Integrated engine waste heat recovery by combination ofevaporative engine cooling and Rankine bottoming cycle.

Abstract: Engine Cooling losses constitutes about 20% of the injected fuel energy in a modern heavy duty truck diesel engine. The objective of this Master Thesis Project is to investigate flow boiling cooling as a thermally efficient method for waste heat recovery as well as a good solution for precision cooling. First, an engine heat transfer model was implemented on GT-suite software in order to estimate heat fluxes within the engine cylinder. Liners being less thermally constrained than the cylinder head, flow boiling cooling was then investigated in the liner’s water jackets. A more adapted heat transfer model taking into account both gas side and cooling side of the liner was thus implemented on Simulink. Unlike commercials software, this simple model allowed to implement the relevant two-phase heat transfer correlations and to study in details the boiling flow behaviors. The hydraulic diameter of the water jackets, the fluid saturated pressure and the surface area of heat transfer are the major parameters and they were studied for various mass flow rate in order to analyze how they influence wall temperature and heat transfer. This study showed good operating conditions for very low mass flow rate (about 1% of the typical mass flow rate for liquid convective cooling). Due to flow control issues, it implied the consideration of other fluids such as refrigerants but showed good prospect for cooling system simplification. This flow boiling model was finally inserted in a complete Rankine loop model using water as a working fluid to study potential efficiency improvements. A Rankine loop using water as a working fluid would thus improve the heat recovery of the considered engine of about 4.8% of the net engine brake power, recovering heat from the liners and the exhaust gases at 1800RPM, full load. Further simulations have also been led with R245fa, which shows a WHR of about 5.5% of the net engine brake power at 1800RPM, full load.