Performance of a Diesel Engine at High Coolant Temperatures

The current state of the art in waste heat recovery (WHR) from internal combustion engines (ICEs) is limited in part by the low temperature of the engine coolant. In the present study, the effects of operating a diesel engine at elevated coolant temperatures to improve utilization of engine coolant waste heat are investigated. An energy balance was performed on a modified three-cylinder diesel engine at six different coolant temperatures (90 °C, 100 °C, 125 °C, 150 °C, 175 °C, and 200 °C) and 15 different engine loads to determine the impact on waste heat as the coolant temperature increased. The relative brake efficiency of the engine alone decreased between 4.5% and 7.3% as the coolant temperature was increased from 90 °C to 150 °C. However, the engine coolant exergy increased between 20% and 40% over the same interval. The exhaust exergy also increased between 14% and 28% for a total waste heat exergy increase between 19% and 25%. The engine condition was evaluated after testing and problem areas were identified such as overexpansion of pistons, oil breakdown at the piston rings, and head gasket seal failure.