## 2 Experimental System and Data Processing  
### Experimental System and Material  
Figure 1 shows the experimental system. The generator (Shandong Huineng Power Equipment Co., Ltd., 15 KVA, Weifang, China) was driven by a diesel engine (Shandong Weichai Power Equipment Co., Ltd., WP2.1D18E2, Weifang, China) at the rated speed of 1500 r/min. Basic parameters and exhaust flow of the diesel engine are shown in Tables 1 and 2, respectively. No. 5 National Standard diesel oil (sulfur content less than 0.01%) was used in the experiment. The output power of the diesel engine was controlled by an air-cooled electric heating load box. The exhaust gas of the diesel engine passed through the activated carbon reactor. The structure of the AC reactor is shown in Figure 2. The urea nozzle was installed in a hole with a diameter of 46 mm at the front of the reactor, and a grid was installed between the nozzle and the inlet of the reactor to make the urea solution and the exhaust gas mix more uniformly. Two hole-baffles with 250 mm space were installed in the middle of the reactor, and the inside was filled with granular activated carbon. The U-type differential pressure gauge was connected to two holes of 20 mm in diameter. The ammonia for the denitration reaction was hydrolyzed by the 32.5% mass fraction urea solution. The urea metering pump (Emitec, Lohmar, Germany) was air-assisted, which has better atomization effect [23]. The molar ratio of NOx:NH\({}_{3}\) was maintained at 1:1. The basic parameters of the columnar activated carbon (Shanxi Xinhua Activated Carbon Factory, Taiyuan, China) are shown in Table 3. The element composition of AC is shown in Table 4. The activated carbon used in each experiment was about 5 kg. The concentration of PM in the exhaust gas was measured by a diesel particle analyzer (SAXON Junkalor GmbH, SMG 100, Dessau, Germany). The concentrations of O\({}_{2}\), CO, NO, and NO\({}_{2}\) were measured by a flue gas analyzer (Testo company, Testo 350, Freiburg, Germany). In each experiment, the power was increased from the idle load to 15 kW with 3 kW interval. Since the emission of diesel exhaust pollutants was not very constant, in order to reduce the error, the parameters of interest were continuously measured over a period of time after the diesel engine was stable at each power point. The concentrations of the pollutants were the average value at the studied power point. For each power point, the experiment was repeated three times, and the average value of the contaminant concentrations were taken for each power point. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Cylinder** & **Bore** & **Stroke** & **Compression** & **Displacement** & **Air Inlet** & **Power** & **Rated Speed** \\
**(mm)** & **(mm)** & **Ratio** & **(L)** & **Method** & **(kW)** & **(r/min)** \\ \hline
4 & 85 & 92 & 18:1 & 2.09 & Natural & 17.5 & 1500 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of diesel engine. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Diameter** & **Length** & **Iodine** & **Fire Point** & **Bulk Density** & **S\({}_{\mathbf{BET}}\)** & **Vtotal** & **Vmic** & **\(\overline{\mathbf{D}}\)(nm)** \\
**(mm)** & **(mm)** & **Value (mg/g)** & **(\({}^{\circ}\)C)** & **(g/L)** & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** \\ \hline
10 & 5.6\(\sim\)11.2 & 371 & 456 & 650 & 326.491 & 0.200 & 0.112 & 2.454 \\ \hline \hline \end{tabular} Note: \({}_{\mathbf{SBET}}\): BET surface area; Vtotal: total pore volume; Vmic: micropore volume \(\overline{\mathbf{D}}\): average pore diameter.  
\end{table} 
Table 4: Element composition of AC. Figure 1: Experimental system schematic. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Element** & **C** & **O** & **Si** & **Al** & **Ca** \\ \hline Mass percentage (\%) & 48.07 & 20.64 & 8.83 & 5.75 & 6.58 \\ Atomic Percentage (\%) & 64.26 & 20.71 & 5.05 & 3.42 & 2.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Element composition of AC.