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A 20 watt thermophotovoltaic (TPV) battery substitute system is being developed that will provide higher storage capacity and lower weight than the batteries currently used for many military missions. It can also be instantaneous recharged by refueling with propane. The TPV battery substitute incorporates several advanced design features. These include: an evacuated and sealed enclosure for the emitter and photovoltaic (PV) cells to minimize unwanted convection heat transfer from the emitter to the PV cells; a selective tungsten emitter with a well matched gallium antimonide PV cell receiver, spectral control optical filters to recycle non-convertible radiant energy, and a silicon carbide thermal recuperator to recover thermal energy from the exhaust gases. The design of the system and fabrication of the components are discussed.

An organic Rankine-cycle system (ORCS) operating on the heat from the exhaust gases of a truck diesel engine is described. The addition of an ORCS to a long haul diesel truck can improve the fuel economy by 15% over a typical duty cycle. This represents a potential reduction of 1.8 billion gal/yr (120,000 barrels/day) in near-term transportation fuel requirements. Emission levels will also be reduced by an amount equal to the gain in efficiency. At current diesel fuel cost, the potential fuel savings also provide an economic incentive to the fleet operator to invest in the added cost of a bottoming cycle system. Results from tests conducted with a Mack 676 diesel engine and an organic Rankine bottoming cycle (not specifically designed for this application) are presented. At the peak power condition, 36 additional horsepower was produced, a gain of 13% in power without additional fuel.

Three steam engine driven prototype portable generator sets ranging in power from 100 W (e) to 1500 W (e) are described. To a large extent, these sets have demonstrated the potential capability of the Rankine cycle for low noise, low exhaust emissions, high reliability, acceptable efficiency, and multi-fuel operation. Design criteria used in the development of these units and their general applicability to reciprocating Rankine cycle systems are discussed. Recent developments make this power cycle attractive for commercial applications in present sizes as well as in scaled-up versions.