The Controllability of Vapour Based Thermal Recovery Systems in Vehicles

The idea of thermal energy recovery from vehicle engine exhaust flow is now well supported and funded. Through a number of research projects, several component technologies have been identified. Rankine cycle, turbo-compounding and thermo-electric systems have all attracted interest. Fuel economy improvements vary depending on the drive cycle and the capability of the underlying technologies, but have been reported as high as 25%.

Our work at Sussex on a form of Rankine cycle has revealed generic issues about the control of thermal recovery and the associated modelling requirements. Typical issues include the balancing the rate of heat input to the recovery system with the loss of useful work from large temperature differences. The size of components dictates the control authority over the system and consequently its ability to follow changing conditions.

In this paper we take a broad look at the control issues and use illustrations from both our experience with vapour based systems and published results. We will propose control architectures that match the particular characteristics of the component technologies. We comment on control issues and how the choice of system architecture influences both the timing and amount of work production from recovery systems.