Impending emission regulations of diesel engines for construction machineries would regulate nitrogen oxide emissions strictly in cold operating conditions. The urea-based selective catalytic reduction (urea-SCR) system coupled with the electrically heated catalyst (EHC) has been considered as a potential measure to meet the strict emission regulations by promoting evaporation and thermal decomposition of urea–water solution in cold operating conditions. Analyzing the thermal conditions in the EHC is crucial for the optimized operation and control of EHC-based urea-SCR systems under various engine operating conditions. In the current study, we introduce a simple one-dimensional analysis scheme to characterize the surface temperature distribution in the EHC based on energy conservation and the theories of forced internal convection. Since the EHC has a complicated internal structure with fine flow cells inside it, a flow cell in the EHC is extracted for the one-dimensional heat transfer analysis. EHC operation parameters such as exhaust gas flow rate and supplied electric power to the EHC are scaled to be applied for the flow cell analysis. The adequacy of the analysis scheme is then validated by surface temperature measurement results at the EHC outlet. The validation results showed over 95% prediction accuracy of the 1D analysis scheme in the operating conditions of a heavy-duty diesel engine. Based on proven reliability, the effects of geometric and operation parameters on the surface temperature distribution in the EHC were analyzed and discussed using the analysis results.

In this study, an exhaust system compliant with future regulations was developed for a non-road 110PS engine with a Tier-4f aftertreatment system, and the emission characteristics of the engine were investigated in the non-road transient mode (NRTC). For the system to comply with future exhaust regulations, a DPF was installed, and an electrical heated catalyst (EHC) device was installed to manage exhaust gas temperature. The emission characteristics of exhaust gas were examined according to the power and applied duration of EHC, and the effects of catalyst coating and the urea water solution (UWS) injection map on NOx reduction, NH₃ slip, and N₂O emissions in NRTC mode were investigated. The application of a 4 kW class EHC system enables the lowering of the injection starting temperature of the UWS, as reliable gas heating (heating duration control) is guaranteed. When the injection starting temperature (based on the SCR inlet temperature) was set to 150 °C, NSR map, (III) in conjunction with the operation of the EHC, effectively achieved significant NOx reduction in NRTC mode without deposit and wetting occurring in the mixer and exhaust pipe. Regarding changes in EHC power from 3 kW to 4 kW, it was observed that a NOx reduction of 0.05 g/kWh occurs in the cold NRTC mode, but in the hot NRTC mode, it was found that the relative decrease in the UWS is due to the increased NO₂ conversion efficiency as a result of the oxidation catalyst, making 3 kW more advantageous. Furthermore, due to the increase in NO₂ concentration caused by the oxidation catalyst and the increase in the low-temperature injected UWS, NH₄NO₃ was formed, which resulted in an increase in PM emissions and a significant increase in N₂O emissions around an exhaust temperature of 250 °C. When the EHC power was set to 3 kW and the volume of oxidation catalyst and the amount of UWS injection were adjusted, applying EHC in the NRTC mode resulted in an additional NOx reduction of 58.6% and 88.4% in cold and hot modes, respectively, compared with not using EHC, with a fuel penalty of approximately 1.67%, while limiting the peak concentrations of N₂O and NH₃.

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.