Experimental investigation on melting characteristics of frozen urea–water-solutions for a diesel SCR de-NOx-system

The purpose of the study is to investigate a system that can prepare a sufficient amount of urea–water-solution to ensure normal de-NOx performance within the shortest time from the cold start of a diesel vehicle with a urea-SCR system. Main experimental parameters are the flow rates and temperatures of the engine coolant, shapes of the heating tube, and power of the electric heater in the diesel vehicle. The frozen urea is melted by two heating sources as an engine coolant heating and an electric heating. The urea-melting performance of a combined system of both heating sources and that of a single heating source were investigated by experiments. The results showed that it was best to supply the 70 °C coolant at 200 L/h to the heat exchanger of the frozen urea tank. The BWT (bottom winding tube) heat exchange tube, whose surface area of the heat transfer is concentrated at the bottom of the urea tank to supply concentrated heat around the inlet of the urea suction tube, is recommended to ensure a proper amount of urea solution within the shortest time from a cold start for diesel vehicles equipped with a urea-SCR system. The combined system of the BWT and the urea suction tube equipped with an electric heater (100 W) could ensure the supply of 330 mL molten urea within 5 min from cold start, an amount of urea solution which can be injected in the urea-SCR system of a diesel vehicle for 10 min.