354 1134





3000 2000 1000 0 5 10 15

Fto. 18.7. Energy density of mctnl/oxidant combinations on a weight and volume basis

(after Mnttavl a al. 1969).

weight. In this case, the bulk modulus of the rcactants should equal that of the ambient sea-water in order to minimize changes in buoyancy during storage periods.

10. The reactants should be economically feasible.

Unfortunately no combination meeting all these requirements has been located. A preferred combination is the metal lithium with various halogen compounds, sulphur hexafluoride or chlorine trifluOride. The halogen compounds, identified generally by the proprietory term ;Freons\ and sulphur hexafluoride SF<, arc safe oxidants for storage and handling purposes. They combine with lithium in an intense but non-violent reaction accompanied by the release of heat. Some details of the experimental work on open and closed systems have been given by Mattavi el ai (1%9). Average temperatures outside the reaction zone ranged from 650 to 1040 °C (1200 to 1900°F) and were easily controlled by the admission of an oxidant.

Weight and volume estimates for Stirling-engine underwater power-systems energized by metal combustion are shown in big. 18.8 (Mattavi el ai 1969) as a function of the mission duration and for the three power levels 7.3, 37, and 74 kW (10, 50, and 100 hp). These curves are directly comparable with the corresponding data for thermal storage given in Fig. 18.5. Comparison of the data indicates that a metal-combustion system could be about half the size and one-third the weight of a thermal-storage system of equivalent power on a mission of similar duration.

Pcrcival (1967) presented the interesting comparison reproduced in Fig. 18.9 of the weight per horsepower of various underwaie! ^rOpulsioji systems as a function of the hours of Operation. This comparison indicated the metal-combustion system to be far superior to any other candidate. In the same paper Percival also presented a comparison of torpedo propulsion systems. This is reproduced in Fig. 18.10 and again the Stirling engine with metal combustion emerges as the preferred candidate.

The interest in underwater power systems at General Motors stimulated a renewal of interest in double-acting engines to achieve a more compact design (Mattavi ct ai 1969). In particular the Siemens arrangement of a multiple-cylinder double-acting engine driving a wobble-plate or swash-plate received substantial attention. This configuration, shown in Fig. 18.11, is clearly ideally suited for a torpedo drive. Substantial effort was invested in the development of swash-plate drive systems of improved performance (Maki and Dellart 1971).

Following the abrupt termination of the General Motors program iti 1970 (Percival 1974). the General Motors work on underwater power systems was not entirely lost. Philips appears to have taken over much of it. As described in Chapter 12, all the Philips development effort in the

¿ithiutn fuel • -reon 115 oxidant Sulphur hcxailuoride oxidant

Mission duration (hrl

Mission duration (hr)

Lithium fuel

Frcon 115 oxidant

Sulphur hcxalluor.dc oxidant

Fig. 18.8. Weight and volume requirements as a lunction of power level and mission duration for Stirling-engine underwater power-system with metal combustion (after Mattavi eial. 1969).

1970s has been devoted to Siemens-type swash-plate engines. The automotive engines being developed by Philips for Ford under Department of Energy sponsorship are swash-plate engines. It is ironic that an engine which started life as a torpedo motor at General Motors will most likely end up a decade later as the automotive engine of its principal competitor.

Philips also continued work on metal combustion as an energy source for underwater power systems. Two papers (van dcr Sluys 1975, and

FlO. 18.9 Comparison of the specific power of different underwater power systems (after

Pcrdval 1967).

FlO. 18.9 Comparison of the specific power of different underwater power systems (after

Pcrdval 1967).

Lead-acid battery »

Stirling engine heal storage (Li F)

Lithium-chlorine battery

Stirling engine metal combustion (Li-Freon)

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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