Characterizing the gaseous and particulate SVOC emissions of a commercial light-duty compression ignition engine via GCxGC-ToF-MS

Abstract

Semi-volatile organic compounds (SVOCs) in gaseous and particulate states from a commercial light-duty compression ignition (CI) engine burning diesel fuel have been investigated by adopting two dimensional Gas-Chromatography Time-of-Flight Mass-Spectrometry (GC × GC-ToF-MS) coupled with a thermal desorption technique. Owing to the enhanced separation capability of the multidimensional gas chromatography, the SVOCs including 21n-alkanes (C12-C32), 16n-alkylcyclohexanes (C11-C25 and C33) and 13 polycyclic aromatic hydrocarbons (PAHs) (2–5 rings) have been identified and quantified under different steady engine loads. The experimental results demonstrated that at high engine load (8 bar BMEP @ 1800 rpm), SVOC emissions were higher than those at low engine load (2 bar BMEP @ 1800 rpm) by factors of 2.74 and 2.02 for gaseous and particulate states respectively. The impact of the diesel oxidation catalyst (DOC) on engine-out SVOCs was also analyzed. The results demonstrated that SVOCs did not reduce significantly (less than 16% for different compounds) at low engine load but decrease more dramatically at high engine load (by 37%–55%) when the DOC was above its light-off temperature. At high engine load, it turned out to be that the DOC mitigating effect was more remarkably on the gaseous SVOCs (38%–62%) than on the particulate SVOCs (26%–46%). Limited SVOC reductive capability of the DOC spurs the need of catalyst improvement, especially for capturing high molecular weight (HMW) organic compounds. Therefore, it would be desirable to further investigate the relationship between SVOC emissions and different types of aftertreatment techniques (i.e. DPF) in a more specific way.