Totalenergy Systems

A total-energy or co-generation system is an ensemble of machinery utilizing a single or varied energy source to provide a range of utilities in a building or plant. Typically the total energy plant in the basement of an office building is supplied with natural gas fuel. Combustion of the gas produces heal, part of which is used in an engine to drive electric generators providing high frequency (400 cycle per second) power for lighting and low frequency (60 cycles per second) power for other purposes. The waste heat may be utilized to generate high-pressure steam for heating, for process purposes or. in an absorption chiller, to produce chilled water. Similarly low pressure steam or hot water may be produced for laundry heating and bathrooms.

Stirling engines appear to be well suited for use in total energy systems as prime movers, heat pumps, or refrigerating engines. The particular characteristics of the Stirling engine which are advantageous in total energy applications arc, primarily, the multifuel capability, quiet operation, minimal exhaust emissions, excellent part-load efficiency, and good starting, control, and torque characteristics.

Walker (1967) appears to have been the lirst to consider Stirling engines for total-energy systems in a survey carried out for the Institute of Gas Technology. loiter Jaspers and du Pre (1973) assessed the prospects of the Stirling engine in total energy systems to be highly favourable.

Lehrfeld (1977a) analysed, very comprehensively, the use of Philips Stirling engines in total energy systems in a variety of applications, commercial and hospital buildings, residential apartment buildings, and offices. This study was summarized (Lehrfeld (1977b) and further referred to in a survey of the Stirling engine for co-generation applications. Co-generation is a term used interchangeably with total energy to describe an on-site electric power plant fulfilling electric power demands while utilizing waste heat from the prime mover to supply heating and/or cooling requirements. Marciniak ci a! (1978) of the Argonne National Laboratory carried out an assessment of potential applications of Stirling engines in total and integrated energy systems as part of the U.S. Department of Energy Total Energy Technology Alternatives Studies (TETAS). Simultaneously workers at NASA Lewis Research Centre were engaged in similar studies for industrial-plant applications of Stirling-engine total-energy systems as part of the U.S. Department of Energy Co-generation Energy Technology Alternatives Studies (CETAS).

Somewhat earlier Gadsby (1977) assessed the market potential for Stirling engines in the 750 kW (1000 hp) range in relation to industrial diesel and gas-turbine engines, in an ellort to define limits and targets for U.S. government funding priorities.

This chapter on model Stirling engines was contributed by Mr. Andrew Ross, of Columbus, Ohio. Mr. Ross is an attorney at law and an avid collcctor of historical Stirling engines and related memorabilia. He is a machinist par excellence and has an intuitive grasp of engineering fundamentals permitting the reduction to practice of his creative ingenuity. G.W.

introduction

The increasing interest among professional engineers and scientists in Stirling-cycle machines has created a corresponding interest among model-building engineers. Such engineers are amateurs in the best sense of the word; they design and make their own engines, clocks, and other mechanical devices in home workshops for the sheer enjoyment of it. Although their experimental Stirling-engine work is still at an early stage of development, it is nevertheless worthwhile to review what they have accomplished on limited time and modest resources.

The 65 cm3 (4 in3) rhombic-drive engine illustrated in Fig. 20.1 was originally 'completed' in 1973 by Ross of Columbus, Ohio, after a year of spare-time effort. On its initial test it did not run. After helpful correspondence with several professional engineers in the field, Ross rebuilt this engine to reduce heat leaks and dead volume. In the revised configuration it immediately ran, although initially it produced a mere 1.5 watts at 750 rpm, at atmospheric pressure.

Various modifications were made in the burner and the regenerator, and vast improvements in performance resulted. The most important of these modifications was the development of a high-temperature annular propane burner. The engine now reliably produces well over 25 watts on air at atmospheric pressure, over 50 watts on air at 0.2 MN/m2 (301b per sq in), and over 75 watts on helium at just over 0.2 MN/m3 (301b per sq in), as is shown in Fig. 20.2. Although it has been run at internal pressures of up to 0.4 MN/m* (601b per sq in), power tests have not been conducted at these higher pressures.

Typical efficiency figures are 4 per cent nei thermal efficiency (power out/fuel in) on helium, 17 per cent internal thermal efficiency (power out/fheat into cooler-¡-power out]) on helium and 14 per cent internal thermal efficiency on air.

Among the regenerator matrices tested were stainless wire, steel wool, stainless wool, stainless woven cable, stainless foil, and quartz wool. The metal wool, cable, and foil generally worked well, but the quartz wool was a disaster; its fibres were blown to and fro throughout the engine, necessitating a thorough clean-up.

Solar Stirling Ensine Parts

PiO. 20.1. Rhombic-drive model Stirling engine. Piston displacement 65 cm3. By A. Ross

Fig. 2u.2. Power/speed characteri>tic> for 65 cm1 Ross rhomhic-drivc Stirling engine and

38 cm3 Vee Engine.

Fig. 2u.2. Power/speed characteri>tic> for 65 cm1 Ross rhomhic-drivc Stirling engine and

38 cm3 Vee Engine.

Nor were all the modifications on this engine successful. For example, a low dead-volume, high surface-area milled aluminum cooler was substituted for the original drilled cast-iron cooler, with essentially no improvement in performance. Eventually, work on this engine was discontinued in the belief that the bearings had about reached their limit.

A piston-displacer vee two cylinder engine of 38 cm' (2.3 in3) piston displacement was then made by Ross. This design used an identical heater regenerator and cooler as the 65 cm3 (4 in ') rhombic. Needle bearings were used on the connecting rods' lower ends to ease bearing problems with the essentially dry crankcase. After certain pumping loss problems caused by a porous crankcase-casting were eliminated, power tests were satisfactory. As can be seen in Fig. 20.2. the engine produced 24 watts on air at 0.2 MN/nr (301b per sq in), and up to 31 watts on air at 0.27 MN/m" (401b per sq in). Subsequent efficiency tests, however, were very disappointing, showing only slightly over 1 per cent net thermal efficiency, with 5 per cení internal efficiency on air anil 6 per cent on helium. During these tests, performance was not up to par, and it is quite likely elusive leaks were at least partly to blame for the poor figures.

Fig. 20.3 shows two simple engines, described by Ross (1976) and Ross (1977b). The engine on the left is a small 12 cm3 (0.73 in3) rhombic-drive

Fig. 20.3. Two Stirling engines by Ross. Engine a: left is ¡1 12cm3 piston displacement engine with rhombic drive. Engine at right ii a two-cylinder Rider-type engine.

machine which, with its annular propane burner, turns a maximum of 3600 rpm on air at atmospheric pressure. A similar engine, built by Thomas, bul incorporating his own external piston and a self-pressurizing pump, produced 4 watts at atmospheric pressure, and 11.5 watts at 0.3 MN/nr (451b per sq in) pressure. The engine to the right is of the two-piston Rider type. The unusual crank geometry shown was added later, primarily as a means of reducing piston side forccs.

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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