###### Abstract  
To achieve diesel engine ultra-low nitrogen oxide emission, light-off selective catalyst reduction (LO-SCR) has been suggested for better performance with lower exhaust temperature. An electric heater upstream of the exhaust aftertreatment system was applied to significantly decrease the NOx emission at a low exhaust temperature. With a 7.2 kW electric heater coupled with LO-SCR, the NOx emission during 200-500 s of the world harmonized transient cycle (WHTC) decreased from 282.6 ppm to 61.5 ppm, which is a decrease of 45%. Application of an upstream diesel oxidation catalyst (DOC) decreased the NOx emission by 63% at the same interval at the cost of worse cold-start performance. The urea input was also adjusted to avoid NOx emission during the latter part of the WHTC. diesel engine; aftertreatment; thermal management; SCR +
Footnote †: journal: Medical Engineering  
kinetic parameter values for Cu-CHA catalysts, and established a global kinetic model, which can better predict the conversion rate of NOx and NH3. [PERSON] et al. [7] reviewed the performance of NH3-SCR using Cu-based catalysts in reducing NOx at low temperatures and compared the ability of several Cu-based catalysts to reduce NOx (standard SCR reaction) in different temperature ranges. Among them, Cu/SSZ is currently the most suitable catalyst for low-temperature reduction of NOx, and the NOx removal rate can reach 100% when the temperature is between 150 and 350 \({}^{\circ}\)C. When the temperature is lower than 150 \({}^{\circ}\)C, the NOx reduction activity of Cu/SSZ drops sharply. [PERSON] et al. [8] studied the effect of exhaust temperature on the efficiency of selective catalytic reduction (SCR) denitrification. [PERSON] summarizes that the change in SCR denitrification efficiency generally includes three states based on exhaust gas temperature. In state I, the SCR carrier temperature is high and urea is injected, resulting in high NOx conversion efficiency (>90%); state III is a cold-start condition with the lowest NOx conversion efficiency (<50%). State II is a transitional stage involving ammonia storage. The NOx conversion efficiency is linearly related to exhaust temperature and increases with increasing temperature; the slope of the NOx conversion efficiency decreases with increasing exhaust temperature. [PERSON] et al. [9] reviewed different NOx emission-reduction technologies and introduced the chemical reaction mechanism of NH3-SCR (standard SCR) under aerobic and anaerobic conditions. [PERSON] et al. [10] conducted experimental research on the NOx conversion efficiency and NH3 leakage of three aftertreatment schemes by introducing SCR size strategies. [PERSON] used postprocessing systems with different SCR lengths of the same SCR diameter and found that the nitrogen oxide emissions of the three SCR systems were similar, but the average NH3 leakage varied greatly. As the SCR length decreased, the average NH3 leakage increased. [PERSON] et al. [11] proposed a novel catalytic mechanism for the fast SCR reaction of NH3, NO, and NO2 at low temperatures and supported a theoretical basis for fast SCR-related research. [PERSON] et al. [12] studied the effect of fast SCR reaction on commercial SCR catalysts and found that fast SCR can apparently promote catalytic activity and decrease catalyst consumption and replacement frequency. However, Cu-based catalysts may generate N2O and have little capability to clarify it. [PERSON] et al. [13] suggested reducing the amount of Cu in Cu-zeolite SCR to reduce N2O generation without increasing NOx emission. [PERSON] et al. [14] examined the Fe-zeolite catalyst and achieved significant suppression of N2O formation. [PERSON] and [PERSON] analyzed the formation pathways of N2O in a combined zeolite-supported SCR with both Fe and Cu catalysts. The later research of [PERSON] et al. also selected this method for better N2O reduction [15]. The DOC is applied to oxidize CO, HC, and other combustible emissions of diesel engines [16].