## 3 Results  
### BC Emission by Fuel Types According to NIER and Regulation Mode  
Only those vehicles that comply with the latest regulations (GDI gasoline vehicles with PM regulation (0.004 g km\({}^{-1}\)) applied, LPG, and EURO 6 diesel vehicles) were selected and compared by fuel types and shown in Figure 4 and Table 2. A decrease in BC emission was observed with an increase in the average speed of the mode according to vehicle displacement, and the emission increased after reaching the NIER-12 (avg. 65.4 km h\({}^{-1}\)) or NIER-14 (avg. 97.3 km h\({}^{-1}\)) modes for GDI gasoline and LPG vehicles. The low-speed NIER mode (NIER-01, avg. 4.7 km h\({}^{-1}\)) has a shorter mileage than the high-speed mode, and the stop section accounts for 49.7%, about half of the total driving mode, resulting in high emission measured for a short mileage with frequent stops and acceleration. In the high-speed modes (NIER-12 and NIER-14), the stopping sections are reduced; however, the BC emissions are ascertained to increase because of the high engine power output required for the high-speed driving.  
Figure 4: BC emission at five different speeds compared by fuel types (gasoline, LPG, and diesel). Gasoline with GDI engine used vehicle after PM regulation (0.004 g km\({}^{-1}\)), LPG vehicles, and diesel vehicle in EURO 6.  
For NIER modes in the heated state, GDI gasoline vehicles (0.032-0.27 mg km\({}^{-1}\)) were found to have BC emission values at least 25 times higher than those of LPG vehicles (0.0004-0.0054 mg km\({}^{-1}\)) and diesel vehicles (0.0002-0.0007 mg km\({}^{-1}\)). The high levels of BC are believed to be attributable to GDI engine combustion system that caused incomplete fuel volatilization and mixing in a cylinder [22; 23]. For diesel vehicles using the same direct injection principles, the DPF installed in the vehicles is believed to reduce the level of BC emissions.  
Figure 5 and Table 3 show the BC emissions generated by vehicles driven under the emission certification modes (CVS-75 and NEDC) according to the fuel oil type. As the results of the all phase, gasoline vehicles using PM-regulated GDI engines showed the highest emission at 0.16 mg km\({}^{-1}\), while diesel vehicles with DPF and LPG vehicles showed low emission values of 0.045 mg km\({}^{-1}\) and 0.0009 mg km\({}^{-1}\), respectively. Gasoline vehicles and LPG vehicles showed the highest emissions in phase 1 with cold start. This is because a large amount of fuel is injected to produce the necessary power output while the vehicle is not heated sufficiently. As regards diesel vehicles in the NEDC mode, high emission was observed in the high-speed section (phase 2). In phase 1, a large amount of fuel is consumed due to cold start until the vehicle stabilizes. However, in phase 2, the high-speed section is included. Thus, the emission value becomes higher compared with that of phase 1.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Fuel** & **NIER-01** & **NIER-05** & **NIER-09** & **NIER-12** & **NIER-14** \\ \hline
**Gasoline** & 0.27 \(\pm\) 0.14 & 0.08 \(\pm\) 0.028 & 0.037 \(\pm\) 0.016 & 0.032 \(\pm\) 0.016 & 0.035 \(\pm\) 0.0022 \\
**LPG** & 0.0054 \(\pm\) 0.003 & 0.0021 \(\pm\) 0.0023 & 0.0006 \(\pm\) 0.0002 & 0.0004 \(\pm\) 0.00001 & 0.0014 \(\pm\) 0.0001 \\
**Diesel** & 0.0007 \(\pm\) 0.0001 & 0.0005 \(\pm\) 0.0003 & 0.00023 \(\pm\) 0.00007 & 0.0002 \(\pm\) 0.00008 & 0.0002 \(\pm\) 0.00005 \\ \hline \hline \end{tabular}
\end{table}
Table 2: BC emission from different types of fuels; gasoline indicates GDI vehicles applied PM regulation (0.004 g km\({}^{-1}\)), LPG vehicles and diesel in EURO 6 vehicle at various speeds in the NIER mode.  
Figure 5: BC emission from different fuel types by regulation mode. CVS-75 for gasoline vehicle with GDI engine after PM regulation and LPG vehicle. NEDC for diesel vehicle of EURO 6.