Experimental investigation of the cold start behavior of different coolant circuits for a waste heat recovery system and their influence on the engine

One of the most promising technologies to increase efficiency and to decrease CO₂-emissions for future combustion engines is the utilization of exhaust gas heat through a Rankine cycle. A so called waste heat recovery system (WHR) converts the thermal energy of the exhaust gas into mechanical or electrical energy which can be used to propel the vehicle or to lower the generator load and thereby reduce the fuel consumption.Additional to the recovered electric or mechanic energy the engine can also benefit from the recovered heat, which can be regained through the condenser. The condenser can be connected to the coolant circuit where the heat can be used to improve the warm up of the engine and passenger cabin of the vehicle. This creates further potential to increase the efficiency of the whole system during warm up.The target of this study was to display the warm up behavior of WHR system and engine during cold start at different starting temperatures (0° to +20°C) under realistic conditions for different coolant circuit configurations. Preliminary investigations were performed to identify the appropriate coolant volume flow rates and circuit configurations to improve the warm up of the desired component. The resulting temperatures of the components and the fuel consumption of the whole system were the main focus points.The tests were conducted on a 4-cylinder 2.0 l SI engine which fulfils the EURO6 standard. A WHR system consisting of components as close-to-production as possible was applied. Engine and WHR system were put on a test bench which allowed lowering its chamber temperature down to 0°C.The results show that a Rankine WHR system is able to improve warm up of the engine and its components. The fuel consumption can be decreased due to the reduced warm up time while the cabin temperature can be increased. Power output seems not to be affected by the lower environment temperatures, which means a WHR system is able to provide even more benefits in efficiency for cold start scenarios.