# Machine Learning Applied to the NOx Prediction of Diesel Vehicle under Real Driving Cycle
## 3 Data Description
### Dataset
For example, NO\({}_{\rm x}\) emissions are highly affected by the ambient temperature and relative humidity, and higher NO\({}_{\rm x}\) concentrations result from lower temperatures and higher relative humidity values [45; 46]. As an after-treatment performance factor, the EGR rate is a critical parameter for NO\({}_{\rm x}\) emissions, defined as the percentage of exhaust gases constituting the total gas mass induced into the engine. A higher EGR rate denotes lower NO\({}_{\rm x}\) emissions levels [47]. Therefore, the EGR rate value was used in this study. The intake air temperature has a dominant effect on the NO\({}_{\rm x}\) emissions from internal combustion engines [48]. The intake air temperature is measured by a sensor located on the bottom of the intake manifold inside the vehicle, placed directly behind the throttle valve housing. In general, temperature readings can be \(\pm 10\)\({}^{\circ}\)C compared to the ambient \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Vehicle Type**} & \multicolumn{1}{c}{**Fuel**} & \multicolumn{1}{c}{**Emissions Level**} & \multicolumn{1}{c}{**Emission Reduction**} & \multicolumn{1}{c}{**Test Day**} \\ \hline SUV & & & - Selective catalytic reduction & Hot test: 24 September 2019 \\  & & & - Exhaust gas recirculation & Cold test: 20 September 2019 \\ SUV & & & - Lean NO\({}_{\rm x}\) trap & Hot test: 14 October 2019 \\  & & & - Diesel particulate filter & Cold test: 10 October 2019 \\ Sedan & & & - Selective catalytic reduction & Hot test: 6 August 2018 \\  & & & - Exhaust gas recirculation & Cold test: 6 July 2018 \\  & & & - Diesel particulate filter & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Information about the vehicles tested in this study. temperature of the vehicle, depending on the outside temperature and the temperature of the engine. The mean intake air temperature was approximately 7 \({}^{\circ}\)C higher than the mean ambient temperature, as presented in Table 3.  
NO\({}_{\text{x}}\) emissions can differ between hot and cold tests during engine starting. NOx emissions increase when a diesel catalyst temperature at the inlet of the Urea-SCR catalyst is not sufficiently high [49]. A few researchers indicated that the NOx emissions during cold starts were higher than during warm-engine operation. Cold starting is a major contributor of NOx emissions in diesel cars [50]. After-treatment systems deteriorate functionally at low temperatures during an engine cold start [51]. The catalytic converter then generates smoke pollution [52,53]. Therefore, the EC added cold-start provisions as part of the third regulatory RDE package [54]. Nonetheless, there were no measured SCR performance data (Urea-SCR catalyst temperature) or LNT data from PEMSs in these tests. Consequently, the Urea-SCR catalyst temperature data were replaced with exhaust temperature data, as the exhaust is directly related to the catalyst temperature in a diesel engine. Generally, SCR performance can be effective at temperatures around 200 \({}^{\circ}\)C in rural and motorway regions. LNT catalysts can store NOx effectively at lower temperatures in urban regions with low speed; subsequently, trapped NOx is released from the catalyst when the engine operation mode is switched to rich conditions. Figure 3 presents a comparison of NOx concentrations during a cold start (KOR-NIER Route 1) and hot start (KOR-NIER Route 2) in an example of one diesel test vehicle listed in Table 2. The figure shows that the NOx mean value is 8.3 ppm during the cold test, which is 8.3 times higher than the 1.0 ppm obtained during the hot test over 500 s. These results indicate that catalyst light-off issues during cold start are very important for pollutant emissions [55].