Modeling and Testing of a Novel Ultra-Low Temperature sCO2 Opposing Piston Expander Available to Purchase

Southwest Research Institute (SwRI) along with Thermal Tech Holdings (TTH) have modeled, built, and tested a piston expander for generating power from low temperature heat sources. The piston was developed with the goal of creating an engine that operates as a recuperated sCO₂ Ericsson cycle. A cycle model based on fluid properties from REFPROP is applied for various hot and cold temperatures to demonstrate the potential of the novel expander to improve cycle efficiency. Cycle modeling results demonstrate the potential improvements in cycle efficiency when compared to the sCO₂ Brayton cycle. Small-scale bench testing is used to validate the novel piston concept for achieving a sCO₂ Ericsson cycle. The concept is scaled up to a full-sized, opposing piston cylinder that acts as an expander in the theoretical Ericsson cycle. Testing is performed on the full-scale piston cylinder for a variety of inlet temperatures and pressures. The full-scale tests are run continuously to track the transient effects. The results of the full-scale test are discussed. The expander piston cylinder test results show high temperatures at the outlet, better than the ideal sCO₂ Brayton cycle, but less than an ideal recuperated sCO₂ Ericsson cycle. Comparisons are made to demonstrate the projected cycle efficiency improvements over a sCO₂ Brayton cycle.