Organic carbon, elemental carbon and particulate semivolatile organic compound emissions from a common-rail diesel engine: Insight into effect of fuel injection pressure at different loads

Abstract

Effect of fuel injection pressure on organic carbon (OC), elemental carbon (EC) and particulate semivolatile organic compounds (SVOCs), i.e., n-alkanes and polycyclic aromatic hydrocarbons (PAHs), emissions from a common-rail diesel engine was analyzed comprehensively. EC emission rate evidently decreased with increasing injection pressure at low fuel injection pressure ranges (80–120 MPa), while engine load effect on the EC emission was insignificant at high injection pressure ranges (140–160 MPa). The higher fraction of EC2 in the total EC emission appeared at the highest injection pressure ranges (140–160 MPa) under middle and high loads, suggesting the spontaneous carbonization process from soot precursor to ordered soot during the high temperature process. Low injection pressure provided poor combustion condition and caused unburned diesel fuel to volatilize more 2–3 ring PAHs. The percentage of 4-ring PAHs exhibited a rise-then-fall trend with increasing injection pressure, while the maximum percentage of 5–7 ring PAHs appeared at the highest injection pressure ranges (140–160 MPa) under high load condition, suggesting that higher combustion temperature and larger pyrolysis zone under the high injection pressure promoted the formation of lager and more stable PAHs. The fractions of fuel-derived short chain (C16-C21) and oil-derived long chain (C22-C33) in the total n-alkanes exhibited obvious load and injection pressure dependence.