Melting and Heat Transfer Characteristics of Urea Water Solution According to a Heating Module’s Operating Conditions in a Frozen Urea Tank

Abstract

The urea-selective catalytic reduction (SCR) system, a nitrogen oxide reduction device for diesel vehicles, is a catalytic system that uses urea water solution (UWS) as a reducing agent. This system has a relatively wide range of operating temperatures. However, the freezing point of the reducing urea solution used in this system is −11 °C. When the ambient temperature dips below this freezing point in winter, the solution may freeze. Therefore, it is important to understand the melting characteristics of frozen UWS in relation to the operating conditions of the heating device to supply the minimum amount of aqueous solution required by the system in the initial stage of normal operation and startup of the urea–SCR system. In this study, we artificially froze a liquid solution by placing it along with a heating module in an acrylic chamber to simulate a urea solution tank. Two types of heating modules (P120 and P160) consisting of two heating elements and heat transfer bodies were used to melt the frozen solution. The melting characteristics of the frozen solution were observed, for example, changes in the temperature distribution around the heating module and the cross-sectional melting shape with the passage of time since the start of the power supply to the heating module. The shape of melting around the heating module differed depending on the level of UWS relative to the heater inside the urea tank. In case 1, it melted in a wide shape with an open top, and in case 2, it melted in a closed shape. This shape change was attributed to the formation of internal gaseous space due to volume reduction during melting and the heat transfer characteristics of the fluid and solid substances.

Fuel Consumption and Emission Reduction for Non-Road Diesel Engines with Electrically Heated Catalysts

“…The PM emissions from diesel engines have been drastically reduced with the development of the diesel particulate filter (DPF) to meet the Euro-4 emission regulations, and DPFs are now applied to almost all diesel vehicles [8,9], which are equipped with PM sensors for monitoring DPF failures [10]. For PM reduction, the aforementioned DPF is a reliable technology, but for NOx reduction, various catalytic systems such as lean NOx trap (LNT) [11,12], hydrocarbon selective catalytic reduction (SCR) [11,13], and urea SCR [11,[14][15][16][17] have been proposed depending on the exhaust conditions and various operational characteristics. Under current exhaust regulations (Euro-6 and Tier-4), LNT and SCR systems or a combination of these two catalysts are used for passenger cars [11,18], while urea-SCR systems, which can guarantee a reliable reduction in an appropriate exhaust temperature window without fuel penalty and complex operation, are widely used in commercial and non-road vehicles [18][19][20][21].…”