Waste Heat Recovery is a promising method to reduce fuel consumption and CO2emissions in heavy-duty vehicles. An Organic Rankine Cycle (ORC) is used to convert the thermal energy of the exhaust gases into useable energy to support the power train.
A key component of the ORC is the expansion machine where the conversion of thermal into mechanical energy takes place. In the case of volumetric expansion machines such as axial piston expanders, lubrication oil is mixed in with the working fluid to reduce friction and increase the component durability. However, the presence of oil also affects both the efflciency and the fluid dynamical behavior inside the expander.
To develop a one-dimensional simulation model that considers the oil influence, a continuous flow approach is selected. Particular attention is dedicated to the inlet and outlet valve modeling, as these have to account for two-phase flow and multi-component fluid mixtures. A valve model is developed in the simulation environment Dymola, based on the homogeneous-non-equilibrium (HNE) approach. A virtual one-cylinder test bench is setup to calibrate and validate the model. The simulation results show good correspondence with measurement data.
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