Thermoelectric Stirling Engine (TEG-Stirling Engine) Based on the Analysis of Thermomechanical Dynamics (TMD)

The thermoelectric energy conversion technique by employing the Disk-Magnet Electromagnetic Induction (DM-EMI) is examined in detail, and possible applications to heat engines as one of the energy-harvesting technologies are discussed. The idea is induced by the analysis of thermomechanical dynamics (TMD) for a nonequilibrium irreversible thermodynamic system of heat engines, such as a drinking bird and a low temperature Stirling engine, resulting in thermoelectric energy generation different from conventional heat engines. The current thermoelectric energy conversion with DM-EMI can be applied to wide ranges of machines and temperature differences. The mechanism of DM-EMI energy converter is categorized as the axial flux generator (AFG), which is the reason why the technology is applicable to sensitive thermoelectric conversions. On the other hand, almost all the conventional turbines use the radius flux generator to extract huge electric power, which uses the radial flux generator (RFG). The axial flux generator is helpful for a low mechanoelectric energy conversion and activations of waste heat from macroscopic energy generators such as wind, geothermal, thermal, nuclear power plants and heat-dissipation lines. The technique of DM-EMI will contribute to solving environmental problems to maintain clean and sustainable energy as one of the energy harvesting technologies.

The Application of Thermomechanical Dynamics (TMD) to Thermoelectric Energy Generation by Employing a Low Temperature Stirling Engine

A thermoelectric generation Stirling engine (TEG-Stirling engine) is discussed by employing a low temperature Stirling engine and the dissipative equation of motion derived from the method of thermomechanical dynamics (TMD). The results and mechanism of axial flux electromagnetic induction (AF-EMI) are applied to a low temperature Stirling engine, resulting in a TEG-Stirling engine. The method of TMD produced thermodynamically consistent and time-dependent physical quantities for the first time, such as internal energy ℰ(t), thermodynamic work Wth(t), the total entropy (heat dissipation) Qd(t)and measure or temperature of a nonequilibrium state T˜(t). The TMD analysis produced a lightweight mechanical system of TEG-Stirling engine which derives electric power from waste heat of temperature (40˚CT100˚C) by a thermoelectric conversion method. An optimal low rotational speed about 30θ′(t)/(2π)60(rpm) is found, applicable to devices for sustainable, clean energy technologies. The stability of a thermal state and angular rotations of TEG-Stirling engine are specifically shown by employing properties of nonequilibrium temperature T˜(t), which is also applied to study optimal fuel-injection and combustion timings of heat engines.

The Application of Thermomechanical Dynamics (TMD) to the Analysis of Nonequilibrium Irreversible Motion and a Low-Temperature Stirling Engine

We applied the method of Thermomechanical Dynamics (TMD) to a low-temperature Stirling engine, and the dissipative equation of motion and time-evolving physical quantities are self-consistently calculated for the first time in this field. The thermomechanical states of the heat engine are in Nonequilibrium Irreversible States (NISs), and time-dependent thermodynamic work W(t), internal energy E(t), energy dissipation or entropy Qd(t), and temperature T(t), are precisely studied and computed in TMD. We also introduced the new formalism, Q(t)-picture of thermodynamic heat-energy flows, for consistent analyses of NISs. Thermal flows in a long-time uniform heat flow and in a short-time heat flow are numerically studied as examples. In addition to the analysis of time-dependent physical quantities, the TMD analysis suggests that the concept of force and acceleration in Newtonian mechanics should be modified. The acceleration is defined as a continuously differentiable function of Class C2 in Newtonian mechanics, but the thermomechanical dynamics demands piecewise continuity for acceleration and thermal force, required from physical reasons caused by frictional variations and thermal fluctuations. The acceleration has no direct physical meaning associated with force in TMD. The physical implications are fundamental for the concept of the macroscopic phenomena in NISs composed of systems in thermal and mechanical motion.

Design of a Transverse-flux Permanent-magnet Linear Generator and Controller for Use with a Free-piston Stirling Engine

Transverse-flux with high efficiency has been applied in Stirling engine and permanent magnet synchronous linear generator system,however it is restricted for large application because of low and complex process.A novel type of cylindrical,non-overlapping,transverse-flux,and permanent-magnet linear motor（TFPLM） is investigated,furthermore,a high power factor and less process complexity structure research is developed.The impact of magnetic leakage factor on power factor is discussed,by using the Finite Element Analysis（FEA） model of stirling engine and TFPLM,an optimization method for electro-magnetic design of TFPLM is proposed based on magnetic leakage factor.The relation between power factor and structure parameter is investigated,and a structure parameter optimization method is proposed taking power factor maximum as a goal.At last,the test bench is founded,starting experimental and generating experimental are performed,and a good agreement of simulation and experimental is achieved.The power factor is improved and the process complexity is decreased.This research provides the instruction to design high-power factor permanent-magnet linear generator.

Influence of quantum degeneracy on the performance of a gas Stirling engine cycle

Based on the state equation of an ideal quantum gas, the regenerative loss of a Stirling engine cycle working with an ideal quantum gas is calculated. Thermal efficiency of the cycle is derived. Furthermore, under the condition of quantum degeneracy, several special thermal efficiencies are discussed. Ratios of thermal efficiencies versus the temperature ratio and volume ratio of the cycle are made. It is found that the thermal efficiency of the cycle not only depends on high and low temperatures but also on maximum and minimum volumes. In a classical gas state the thermal efficiency of the cycle is equal to that of the Carnot cycle. In an ideal quantum gas state the thermal efficiency of the cycle is smaller than that of the Carnot cycle. This will be significant for deeper understanding of the gas Stirling engine cycle.

Design, Manufacture and Measurements of Beta-Type Stirling Engine with Rhombic Drive Mechanism

The purpose of carrying out present work is to design, build and test a rhombic drive Stirling engine with a β-type configuration consisting of two dynamic pistons (displacer and power) reciprocates in the in-line concentric cylinder arrangement. The displacement rod is assembled concentrically inside the power piston rod. The rhombic drive mechanism is proposed in such a way that, by using a pair of gear wheels the sliding motion of both piston rods is controlled and thus, an engine is balanced. The developed prototype has a swept volume of 75 cm3 with the displacer piston and power piston cylinder hot ends heated by liquefied petroleum gas (LPG) burner and cooled water, respectively. It uses air as the working gas at atmospheric pressure for initial charging of the engine. Several designs were studied before settling on a β-type configuration. The LPG gas burner was considered as a potential heat source. The various elements of an engine (heater, cooler, re-generator, flywheel and piping systems) were designed, constructed and analyzed. The testing results revealed that the engine at initial atmospheric air filling started working in only about 120 seconds at an LPG heater temperature of 400℃ (824°F) with 280 rpm. At a heater temperature of 550℃ (1022°F), the engine speed was 630 rpm. At the engine speed of 245 rpm, the maximum torque was 0.215 Nm, while the maximum power was 8 Watts at 355 rpm. Engine speed increased with the increase of flame temperature. Several tests were performed on the engine to improve its running efficiency and critical problem areas were isolated and addressed. Moreover, results revealed that Stirling engines working with relatively low-temperature air are potentially attractive engines of the future, especially LPG powered low temperature differential Stirling engines. The Stirling engine was capable of generating between 50 to 100 Watts of electricity.

Experimental Investigation on Heat Transfer and Combustion of a Stirling Engine Combustor Fueled by Reformed Gas and Diesel Fuel

Thermochemical recuperation heat recovery is an advanced waste heat utilization technology that can effectively recover exhaust waste heat from oxy-fuel Stirling engines.The novel combustor of a Stirling engine with thermochemical recuperation heat recovery system is expected to utilize both reformed gas and diesel fuels as sources of combustion.In this research,the effects of various factors,including the H_(2)O addition,fuel distribution ratio(FDR),excess oxygen coefficient,and cyclone structure on the temperature distribution in the combustor,combustion emissions,and external combustion system efficiency of the Stirling engine were experimentally investigated.With the increase of steam-to-carbon ratio(S/C),the temperature difference between the upper and lower heating tubes reduces and the circumferential temperature fluctuation decreases,and the combustion of diesel and reformed gas remains close to complete combustion.At S/C=2,the external combustion efficiency is 80.6%,indicating a 1.6%decrease compared to conventional combustion.With the increase of FDR,the temperature uniformity of the heater tube is improved,and the CO and HC emissions decrease.However,the impact of the FDR on the maximum temperature difference and temperature fluctuation across the heater is insignificant.When the FDR rises from 21%to 38%,the external combustion efficiency increases from 87.4%to92.3%.The excess oxygen coefficient plays a secondary role in influencing temperature uniformity and temperature difference,and the reformed gas and diesel fuel can be burned efficiently at a low excess oxygen coefficient of 1.04.With an increase in the cyclone angle,the heater tube temperature increases,while the maximum temperature difference at the lower part decreases,and the temperature fluctuation increases.Simultaneously,the CO and HC emissions increase,and the external combustion efficiency experiences a decrease.A cyclone angle of 30°is found to be an appropriate value for achieving optimal mixing between reformed gas and diesel fuel.The research findings present valuable new insights that can be utilized to enhance the performance optimization of Stirling engines.

A novel approach towards the selection of regenerators for optimal Stirling engine performance based on energy and exergy analyses

Regenerators play a vital role in enhancing the overall performance of Stirling engines.Hence,this paper performed an energy and exergy analysis to elucidate the significance of regenerator characteristics concerning system performance,contributing to the optimal regenerator’s design and selection.The relationship between regenerator structure,regenerator exergy destruction,and output power,thermal efficiency,and exergy efficiency for Stirling engines was established by integrating the thermal model of Stirling engines with a mathematical model of regenerators.In contrast to cross-flow and parallel-flow regenerators,a novel concept of inclined-flow regenerators,featuring a matrix surface inclined in the direction of gas flow,was developed to achieve higher and more balanced engine output power and energy utilization efficiency.A comprehensive investigation was conducted into the effects of matrix structure types and regenerator geometries on the performance of both regenerators and engines.The results reveal that,following structural optimization,Stirling engines equipped with the inclined-flow regenerator demonstrate a substantial 16.6%,38.3%,and 37.2%increase in power output,thermal efficiency,and exergy efficiency,respectively,compared to those equipped with cross-flow regenerators.In contrast,when compared to engines fitted with parallel-flow regenerators,they experience a 13.5%reduction in power output but achieve remarkable enhancements of 45.4%and 36.7%in thermal and exergy efficiency,respectively.This study introduces new insights into selecting regenerator structures for enhancing the output performance of Stirling engines.

Transient and Steady Spray Characteristics of Soybean Oil/2,5-Dimethylfuran Blended Fuel in an Underwater Stirling Engine

The reduction of oxygen consumption is a key factor to improve the energy density of underwater Stirling engine.A series of fundamental experiments are carried out to elucidate the spray characteristics of soybean oil/2,5-dimethylfuran(DMF)blended fuel in an underwater Stirling engine.Spray characteristics such as spray penetration,spray angle,spray area,and light intensity level under low injection and ambient pressures are obtained using image post-processing method.The results show that the effects of injection pressure,ambient pressure,and nozzle diameter on the transient spray characteristics of underwater Stirling engine are similar to those of diesel engine.However,in the steady spray process,the injection pressure has little effect on spray near angle,and the spray far angle increases with the increase of the injection pressure.Compared with the spray far angle at injection pressure of 3 MPa,the spray far angle at 5 MPa and 7 MPa increased by 11.38%and 18.14%respectively.The addition of DMF can obviously improve the atomization of soybean oil/DMF blended fuel.The spray angle of blended fuel in transient process increases with the increase of the DMF concentration.The spray near angle has exceeded that of diesel(46.21°)when the DMF volume fraction exceeds 25%.The spray far angle is equivalent to that of diesel when the DMF volume fraction reaches 75%.Moreover,the spray with gas ejection no longer keeps conical,the droplet diameter distribution is more dispersed,and the droplet diameter is smaller.

A bibliometric analysis of Stirling engine and in-depth review of its application for energy supply systems

With the great advantages and continuous innovations,prolific research efforts have been devoted to the Stirling engine(SE)domain driven by the sustainability development.In this study,a bibliometric analysis is conducted to explore the research tend and hotspots of SE.The country co-authorship,institute co-authorship and keyword networks are engendered from the visual map using VOSviewer,showing China ranks the first with the total number of published articles and the majority publications are presented by Chinese Academy of Sciences.Owing to the highest node centrality,the research findings in USA can be considered the most influential and greatly worthy being referred,particularly represented by the early contribution for thermo-acoustic SE.The total 7 keyword clusters are classified through the top terms in Citespace and 4 of them are related to its energy supply system,demonstrating the typical application of SE-based combined heat and power(CHP)and integrated multi-energy complementary system have gained much attention.Based on this,a detailed review of SE-based energy supply systems is further conducted through the system forms,4E performance evaluation and soft model combing optimization solutions.Several relevant issues hindering the improvement of these terms are summa-rized,providing the potential guides to help develop the SE-based energy supply system.

Design and Combustion Characteristic Analysis of Free Piston Stirling Engine External Combustion System

The free piston Stirling engine external combustion system was simulated to investigate the diesel-air combustion characteristics in order to demonstrate its feasibility by computational fluid dynamics(CFD). The different effects on combustion were distinguished by analyzing the combustion burner, the injection position of diesel oil, the front tube arrangement of Stirling heater head and the back fin. The results show that the tilted front tube arrangement of the heater head with the back fin is the best practicable technology while the distance between the diesel nozzle position and the swirler top is 0. Its total heat flux is 15.6 kW, and the average heat transfer coefficients of the front and back tubes are 127 W/(m2· K) and 192 W/(m2· K), respectively. The heat transfer is mainly through convection, and the proportion of radiative heat transfer is only 16.9%. The best combustion efficiency of the free piston Stirling engine external combustion system is 86%.

Development and Test of Combustion Chamber for Stirling Engine Heated by Natural Gas

The combustion chamber is an important component for the Stifling engine heated by natural gas. In the paper, we develop a combustion chamber for the Stifling engine which aims to generate 3-5 kWe electric power. The combustion chamber includes three main components： combustion module, heat exchange cavity and thermal head. Its feature is that the structure can divide ＂combustion＂ process and ＂heat transfer＂ process into two appar- ent individual steps and make them happen one by one. Since natural gas can mix with air fully before burning, the combustion process can be easily completed without the second wind. The flame can avoid contacting the thermal head of Stifling engine, and the temperature fields can be easily controlled. The designed combustion chamber is manufactured and its performance is tested by an experiment which includes two steps. The experi- mental result of the first step proves that the mixture of air and natural gas can be easily ignited and the flame burns stably. In the second step of experiment, the combustion heat flux can reach 20 kW, and the energy utiliza- tion efficiency of thermal head has exceeded 0.5. These test results show that the thermal performance of com- bustion chamber has reached the design goal, The designed combustion chamber can be applied to a real Stifling engine heated by natural gas which is to generate 3-5 kWe electric power.

Thermochemical Recuperation for Stirling Engines by Diesel Steam Reforming: Thermodynamic Analysis

Thermochemical exhaust heat recovery is a prospective way to improve the thermal performance of Stirling engines. Based on Aspen HYSYS software, the simulation model of a Stirling engine combustor with a thermochemical recuperation(TCR) reformer was established to calculate the performance of the TCR system. The reforming temperature, fuel distribution ratio, steam-to-carbon ratio(S/C), and reforming pressure were changed to evaluate their effects on the reforming process and system efficiency. With increased reforming temperature, the equilibrium fuel conversion rate and heat recovery amount in the reformer gradually increase. The maximum combustor efficiency is achieved at the temperature of 600℃ and the fuel distribution ratio of 40%. With the S/C ratio increased from 1 to 2.5, the heat recovery rate and combustor efficiency increase significantly. The results show that the increase of fuel distribution ratio and S/C ratio leads to decreased reforming temperature, and external heat is needed to meet the heat balance for steam reforming. At a given reforming temperature and S/C ratio, increased reforming pressure results in decreased equilibrium fuel conversion rate and reforming reaction heat. At 5 MPa reforming pressure and 550℃ reforming temperature, the efficiency of the Stirling engine combustor is 92.7%, proving that the thermochemical recovery system can be applied to the Stirling engine under high pressure conditions.

Theoretical Research on Stirling Reversible Heat Engine

A mathematical model that describes the relationship between structural parameters and operating parameters was established based on the structure of Stirling reversible heat engine by Schmidt analyses. The calculation formulas of output power and average temperature of Stirling reversible heat engine were deduced, which disclosed the relationship between average temperature and ultimate pressure. A set of theoretical calculation formula of Stirling reversible heat engine was explored by combining definition of efficiency of heat engine. Research results provide theoretical references to design of parts and control system of Stirling reversible heat eneine.

A Theoretical Dynamic Analysis of a Regenerative Heat Exchanger Assembly in a Fluctuating Flow Regime

A fluctuating flow was used to investigate the thermo-fluid characteristic of a regenerative heat exchanger assembly designed, modelled, built and constructed for the used in Stifling engines applications. Vibration of the regenerative heat exchanger assembly was a problem to deal with during the experimental investigation. Hence, a dynamic analysis of the regenerative heat exchanger assembly was undertaken. The main sources of excitation in vibrations of the regenerative heat exchanger assembly were investigated and calculated based initially on the empirical correlations provided in the literature. Thereafter, a mathematical model of the regenerative heat exchanger assembly was developed based on the energy equations for each moving part of the assembly. The kinetic and potential energy equations were formulated for each moving part of the regenerative heat exchanger assembly. From the kinetic and potential equations, the Lag, range operator was defined, and then the Lagrange formulations were used to derive the differential equations representing the dynamic behavior of each moving part of the assembly. The differential equations were integrated to determine the system natural frequencies. These were then compared to the frequency on excitation in vibrations in order to predict the regenerative heat exchanger working conditions despite the existence of vibration in the system.

Analysis and Key Parameter Optimization Design of Leningrader Seal Performance

In order to improve the performance and service life of the Leningrader seal of the Stirling engine piston rod,interference,pre-load and friction coefficient were taken as influencing factors,and the curved surface response method was adopted to reduce the contact stress of sealing surface and von Mises stress of the sealing sleeve as the response index,with the optimization goal of reducing wear and extending life.The above three key parameters are analyzed and optimized,the influence of each parameter on the sealing performance and service life is obtained,and the best combination scheme of the three is determined.The results show that the interaction between pre-tightening force and interference fit has the greatest impact on contact stress.The interaction between interference fit and friction coeffi-cient has the most significant effect on von Mises stress.The optimized parameters can reduce the maximum contact stress and maximum von Mises stress of the sealing sleeve by 26.3%and 20.6%,respectively,under a media pressure of 5-9 MPa.Test bench verification shows that the leakage of the optimized sealing device in 12 h is reduced by 0.44 cc·min^(-1)(1 cc=1 cm^(3)).The wear rate of the sealing sleeve is 1.08%before optimization and 0.45%after optimization,indicating that the optimized parameters in this paper are effective.

Academic fluid power research in the USA

With the formation of the Center for Compact and Efficient Fluid Power （CCEFP） in 2006, there has been a resurgence of academic fluid power research in the USA. The centre’s vision is to make fluid power the technology of choice for power generation, transmission, storage, and motion control. To address fluid power’s key technical barriers, the CCEFP research strategy supports and coordinates pre-competitive research in three thrust areas： efficiency, compactness and effectiveness, where effectiveness means making fluid power safer, easier to use, leak free and quiet. This paper reviews some of the most important results from the first decade of CCEFP research.