CFD Simulation of a Supercritical CO ₂ Rolling Rotor Expander for Waste Heat Recovery System of Engines 2018-01-0058

The supercritical CO₂ power cycle system for waste heat recovery (WHR) of internal combustion engine (ICE) has widely been concerned as a research hotspot. And the expander is a key component in the supercritical CO₂ power system. Rolling rotor expander has the following advantages: compact size, light weight, less moving parts, high stability and long service life, which qualify it a very suitable choice for engine’s waste heat recovery system. For a self-designed rolling rotor expander using supercritical CO₂ as its working fluid, FLUENT software was used to simulate its internal flow field in this study, obtaining the changes of the internal pressure field and turbulent kinetic energy. The causes of local vortex in the expansion process were analyzed. Under different working conditions of the expander, the change of internal pressure and the distribution of P-V curve were observed, and the work capacity under different inlet pressure was analyzed. Results show that, the work capacity increases if the intake pressure increases within a certain range. However, if the inlet pressure keeps increasing and exceeds a reasonable limit, the local vortex in the suction process is enhanced and the pressure loss is increased and the degree of the turbulence is strengthened, which causes a certain impact on the expansion process and expander service life. The rotating speed has a great influence on the operation of the expander. These results provide guidance for the design and optimization of the supercritical CO₂ expander in the future.