Development and numerical assessment of a regulation strategy for Sliding Rotary Vane Expander based on revolution speed variation

Sliding Rotary Vane Expanders (SVRE) are widely used in ORC-based power units for waste heat recovery in internal combustion engine (ICE) thanks to the capability to handle off-design conditions and their lower speed. In particular, SVRE revolution speed is usually varied together with the pump one to regulate the recovery unit. Nevertheless, this parameter affects SVRE performance and such effects should be taken into account. Thus, in order to reach this goal, in this paper a control strategy based on revolution speed variation was developed for SVRE. Its suitability and effects on expander performance were analyzed through a SVRE model developed in GT-Suite™ environment. The model was experimentally validated thanks to an extensive experimental campaign carried out on a 1.5 kW SVRE installed on an ORC-based power unit fed by the exhaust gases of a 3 liters supercharged Diesel engine. The results confirm the regulation strategy effectiveness as the maximum deviation between the intake-end pressure (object of regulation) and the set-point is 4% of its value for a wide range of operating conditions. Moreover, the numerical results show that the increase of revolution speed until a certain value leads to the expander global efficiency increase and mechanical power too.