## 3 Results
### Emission Rate of Ammonia  
Measurements were conducted using the CVS-75 mode for gasoline and LPG vehicles, the WLTC mode for EURO6 vehicles, and the NEDC mode for EURO4 vehicles in Table 5 to assess NH\({}_{3}\) emissions based on the regulatory test mode. The findings indicate that gasoline vehicles emit the highest levels of NH\({}_{3}\), followed by LPG and diesel vehicles. During the CVS-75 cycle, the gasoline vehicle G1 exhibits the highest NH\({}_{3}\) ER of 61.8 mg/km, while the LPG vehicle L2 displays the second-highest ER, measuring 17.8 mg/km. In contrast, both EURO4 and EURO6 diesel vehicles demonstrate negligible NH\({}_{3}\) emissions, with values of 0.2 mg/km or lower. Table 5 provides the NH\({}_{3}\) emissions of each vehicle type in different test modes. Among the gasoline vehicles, G1 exhibits the lowest NH\({}_{3}\) emissions in the CVS-75 mode, a regulatory test mode, but emits the highest levels of NH\({}_{3}\) in the US06 and WLTC modes, which are preheating modes (hot start). In the US06 mode, characterized by an average speed of 77 km/h and maximum acceleration of 3.8 m/s\({}^{2}\), the increased NH\({}_{3}\) emissions can be attributed to the more rapid driving characteristics compared with other modes. The higher NH\({}_{3}\) emission rate in US06 can be mainly attributed to the higher emission during the aggressive acceleration section [40]. Furthermore, NH\({}_{3}\) emissions in the NEDC mode are higher than those in the CVS-75 mode. This result suggests that the emission variation is influenced by the difference in driving stability between the CVS-75 and NEDC modes, despite both being under the same cold start condition. Similarly, G2 exhibits the lowest NH\({}_{3}\) emissions in the CVS-75 mode, consistent with G1 but with a different absolute value. In addition, G2 demonstrates similar NH\({}_{3}\) emission levels in the US06 and WLTC modes compared with G1, highlighting the impact of turbocharger absence, unlike G1, and resulting in differing NH\({}_{3}\) emissions during rapid acceleration/deceleration. Consequently, G2 exhibits the highest NH\({}_{3}\) emissions in modes characterized by frequent acceleration sections. Among the two LPG vehicles, emissions tests were conducted solely in the CVS-75 and US06 modes. The 2.0 L class L1 exhibits minimal NH\({}_{3}\) emissions of 4.4 mg/km, lower than \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Mode** & **G1** & **G2** & **L1** & **L2** & **D6-1** & **D6–2** & **D4-1** & **D4-2** \\ \hline CVS-75 & 61.8 & 8.7 & 4.4 & 17.8 & - & - & - & - \\ WLTC & 114.9 & 27.4 & - & - & 0.2 & 0.00 & 0.07 & 0.03 \\ US06 & 123.9 & 22.0 & 4.7 & 30.3 & 0.4 & 0.05 & 0.01 & 0.03 \\ NEDC & 106.0 & 15.0 & - & - & 0.4 & 0.09- & 0.04 & 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Emission rate of NH\({}_{3}\) by test mode (mg/km). that of the equivalent 2.0 L class G1. L2 emits higher levels of NH\({}_{3}\) compared with L1, with NH\({}_{3}\) emissions in the US06 mode, a rapid acceleration/deceleration mode, being 1.7 times higher than those in the CVS-75 mode. These two vehicles share the same displacement but differ in fuel control method, suggesting that the fuel injection method of LPG vehicles influenced NH\({}_{3}\) generation. All four diesel vehicles emit small amounts of NH\({}_{3}\), measuring 0.4 mg/km or less across all modes. Despite EURO6 vehicles being equipped with SCR, which could result in ammonia slip, no NH\({}_{3}\) emissions indicative of slip are detected in the actual regulatory and rapid acceleration/deceleration modes. In addition, minimal NH\({}_{3}\) emissions are observed in the driving mode after initial startup, distinguishing diesel vehicles from gasoline and LPG vehicles. This discrepancy can be attributed to differences in the combustion method, with diesel vehicles employing lean combustion compared with gasoline and LPG vehicles equipped with air-fuel ratio control devices.