Pollutant emissions and diesel oxidation catalyst performance at low ambient temperatures in transient load conditions

Abstract

In this paper an experimental analysis of the ambient temperature effect on diesel engine pollutant emissions is carried out. The study is focused on hydrocarbons and carbon monoxide of both engine out pollutants formation analysis and diesel oxidation catalyzer (DOC) performance. The experiments were carried out at transient engine load conditions of Worldwide harmonized Light vehicles Test Cycle (WLTC) at two levels of ambient temperature: 20 °C and −7 °C. The study presented in this work shows significant different results depending on the pollutant analysed. Regarding hydrocarbons, a significant dependence of pollutant formation on ambient temperature is observed, being the emissions at −7 °C between two and three times the emissions at 20 °C. The DOC performance between temperatures shows similar conversion efficiency. In the case of carbon monoxide formation, temperature dependence plays a less important role than the engine load conditions. The reduction of air fuel ratio at transient conditions drives to unsteady CO profiles emissions along the WLTC that reduce the pollutant conversion with a greater negative impact at −7 °C.