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A requirement to dispose of waste oils in remote communities, in an environmentally friendly and cost effective manner, has initiated interest in developing an engine for small electrical power generation that is capable of utilizing waste oils. Through an assessment of numerous engine technologies, it has been determined that the closed Brayton cycle (CBC) engine is most suitable and potentially most cost effective technology for this market requirement. As a result, a program to design and develop a technology demonstration CBC engine has been initiated. The program objective is to initiate the design of an operational, low cost unit that does not necessarily operate at high cycle efficiencies. The CBC engine design is initiated by performing detailed thermodynamic cycle calculations, for which the theory is presented. Cycle arrangement and working fluid is selected based on cycle calculations and CBC engine requirements. Gas operating conditions and component performance specifications are selected by performing a parametric analysis on the effect on cycle performance. It has been decided to utilize air as a working fluid since it is cost-effective to replenish in remote areas. The recuperated free-turbine arrangement has been selected since it offers the highest performance at lowest cost, and offers a simple means of mechanical attachment of the alternator. Cycle efficiency is predicted to be 15.1 percent at the design-point turbine inlet temperature of 1025 K and compressor pressure ratio of 2.98. The compressor inlet temperature and pressure has been selected as 298 K and 119 kPa respectively. Low CBC engine cost is achieved by utilizing off-the-shelf components, which includes application of readily available turbochargers for turbomachinery. The gas generator and the free-turbine turbocharger have been selected. The performance map for each turbocharger has been obtained in order to perform off-design cycle calculations. The design-point compressor, High-Pressure turbine, and Low-Pressure turbine isentropic efficiency is predicted as 77 percent, 70 percent, and 78 percent respectively. ii R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm ission . The thermal hydraulic sizing of the tube-fin heat exchanger and the shell and tube heat exchanger for the application as a hot-side heat exchanger HSHE has been performed. Detailed thermal hydraulic theory is presented. Selection of heat exchanger type is performed by a weighted quantitative analysis. The shell and tube heat exchanger has been selected for application as a HSHE. The preliminary design dictates that it is possible to develop a low-cost CBC engine by utilizing off-the-shelf components such as turbochargers. The highest costing component will be the Hot Side Heat Exchanger due to the requirement to utilize hightemperature materials. HSHE sizing does not dictate prohibitive costs that would prevent competitiveness of the CBC engine. However, due to the modest efficiency of the technology demonstration unit (predicted at 15 percent), CBC engine application will be limited to areas with high energy cost and the requirement for waste fuel disposal.

Design of a technology demonstration closed Brayton cycle engine for small electrical power generation application