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

Abstract

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 NOx reductions (deNOx) 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 °C, respectively. The 92% of the tailpipe NOx peaks appeared under high power (VSP ≥ 10 W kg−1) and an insufficient deNOx level. Urban driving and long downhill sections in rural conditions caused cooling down of the SCR-inlet gas to below 200 °C, where the deNOx 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 °C resulted in the best NOx/CO₂ trade-off, reducing on average 4.7 mg of NOx per gram of CO₂.