), Turkish Journal of Engineering and Environmental Sciences, 24(2), International Journal of Energy Research, 26(12), Journal of Energy in Southern Africa, 19(3), http://www.aremco.com/products/machinable-dense-ceramics/.htm, http://sleekfreak.ath.cx:81/3wdev/VITAHTML/SUBLEV/EN1/STIRLING.HTM, http://www.robertstirlingengine.com/principles.php, Contact Scholarly Communication at Virginia Tech, Check Out Recent Publications from Virginia Tech Publishing. The latter is the displacer volume alone. The displacer piston moves the air (displaces PEEK (PolyEtherEtherKetone) Specifications. These include: tensile strength of 16 ksi, compressive strength of 20 ksi, maximum operating temperature of 480F, thermal conductivity of 1.75 BTU-in./ft.2-hr.-F, and a coefficient of thermal expansion, 2.6 X 10-5in./in./F ( Figure 6 shows a single displacer segment in a partial assembly with half of the displacer housing. All modern engines encountered in day-today use operate on a well-known cycle characteristic of their operation. The idea of using the Stirling cycle in hybrid electric applications is not new. Because there is a patent pending on the engine, it is now possible to release some design and performance information. The Beta Stirling engine included design features that eliminated the hot seal failure issues of the Alpha. Rather, after combustion imparts work to the mechanism, the remains of the working fluid are expelled from the engine and replaced with fresh mixture. A single displacer segment is shown here to clarify the internal configuration of the housing, the cold workspace. , p. 472). In the 360 rotation representing one complete cycle, the displacer changes direction twice. Its function is to simply shuttle working fluid within the hot and cold workspaces. The displacer is a reciprocating piston that moves along the axis of the displacer housing, thus alternately communicating the working fluid to the hot and cold workspaces of the engine ( Also included in their research was an experimental setup, using an instrumented Beta Stirling, which was powered by exhaust gases from the combustion of propane. The mean T at initial start is noteworthy. This area contains the bulk of the working fluid and has provisions for the addition and rejection of heat. (2006). Aremco Products, Inc. (2011). also studied waste heat recovery for electricity generation utilizing the Stirling cycle. A crank pin, which engages the power piston connecting rod, screws into the eccentric. . Beale, 1984 Retrieved from This table, however, can be condensed through the elimination of the run data accrued during the 23-minute stabilization period. stirling engine solar energy engines plans stirlingengine cycle generator heat illustration displacer sterling build motor own temperature courtesy company american

When the gas is on the hot side it expands and pushes up on a piston. stirling engines gamma type engine mechanical ohio edu This is the second consecutive drop in RPM, and it represents a substantial loss from the peak RPM value obtained with a 125 phase angle. , 4-19. In order to run the engine, various auxiliary units must be connected. http://www.boedeker.com/peek_p.htm. Unlike a piston, the displacer does not require a tight tolerance seal along its surfaces. In the preceding explanation, the reciprocating and rotating part count was always prefaced by the phrase in simplest form. The reality of conventional commercial Stirling design seldom if ever adheres to the simplest form. Contained in Table 6 are findings from the 130 phase angle test. , 021013-1-021013-11. Figure 7 shows the assembled engine from the perspective of the cold workspace. A basic knowledge of selected Stirling engine terminology will help the reader understand the narrative pertaining to contemporary engine configurations. Der Minassians, A., & Sanders, S. R. (2009). This engine has been under development for approximately 10 years, and much of this time has been spent on design and fabrication. Dr. Phillip R. Foster is an Associate Professor in the Department of Engineering Technology in the College of Engineering at the University of North Texas.

Also affected are the physical design, the axial orientation (vertical vs. horizontal), and displacer surface topology (i.e., its axial cross-section). These are mechanical cycles in which the working fluid, a fuel-air mixture, does not undergo a thermodynamic cycle involving cooling to the initial state. A complete cycle may require one or two 360 revolutions ( Design analysis methods for Stirling engines. ). Advances in Mechanical Engineering The ends of the housing contain the bearings and provisions for liquid cooling. Senft, 2002 A feature consisting of layers or coils of heat-absorbent material located on the internal surfaces of working fluid conduits or passageways. This arrangement does not add additional moving parts, but it effectively directs the working fluid in the following way. Obtaining reliable, sustained engine operation coupled with reasonable power output, however, constitutes the real problem. The 90 phase angle also rendered a mean T of 95F and an RPM of 411. http://www.aremco.com/products/machinable-dense-ceramics/.htm, Beale, W. (1984).

The SWATT engine is a Stirling, however, it functions best with a phase angle that is significantly different from other Stirling engine configurations. Optimizing the power generation of a radiation driven Stirling engine used in the combustion chamber of an incinerator. The balancing holes, in the fully assembled displacer, are filled with an expanded foam insert that has a very low mass coupled with a high temperature resistance. The distance from the eccentric centerline to that of the crank pin establishes the stroke of the engine. Renewable Energy, 28 Findings indicate consistency in all cold workspace temperature readings (grand mean of 82F). piston is continuously warmed by a heat source. The displacer is accelerated from rest at 0. Keywords: Stirling engine, electric power generation, renewable energy. In this application, solid biomass fueled a fixed-bed gasifier with a combustor. ; Journal of Energy in Southern Africa, 19(3) Senft (2007, p. 64) The following sections characterize the three prevalent reciprocating piston-type Stirling cycle engines. Snyman et al., 2008 stirling gamma type engines engine piston mechanical ohio edu studied the viability of biomass as a heat source for small-scale electrical generation using the Stirling engine. This space allows for the thermal growth that is inevitable as the segment warms from close proximity with the hot workspace. stirling engines gamma ltd type engine mechanical ohio The researchers selected the free-piston Stirling because crank-driven Stirling engines presented some challenging design problems, including power modulation, leakage of working fluid, isolation of lubricants, etc. (Hsu et al., p. 61). Findings indicate a high level of consistency for virtually all temperature readings. This expansion is easily accommodated in the sizing of the corresponding workspace for a given segment, even though the stainless grows very little by comparison. The hot workspace piston and cylinder do represent a problem with regard to maintaining a reliable seal in an environment with high heat coupled with sliding friction. The Stirling cycle is a reversible thermodynamic cycle consisting of four phases: heat addition (isovolumetric heating), expansion (isothermal expansion), heat rejection (isovolumetric cooling), and compression (isothermal compression). Further, it is essential to an understanding of the major objectives of this article, that is, the discussion of an innovative rotary displacer Stirling engine. However, gases with lighter molecular weight (i.e., helium or hydrogen) provide thermodynamic advantages over air. B. The authors findings indicated that actual engine performance could be predicted by the simulation analysis. Experience running the engine has demonstrated that it needs approximately 20-23 minutes of initial run time to stabilize operation. This represents steady state and the performance remains basically unchanged for the length of an individual test run (maximum to date of about six hours). Workspace. During isovolumetric heating (expansion), therefore, the hot working fluid is inhibited from moving through the cold passageway, even though pressure throughout the engine is the same. Wood, 1991 Increased design flexibility. Though high temperatures and RPMs can occur during this time, they do not characterize sustainable operation. The hot port and its passageway represent thermal energy input, being in communication with the hot workspace. ). (1990). These are reduced cycle power needs and increased design flexibility. The type of stainless steel used in the water-cooled displacer housing is AISI 304, which has a much lower coefficient of thermal expansion, 9.6 in./in..-F ( Wood, B. D. (1991). Note that the first data row, highlighted in red, shows only time and thermocouple temperatures at the start of the test. Manufacturing and testing of a v-type Stirling engine. piston is continuously cooled. Their findings demonstrated the difficulty in simulating actual engine performance, but on a larger scale, these authors pointed the way for other researchers to pursue the topic. , pp. beta ks18 stirling engine type stirlingengine run models gyroscope assembled ass If left unfilled, balancing holes would add substantially to the engines dead space. (1992). The Beta, in its simplest form, consists of four reciprocating parts and one rotary part. When the displacer rotates through its cycle, it alternately blocks and opens the hot and cold ports. stirling engine gamma animation works Reciprocating displacers limit the design options available for optimizing engine operation. Thus, PEEK is a very good insulator that will neither absorb nor transmit too much thermal energy. Actual commercial engines are typically more complex (i.e., have more moving parts per power cylinder). Data from thermocouples monitoring hot workspace temperature (T1 and T3), however, display some variability that was not evident in previous tests. Cengel, Y. The interior volume of the displacer housing, excluding the displacer itself and any engine dead space, constitutes the workspace. Understanding Stirling engines. Dead space (dead volume). All of these configurations utilize the conventional piston, crankshaft, and cylinder arrangement, but two of the three (i.e., Beta and Gamma) use them in conjunction with a uniquely Stirling cycle addition, the displacer. Reduced cycle power needs. Adoption of a rotary displacer over a reciprocating one provided two significant advantages. This insulates the power piston from the high temperatures that exist in the hot workspace. The ratio of the maximum engine volume to the minimum engine volume is referred to as the volume compression ratio ( Rather, it is made up of 16 polymer segments, 14 of which are virtually identical. The Gamma power piston does not share a common cylinder with the displacer. ; Again, temperatures display consistency. The conduit that joins the two workspaces, however, adds to the dead space associated with this design. This permitted the use of one of several relatively new engineered polymers. It is instrumented with five externally mounted surface contact type K thermocouple probes. Regenerator. The Gamma shares the same advantages as the Beta and also holds the potential for being mechanically simpler. The average T returned to 100F. Regardless, it is situated 180 from the hot port and lies on the same circular centerline in the side of the displacer housing. piston is continously warmed by a heat source.

The same profile is mirror imaged in the internal surfaces of the two-piece stainless steel displacer housing. Individual hot workspace thermocouples (T1 and T3) indicated temperatures that remained consistent, but to a somewhat lesser degree than the previous test. These function according to the Otto cycle. The displacer housing consists of four major components, all of type 304 stainless steel. The junction of Beta hot and cold workspaces must include an additional thermal barrier to reduce conduction and maintain efficiency. Multiphase Stirling engines.

When in the hot workspace, the working fluid is heated, its pressure increases and it expands, thus moving a power piston and doing work. ). Hsu, S. T., Lin, F. Y., & Chiou, J. S. (2003). These are located at various positions to collect temperature distribution data.

When the displacer shuttles the working fluid into the cold workspace, it is cooled, its pressure is reduced, and the power piston compresses the working fluid back to its original volume ( These ports are positioned immediately adjacent to the stepped profile groove occupied by the first displacer segment. An engine performance log was developed to standardize data collection during phase angle testing. It is not possible, at this time, to speculate as to why. For example, high stiffness, low weight, low thermal conductivity, and high thermal resistance are also very desirable displacer material characteristics. Deep discharge always required excessive grid time recharging and could also be potentially damaging to the batteries. Materials selected included stainless steel for all major structural components, graphite for the piston, titanium for the connecting rod assembly, and polymer for the rotary displacer. (1), 59-69. Journal of Solar Energy Engineering, 131 Their work focused on the utilization of three design analysis methods for simulating the optimization of a Beta configuration Stirling engine utilizing waste heat.

Also recorded were the mean hot workspace temperature, the mean cold workspace temperature, and the temperature difference (T) between each. The same results occurred with the 80 phase angle. These provisions subdivide the workspace into the hot workspace and the cold workspace, areas that are thermally insulated from each other.

Every Stirling engine has a sealed cylinder with one part hot This gas, referred to as the working fluid or working gas, is commonly air. All temperatures were recorded in degrees Fahrenheit (F). The author was convinced that the cycle could be effectively achieved with fewer than five moving parts per power cylinder. Strong, A. This feature provides excellent thermal isolation for the two workspaces. Thermocouple probes are connected to two Fluke 52 II and one Fluke 51 II digital thermometers. the Coffee Cup engine should never be warmed with any heat source hotter Machinerys handbook

; The storage batteries used by these vehicles provided sufficient charge for intra-city commuting for up to four hours, after which recharging was necessary. Energy is consumed in both acceleration and deceleration. A representation of this form is depicted in Table 1. It has been documented on all engine tests utilizing the 125 phase angle. Some dead space is inevitable, but it must be minimized because it is detrimental to the indicated work of the cycle ( ). . Although work on the design parameters it still under way, some unexpected findings regarding one, the phase angle, have come to light. Robert Stirling, in 1816, developed and patented the air engine that bears his name. Calculation of mean hot and cold workspace temperatures as well as the engine workspace temperature difference (T) are irrelevant at this point. Retrieved from Therefore, in its simplest form, the Gamma configuration also consists of four reciprocating parts and one rotary part. A similar statement can be said of hot workspace temperatures taken from locations T1 and T3 (grand mean of 177F). (1998). Heat-transfer aspects of Stirling power generation using incinerator waste energy. This arrangement is shown in Figure 1. When assembled, only one orientation is possible. Each will be briefly discussed. The rotary part was the displacer. Der Minassians & Sanders, 2009 The last three quantities are calculated and recorded post test. Major subassemblies have been identified. Its design employs two distinct cylinders, a feature evident in Figure 3. Prospect Heights, IL: Waveland Press, Inc. Woodbank Communications, Ltd. (2011).

Descriptions and figures are generic interpretations of these configurations. Retrieved from This condition is termed steady state, and once achieved, heat input and RPM output remain relatively consistent over the duration of the engine test run. The average RPM recorded during the test increased to 789, the highest yet obtained. For example, four-stroke reciprocating internal combustion engines utilize spark ignition. This arrangement is shown in Figure 2. Boston: WCB/McGraw-Hill. Although it seems to cluster around or at 100F, it is not speculated that this has any relationship whatsoever to a maximized RPM for a given phase angle. These shortcomings include the complexity of design and a relatively low power output per size and weight ( Early research in this area, as cited in the introductory sections of this paper, indicates a potential contribution. Three conventional engine configurations that utilize a reciprocating power piston and crank shaft (the Alpha, Beta, and Gamma) are characterized, in terms of minimum number of components, advantages, and disadvantages. Gras, P. (2011). ), Journal of the Chinese Institute of Engineers, 32(1), Fundamentals of engineering thermodynamics (2nd ed. , 71-80. The internal configuration of the hot side of the displacer housing is identical to that of the cold side. Of particular consequence is the configuration of the first displacer segment. Senft, 2007 The four phases, which constitute one complete cycle, are completed in a single 360 revolution. than boiling water. It was proposed that the cycle be represented by three moving parts, two reciprocating and one rotary. An eccentric having the 90 phase angle suggested by the literature was initially built with the engine. Unfortunately, it is difficult to identify a cost-effective material selection that offers such diverse characteristics and is, at the same time, low mass. The really significant optimization, however, will focus on the configuration of the rotary displacer itself. Had the test procedure specified temperature measurements in C, the derived values for mean T would not have appeared so calculated.. The vehicles could operate somewhat longer, however, failure to recharge at this point would shortly cause a condition known as deep discharge. Upper Saddle River, NJ: Pearson Prentice Hall. Therefore, there is no performance data for the first three tests. The Alpha is known for its high power-to-volume ratio. Click the following links to see the principles of operation The term stabilize implies that engine RPM is at or very near maximum, and minimal burner adjustment is necessary to maintain that RPM. The hot workspace temperatures indicate a grand mean of 176F. The complete setup has been operable for about two years and has accrued data from about 120 hours of run time. (2000). Further, its mass contributes to that required by the flywheel/crankshaft assembly that is essential to the Stirling cycle. This is characteristic of steady state operation. Using a segmented displacer that had a stepped profile that could enhance the heat transfer area was possible because the displacer was rotary. stirling engine heat modern piston engines type space diagram energy stirlingengine above peltier applications device faq structure animation shown figure Biwa, T., Tashiro, Y., & Yazaki, T. (2008). Additionally, the right-hand end contains features that contribute to the rotary valve mechanism as well as the means for the hot and cold workspaces to communicate with the power piston. It was not possible to start the engine. Because the initial engine configuration successfully employed a 90 phase angle, the difficulties encountered with angles of 75, 80, and 85 demonstrated that if there were potential for improved engine RPM performance through phase angle manipulation, that manipulation would involve phase angles of 90 or more. Cengel & Boles, 1998 ; Worldwide concern over global warming and depletion of nonrenewable energy sources has renewed interest in the Stirling cycle being used for generating green or sustainable energy. The design of Stirling engines is such that the internal spaces contain a gas that is alternately heated and cooled during the cycle but is unable to escape from the mechanism. helium, or hydrogen) is moved by a mechanism from the hot side to the cold The six holes adjacent to the stepped area balance the segment by removing a mass equivalent to that removed in the creation of the stepped profile.

The experimental setup replicated the simulation conditions. Karabulut, H., Yucesu, H. S., & Koca, A. The displacer piston always moves in advance of the power piston. The log provided for manual recording of the time of an observation, the temperatures at the five thermocouples, and the RPM. The fabrication of this enclosure is incomplete at this writing. It is also strong for a polymer and has a high operating temperature ceiling. Contemporary engines display a range of mechanisms, some fairly complex, to change linear motion into rotary. No attempt has been made to describe or render the complexities associated with actual working engines. 2-3). This has been provided for information purposes only. The Alpha Stirling engine consists of two power pistons, each with a separate cylinder and connecting rod. Although its appearance is radically different from Alpha, Beta, or Gamma Stirling engines, the SWATT engine definitely functions on the Stirling cycle (i.e., the nonconsumed working fluid is alternately heated and cooled but always returns to its initial state with each revolution). Oberg, E., Jones, F. D., Horton, H. L., & Ryffel, H. R. (2004).

During the initial 20 minutes of operation, however, constant adjustment of the burner is required. The space below the displacer Therefore, no engine energy is consumed in the constant acceleration-deceleration associated with the reciprocating arrangement. Woodbank Communications, Ltd., 2011 Working fluid (working gas). ; ). Snyman et al., 2008 the air) from the hot side to the cold side. Beale, 1984 The consistency of cold workspace temperatures (taken from locations T2, T4, and T5,) indicates sustainable, effective cooling (grand mean of 82F). Again, temperatures remained consistent. The renewable heat source used in their research originated from a waste incinerator.

This contains test data for the 90 phase angle. Fundamentals of engineering thermodynamics (2nd ed.) Recent research provides ample evidence.

Reciprocating piston-type Stirling engines, particularly the Alpha, the Beta, and the Gamma, have been harnessed in these applications and have been reported to be effective. and the other cold.

There is a renewed interest in the Stirling cycle for sustainable and/or environmentally friendly electrical generation. ). side. Eccentrics were constructed to enable engine operation with phase angles of 75, 80, 85, 115, 120, 125, 130, and 135 degrees. , 2010, 1-7. stirling gases engines Other performance characteristics have been observed during the initial running of the engine.

One segment retaining ring also appears clearly. The internal ends of the housing are faced with PEEK seals to prevent thermal conduction. This controls the opening and closing of the hot and cold ports and also the duration of same as well as any overlap, during which times both ports are simultaneously open. Flue gas from the combustor provided the energy input for the Stirling engine-generator set. Because the displacer segments are individually located along the axis of the housing using retaining rings, their relatively large coefficient of expansion is of consequence for a relatively short lateral dimension, their individual thickness. New York: Industrial Press.

A design in which there is sharing of a common cylinder presents thermal conduction issues not encountered in the Alpha. Thus, most innovation in Stirling engine design has not been adopted. This instrumentation displays data that provides the mean hot workspace temperature, the mean cold workspace temperature, and the resulting difference in temperature (T). (27th ed.). This reformatting (see Table 2), which will be used in the discussion of remaining phase angles as well, makes it possible to compile means for temperatures and RPMs that are not influenced by startup fluctuations. New York: Cambridge University Press. key points. The rotary displacer can be long, can incorporate features for increased surface area, and can still function from ambient to operating temperature within the close confines of the stainless housing. Individually balanced, each has a stepped profile along about 180 of the outer circumference (see Figure 4), which is evident along the lower half of the segment in the figure. Operating principles of Stirling engine. Table 5 contains the findings for the 125 phase angle test. Clearances between the rotary displacer and the housing are tight to minimize dead space but sufficient to ensure no contact. Initial engine runs, however, indicated ceiling RPM of about 400, which was less than anticipated. The radial displacement of the crank pin, in relation to that of the rotary displacer, establishes the phase angle.

Senft, J. R. (2007). A new type of Stirling engine that employs a segmented rotary displacer and other related design improvements is presented along with preliminary findings from engine test runs. The SWATT engine was also designed for pressurized helium, which requires a gas-tight enclosure surrounding the flywheel/crankshaft and power piston/cylinder assemblies. The heat source was an incinerator. Another design feature that is possible because of the rotary displacer is a rotary valve integral with the first displacer segment and the adjacent portion of the housing. These engine configurations, in their simplest form, utilize four reciprocating parts and one rotary part (per power cylinder).

This configuration requires a close tolerance fit between each power piston and its respective cylinder. Any given engine has a maximum volume and a minimum volume. Senft, J. R. (2002).

International Journal of Energy Research, 26(12) Table 4 contains the findings for the 120 phase angle test. Cold workspace temperatures had a grand mean of 75 F, whereas hot workspace temperatures indicate a grand mean of 175F. The displacer represents a major improvement. This would eliminate the added cost of individual on-board Stirling engines and would enable the use of exclusively electric propulsion without extra demands on the power grid. For this reason, it was decided that all test runs in the phase angle study would be 31 minutes in duration with a 23-minute stabilization period, during which collected data would not be utilized to assess the effectiveness of a given angle.



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