Comparison of HC species from diesel combustion modes and characterization of a heat-up doc formulation

Abstract

This study summarizes engine speed and load effects on HC species emissions from premixed charge compression ignition (PCI) and conventional diesel combustion, and it evaluates diesel oxidation catalyst (DOC) formulations on a gas flow reactor for the purpose of diesel particulate filter regeneration or lean NO x trap desulfation. HC emissions are sampled simultaneously by a Tedlar bag for light HC species and by a Tenax TA TM adsorption trap for semi-volatile HC species, and they are analyzed by gas chromatography with a flame ionization detector. The bulk temperature and residence time during combustion are key parameters that are important for understanding the effects of speed and load on engine-out HC emissions. The degree of post-flame oxidation is higher in PCI than in conventional combustion, and it is increased for PCI with a higher speed and load, as indicated by a lower fuel alkanes/THC ratio, a higher alkenes/fuel alkanes ratio, and a higher methane/THC ratio. Ethene and n-undecane are two representative HC species, and they are used as a surrogate mixture in the gas flow reactor to simulate PCI and conventional combustion with in-cylinder post fuel injection. Among the three DOC formulations tested, the catalyst with constituent precious metals of platinum and palladium (PtPd) showed the best light-off performance, followed by PtPd with an addition of cerium dioxide (PtPd+CeO 2 ), and platinum (Pt), regardless of exhaust compositions. Conventional combustion exhaust composition shows a lower light-off temperature than that of PCI, regardless of catalyst formulation.

Fractionation of engine exhaust hydrocarbons using flame ionization detection with variable temperature sample conditioner

“…The heavy hydrocarbon fraction appears to be independent of load and combustion mode as it exhibits no discernible trend over the tested conditions. The fractions of unburned versus partially burned species closely match the findings of Han et al 24 where a comprehensive GC speciation study was used to determine similar fractionation information. They found that the fraction of unburned (fuel-like) hydrocarbons decreased from 70% to 60% between 2 and 4 bar LTC engine conditions for a similar light-duty engine to that used in our study.…”

Volatility characterization of nanoparticles from single and dual-fuel low temperature combustion in compression ignition engines

“…These emissions contain a range of organic compounds with molecular weight ranging from methane to unburned fuel molecules and heavy polycyclic aromatic (PAH) compounds (Merritt et al 2006). In-cylinder formation mechanisms and speciation of HCs from LTC have been studied (Knafl et al 2006;Colban et al 2007;Han et al 2008). Although solid particle mass concentrations are very low for LTC, high concentrations of semivolatile HC in LTC exhaust are known to form nanoparticles through nucleation and growth mechanisms upon primary dilution (Northrop et al 2011a).…”

Modeling of diesel oxidation catalysts for calibration and control purpose

“…[11][12][13][14][15][16][17][18] Finally, the effect of the H 2 O adsorption mechanism is also implemented in the model. This is an important phenomenon that can strongly influence the HC adsorption and therefore the general DOC performance, especially during the engine warm-up.…”