Energy Sources, Vol.20, No.3, 199-208, 1998
Thermocompression engine cycle with isothermal expansion
An engine cycle based on thermocompression, isothermal expansion, and isobaric reduction in volume is presented in this study. It is a closed cycle utilizing an external heat source; thus application to solar, geothermal, and waste heat utilization may be possible. One aspect of implementing the cycle allows for a heat exchanger located outside the working volume of the engine. This would permit a much larger heat transfer area than current Stirling cycle engines can accommodate, thus lending to higher practical efficiency without the penalty of increasing the dead volume of the device. Expressions for the ideal thermal efficiency and maximum work output point are derived. Results show a lower ideal efficiency than the Carnot cycle for all relevant expansion ratios, although for moderate expansion ratios, the deviation is not large if the temperature ratio exceeds 3. Furthermore, the efficiency at which most engines operate, the so-called maximum work output point, is similar to that derived from finite-rate analysis of Otto and Brayton cycles.