Showing papers on "Thermal efficiency published in 1983"

Development and Use of a Spray Combustion Modeling to Predict Diesel Engine Efficiency and Pollutant Emissions : Part 1 Combustion Modeling

Abstract: A mathematical model of a spray combustion in direct-injection diesel engines has been developed to predict engine performance, thermal efficiency and pollutant emissions. Injected fuel spray was divided into many small packages. Gas and fuel droplet temperatures and evaporated mass of fuel in each package were computed. In considering the complete air-fuel jet mixing process and temperature in each package, the model also enabled subsequent spatial and temporal history of burning rate, local temperature and air-fuel ratio to be calculated.

Thermoelectric energy conversion with solid electrolytes.

Abstract: The alkali metal thermoelectric converter (AMTEC) is a device for the direct conversion of heat to electrical energy. The sodium ion conductor beta"- alumina is used to form a high-temperature regenerative concentration cell for elemental sodium. An AMTEC of mature design should have an efficiency of 20 to 40 percent, a power density of 0.5 kilowatt per kilogram or more, no moving parts, low maintenance requirements, high durability, and efficiency independent of size. It should be usable with high-temperature combustion, nuclear, or solar heat sources. Experiments have demonstrated the feasibility of the AMTEC and confirmed the theoretical analysis of the device. A wide range of applications from aerospace power to utility power plants appears possible.

Combined Cycle and Waste Heat Recovery Power Systems Based on a Novel Thermodynamic Energy Cycle Utilizing Low-Temperature Heat for Power Generation

Abstract: A new thermodynamic energy cycle has been developed, using a multicomponent working agent. Condensation is supplemented with absorption, following expansion in the turbine. Several combined power systems based on this cycle have been designed and cost-estimated. Efficiencies of these new systems are 1.35 to 1.5 times higher than the best Rankine Cycle system, at the same border conditions. Investment cost per unit of power output is about two-thirds of the cost of a comparable Rankine Cycle system. Results make cogeneration economically attractive at current energy prices. The first experimental installation is planned by Fayette Manufacturing Company and Detroit Diesel Allison Division of General Motors.Copyright © 1983 by ASME

Tacom/cummins adiabatic engine program

Abstract: This paper discusses the goals, progress, and future plans of the TACOM/Cummins Adiabatic Engine Program. The Adiabatic Engine concept insulates the diesel combustion chamber with high temperature materials to allow hot operation near an adiabatic operation condition. Additional power and improved efficiency derived from this concept occur because thermal energy, normally lost to the cooling and exhaust systems, is converted to useful power through the use of turbomachinery and high-temperature materials. Engine testing has repeatedly demonstrated the Adiabatic Engine to be the most fuel efficient engine in the world with multi-cylinder engine performance levels of 0.285 LB/BHP-HR (48% thermal efficiency) at 450 HP representative. Installation of an early version of the Adiabatic Engine within a military 5 ton truck has been completed, with initial vehicle evaluation successfully accomplished. Design and procurement of long lead time items for the next generation of Adiabatic Engine in the 600-750 HP power range is continuing. Work on the minimum-friction Adiabatic Engine version continues.

A Thermodynamic Efficiency Concept for Heat Exchange Devices

Abstract: A thermodynamic efficiency based on the second law of thermodynamics is defined for heat exchange devices. The efficiency can be simply written in terms of the mean absolute temperatures of the two fluids exchanging heat, and the appropriate environment temperature. It is also shown that for a given ratio of hot to cold inlet temperatures, the efficiency and effectiveness for particular heat exchange configurations are related. This efficiency is compared to second-law efficiencies proposed by other authors, and is shown to be superior in its ability to predict the effect of heat exchanger parameter changes upon the efficiency of energy use. The concept is applied to typical heat exchange cases to demonstrate its usefulness and sensitivity.

Efficiencies of various esters of fatty acids as diesel fuels

Abstract: Methyl esters of commercial grades of lauric, myristic, palmitic, stearic, linoleic and linolenic acids, as well as ethyl and butyl esters of oleic acid, were burned in a diesel engine to determine their efficiencies as fuels. Triolein and some common vegetable oils were burned as comparison fuels and No. 2 diesel fuel was used as a control. The fuels were tested in a single-cylinder direct-injection engine running at rated speed and load in short-term, performance engine tests. Specific fuel consumption and thermal efficiencies of the engine burning these fuels were then determined. Among the methyl esters of the saturated acids, thermal efficiency was inversely related to chain length of the fatty acid. Introduction of a double bond resulted in increased efficiency. Further increases in unsaturation had negligible effects on thermal efficiencies. Ethyl oleate had the highest thermal efficiency and butyl oleate had the lowest thermal efficiency of any of the ester fuels tested. Most of the ester fuels produced higher thermal efficiencies than did No. 2 diesel fuel. Triolein produced the lowest specific fuel consumption of the triglyceride fuels and peanut oil produced the lowest specific fuel consumption of the vegetable oils. The data suggest that ethyl esters of monounsaturated or short-chain fatty acids should make good alternative fuels and that they should be further evaluated in longterm engine tests.

A Comparative Study of the Influence of Different Means of Turbine Cooling on Gas Turbine Performance

Abstract: A comparative study of the influence of different means of turbine cooling on the thermodynamic efficiency and specific work of gas turbines is presented. A common general model of a simple open cycle gas turbine is used to compare the performance of turbines using different types of cooling; internal convection and impingement by air, film cooling by air, internal convection and impingement by steam, film cooling by steam and closed loop cooling by water. The results are also compared to the previously published results of the analysis of open loop water cooled gas turbines. The model evaluates the efficiency and specific work of simple cycle gas turbines as it is influenced by mixing losses of coolant with combustion gases, pumping work of coolant and heat transfer from the expanding gas. The study is performed in terms of dimensionless variables in order to achieve generality and to provide useful design guidelines and insights. Blades internally cooled by convection and impingement are treated as heat exchangers operating at constant metal temperature and the coolant exit temperature is simply expressed as a function of a heat exchanger effectiveness, an independent parameter which is normally a function of the intricacy of the layout of the cooling passages. The coolant requirements and heat transfer with film cooling are determined using a dimensionless correlation derived experimentally at M.I.T. Sample calculations give the optimum turbine inlet temperature of thermodynamic efficiency and specific work for different pressure ratios and typical dimensionless numbers. The data on specific work are significant because they can be readily used in evaluations of a given type of gas turbine in a combined cycle. The sensitivity of the efficiency and specific work to each key input parameter is reported.The use of superheated steam as a coolant can provide some performance advantages since the steam raised in a waste heat boiler expands with the combustion gases, increases the turbine mass flow and also provides a certain amount of heat regeneration. Performance results are also reported for this steam cooled gas turbine operating with mixed working fluid.Copyright © 1983 by ASME

Heat Insulated Turbocompound Engine

Abstract: A program to demonstrate high thermal efficiency of a heat insulated turbocompound diesel engine was carried out. Major problems were choosing proper heat resisting materials, obtaining high mechanical and thermal efficiency of components, providing lubrication oil which works at high temperature and controling heat flux from a combustion chamber. A six cylinder, 125mm bore, turbocharged diesel engine was chosen for this program. Ceramic coating was mainly employed as a means of insulating heat and protecting engine parts. For the heat insulation, a ductile cast iron piston coated with Zr02 was used and the cooling water was entirely eliminated. Heat flow analysis was conducted both analytically and experimentally. Thus, heat rejection was reduced by about 35%. While maximum temperature of the cylinder wall was raised up to 350 deg C, no scuffing and excessive wear took place in the sliding parts of a single cylinder engine for 500 hours. It was found that improvement in efficiency of components such as a turbocharger, an aftercooler, a gear train and a power recovery turbine was very important to increase the thermal efficiency of the total system. The heat insulation including the effect of the reduction in fan driving power and turbocompounding contributed to improve the fuel consumption by an amount of 11.2%. As a result of the program, the engine with the thermal efficiency of 48% (171g/kwh) was obtained.

Method of and system for utilizing thermal energy accumulator

Abstract: A method and system is described which employs a thermal energy accumulator in which a thermal energy fluid and hot water coexist with each other. Hot water is taken out of the accumulator and supplied as thermal energy to an energy utilization compound arrangement of a total flow turbine and a steam turbine driving an electric power generator. The thermal energy fluid may be in the form of saturated steam, for example.

Development of a metal hydride compressor

Abstract: The National Chemical Laboratory for Industry (NCL) model 4 chemical engine has been completed. This is a type of hydrogen compressor using LaNi5 as the energy conversion medium. The container, consisting of 19 copper tube elements with aluminium inner fins and covered with a stainless steel heat-insulated water jacket, is filled with 18.9 mol of LaNi5. The compressor is composed of a pair of these containers, two electrical boilers (9 kW), a circulating pump, valves and other components. The container is able to absorb 1.3 m3 (at normal temperature and pressure (NTP)) of hydrogen and the time needed for preheating (90 °C) and cooling (27 °C) is less than 3 min. In the present investigation, using this container, the basic operating characteristics such as the hydrogen-absorbing and hydrogen-desorbing ability, the thermal efficiency, the heat transfer coefficient and the reaction velocity have been examined. Because of the circulating hot water (90 °C; 30 1 min−1), the NCL model 4 compressor is able to desorb 360 1 min−1 (NTP) of high pressure (18-12 atm) hydrogen gas continuously in 3 min. However, this is its maximum ability under stable conditions. The overall heat transfer coefficient estimated is about 300–1200 kcal m−2 h−1 °C−1. Using a plunger pump, the NCL model 4 compressor has been combined with a reverse osmosis type of desalination apparatus and a practical test is now under way.

Thermal barrier pistons and their effect on the performance of compound diesel engine cycles

Abstract: The paper describes the basic design concept of a heat barrier piston comprising a Nimonic crown separated from the aluminium piston body by an air gap. Heat flow, temperature and stress levels have been evaluated using a series of specially developed finite element programs. Preliminary experimental results obtained with the insulating piston on a Petter PH1 W engine indicate a very substantial rise in exhaust temperature, coupled with considerable reduction in volumetric efficiency under naturally aspirated conditions. In a final theoretical section, the effects of insulated pistons and of insulated cylinder walls in general are discussed both with respect to their effect on thermodynamic cycle parameters and to the possibility of substantial improvements in thermal efficiency using the compounding principle. Final guidelines are laid down for the most effective use of thermal insulation in compounded diesel engines.

Feed forward combustion control system

Abstract: A feed forward control system maximizes combustion efficiency in a combustion system, by controlling the amount of excess air supplied to the burner. The feed forward control system includes flow sensors for sensing the flow of air and fuel to the burner. Based upon the fuel flow measurement, a digital computer determines the correct stoichiometric amount of combustion air required and the firing rate of the burner. Based upon the firing rate, the digital computer determines, from stored data in a look-up table, the necessary excess air required. Based upon the stoichiometric combustion air and the excess air, the computer determines the actual air that is required. This air required is then compared with the air flow measurement received by the digital computer. Based upon this comparison, an air trim actuator is driven by the computer until the required air flow is attained.

Gas Turbine Airflow Control for Optimum Heat Recovery

Abstract: Gas turbines furnished with heat recovery equipment generally have maximum cycle efficiency when the gas turbine is operated at its ambient capability. At reduced gas turbine output the cycle performance can fall off rapidly as gas turbine exhaust temperature drops, which reduces the heat recovery equipment performance. This paper reviews the economic gains which can be realized through use of several control modes which are currently available to optimize the cycle efficiency at part load operation. These include variable inlet guide vane (VIGV) control for singleshaft units, and combined VIGV and variable high-pressure set (compressor) speed control for two-shaft units. In addition to the normal control optimization mode to maintain the maximum exhaust temperature, a new control mode is discussed which allows airflow to be modulated in response to a process signal while at constant part load. This control feature is desirable for gas turbines which supply preheated combustion air to fired process heaters.

Performance benefits of the direct generation of steam in line-focus solar collectors

Abstract: The performance benefits of the direct (in situ) generation of steam in the receiver tube of a line-focus solar collector are assessed in this paper. Compared to existing technology using steam-flash or unfired boiler systems, the in situ technique could reduce the delivered cost of steam in excess of 25 percent. The analysis indicates that two-phase flow instabilities, if present, can be readily controlled, and that the possibility of freezing is not an impediment to the use of water in cold climates.

Testing and analysis of a heat-pipe solar collector

Abstract: We developed an integral heat pipe/evacuated-tube solar collector in which the inner receiver tubes form the evaporator sections of glass heat pipes. This paper describes both theoretical analyses and empirical tests, comparing the performance of the glass heat pipe solar collector with one of today's high efficiency evacuated tube solar collectors. The comparison demonstrates that the performance of the two collectors is effectively identical. The testing and analysis indicate that the glass wick-type glass heat pipe is an effective heat transfer system for evacuated-tube solar collectors.

Method and system for preheating fuel

Abstract: A method and system for preheating internal combustion engine fuel to an optimum temperature before introducing the fuel into the carburetion system. It has been found that an engine fuel such as gasoline will have an optimum temperature at the point of carburetion for maximum combustion efficiency. A heat exchanger (10) extracts heat from hot engine coolant to add heat to the fuel. A thermostatic switch (14) and solenoid valve (18, 19) controls coolant flow to maintain the optimum temperature. Thermal insulation (35) is provided around the fuel supply system (13, 15, 32) and the heat exchanger to prevent engine heat from causing the fuel temperature to exceed the optimum temperature.

Maximized thermal efficiency hot gas engine

Abstract: An improved closed cycle hot gas engine in which virtually the entire working gas mass performs the same Ericsson Cycle loop thereby achieving maximized thermal efficiency The invention engine embodiments consist of paired cylinders connected together by leak sealed means for controlled working gas operation The working gas is simultaneously heated and expanded in the heating cylinder and then simultaneously cooled and compressed in the cooling cylinder to achieve the isothermal expansion and compression steps respectively of the four step Ericsson Cycle loop The improvements consist of means to provide both the reciprocating operation of the cylinders pistons as well as control of piston relative motion with respect to each other Piston relative motion is such that during the entire simultaneous expansion and heating step virtually all the working gas is contained in the heating cylinder, and, during the entire simultaneous compression and cooling step virtually all the working gas mass is contained in the cooling cylinder In between these two isothermal steps the gas mass is isobarically transferred between the cylinders by the storage or recovery, respectively, of working gas heat in a state-of-the-art regenerator located serially in the flow path between the heating and cooling cylinders

Efficient use of thermal energy from an internal combustion engine in ethanol production

Abstract: An ethanol-producing plant and a method is provided for producing ethanol from sugars, starches, or cellulose. Some ethanol-producing plants consume more thermal energy than they produce. The present invention solves the efficiency problem by utilizing an internal combustion engine with high-efficiency mechanical drives for providing the mechanical power requirements of the ethanol-producing plant and by utilizing the thermal energy of engine coolant and exhaust to provide some, or all, of the thermal energy requirements of the ethanol-producing plant. The method includes electrically loading the internal combustion engine to increase the thermal losses of the engine to equal the thermal energy requirements of the steps of the ethanol-producing process.

Second law analysis of thermal energy storage devices

Abstract: Performance parameters that can be used to evaluate thermal energy storage (TES) devices are presented in this paper. One of these parameters is the second law efficiency which can measure the effectiveness of energy utilization in thermal energy storage devices. The second law analysis presented here required the formulation of models describing the heat transport processes and the solution of the governing equations; the resulting analysis shows that second law efficiencies are always higher for countercurrent flow than for parallel flow for all input conditions. For counter-current flow operations, the second law efficiency increases as the mass flow rates and/or the charge/discharge cycle times of the heat transfer fluids are decreased. In particular, the second law efficiency is more sensitive to a reduction in the mass flow rate and/or cycle time during the discharge cycle than in the charging cycle.

Thermal Efficiency Of Steam Injection Test Well With Insulated Tubing

Abstract: A field test of bare 2.375-in. and insulated 4.500-in. tubulars has been conducted using heat flux sensors and thermocouples to evaluate bare and insulated tubular performance, annulus heat transfer, and overall wellbore heat loss in a cooperative effort between Sandia National Laboratories and Husky Oil Operations, Ltd. The well is part of a steam flood pilot in the Aberfeldy Field near Lloydminster, Saskatchewan. Insulation thermal conductivity was observed to vary by a factor of four between competing designs. Couplings and internal structures (e.g., centralizers) were seen to account for up to half the string heat loss with the annulus dry. For a wet annulus, the typical field case, steam generated at the ot couplings refluxes in the vented annulus and maintained the caisng temperature constant at 212F at all points. Thus wellbore heat loss was 3 to 6 times higher than expected, the same opposite the highest and lowest quality insulated tubing, and the only 30 to 40% less than bare tubing. Insulated couplings or techniques to eliminate annulus steam refluxing are needed to achieve the potential of insulated tubing.

Drive device comprising combustion engine and steam motor

Abstract: The invention relates to a drive device in which a water-cooled combustion engine (10) is coupled to a steam motor (13) driven by the waste heat occurring on the combustion engine. The steam motor (13) is driven by a separate water/steam circulation system (23-29), which is coupled by way of a heat exchanger (15) to the cooling water system of the combustion engine (10) and which is routed via a heat exchanger (17) acting as vaporiser, through which the exhaust gases of the combustion engine (10) are led. The formation of steam in the exhaust gas heat exchanger (17) is adjusted by means of a controlled pump (26) by means of which the quantity of water injected into the exhaust gas heat exchanger (17) can be metered. The exhaust gas heat exchanger (17) is at the same time designed as a heat accumulator.

Combined cycle total energy system

Abstract: The disclosure relates to a system for the co-generation of steam and electricity from a gaseous fuel. A Brayton cycle turbine drives first and second fuel and air compressors as well as an electric generator. Steam is also produced by the system for direct utilization or to drive a steam turbine which also drives the generator.

Supercharged internal combustion engine with heat exchanger for the combustion air

Abstract: A heat exchanger for cooling or preheating combustion air of a supercharged internal combustion engine. The heat exchanger is formed of a self-contained system including elements provided with a heat accumulating active medium which is in a heat exchange relationship with the combustion air. The elements of the self-contained system are preferably filled with a heat accumulating active medium which acts as a latent accumulator at operating temperatures.

Continuous vacuum dryer for energy saving

Abstract: A continuous vacuum dryer for energy saving has been developed in order to produce dried foods without heat denaturation in the products. This drying method is suitable for heat sensitive I and highly viscous foods and can dry to 1 to 4% in moisture content with good quality at around 40°C in product temperature andin 5 -10 min a drying time. Feed material with high viscosity has to I have uniform distribution on the belt in the vacuum chamber to I keep a constant drying for which a special feed nozzle has been developed after considerabl~ testing. Heat transfer on the wet material in the dryer has occurred by both conduction and radiation because of the design so that the thermal efficiency in

Ranking bottoming device of diesel engine

Abstract: PURPOSE:To increase thermal efficiency and form a device to small size, by forming an after cooler in a Rankine cycle, in which thermal energy of exhaust gas is collected and taken off as power, as an integral unit with a regenerator further using the after cooler as a heater of working fluid. CONSTITUTION:An after cooler 4, which cools supercharge air flowing through a compressor 8 of a supercharger 2 and then leads the supercharge air to an engine 1, and a regenerator 11, in which an operating medium flowing out of a turbine 6 driven by the engine 1 is circulated, are constituted as an integral unit. Then the delivery side of a feed pump 3, in which a suction side is connected to a condenser 10 integrally formed with a radiator 5, is connected to one side 11a of low temperature of the regenerator 11, and the other side 11b of high temperature is connected to one side 7a of low temperature of an evaporator 7. In this way, high temperature air flowing out of the compressor 8 is radiated with heat in the after cooler 4 to perform heating of the operating medium of a Rankine cycle flowing in the regenerator 11.