Performance and size assessment of ORCs in mobile military power generation

Abstract: In this study the suitability of small-scale organic Rankine cycles in military power generation is evaluated. It is presupposed that external combustion engines have favorable characteristics in terms of noise, heat and vibration signals.The work is conducted through a process consisting of three blocks; working fluid selection, component selection and modeling. The research community states that the optimal fluid is a matter of application. Therefore, a screening of working fluids is performed on the basis of a few key properties. A simplistic cycle model is used to determine the operating conditions that yield the best thermodynamic performance. Consequently, these conditions are the starting point of the component selection process. Each component that is selected introduces restrictions to the cycle. The upper pressure is, for example, limited by the material of the boiler. Therefore, an iterative selection methodology is employed in order to consider both cycle performance and component limitations. In the last block the model is refined with realistic properties of the selected components. Size and performance of the system are evaluated for electric outputs between 0.1 and 3.0 kW. The model is realized in Excel VBA and constructed for high user flexibility.It is found that the thermal efficiency is proportional to the size of the system. A water-methanol mixture passes the screening process and provides the best cycle performance. Also, scroll expanders are recommended as the prime mover of the system. With the proposed components, the realizable power range is between 1.8 and 3.0 kW. The most critical components, in terms of size, are the expander and condenser. Finally, this study indicates that the system can be built in sizes competitive to existing solutions.