Solid Particle Number and Mass Emissions from a Lean and Stoichiometric Gasoline Direct Injection Engine Operation

Paper #:
  • 2018-01-0359

  • 2018-04-03
Lean gasoline direct injection (GDI) engines are attractive for improving fuel economy; however, they are known to emit higher concentrations of particles due to greater in-cylinder fuel stratification. In this work, engine-out particle mass (PM) and particle number (PN) emissions are explored from a gasoline direct injection (GDI) engine operating in two lean modes and one stoichiometric mode. Operating conditions included four steady state speed and load conditions as well as two constant speed load steps. Results show that solid particles emitted from the engine under steady state conditions have a broad size distribution that is relatively flat between particle diameters of 10 and 100 nm. In certain operating regimes, lean homogenous modes can achieve lower particle number concentrations than stoichiometric modes while still improving engine thermal efficiency. Alternatively, lean stratified operating modes consistently result in significantly higher PN and PM emissions than both lean homogeneous and stoichiometric modes. Lean load steps show negligible soot emissions and only modest ash emissions when air-fuel ratio (AFR) is properly controlled. Stoichiometric load steps show moderate soot emissions, however ash-mode emissions in the 10 nm range spike drastically due to lubricating oil consumption caused by piston ring adjustment. Additionally, a large ash mode on the order of 1x107 #/cm3 exists for low speed and low load stoichiometric conditions under which there is a lack of soot particles that would otherwise scavenge the smaller ash mode particles. Previous studies of GDI particle emissions have mostly focused on soot, but the results of this study show that ash particles need to be considered, especially when implementing gasoline particulate filters (GPF) systems. The high concentration of ash particles found in some operating conditions illustrates that lubricating oil control is important for mitigating impacts on downstream GPF aftertreatment because ash particles cannot be removed during filter regeneration.
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