# Evaluating the Real-World NOx Emission from a China VI Heavy-Duty Diesel Vehicle
## 3 Results and Discussion
### Section NOx Emission Analysis  
Before the discussion, it had to be known that the engine output NOx concentration was from the NOx sensor located at the DOC inlet, and the tailpipe NOx concentration was calculated by the sum of NO and NO\({}_{2}\) concentration from gas analyzers of the AVL-M.O.V.E-PEMS. In this section, we mainly talked about NOx emission characteristics of each section, especially the urban section. Figure 5a shows the cumulative mass of engine NOx emission of each section of the test route, and as it can be seen, the least amount of engine NOx emission was emitted during the urban section of the test route because of its shortest test duration. Figure 5b shows the contribution ratio of each section to the total mass of engine NOx emission. Specifically, the contribution ratio of the urban section was 12.39% in Test 1, 10.91% in Test 2, 9.04% in Test 3, 8.74% in Test 4. The contribution ratios of the motorway section were all more than 60% in the four PEMS tests. So, we may conclude that the contribution \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Test 1** & **Test 2** & **Test 3** & **Test 4** \\ \hline Altitude not more than 2400 m & Yes & Yes & Yes & Yes \\ Cold start & Yes & Yes & Yes & Yes \\ Average Ambient temperature (\({}^{\circ}\)C) & 22.9 & 20.0 & 10.4 & 6.7 \\ Average relative humidity (\%) & 96.3 & 69.6 & 66.2 & 65.9 \\ Payload (\%) & 50 & 50 & 50 & 50 \\ Urban first (urban-rural-motorway) & Yes & Yes & Yes & Yes \\ Urban share driving (\%) & 21.4 & 21.2 & 19.8 & 20.4 \\ Rural share (\%) & 22.1 & 27.0 & 25.1 & 25.2 \\ Motorway share (\%) & 56.5 & 51.7 & 55.0 & 54.4 \\ Urban driving average speed (km/h) & 25.3 & 24.4 & 21.6 & 23.5 \\ Rural driving average speed (km/h) & 55.4 & 60.9 & 60.9 & 57.7 \\ Motorway driving average speed (km/h) & 75.5 & 73.0 & 75.8 & 76.5 \\ Odometer (km) & 2135.3 & 10,557.4 & 47,443.5 & 82,258.3 \\ Trip distance (km) & 168.8 & 159.1 & 178.4 & 145.6 \\ Trip duration (s) & 9102 & 9117 & 10,009 & 8183 \\ Total Work (kWh) & 195.42 & 179.66 & 205.21 & 175.73 \\ Cumulative work (\({}^{\star}\)WHT\({}_{\text{V biof}}\)) & 5.047 & 4.640 & 5.300 & 4.539 \\ Valid MAW Power Threshold (\%) & 20 & 17 & 20 & 20 \\ Percentage of valid MAWs (\%) & 61.5 & 72.3 & 50.2 & 64.3 \\ \hline
95 th NOx concentration (ppm) & 245.1 & 188.0 & 296.2 & 416.2 \\
90 th cumulative percentile of Valid MAWs & & & & \\ NOx emission (g/kWh) & 0.068 & 0.551 & 0.438 & 0.337 \\ Test Valid or not & Valid & Valid & Valid & Valid \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the four PEMS Tests of the tested vehicle. of each section to the total mass of engine NOx emission is positively correlated with the trip share. Figure 6a shows the cumulative mass of tailpipe NOx of each section of the test route, as it can be seen, the greatest amount of tailpipe NOx emission was emitted during the urban section in spite of its lowest contribution to the total mass of the engine NOx emission and shortest test duration. The contribution ratio of urban section to the total mass of tailpipe NOx emission was as high as 69.10% in Test 1, 45.25% in Test 2, 55.52% in Test 3, 62.54% in Test 4 (Figure 6b). So, we may conclude that the tailpipe NOx emission of urban section is very terrible for the in-use N3 category heavy-duty vehicles. Table 4 shows engine output of NOx and tailpipe NOx brake-specific emissions (BSNOx emission: g/kWh) in each section of the test route. Figure 5: **(a)** Each section’s cumulative mass of engine NOx emission; **(b)** each section’s contribution ratio to the total mass of engine NOx emission. As it can be seen, there was a slight difference of the engine out BNOx emissions between rural section and motorway section in all of the four PEMS tests. The engine output of BSNOx emission of urban section is a slightly higher than that of other sections in Test 1, Test 3 and Test 4, but, in Test 2,the engine out BSNOx emission of each section is almost the same.