Quantifying the contributions of diesel fuel and lubricating oil to the SVOC emissions from a diesel engine using GC × GC-ToFMS

Abstract

Semi-volatile organic compounds (SVOCs) from diesel engine emissions have detrimental impact on air quality and human health. This study aims at characterizing the compositional SVOC emissions of a commercial diesel engine in both gaseous and particulate phases concurrently by using a two-dimensional Gas-Chromatography Time-of-Flight Mass-Spectrometry (GC × GC-ToFMS). 52 SVOCs including n-alkanes, n-alkyl-cyclohexanes and PAHs have been identified and quantified, and the contributions of diesel fuel and lubricating oil to the SVOC emissions have been evaluated under different engine loads by using the Positive Matrix Factorization (PMF) method. The distributional patterns of the gaseous SVOC emissions were found to be similar to those of the diesel fuel, while those of the particulate SVOC emissions were strongly associated with the lubricating oil. The PMF analysis illustrated that diesel fuel contributed to the SVOC emissions by nearly 70% at low load (442 ± 38 ug/kg·fuel), while lubricating oil dominated the SVOC emissions by over 50% at high load (595 ± 93 ug/kg·fuel). Additionally, we found that combustion by-products had nontrivial contributions to the SVOC emissions, increasing from 13% to 38% (from 83 ± 10 ug/kg·fuel to 443 ± 63 ug/kg·fuel) as load increased. The results obtained in this study could facilitate a better understanding of the SVOC formation mechanisms, and hence provide guidance for engine optimization towards SVOCs mitigation.