Performance of selective catalytic reduction (SCR) system in a diesel passenger car under real-world conditions

In this study, the influence of real-world conditions on the performance of a selective catalytic reduction (SCR) system in a Euro-6 diesel passenger car was analysed. NOx emissions and exhaust gas temperatures were recorded before and after the SCR system during real-world driving tests. The results showed that engine-out NOx emissions were positively correlated with vehicle specific power (VSP). The average NO(x )reductions (deNO(x)) of the SCR were 82.8%, 91.7%, and 85.5% for SCR-inlet gas temperatures below, within, and above the thermal window of 220-340 degrees C, respectively. The 92% of the tailpipe NOx peaks appeared under high power (VSP >= 10 W kg(-1)) and an insufficient deNO(x) level. Urban driving and long downhill sections in rural conditions caused cooling down of the SCR-inlet gas to below 200 degrees C, where the deNO(x) efficiency decreased and became dependent on the exhaust mass flow rate. To estimate the NOx benefit and CO2 penalty via electrical heating of the SCR-inlet exhaust gas, the vehicle, the real driving dynamics, and the heating were simulated in Passenger car and heavy-duty emission model (PHEM). The minimum threshold of 200 degrees C resulted in the best NOx /CO2 trade-off, reducing on average 4.7 mg of NOx per gram of CO2.