Impacts of ambient temperature, DPF regeneration, and traffic congestion on NOx emissions from a Euro 6-compliant diesel vehicle equipped with an LNT under real-world driving conditions

Abstract

A real driving emissions test procedure was introduced as a supplement to the chassis dynamometer test to diminish the discrepancy between on-road emissions and type approval certification emissions. In this study, on-road NOx emissions from a 2.2 L diesel vehicle equipped with a lean NOx trap were measured not by a portable emissions measurement system but by NOx sensors and an exhaust flow meter. This method provides a strategy for analyzing on-road NOx emissions with a measurement system that is relatively cheap, light and simple. The effects of ambient temperature, diesel particulate filter regeneration, traffic congestion, NOx conversion efficiency and uphill/downhill sections on NOx emissions were evaluated by comparing the NOx emissions characteristics using engine-out and lean NOx trap-out NOx sensors. NOx emissions in congested traffic conditions were 29% higher than those in smooth traffic conditions. NOx emissions at 33 °C were 55% higher than those at 27 °C. Additionally, NOx emissions under specific conditions with diesel particulate filter regeneration were 30% higher than those under normal conditions. The average on-road NOx emission factor for all test cases was 7.35, but this value decreased to 5.7 when an ambient temperature corrective factor (1.6) was applied for extended test conditions.