discusses only those applications where the thermal energy available as waste heat can be converted to chilled water by the absorption process and used either as a commodity beyond the generation process or the enhance the generation process itself