Optimisation and control of thermal recovery for a hybrid vehicle

The automotive industry is currently driven to reducing fuel consumption in internal combustion (IC) engines and hence much research is being done into alternative fuels and power sources. Thermal energy recovery from IC engines has proved to be of considerable interest within the automotive industry. The motivation is that fuel consumption can be reduced with a minimal effect on the “host” technology of the vehicle. This thesis reports on a project that aimed to investigate the architecture and control of a thermal energy recovery system, working towards proving this novel system concept. This was achieved by the use of software modelling techniques and experimental tests on various components of the system, namely heat exchangers and steam expanders. Various modelling toolboxes were used to model a) a hybrid vehicle configuration and b) steam expanders. The hybrid vehicle modelling began as a basic model to demonstrate the hybrid application and configuration of the steam system, and was further developed to control and optimise the system in such a way that the fuel economy, the overall efficiency of the IC engine and the heat recovery system were all maximised. Standard drive cycles were used to run the hybrid vehicle models. The steam expander modelling was performed in order to validate the results from a series of experimental tests and also to deduce if the expander models could be scaled up to predict results for larger expanders. The fuel consumption for the initial modelling showed a reduction of between 8% and 36%, depending on drive cycle and modelling toolbox used. With the development of a simple PID controlled system, the fuel consumption was further reduced resulting in a range of 26% to 41%, again depending on drive cycle and modelling tool box. The experiments on steam expanders point to a uni-flow configuration being the most suitable. The expander modelling presents the groundwork for developing expander models to be used for validating the experimental results; again the uni-flow arrangement gave the most promising results. This thesis presents the results and draws conclusions from each project step; these conclusions are summarised together with some recommendations for future work.