On the Improvement of Combustion Engines with Waste Heat Recovery Systems in Mobile Applications

This dissertation deals with the experimental and simulative investigation of waste heat recovery from combustion engine exhaust gas in passenger car applications. The focus of the investigations lies on the thermodynamic cycle according to Rankine. The boundary conditions of combustion engines and the limitations of an automobile cause new operating conditions and system operating parameters for Rankine-systems, which will be discussed within this work.

The system operating parameters were judged based on their potential to improve the efficiency of a running system, by setting the optimal values for each individual situation. Alternative circuit variants were investigated alongside of the basic configuration, which allowed additional heat input into the system and thereby increase the power output of the Rankine-system. Another operative influence on a waste heat recovery system that was analyzed was the importance of engine operating parameters. This on one hand lays groundwork and on the other hand displays the potentials of different system combinations.

The knowledge gained during stationary operation is transferred to dynamic operation in the following. Cold start was chosen as the most important variant of dynamic operation. Results from measurements at starting temperatures down to -10C are presented. These include the first published measurements of temperature and power output for such scenarios. The basics of the behavior of a Rankine-system in cold start are extended by the impact of system operating parameters and circuit configurations.

Possible synergies through different kinds of connection from the condenser to the coolant system were investigated as a completing facet of the holistic system view. The target of these investigations was to identify potentials for improvements in the cold start of the automobile by utilizing the heat that is available at the condenser.