Investigation of the Formation of Nh3 Emissions as a Function Ofvehicle Load and Operating Condition

The objective of this study was to examine ammonia (NH3) exhaust emissions as a function of different vehicle operating conditions and cycles. A total of eight vehicles with low-emission vehicle (LEV) to super-ultra-low-emission vehicle (SULEV) certification were tested over the Federal Test Procedure (FTP75), a US06 cycle, a hot running 505, a New York City Cycle (NYCC), and a specially designed Modal Emissions Cycle (MEC01v7) using both as-received and bench-aged catalysts. Modal NH3 emissions measurements in the raw exhaust were obtained using a tunable diode laser (TDL). The results show that NH3 emissions are cycle-dependent, with higher emissions found for more aggressive cycles. Modal emissions data show that NH3 emissions are primarily generated during acceleration events, although for some vehicles NH3 emissions are formed in the period immediately after catalyst light-off. Strong correlations were found between tailpipe NH3 measurements and both vehicle specific power (VSP) and engineout carbon monoxide (CO) emissions. The correlation with CO is consistent with the role of CO in forming NH3 emissions via the water-gas shift reaction. Statistically significant but weaker correlations were found between NH3 emissions and engine-out total hydrocarbons (THC), oxides of nitrogen (NOx), and air/fuel (A/F) ratio. * Corresponding author. e-mail: [email protected]