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I Iiti I ,T Ti Ti 1 NASA-TM-86875 NASA TM-86875 19?tJCJOI/S-8S I iiti I ti I lii ,t ti i I LI LANGLEY RESEAHCH CENTER .. L.IBRARY, NASA VIHGINIA Lanny Thieme .. N ional Aeronautics and Space Administration Lewis Research Center 1 Prepared for 111111111111111111111111111111111111111111111 NF00096 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Printed in the United States of America Available from National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, VA 22161 NTIS price codes1 Printed copy:A02 Microfiche copy: A01 1Codes are used for pricing all publications. The code is determined by the number of pages in the publication. Information pertaining to the pricing codes can be found in the current issues of the following publications, which are generally available in most libraries: Energy Research Abstracts (ERA); Government Reports Announcements and Index (GRA and I); Scientific and Technical Abstract Reports (STAR); and publication, NTIS-PR-360 available from NTIS at the above address. DOE/NASA/51 040-58 NASA TM-86875 Initial Testing of a Variable­ Stroke Stirling Engine Lanny G. Thieme National Aeronautics and Space Administration Lewis Research Center ClevE~land, Ohio 44135 February 1985 Work performed for U.S. DEPARTMENT OF ENERGY Conservation and Renewable Energy Office of Vehicle and Engine R&D Washington, D.C. 20545 Under Interagency Agreement DE-AI01-77CS51 040 INITIAL TESTING OF A VARIABLE-S1ROK~ SllRLING ~NGINE Lanny G. Thieme National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135 SUMMARY As part of the Department of Energy's Stirling Engine Highway Vehicle Systems Program, NASA Lewis is investigating the use of variable stroke as an alternative to the complex mean-pressure control system for controlling the power output of an automotive Stirling engine. For this purpose the Advenco (Advanced Engine Concept) Stirling engine has been purchased from Philips Research Laboratories of the Netherlands. The Advenco ;s a four--cylinder, double-acting engine designed for a maxi­ mum engine output of 44 kW with hydrogen working fluid at a design mean com-­ pression-space pressure of 10 MPa. Variable-stroke operation is achieved with a variable--angle swash-plate drive system. The stroke can be varied from 10 mm at a 50 swash-plate angle to 48.5 mm at a 22 0 swash--plate angle. Steady-state performance tests were run over a limited range of stroke, mean compression-space pressure, and engine speed with helium working fluid. For constant pressure and speed, the engine power output varied approximately with the square of the stroke. Considering all testing to date (with helium working fluid) the maximum brake power and brake gross thermal efficiency ob­ taioed were 5.10 kW and 19.3 percent, respectively. These values were recorded for a run at 5 MPa mean compression-space pressure and a 35 mm stroke, While attempting to continue an upward progression of pressure and stroke, a major drive system failure occurred. A sleeve on one end of a crosshead seized in its bore, causing extensive damage to the drive system. Repairs and corrective measures were completed before resuming testing. These included properly aligning the crosshead bores in the two separate crankcase sections, plating the crossheads rather than sleeving, and adding pressurized lubrication to the crosshead bores of the rear crankcase. Finally. computer simulation predictions were made comparing- steady-state performance at part loads obtained tow ways: (1) by varying the stroke at maximum pressure (variable-stroke control) and (2) by varying the pressure at maximum stroke (mean-pressure control). These predictions indicated a part­ load efficiency gain for variable stroke control that increased with increasing engine speed and decreasing power level. These efficiency gains are primarily due to lower flow losses through the heat exchangers and to reduced heat losses that tend to decrease with reduced stroke and pressure ratio (such as shuttle losses). This work was done in support of the U.S. Department of ~nergy (DOE) Stirling Engine Highway Vehicle Systems Program. The NASA Lewis Research Center, through interagency agreement DEAIOl-77CS51040 with DOE, is responsible for management of the project under the program direction of the DOE Office of Conservation, Division of Vehicle and [nergy R&D. The power output of most kinematic Stirling engines is varied by changing the mean pressure level of the working fluid. For automotive applications a 'complex mean-pressure control system is required with attendant reliability and maintenance problems. Also. with this control system the many connections to the working space add more potential leakage paths for the working fluid. These possible problems have raised interest in investigating alternatives to the mean-pressure control system for controlling the power output of a Stirling engine. This interest led to the purchase of the Advenco (Advanced Engine Concept) Stirling engine from Philips Research Laboratories of the Netherlands. The engine is a four-cyl"inder. double-acting engine designed for a maximum engine output of about 44 kW with hydrogen working fluid. The major difference be­ tween this and current kinematic Stirl'ing engines is the use of variable stroke as a method of power control. The stroke is varied with a variable-angle swash-plate drive system. Philips tried two other advanced concepts in their original version of this engine. One was using ceramic liners in the regenerator housings and cylinders of the heater head to reduce the amount of expensive heat-resistant materials needed in the engine. The use of liners would permit the use of an inexpensive steel for the housing. However. problems were encountered in in­ stalling the liners into the heater head. Thus. the engine as delivered to Lewis has a standard all-metal heater head without the ceramic liners. The other new idea was to enclose the rollsock shaft seal in a cartridge assembly to allow for easier replacement. This assembly is used on the engine as pur­ chased by Lewis. The objectives of the Advenco testing at Lewis are as follows: (1) To evaluate the benefits of variable-stroke control (relative to mean­ pressure control) in terms of increased engine efficiency. reduced control--system complexity, and reduced working-fluid leakage (2) To evaluate the variable-angle swash-plate drive as a system for ob­ taining variable stroke (3) To investigate any functional problems of operation over a range of strokes The Advenco engine has been installed in a test cell at Lewis Research Center. Planned testing includes a steady-state evaluation over a range of ,strokes and pressures to allow comparison of engine performance obtained (1) by varying pressure at constant stroke and (2) by varying stroke at constant pressure. Following the steady-state tests a simplified transient evaluation ,of the power control system will be made. Initial testing concentrated on solving a number of problems involving the power control system, the sealing areas in the cooling block, the rollsock cartridge assembly, and the seals on the rotating preheater core. With every­ thing functioning properly. steady-state tests with helium working fluid were begun. Thirty-six data points were taken before a major failure occurred in 2 the crankcase. A sleeve on one end of a crosshead seized in its bore causing extensive damage to the drive system. Repairs and corrective measures were made before testing was resumed. This report describes the Advenco Stirling engine and its test setup at lewis. Results of the initial tests are presented as well as a description of the drive system failure and subsequent engine modifications. Several computer simulation predictions are shown comparing steady-state performance obtained by varying stroke with that obtained by varying pressure. APPARATUS AND PROCEDURE Description of Advenco Stirling Engine The Advenco engine is a four-cylinder, double-acting Stirling engine designed for a maximum output of about 44 kW with hydrogen working fluid. The Advenco was built by Philips Research Labs of the Netherlands. The engine burns natural gas as a fuel and uses rollsock shaft seals. The drive system is a variable-angle swash-plate drive which varies piston stroke to control engine power output. The stroke can be varied from 10 mm at a 5° swash-plate angle to 48.5 mm at a 22° swash-plate angle. The design mean-pressure level is 10 MPa. The efficiency was maximized at a part-power condition corre­ sponding to a 14° swash-plate angle and a 4500 rpm engine speed. Figure 1 presents photographs of the Advenco engine in its test facility at Lewis, and figure 2 shows a cross-section of the engine. The Advenco engine is further described as originally manufactured by Philips Research Labora­ tories in reference 1. Burner-preheater system. - Natural gas enters the vortex gas burner (fig. 3) through the two long tubes entering the top of the burner and is injE~cted into the mixing chamber through small holes in the vertical distri­ bution struts. Air for combustion enters between the struts as well as through the burner cone.
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