The contributions to Stirling engine technology made by General Motors in the period 1958-1970 were summarized by Percival (1974) as follows:

1. Their program developed smokeless, turbine-tvpe burners and the direct ignition of diesel fuel.

2. Their program developed complete, self-contained Stirling Ground Power generator sets and introduced these to the U.S. Army Research Laboratories for evaluation. These were the only modern low-noise engine packages to formally-specified military performance tests

3. Their program developed the first precision-control constant-speed governor for Stirling engines, which embodied entirely new-concepts to the field of governing and which accomplished the following:

(a) Speed variation at constant load per cent

(b) No load to full load droop \ per cent

(c) 100 per cent sudden load change, off speed surge of 4 per cent and recovery in 6 seconds.

4. Their program developed the first automatic fuel controls for starting a Stirling engine over a wide ambient temperature range, without smoke emissions.

5. It developed the first engine to be manually started and operated entirely from hydraulic controls.

6. It developed two new hydrogen compressor systems having zero leakage capability.

7. It developed the first mechanical temperature control of proven reliability for many thousands of hours.

8. 'Hie program also initiated and completed analyses and tests of low-cost regenerator materials, particularly the proprietary MetNet material, which have shown a reduction in cost per unit power output over 50 to 1.

9. It made detailed cost and design studies with several General Motors' Divisions of a 35 kW (50 hp) single-cylinder engine, which included cost reduction techniques in cylinder construction, pre-heater sheet metal construction, and simplified crankcase construction.

10. The program made the following contributions to the analysis of the Stirling cycle:

(a) It corrected errors in cooler calculations so that thermodynamic cycle heal rejection and cooler heat transfer rate were equal.

(b) ft introduced routine How measurements of heater, cooler, regenerators, and assemblies, to provide correct data for calculation of How losses.

(c) 11 developed a theory for heal flux distribution on the Stirling heater tubes and ran experiments to show the effect of radically different heat How patterns.

(d) It made the first analytical and experimental determination of heat transfer film coefficients on the heater tubes and concluded they were 2 to 3 times greater than could be deduced from the literature.

(e) It developed an original analysis of combined thermal and pressure stresses in non-uniform wall cylinders.

(f) It added and refined calculations related to drive mechanisms.

I L. The program developed piston-sealing technology which included the following items:

(a) Systematic piston-seal studies to eliminate white-metal clearance seals which were Philips' standard at the beginning of program.

(b) The first screening of Teflon and other self-lubricated materials (in the Allison Division studies).

(c) A method of measuring piston leakage in operating engine.

(d) Experimental verification of accuracy of piston-seal leakage power loss.

(e) Data indicating an optimum combination of piston-seal leakage and friction.

(f) Concepts for controlling the relationship between working-

space and buffer-space pressures by slots in cylinder walls.

(g) Basic ideas tor the present Rulon piston rings (the development of the rings used in all Philips and OMR engines is a closely integrated result of contributions from both sources).

12. The program developed new engine-drive mechanisms and explored different types of cylinder/piston arrangements, including the following, which were all designed and tested:

(a) The first modern, four-cylinder, 275 kW (350 hp) phase-angle control engine, which could also be directly reversed (Electromotive Division).

(b) The first 'W' configuration, double-acting engine of 100 kW (140 hp) (Electromotive Division).

(c) The idea of swash-plate-type axial Stirling engines (the program provided analytical and experimental verification of the low-friction characteristics of properly designed swash-plate mechanisms with hydrodynamic type bearings).

(d) The first hermetically-sealed 7.3 kW (10 hp) engine with pressurized crankcase (Allison Division).

(c) A single crank-displacer engine of 7.3 kW (10 hp).

(f) The first minimum weight. 1.5 kW (2 hp) *V' type displacer engine, with separated cylinders, which could be adapted to isotope heat sources.

(g) The first 90 k\V (120 hp), four-cylinder, in-line double acting Stirling engine for a proposed bus installation. The General Motors program was cancelled as testing just started.

13. The program developed special fuels and heat sources as follows:

(a) The only potassium-sodium (NaK) heated engine, under a Government contract (Allison Division.)

(b) The concept of thermal energy (heat) storage with the Stirling engine. (Initial work on heat storage began at G.M. Research in the early 1950s and led on to the first heat-storage power-plant using specially shaped aluminum oxide pellets; the first Stirling-engine automobile (the Calvair) with heat supplied from an aluminum oxide heat-storage container: and tests on lithium fluoride and lithium hydroxide as energy storage materials, including a joint program with Oak Ridge National Laboratory which determined suitability of various alloys for containment of lithium fluoride.)

(c) Tests to demonstrate controlled combustion of lithium fuel with Freon oxidizers, including operation of a Stirling engine from lithium combustion heat.

(d) The first Stirling engine with natural gas fuel.

Tabic 13.2. Summitry of design or lest

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Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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