## 2 Test Equipment and Data Acquisition  
A 3-L, four-cylinder inline diesel engine with supercharged intercooling was selected for the test, and the aftertreatment system was a combination of Diesel Oxidation Catalyst (DOC) + Diesel Particulate Filter (DPF) + SCR + Ammonia Slip Catalyst (ASC). The parameters of each component of the aftertreatment system are shown in Table 1. The bench test utilized a Dynas3 electric dynamometer to control the speed and torque of the diesel engine. The engine raw NOx and post-SCR NOx were collected and measured by a HORIBA MEXA-ONE gas analyzer (\(\pm\)2.0 per cent of the reading), and the NH\({}_{3}\) slip was collected and measured by a HORIBA FTX-ONE-CS/RS (\(\pm\)2.0 per cent of the reading). Other data, such as exhaust temperature and exhaust flow, were displayed and saved in real time by the STARS system. The engine parameters are shown in Table 2. The type of urea used in the test was an aqueous urea solution of 32.5. Specific information about the test equipment, such as temperature and pressure, is shown in Table 3.  
In this study, the diesel engine bench test procedure was to regulate the speed of the diesel engine from 1000 rpm to 2800 rpm at intervals of 100 rpm, with test data collection at 50 N\(\cdot\)m intervals. The collected data include the following: diesel engine speed, torque, exhaust temperature, SCR inlet temperature, exhaust flow rate, NOx emission before SCR, NOx emission after SCR, NH\({}_{3}\) slip and other parameters. The original engine emission parameters are shown in Figure 1.  
The test data for engine performance and emission parameters under some operating conditions are shown in Table 4. As shown in the table, each SCR inlet NOx concentration corresponds to a unique set of SCR inlet temperatures as well as exhaust flow rates. Therefore, the urea injection volume can be used as a unique parameter to control the SCR outlet NOx concentration. Considering the constant SCR inlet temperature, NOx concentration and exhaust flow rate for each operating condition, different SCR outlet NOx concentrations and NH\({}_{3}\) slip are obtained for each urea injection amount. Therefore, for all operating conditions, varying the urea injection amount, 25 sets of corresponding SCR outlet NOx concentrations and NH\({}_{3}\) slip amounts were obtained.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **DOC** & **DPF** & **SCR (Cu-Based)** & **ASC (Cu-Based)** \\ \hline Volumetric (L) & 2.17 & 3.62 & 3.62 & 1.45 \\ Diameter (mm) & 190.5 & 190.5 & 190.5 & 190.5 \\ Lengths (mm) & 76.2 & 127 & 127 & 50.8 \\ cell & 400 & 300 & 400 & 400 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Test bench aftertreatment system parameter.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Figure** **Power** & **Four-Cylinder Compression Ignition** \\ \hline Bone [mm] & 94 \\ Stroke [mm] & 107 \\ Displacement volume [cc] & 2970 \\ Compression ratio & 18.4 \\ Maximum power [kW] & 121 \\ Maximum torque [N\(\cdot\) m] & 500 \\ Rated speed [rpm] & 2800 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Engine specifications.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Equipment Name** & **Model Number** & **Test Accuracy** \\ \hline Electricity Dynamometer & Dynas3 &
\begin{tabular}{c} Torque: \(\pm\)0.1\% to \(\pm\)0.2\% FS \\ RPM: \(\pm\)0.01\% to \(\pm\)0.1\% FS \\ \end{tabular} \\ Fuel Consumption Meter & AVL735 & \multicolumn{1}{c}{—} \\ Gas Analyzer & HORIBA MEXA-ONE & \(\pm\)2.0\% of reading or \(\pm\)1.0\% of FS \\ Thermocouples & WRNK-2911 & \multicolumn{1}{c}{\(\pm\)0.25\%} \\ Pressure Transmitter & DRUCK & \multicolumn{1}{c}{\(\pm\)0.2\%} \\ \hline \hline \end{tabular}
\end{table}
Table 3: Test Equipment.