Performance Analysis of Two-Loop Rankine Cycle for Engine Waste Heat Recovery

Optimization of Design Pressure Ratio of Positive Displacement Expander for Vehicle Engine Waste Heat Recovery

“…The cycle efficiency increases with the design expansion pressure ratio as the condensation temperature in the HT cycle TC,HT decreases, but the size of the swash plate-type expander also increases. In a previous study [11], decreasing TC,HT from 139 to 120 °C and then 105 °C caused the HT cycle power to increase by about 21% and 38%, respectively, although the LT cycle power was constant. However, the volume of the HT expander had to be increased by approximately 67% and 165%, respectively, to achieve this, which is a disadvantage.…”

“…In [11], the design pressure ratio was set to 10 in consideration of the size of the swash plate-type expander in the HT cycle under the target operating conditions, while the condensation pressure and temperature were set to 3.5 bar and 139 °C, respectively. However, if TC,HT is greater than the reference temperature of 139 °C, the design pressure ratio becomes higher than the actual operating pressure ratio, and over-expansion occurs.…”