Under these operating conditions, the reliability of the heater head assembly is influenced by the ultimate creep behavior of the material used. Therefore, the design is always a balance between minimizing thermal losses while maintaining structural integrity. Stirling Engine Generator Hot Air Stirling Engine Model with Colorful LED - Enginediy The Stirling engine is mainly constructed by metal, so the Stirling engine model is heavy thereby can work stably on table. One of the wonderful things about the United Kingdom is there’s a great tolerance of eccentricity and enough people have the talent and money to do interesting things like building a Stirling engine to power a boat. The largest stress occurs at the bottom flange and is 106.9 MPa at a temperature of 115°C. Results of Stirling engine design analysis model. Login to your personal dashboard for more detailed statistics on your publications. There are many types of Stirling engine but all works in the same process. Lastly, fixed supports are applied to the faces where the flexures are connected to the displacer assembly. For the beta configuration the displacer and power piston are housed in the same cylinder. Or perhaps funding was no longer available. If the cross-sectional area of the heater head wall is further reduced by using a double taper the conduction losses decrease an additional 4%. Hot Air Stirling Engine Motor Model (2-Cylinder) Electricity Generator Model. In the alpha configuration the engine consists of two pistons that are housed in separate cylinders which are connected by the hot heat exchanger, regenerator, and cold heat exchanger. There was a big government-funded research project to put Stirling engines in cars. An evaluation of the use of various superalloys for the manufacturing of heater heads is presented in Ref. Below is a list of all the power producing engine projects we could find in the market place as at this writing. £6.10 . They turned the marketing to a big company that didn’t care and, not surprisingly, the project failed. Both the displacer configuration and dynamics are critical to the performance of the engine, thus during the design of a FPSE, a dynamic analysis of the displacer assembly must be conducted. The same boundary conditions used in the coupled thermal-structural model were used, Figure 7. Regenerators play an important role in the cycle, as the heat stored in the regenerator during the early stage is recovered by the gas in the fourth stage. FPSE are truly a closed cycle system that works using variations in the internal pressure to drive the power piston that is connected to the reciprocating magnets in a linear alternator for energy conversion. HeadquartersIntechOpen Limited5 Princes Gate Court,London, SW7 2QJ,UNITED KINGDOM. (a) Knuckle and dome sections, (b) curved section of regenerator. A Stirling cryocooler made by Janis. The hot heat exchanger in this study is a tubular type heat exchanger which has high heat transfer effectiveness while also exhibiting good fuel source integration capabilities. For example, if the design operation is at 60 Hz the performance should be mapped in the 50–70 Hz range. The diameter and length of the tubes are dependent upon the desired FPSE power output and the fuel combustor used. If you have enough money and would like to hire a company to research a Stirling engine for you and develop another prototype, you are in luck. The limitations on operating frequency are due to the high velocities that can occur in the heat exchanges and regenerators with high frequencies, limited flexure spring forces for a given geometry, and the proximity to grid power of 60 Hz. The outer wall of the heater head however does experience a large difference in pressure between the inner and outer surfaces. These desirable attributes coupled with the fuel independence of FPSE makes them ideal candidates for use in remote power generation applications, particularly where maintenance is a high concern such as in NASA deep space missions, solar power generator, and combined heat and power systems. In the hot space area, the dead volume occurs in the knuckle section, Figure 4a. The predicted temperature and stress distributions are shown in Figure 15. Most of these are set up to produce both heat and electricity at a high combined efficiency level. Engineers love to engineer and marketers love to market. A modern Stirling engine and generator set with 55 kW electrical output, for combined heat and power applications. At least one person has died in such an explosion. One application where FPSE are gaining interest is in combined heat and power (CHP) because of its operation on a closed cycle, FPSE can be run on a variety of fuels such as solar [1], biogas [2], natural gas [3], waste gas [4] etc. There is a curved section at the top of the regenerator that is designed to fit into the space between the knuckle wall and displacer cylinder wall of the heater head to reduce the detrimental dead volumes. If the foil spacing changes, the performance dramatically reduces. Because FPSE have no manual linkages and they use clearance seals both the reliability and life expectancy of the engine are increased as there is no wear in the system. How? Usually, the prototypes weren’t thrown away. Starting with little model engines that generate just enough electricity to light an LED Light to large 25 KW Stirling engine generators that power many homes. The first thing you should know is that you shouldn’t waste your time trying to buy one at your local construction supply store because they won’t have one. So, it never was a good match between the technology and the application. State of the art Stirling engines have efficiencies near 40%. Thus, additive manufacturing can be used to produce a robust foil regenerator that can achieve the theoretically high figure of merit and vastly improve the performance of modern FPSE. However, the development of modern high-temperature superalloys has drastically increased the operational temperature of Stirling engines to nearly 1200 K. Research is ongoing to use cutting-edge manufacturing techniques such as additive manufacturing of metals to further increase the efficiency, improve the reliability, and reduce the manufacturing cost of the next generation of Stirling engines. The general engineering analysis and numerical modeling approaches of Stirling engines will be discussed, followed by a section of engine design and efficiency calculations. The high surface area and efficiency of the vertical U-shaped tubular heater head makes it ideal for use in larger Stirling convertors. The main reason the dynamic analysis is conducted is to determine the number of flexures required. A Stirling engine is a heat engine that works on the basis of an external applied temperature difference. As the size of the gaps is reduced the thermal losses decrease however if they become to small it leads to unwanted wear on both the moving and non-moving components resulting in a reduction in the expected lifespan of the convertor. Furthermore, novel flow guides were used to increase the convective heat transfer around the tubes to further improve the system efficiency. Model Stirling engines High Quality Educational models. Therefore, the use of emerging manufacturing techniques can help to achieve higher system efficiency, better reliability, and enhanced robustness while reducing the cost. Robert Stirling who sought to create a safer alternative to the steam engines, whose boilers often exploded due to the high steam pressures used and limitations of the primitive materials available at the time. The key to the high efficiency of the Stirling engine is what Stirling called an economizer but it more commonly referred to today as a regenerator [2]. The foils radially deform a maximum of 0.6 mm although this level of deformation may seem detrimental, there is only a 0.01 mm maximum deformation between foils. A combined heat and power unit, made by Whispergen. The 6-part tapper has the lowest conduction losses of the four cases shown. While the effects of jetting into the regenerator may be small for a random fiber regenerator where the flow can radially distribute within the regenerator, it is highly detrimental to the performance of a foil type regenerator where the flow in between foils cannot spread radially. Can Home Shop Machinists build a credible Solar Stirling Electric Generator? The heater head assembly not only experiences high pressures, but also a large thermal gradient. There are a lot of home machine shops and small machine shops with enough capability to make a small Stirling engine that produces some power. *Address all correspondence to: songgang.qiu@mail.wvu.edu, Energy Conversion - Current Technologies and Future Trends. The efficiency of an ideal Stirling cycle approaches that of a Carnot cycle which depends only on the hot and cold temperatures. Additionally, the geometry of the tubes can be manipulated to further improve heat transfer with the chosen fuel sources burner. The temperature difference between the coolant and the working gas in the cold heat exchanger is significantly smaller than that seen in the hot heat exchanger therefore the cold heat exchanger is typically larger compared to the hot heat exchanger. The addition of the diffuser in the plenum space between the hot heat exchanger and the regenerator increases the Stirling convertors efficiency although there are added flow losses across the diffuser. Thermo USB charger. The continuing depletion of fossil fuel resources has led to the increase of global research into sustainable energy. I started this website, www.stirlingengine.com, in 1998 and I had been interested in Stirling engines for a couple of years before that. While monolithic heater heads are cheap and easy to manufacture, they have a limited heat flux and often used for small convertors. 4. where a is the distance between the flexure stacks centers and wheelbase, b is the distance between the center of gravity of displacer assembly and flexure stacks centers, Kr is the total radical spring rate of the flexures, m is the total moving mass of displacer assembly, and g is the gravity of earth. When people are considering buying a Stirling engine, they will always compare it to some other power producing option. A rocking mode analysis is used to determine the natural frequency of the system rocking mode to ensure that it is far from the operating frequency. The dead volume can be reduced as well as minimizing flow separation by adding a curved section to the bottom of the heat exchanger. But then, that engine will have to compete in the marketplace with gasoline and diesel engines that have been priced reduced over many, many generations. The thermal and structural boundary conditions are shown in Figure 14b–d. Engineers developing new Stirling engines should pay very close attention to how much the customers they hope to sell to will pay per watt of power. And whether you call them Stirling Engines, Atmospheric Engines or Hot Air Engines, there’s not much difference. Another major design challenge is the thickness of the pressure vessel wall. This allows for a reduction in the total amount of thermal energy input to the engine leading to an increase in the cycle efficiency. The estimated axial conductions losses for the cases shown are listed in Table 2. Aibecy Mini Hot Air Stirling Engine Motor Model Electricity Generator X9B2. We are IntechOpen, the world's leading publisher of Open Access books. The rocking mode analysis is also used to determine the height between flexure stacks and verify the quantity from the dynamic analysis. Keep your first do-it-yourself project very close to a well-proven design with good performance. Webs are designed to strengthen the regenerator and to keep the foil spacing unchanged. Stirling engines are capable of reaching 50% efficiency, which far outperforms the steam engine. The velocity of the displacer assembly is calculated using Eq. £47.05. The tolerance needed to achieve the optimal gap size requires high precision machining and often additional finish machining is required to obtain the desired fit. A detailed description and numerical simulation of the flow guides and burner interface for the enhancement of heat transfer is available in Ref. The now-bankrupt WhisperGen of New Zealand made some Stirling engines for combined heating power. In addition to the maximum stress in the entire assembly, the maximum and membrane stresses for the individual displacer assembly parts has to be evaluated. Figure 7 shows four types of wall profiles often used. [13]. In addition to the design constraints and approaches of various components, dynamic and rocking mode analyses of the engine are also presented. There are some engines that are available as complete, ready-to-use products today. Using additive manufacturing to reduce the thermal losses are possible by reducing the dead volumes between the heat exchangers and regenerator through controlling the size and shape of these plenum spaces. To achieve a long operational life of a FPSE, the hot end of the heater head assembly must withstand high temperatures and pressure over extended periods of time. For the thermal model, the bottom portion of the heater head assembly is set to 80°C and the outer surface of the hot heat exchanger tubes has an applied temperature of 810°C. Using FEA, the robustness of the regenerator is investigated. However, using additive manufacturing, the tubular heat exchanger and pressure vessel can be printed as one continuous part eliminating potential leaks and greatly increase the reliability. Thus, the geometry of the knuckle and dome region must be optimized to balance axial conduction loses, localized stress, and dead volume. This reduces the length of the extended heater tubes, thus decreasing the dead volume. The system efficiency (fuel to electricity) is around 38.3%. The maximum stress of 64.5 MPa occurs at the interface between the displacer cap and the displacer body connector. The current state of the art in additive manufacturing has a limit on the minimum thickness based on the nominal diameter of the powder metals used. However, the shape of the tube can be manipulated based on the feedback from additive manufactures and to increase the heat transfer, Figure 5. As seen in Figure 14a, the flexures are separated into two stacks. The thickness at the cold end can also be decided based on the local allowable stresses at the rejection temperature. If it is, it can result in rubbing of the displacer on the pressure vessel inner wall leading to unwanted wear and a decrease in lifespan (Table 3). If you have any questions or if you’ve found other sources of Stirling engine generators, please leave them in the comments below. Based on the creep and rupture life properties of Inconel 625, for the designed presented at locations C it would take over 6000 hours to reach an estimated 2% creep. This has resulted in the resurrection of the forgotten Stirling engine which is an external combustion engine unlike the more widely known Otto and Diesel engines which are internal combustion engines. Free-Piston Stirling Engine Generators, Energy Conversion - Current Technologies and Future Trends, Ibrahim H. Al-Bahadly, IntechOpen, DOI: 10.5772/intechopen.79413. By maintaining a hot and cold temperature difference the engine is able to run and produce mechanical power. This stress is well below the yield stress of Inconel 718 even at high temperatures leading to large margins of safety. This model can be used to predict dimension of the Stirling engine components as well as the estimated performance of the engine. Because of their compact multi-cylinder configuration, alpha type engines were explored by the automotive industry as high specific power outputs are possible [2]. Theoretically, a foil regenerator would have the best performance as it has the highest possible figure of merit which is the ratio of the heat transfer coefficient to the friction coefficient. £74.99 £ 74. And, they are likely to be very generous with assisting a new hobbyist in starting to build a new engine that could work. Check out our complete list of Combined Heat and Power Systems that are available for purchase on our recommended page. Therefore, FPSE manufactures use a less efficient albeit more reliable regenerator to ensure consistent operation. Like other heat engines the Stirling engine converts heat energy into mechanical energy. The authors declare no conflict of interest. Thus, based on variations in fabrication and uncertainties a total of 10 flexures shall be chosen. Free postage. This makes designing a FPSE more complicated as the performance of each individual component is tied to the other parts of the engine. Perhaps the style in granting research money changed and they didn’t get the next generation of grants. Microgen’s Free Piston Stirling Engine is the result of the meticulous engineering and development of a high tech, game changing solid-base technology with a focus on carefree and lifelong use. I’m not recommending any of these companies. Therefore, the spacing between the foils remains constant even at high temperatures. For the other cases considered a non-linear profiles forms.