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. Phase angles on either side of 90 were selected because it was not known whether an ideal angle was less than or greater than 90. Calculation of mean hot and cold workspace temperatures as well as the engine workspace temperature difference (T) are irrelevant at this point. Der Minassians & Sanders, 2009 The power cylinder specifications and the volume compression ratio established the volume of the rotary displacer at 2.009 in3. ). Table 4 contains the findings for the 120 phase angle test. The experimental setup replicated the simulation conditions. The idea of using the Stirling cycle in hybrid electric applications is not new. Leu (2010) Design analysis methods for Stirling engines. It achieves maximum velocity at 90, followed by deceleration and rest again at 180. 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. The same profile is mirror imaged in the internal surfaces of the two-piece stainless steel displacer housing. Retrieved from Der Minassians, A., & Sanders, S. R. (2009). side.
Thus, PEEK is a very good insulator that will neither absorb nor transmit too much thermal energy. PEEK (PolyEtherEtherKetone) Specifications. Boston: WCB/McGraw-Hill. It is also strong for a polymer and has a high operating temperature ceiling. Beale, 1984 The distance from the eccentric centerline to that of the crank pin establishes the stroke of the engine. Figure 7 shows the assembled engine from the perspective of the cold workspace. The mean T was 100F and the mean RPM was 701. Cup Stirling engine is this type of engine. The consistency of cold workspace temperatures (taken from locations T2, T4, and T5,) indicates sustainable, effective cooling (grand mean of 82F). A rotary displacer, however, never changes direction.
Oberg, Jones, Horton, & Ryffel 2004 The internal configuration of the hot side of the displacer housing is identical to that of the cold side. This space allows for the thermal growth that is inevitable as the segment warms from close proximity with the hot workspace.
Each segment is restricted in its lateral movement associated with this growth, by two retaining rings. These initial temperature and RPM figures are useful, even essential, in stabilizing operation, but that is the extent of their utility.
The SWATT engine was also designed for pressurized helium, which requires a gas-tight enclosure surrounding the flywheel/crankshaft and power piston/cylinder assemblies. Although work on the design parameters it still under way, some unexpected findings regarding one, the phase angle, have come to light. 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. 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. The Gamma Stirling engine is similar to the Beta it that it utilizes the same type of moving parts. displacer type Stirling engine is shown here. This feature is used to increase the efficiency of the cycle by (a) accumulating excess heat from the expanding working fluid, which can then be transferred to the fluid during subsequent cycles, and (b) reducing the amount of heat that must be accommodated by the external heat sink through the cold workspace ( 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). PolyEtherEtherKetone (PEEK) has mechanical and thermal properties that make it ideal for this application. 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. This is characteristic of steady state operation. Contained in Table 8 is a brief summary of findings that support a phase angle of 125. ). , pp. The initial application of this technology, as far as the author was concerned, was in association with the small electric-powered vehicles that were recharged from the grid during non-operational periods. Though high temperatures and RPMs can occur during this time, they do not characterize sustainable operation. 
The 90 phase angle also rendered a mean T of 95F and an RPM of 411. Cold workspace temperatures had a grand mean of 75 F, whereas hot workspace temperatures indicate a grand mean of 175F. Selected contemporary research involving the cycle in environmentally friendly applications is cited. Shortcomings of the Stirling cycle have hindered its wider application in competition with steam, electric, and internal combustion. In 2008, Snyman, Harms, and Strauss investigated applying the Stirling engine to energy generation through waste heat recovery. However, the hot and cold workspaces of the displacer cylinder require the addition of a thermal barrier. Experience running the engine has demonstrated that it needs approximately 20-23 minutes of initial run time to stabilize operation. It is not possible, at this time, to speculate as to why. The displacer is accelerated from rest at 0. Again, temperatures remained consistent. Commercial Stirling engines utilize noble gasses, such as hydrogen or helium, as the working fluid. also studied waste heat recovery for electricity generation utilizing the Stirling cycle. The renewable heat source used in their research originated from a waste incinerator. Integrated into the displacer were the crankshaft/flywheel and a valve mechanism. 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. . The following sections characterize the three prevalent reciprocating piston-type Stirling cycle engines. The interior volume of the displacer housing, excluding the displacer itself and any engine dead space, constitutes the workspace. Displacer. Senft, 2007 It was not possible to start the engine. Understanding Stirling engines. This area contains the bulk of the working fluid and has provisions for the addition and rejection of heat. The mean T from ambient at which initial running occurs is 70F with a corresponding RPM of about 550. The cold port and its passageway represent a heat sink in that they are kept cold by the engines liquid cooling system. Wood, 1991 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. piston is continously warmed by a heat source. , 021013-1-021013-11. In this application, solid biomass fueled a fixed-bed gasifier with a combustor. The Physics Teacher, 28 The mean T was 100F, but the RPM dropped to 738. Both pistons are mechanically connected to a common flywheel and crankshaft. http://www.boedeker.com/peek_p.htm. 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. Despite its shortcomings, the Stirling cycle engine is once again under study, but for entirely different reasons. The displacer of the subject engine is not of one-piece construction.
Lack of run data, however, did provide valuable insight. The author was convinced that the cycle could be effectively achieved with fewer than five moving parts per power cylinder. These provisions subdivide the workspace into the hot workspace and the cold workspace, areas that are thermally insulated from each other. By varying the phase angle on the flywheel/crankshaft assembly, it was possible to experimentally determine an ideal phase angle through observation of tachometer readings. Individual hot workspace thermocouples (T1 and T3) indicated temperatures that remained consistent, but to a somewhat lesser degree than the previous test. To facilitate collection of engine performance data, a test bed was constructed to hold the engine and auxiliary units. These shortcomings include the complexity of design and a relatively low power output per size and weight ( Rather, it is made up of 16 polymer segments, 14 of which are virtually identical. Dead space (dead volume). Cold workspace temperatures had a grand mean of 80 F, whereas hot workspace temperatures indicate a grand mean of 180F. Beale, 1984 Note that the first data row, highlighted in red, shows only time and thermocouple temperatures at the start of the test. (27th ed.). ).
Each of the radial grooves along the inner surface of the cold workspace corresponds to one of the 15 segments not yet in the displacer assembly.
Thermocouple probes are connected to two Fluke 52 II and one Fluke 51 II digital thermometers. Machinable & dense ceramics technical bulletin A1. Biwa, Tashiro, & Yazaki, 2008 The ideal phase angle was found to be remarkably different from that typically attributed to either Beta or Gamma engines, which operate with a phase angle of approximately 90. Minimal surface area for effective heat transfer has been cited as an issue.
A rotary displacer also opens up design options in other ways. 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. Prospect Heights, IL: Waveland Press, Inc. Woodbank Communications, Ltd. (2011). This is not an issue for those components operating within the cold workspace. At the 85 phase angle, the engine started, but it proved very difficult to stabilize, and the test run was aborted. Reduced cycle power needs. The Alpha Stirling engine consists of two power pistons, each with a separate cylinder and connecting rod. This contains test data for the 90 phase angle. Unfortunately, it is difficult to identify a cost-effective material selection that offers such diverse characteristics and is, at the same time, low mass. Initial engine runs, however, indicated ceiling RPM of about 400, which was less than anticipated. and heat engines (with a little bit of thermodynamics). He is a Member-at-large of Epsilon Pi Tau. Hsu, S. T., Lin, F. Y., & Chiou, J. S. (2003). Once the enclosure is complete, the research will commence with optimization of selected traditional Stirling design parameters (e.g., volume compression ratio). The latter is the displacer volume alone. Rather, after combustion imparts work to the mechanism, the remains of the working fluid are expelled from the engine and replaced with fresh mixture. Findings indicate a high level of consistency for virtually all temperature readings. Karabulut, H., Yucesu, H. S., & Koca, A. This insulates the power piston from the high temperatures that exist in the hot workspace. Some dead space is inevitable, but it must be minimized because it is detrimental to the indicated work of the cycle ( , 141-147. ; ). The term stabilize implies that engine RPM is at or very near maximum, and minimal burner adjustment is necessary to maintain that RPM. ). The average T returned to 100F. Therefore, there is no performance data for the first three tests. The RPM statistic represents a major improvement over that obtained with the 90 angle suggested by the literature. The authors findings indicated that actual engine performance could be predicted by the simulation analysis. The Stirling cycle and related terminology is defined. The ends of the housing contain the bearings and provisions for liquid cooling. It is instrumented with five externally mounted surface contact type K thermocouple probes. Wood, B. D. (1991). Beale, 1984 http://www.mpoweruk.com/heat_engines.htm, Figure 1: Alpha Configuration of Stirling Engine, Figure 2: Beta Configuration of Stirling Engine, Figure 3: Gamma Configuration of Stirling Engine, Figure 4: Typical Rotary Displacer Segment, Figure 5: Complete Segmented Rotary Displacer, Figure 6: Open Displacer Housing Showing Cold Workspace and Partially Assembled Rotary Displacer, Journal of Power and Energy Systems, 2(5), Thermodynamics: An engineering approach (3rd ed. Operating principles of Stirling engine. These are reduced cycle power needs and increased design flexibility. A feature consisting of layers or coils of heat-absorbent material located on the internal surfaces of working fluid conduits or passageways. This is believed to be the key feature in terms of simplicity, reliability, and, hopefully, increased power output. Machinerys handbook 
; Eccentrics were constructed to enable engine operation with phase angles of 75, 80, 85, 115, 120, 125, 130, and 135 degrees. Senft, 2002 The Every Stirling engine has a sealed cylinder with one part hot 
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