Lumped-Parameter Modeling and Analysis of Automotive Waste Heat Recovery Systems Based on an Organic Rankine Cycle.

This paper presents a lumped-parameter model of an ORC system for exhaust waste heat recovery in an automotive SI engine. The study focuses on the prediction of the dynamic behavior of the plant, accounting for the characteristics of the refrigerant. Particular consideration is given to the optimization and control of the system during transient operations to improve the power output. The dynamics of the heat exchang- ers is modeled using a Moving-Boundary Modeling (MBM) approach, based on a physical description of the system that relies on the conservation laws for single and two-phase fluid flows. Grey-box models for the pump and expanders have been de- veloped starting from the steady-state characteristic maps. The resulting model is ex- pressed as a low-order system of nonlinear Ordinary Differential Equations (ODEs), which facilitates system analysis and control design. The proposed model is calibrated on components data and compared against a detailed GT-Power model of the system. The paper presents a thorough analysis of the dynam- ic behavior of the system focusing on the evaporator heat exchanger and investigating the impact of various control inputs and boundary conditions on the system pressure, superheat temperature and expander performance metrics.