Temperature control of evaporators in automotive waste heat recovery systems

his paper presents a control strategy for the steam generation process in automotive waste heat recovery systems that are based on the subcritical Rankine cycle. The central question is how to regulate the flow of water into the evaporator such that dry steam is generated at its outlet, subject to large variations in the heat input. Tight control of this process increases the amount of recovered energy while ensuring safe system operation. The method consists of inversion-based feedforward combined with output feedback on the temperature of the evaporator, which is estimated using exhaust gas measurements. As this method does not require a high fidelity evaporator model, it is easy to implement. It is demonstrated on an experimental setup, where the exhaust flow is imitated by electrically heated air. On an automotive driving cycle, steam was generated reliably with a superheating temperature of 10-20 [K]