The negative environmental effects of refrigerant have attracted more and more attention. The natural refrigerant CO_2 should be commended and promoted because of its superior environmental protection. Expander is the fundamental measure to improve the efficiency of CO_2 tanscritical cycle. Aimed at the preliminary designed CO_2 double rolling piston expander, the theoretical analysis and experimental research were to identify the reasons for its low efficiency and the corresponding improvement programs wer...