Stirling Engine Research Articles

A thermodynamic probe of the topological phase transition in epitaxial graphene based Floquet topological insulator

One can use light to tune certain materials from a trivial to a topological phase. A prime example of such materials, classified as Floquet topological insulators (FTIs), is epitaxial graphene. In this paper, we probe the topological phase transition of a FTI via the efficiency and work output of quantum Otto and quantum Stirling heat engines. A maximum/minimum in the efficiency or work output invariably signals the phase transition point. Furthermore, both engines’ work output and efficiency are markedly robust against the polarization direction of light.

Numerical Optimization of the β-Type Stirling Engine Performance Using the Variable-Step Simplified Conjugate Gradient Method

This study focuses on optimizing a 100-W-class β-Type Stirling engine by combining the modified thermodynamic model and the variable-step simplified conjugate gradient (VSCGM) method. For the modified thermodynamic model, non-uniform pressure is directly introduced into the energy equation, so the indicated power and heat transfer rates can reach energy balance while the VSCGM is an updated version of the simplified conjugate gradient method (SCGM) with adaptive increments and step lengths to the optimization process; thus, it requires fewer iterations to reach the optimal solution than the SCGM. For the baseline case, the indicated power progressively raises from 88.2 to 210.2 W and the thermal efficiency increases from 34.8 to 46.4% before and after optimization, respectively. The study shows the VSCGM possesses robust property. All optimal results from the VSCGM are well-matched with those of the computational fluid dynamics (CFD) model. Heating temperature and rotation speed have positive effects on optimal engine performance. The optimal indicated power rises linearly with the charged pressure, whereas the optimal thermal efficiency tends to decrease. The study also points out that results of the modified thermodynamic model with fixed values of unknowns agree well with the CFD results at points far from the baseline case.

Thermal Analysis of Electric Machines for Combined Stirling Engine-Generator Performance

The performance of an electric machine depends on its ability to resist rising internal temperature and ambient temperature. In particular when it is a combination with a heat engine, it is essential to know the thermal characteristics of the electric machine in connection with its operating environment to decide which type of machine for a better result. This work will make a comparative thermal study of three types of generators namely: the permanent magnet generator (PMSG), the squirrel cage asynchronous generator (SCIG) and the switched reluctance generator (SRG), all driven by Stirling engine. The method involves solving the heat propagation equation to determine the thermal resistance network for each machine. The resolution of the network combined with the finite element method will allow a comparison of the temperature rise and its effect on the performance of each machine. The simulation results show that the temperature of the PMSG windings stabilizes at 430 K while that of the others stabilizes at 373 K and 346 K respectively. However, when comparing the performances for the specifications of this work (i.e., produce minimum electric power of 2kW at low speed generated by the Stirling engine), PMSG is the one that fulfil all the requirements. For the use of this machine for the generator set, it will be necessary to use magnets of types GNS-39EH whose operating temperature is approximately 473K (200 ° C) with magnetic induction of 1.22 T. Keywords: choice of machines, thermal network, Finite Element Method, machine’s performances, Stirling engine.

Thermal Analysis of Electric Machines for Combined Stirling Engine-Generator Performance

The performance of an electric machine depends on its ability to resist rising internal temperature and ambient temperature. In particular when it is a combination with a heat engine, it is essential to know the thermal characteristics of the electric machine in connection with its operating environment to decide which type of machine for a better result. This work will make a comparative thermal study of three types of generators namely: the permanent magnet generator (PMSG), the squirrel cage asynchronous generator (SCIG) and the switched reluctance generator (SRG), all driven by Stirling engine. The method involves solving the heat propagation equation to determine the thermal resistance network for each machine. The resolution of the network combined with the finite element method will allow a comparison of the temperature rise and its effect on the performance of each machine. The simulation results show that the temperature of the PMSG windings stabilizes at 430 K while that of the others stabilizes at 373 K and 346 K respectively. However, when comparing the performances for the specifications of this work (i.e., produce minimum electric power of 2kW at low speed generated by the Stirling engine), PMSG is the one that fulfil all the requirements. For the use of this machine for the generator set, it will be necessary to use magnets of types GNS-39EH whose operating temperature is approximately 473K (200 ° C) with magnetic induction of 1.22 T. Keywords: choice of machines, thermal network, Finite Element Method, machine’s performances, Stirling engine.

Energy, exergy, exergoeconomic, and environmental analyses and multi-objective optimization of a biomass-to-energy integrated thermal power plant

A novel biomass-driven heat and power cogeneration system comprising biomass gasification, a gas turbine, a Stirling engine, and a supercritical carbon dioxide cycle integrated with a domestic water heater was proposed in this work. Different biomass feedstocks (paper, wood, paddy husk, and municipal solid waste) were used in the gasifier as the input fuel. The devised system was analyzed from energy, exergy, exergoeconomic, and environmental viewpoints. Moreover, the effect of integrating the Stirling engine with the stand-alone CHP system is studied. Moreover, a detailed parametric analysis was performed to assess the effect of varying operating parameters on system efficiency. Finally, multi-objective optimization using genetic algorithm in MATLAB software was performed to obtain the optimum operating points. According to the results, using municipal solid waste as the input biomass resulted in the highest exergy efficiency by 41.36% and the lowest CO2 emission by 0.9021t/MWh. Also, the system with the Stirling engine had a higher exergy efficiency and lower CO2 emission than the system without the Stirling engine. According to the optimization results, the maximum obtainable exergy efficiency was 42.03%, which was related to MSW. Also, the minimum achievable cp,tot was 10.94$/GJ, attributable to the respective paddy husk.

Investigating student understanding of a heat engine: a case study of a Stirling engine

We report on the study of student difficulties regarding a heat engine in the context of a Stirling cycle by the method of measurement. An in-class test about a Stirling engine with a regenerator was taken by three classes, and the students were asked to perform one of the most basic activities—calculate the efficiency of the heat engine. Our data indicate that quite a few students have not developed a robust conceptual understanding of basic engineering knowledge of the heat engine. Notably, the error ratio of the class given a simple tutorial of engineering knowledge is smaller than those of the other two classes by more than 20%. In addition, both the written answers and post-test interviews show that most of the students cannot associate Carnot’s theorem with a Stirling cycle. Our results suggest that both scientific and engineering knowledge are important and should be included in instructional approaches, especially in the thermodynamics course taught in the countries and regions with a tradition of not paying much attention to experimental education or engineering training.

Renewable hydrogen driven CHCP device

Rural Research Stations (RRS), Refugee Camps Motorhomes and Caravans are in need of a portable Compact Heating, Cooling and Power (CHCP) generating device. Heating and power generation devices with diesel as driving source of energy are available commercially. In this paper, an innovative compact heating, cooling and power generating device which uses renewable hydrogen and suits rural areas, extreme weather conditions and disastrous situations is proposed. The device is driven by renewable hydrogen fuel generated by PV electrolysis as the source of energy. Low vibration low noise Stirling Engine (SE) is used as mechanical energy converter. Generator is used as electrical energy converter and heat pump is used for supplying heating and cooling effects. The proposed device has many advantages such as encouraging the rural tourism, supply rural research stations the heating and/or cooling loads and contribute in saving lives in the extreme weather conditions and disastrous situations. Analysis of the proposed device in terms of workability and performance was performed. Results showed that renewable energy base, electricity independent, silent, low vibration and better performance were achieved (OHR = 2.662) with the current device compared to available devices.

Comparative Study of Electric Machines for Stirling Generator Application

The choice of a machine for an application and a given specification remains a complex problem. This will involve, for example, bringing together criteria such as: performance, space saving, economical, reliable, little acoustic noise and others. The best machine selection to fulfill all constraints is an important step for the project to be realized. This work focus on Stirling Engine based Generator and study all types of rotating machines that can be employed for maximum electric power production. Analytical electromagnetic models where developed for all types of rotating machines that satisfied minimum requirement for the project by solving Maxwell equations. The purpose is to develop the design model and combine electromagnetic and thermal study of the machines. Finite Element Method is used to compare the performances of the generators for the best choice. Results show that for applications not requiring bigger output power, the major criteria for the selection is the optimal magnetic induction created by the inducer in the stationary part of the machine. For application such as Stirling generators, permanent magnet (PM) machine satisfy many comparison criteria such as maximum power at low speed, torque density, high efficiency. Beyond exposing a selection method for a project, this work lay down a step-by-step method for engineers and scientists for the crucial stage of design and conception work

Numerical study on regenerative effectiveness of parallel-plate regenerator for Stirling engine

ABSTRACT Due to the excellent heat transfer performance and low pressure drop, the parallel-plate regenerator (PPR) is very suitable for use in Stirling engines. At present, researches on the application of PPR in Stirling engines are rare. The axial heat conduction loss in PPR is a key factor that affects the heat transfer performance. Therefore, in this paper, the theoretical model of PPR operated under the Stirling engine working conditions is studied numerically, the regenerative effectiveness is taken as the target parameter, and the influence of axial heat conduction and other important parameters are explored. The results show that the axial heat conduction is detrimental to regenerative effectiveness, the regenerative effectiveness does not vary monotonically with the increase in the thermal conductivity, the copper regenerator with higher thermal conductivity has a lower regenerative effectiveness because of its higher axial thermal conductivity. The working frequency and the thermal properties of the working fluids have a comprehensive effect on the regenerative effectiveness, for high thermal diffusivity working fluids, such as helium and hydrogen, the regenerative effectiveness is high, while for low thermal diffusivity working fluid, such as carbon dioxide, the regenerative effectiveness is relatively low, and does not vary monotonously with frequency. The regenerative effectiveness increases with the reduction of the plate spacing, the plate spacing should be determined by considering the regenerative effectiveness and the pressure drop comprehensively. It is recommended that the stainless steel be a suitable material for the plates, and helium be the suitable working fluid.

Performance analysis of stirling engine double-effect absorption chiller hybrid system for waste heat utilization from gas turbine modular helium reactor

In this study, a cogeneration system that consists of a Stirling engine, Double Effect H2O/LiBr Absorption Chiller, and Gas Turbine Modular Helium Reactor cycle was examined. The rejected heat from the Gas Turbine Modular Helium Reactor cycle was used as input energy for both, the Stirling engine and the Double Effect Absorption Chiller to produce additional power and chilled water, respectively. A thermodynamic analysis was performed and optimized for the proposed cycle based on the first law of thermodynamics/energy utilization efficiency. The effects of some parameters were studied, including compressor pressure ratio, turbine inlet temperature, the low-pressure compressor inlet temperature, in addition to the operating temperatures of the Stirling engine and the Double Effect Absorption Chiller. Our results indicate that integrating the two systems into the GT-MHR cycle will increase the energy utilization efficiency by 4.73%−5.46%-points at a turbine inlet temperature range of 700–900 °C. Moreover, the results show that the helium mass flow rate of the combined cycle at the same turbine inlet temperature range is lower than that of the standalone Gas Turbine Modular Helium Reactor cycle by 16.1%−17.78%.

Increasing the energy efficiency of a building by thermal insulation to reduce the thermal load of the micro-combined cooling, heating and power system

The paper analyzes the energy consumption of an energy-independent house in two different situations, namely when the exterior insulation is installed and, respectively, in its absence. The result of the analysis was used to assess the reduction of fuel consumption and greenhouse gas emissions of the auxiliary heating system, namely a biomass boiler. The home’s heating system consists of a Stirling cogeneration system with biogas, which produces 3 kW of electricity and 9 kW of heat, and a 50 kW biomass boiler. The biomass boiler must provide the additional heat necessary to cover the consumption of the house when the Stirling engine is running and respectively ensure the coverage of the complete heat consumption of the building when the Stirling engine is in standby mode. The analysis showed that the installation of external insulation on the building walls will reduce energy consumption by 13%–16%, depending on the variation of the outside air temperature.

Thermodynamic modeling and controlling of a combined Free Piston Stirling Engine System (FPSE) with a Permanent Magnet Linear Synchronous Machine (PMLSM)

Converting thermal energy to electricity is one of the most common energy conversions in the field of electricity production. This transformation of energy is essential for both renewable and non-renewable heat sources. One of the main parameters of such a system that is responsible for this conversion is its efficiency. To have an efficient transformation, many improvements have been made to the old methods, and also new techniques were developed. One of these new methods that will be discussed here is a combined system of a Free Piston Stirling Engine (FPSE) with a Permanent Magnet Linear Synchronous Machine (PMLSM). The two purposes of presenting such a system are that firstly, the theoretical efficiency of a Stirling engine is high. Secondly, by eliminating crank-shaft from this system compared to the standard Stirling engine system, some of the losses will be removed. To study this system, a thermodynamic model of a RE-1000 FPSE was presented and validated. Then it was coupled with a PMLSM, and the combined system was controlled. The total efficiency of this system in steady-state is 14.4%.

Heat transfer of a Stirling engine for waste heat recovery application from internal combustion engines

This work analyzes the performances of a Stirling engine for waste heat recovery from the exhaust gas of internal combustion engines. Both experimental and numerical approaches were used. Experimental tests have been carried out on a research Stirling engine coupled to compression ignition engine by a thermally insulate pipe and a cap. Three configurations of coupling have been analyzed. Then, a three-dimensional numerical model has been developed by the authors to deepen the heat transfer between exhaust gas and working gas in the Stirling engine. The cap-heater system has been studied as a shell-and-tube heat exchanger. Experimental results have been set as boundary condition values for the cap, whereas for the heater, pressure and velocity have been evaluated using a 1D adiabatic model properly modified according to Stirling engine configuration. Velocity fields and temperature distribution inside the cap and heater have been analyzed, remarking that the layout of the heat exchanger becomes important for system efficiency. The method presented in this work could be useful to improve in wider terms the coupling between Stirling engine and internal combustion engines.

THERMAL PERFORMANCE ANALYSIS OF A STIRLING ENGINE ENERGIZED WITH EXHAUST GAS OF A DIESEL ENGINE

Theoretical and experimental investigations indicate that at high loads such as 3/4 throttling or more and high speeds such as 3000 rpm or more, the exhaust gas temperatures of the Internal Combustion engines are about 900-1000 K. The amount of heat wasted with exhaust gas of the Internal Combustion engines is equivalent to the power of them. By considering this feature of the Internal Combustion engines, a Hybrid engine consisting of an Internal Combustion (IC) engine and a gamma type Stirling engine was proposed and analyzed from the thermodynamic point of view. Hybrid engine is formed by combining the Stirling and IC engines via a common crankshaft and a common cylinder. The Internal Combustion engine may be a four stroke Diesel engine having an unconventional piston consisting of a crown and a rod. Via using this kind of pistons, two chambers are created in the same cylinder where one of them take part at above of the piston crown, while the other is taking part at below of the piston crown. In the combined engine presented here, the chamber at below of the piston crown is used as the expansion volume of the Stirling engine while the other chamber is being used as operational volume of the Diesel engine. In this study the thermodynamic performance of the Hybrid engine was investigated via using statistical values of common Diesel engines. For Stirling engine; 800 K heater surface temperature, 392 K cooler surface temperature, 800 W/m2K heat transfer coefficient in regenerator, 300 W/m2K heat transfer coefficient in cooler and heater, 250 rad/s engine speed and 12.5 bar air charging pressure were used as principal inputs. The output power of the Diesel engine was assumed to be 120 kW which provides 120 kW heat to Stirling engine. The heat transfer areas of cooler, heater and regenerator were optimized as 0.33 m2, 0.6 m2 and 4.6 m2 respectively. The optimum thermal efficiency and power of the Stirling engine were determined as 47 % and 24 kW. The total thermal efficiency of the combined engine is expected to increase 6 % compared to the stand-alone Internal Combustion engine. For 12.5 bar average gas pressure in the cylinder of Diesel engine, the working fluid mass in the Stirling engine was determined as 17g

A Potential Method to Predict Performance of Positive Stirling Cycles Based on Reverse Ones

There are two kinds of working mechanisms for the Stirling cycle, i.e., the positive and the reverse cycles, and a Stirling engine (SE) can be operated as a Stirling refrigerator (SR). This indicates that a probable practical method for evaluating the performance of a Stirling engine is to run it as a refrigerator, which is much easier to operate. For this purpose, an improved Simple model for both the positive and the reverse Stirling cycles, considering the various loss mechanisms and actual operating conditions, is proposed and verified by a self-designed Stirling engine. As to the positive cycle with helium and nitrogen at 2.8 MPa, the model errors range from 5.4–11.3% for the indicated power, and 1–10.2% for the cycle efficiency. As to the reverse cycle with helium and nitrogen, the errors of the predicted input power range from 7.9–15.3% and from 2.5–10.9%, respectively. The experimental cooling temperatures can reach −92.2 and −53.6 °C, respectively, for the reverse cycle with the helium and nitrogen at 2.8 MPa. This Stirling-cycle analysis model shows a good adaptability for both the positive and the reverse cycles. In addition, the p-V maps of the positive and reverse cycles are compared in terms of “pressure ratio” and “curve shape”. The pressure ratio of the reverse cycle is significantly higher than that of the positive one at the same mean pressure. A method is proposed to predict the indicated work of the positive Stirling cycles using the reverse ones. A mathematical model to predict the indicated power of the positive Stirling cycles based on the reverse ones is proposed: Wheat2−Wcool1=A·(Tge2−Tgc2Tgc1−Tge1)B. The most critical issue with this method is to establish an associated model of the temperatures of the expansion and the compression space. This model shows a good adaptability for both the positive and the reverse cycles and can provide detailed information for deep discussion between the positive and the reverse cycles.

Free-Piston Stirling Engine Technologies and Models: A Review

The Stirling engine is an alternative solution to produce cleaner energy in order to achieve the reduction of the fossil fuel consumption and the CO2 emissions. It comprises an external combustion engine that can convert any external heat source into mechanical power, through cyclic expansion and compression of a working gas in a closed-regenerative cycle, with or without driving mechanisms. The free-piston Stirling Engine is significantly preferred because of the absence of any mechanical linkage resulting in longer operating life, lower noise pollution, maintenance and vibration free, self-starting and high thermal efficiency. The aim of this paper is to summarize the research works on the free-piston Stirling engine technologies and models. First, the working principles of the free-piston Stirling engine are described, identifying different configurations. Then, several applications are presented. Finally, a detailed review of the models available in literature is given, pointing out the main assumptions and equations.

The application of an innovative integrated Swiss-roll-combustor/Stirling-hot-end component on an unpressurized Stirling engine

An innovative integrated Swiss-roll-combustor/Stirling-hot-end component is proposed in this paper. A power generation system in conjunction with a Stirling engine is also built around the component and tested. The Stirling engine is a compact-size, unpressurized, γ-type engine that uses air as working gas. The Swiss-roll combustor is laden with small catalytic beads to decrease the ignition temperature and improve combustion efficiency. Experiments respectively burning dimethyl ether and syngas were conducted to better understand the potential of the system on tapping into green biomass energy. The marriage between the Swiss-roll combustor and the Stirling engine’s hot end offers many advantages as follows: The structural support from the spiral-channel wall in the Swiss-roll combustor enables the bottom wall of the Stirling engine to be made very thin, which improves the rate of heat transfer from the heat source to the engine significantly. Meanwhile, the system inherits those advantageous features in combustion from the Swiss-roll combustor, including a broader range of fuel/air ratio, higher combustion efficiency, and higher efficiency in harvesting the heat of flue gas. Compared to the predecessor of the present engine, the incorporation of the proposed component is proven to improve engine’s performance remarkably. In the experiment of burning dimethyl ether, the system produced 18.7 W of electric power and achieved 2.4% thermal to electric efficiency under a temperature difference of 254 °C. Such performance is remarkable among atmospheric-pressure Stirling engines. The proposed component has accomplished its design goal and would hopefully inspire new ideas for the development of green-energy Stirling-engine power generation systems in the future.

Thermo-environmental analysis of a new molten carbonate fuel cell-based tri-generation plant using stirling engine, generator absorber exchanger and vapour absorption refrigeration: A comparative study

This study aims to present a novel tri-generation plant consisting of a molten carbonate fuel cell (MCFC) unit coupled with a Stirling engine (SE), a heat recovery steam generator (HRSG), and two types of absorption refrigeration cycles (ARCs), i.e., Generator Absorber eXchanger (GAX) and Vapour Absorption Refrigeration (VAR). The proposed system is evaluated from energy, exergy, as well as environmental impact (3E) points of view. To carry out the parametric study, three sub-models are also introduced for the whole system. The sub-model (1) investigates the solo MCFC with the new configuration. In the sub-model (2), the SE and HRSG are added to boost the power generation and overall system efficiency through employing the heat wasted in the sub-model (1). In the last sub-model, for cooling purposes, the surplus heat of MCFC is reutilized using an absorption refrigeration cycle. Besides, to make a comparative study between GAX and VAR systems, the sub-model (3) is classified into two different schemes: (a) with a VAR cycle, and (b) with a GAX cycle. The results reveal that the exergy efficiency and CO2 emissions of the sub-models (1), (2), and (3) are 48.04%, 51.24%, 52.35% (VAR cycle), 52.12% (GAX cycle), 0.388 t/MWh, 0.364 t/MWh, 0.357 t/MWh (VAR cycle), and 0.358 t/MWh (GAX cycle), respectively. Either with GAX or VAR cycle, the proposed system indicates an acceptable standard of functionality in thermodynamic and environmental perspectives.

Experimental and Simulation Study for Two LTD Stirling Engines

AbstractThe low temperature difference (LTD) Stirling engine is important for solar power application. This study focuses mainly on the influence of physical and geometrical parameters on the opera...

COMBINED POWER PLANT OF A MOTOR VEHICLE

Currently, the most promising areas of development of motor transport are an increase of the horsepower characteristic of their power plants as well as increase of fuel efficiency, and reduction of the toxicity level of exhaust fumes. An internal combustion engine as a power unit of the car in a number of operation modes (supplemental motion, small work load, idling, etc.) works extremely inefficiently and contains the high concentration of harmful components in the exhaust fumes. Additionally, in a context of growing shortage of carbohydrate fuels and increase in their value, the problem of the fuel-burn improvement is especially acute. To improve the environmental compatibility and efficiency of power plants of the vehicles, combined cycle power plants are used. One of the most important problems that the machine construction faces is the creation of environmentally friendly and economical power plants. A hybrid power plant, which contains several power units operating on different physical principles, is proposed by the authors. The main power unit uses the energy of liquid or gaseous fuel in the mode of an internal combustion engine; the auxiliary power unit which is made as a reverse volumetrical driving machine with swinging motion of the work tools (forcers or blades), uses air power which comes from a pneumocylinder through a cooler and / or pneumatic air tank. The auxiliary power unit is equipped with a reversible invertor of the driving direction, made on the basis of a spherical slider-crank mechanism. This insures the operation of the auxiliary power unit in the mode of a pneumatic motor or compressor in accordance with the algorithm generated by the electronic control unit of the combined power plant of the vehicle. To utilize the heat energy of the exhaust fumes of the main power unit, the combined power plant is additionally equipped with a Stirling engine or steam generation module and a steam engine; in order to break energy recuperation of the vehicle it is additionally equipped with a hydraulic or electrodrive. Naturally, when choosing the specific forms of application of combined cycle power plants, any combinations of auxiliary power units are possible. They can be supplemented and / or specified based on the knowledge of specialists. Combined cycle power plants are technically complete solution. Their industrial applicability is obvious and is substantiated by experiments. Nowadays, the creation of a combined cycle power plants of a vehicle, which are a combination of several engines operating on different physical principles is the task of great economic importance. Combined power plants this allows to reduce fuel consumption per 100 km significantly, increase energy potential, horsepower characteristic and improve the environmental performance of the vehicle. The work is planned to be continued in the direction of optimization synthesis of auxiliary power units that work on different physical principles.