Morphological Examination of Nano-Particles Derived From Combustion of Cerium Fuel-Borne Catalyst Doped With Diesel Fuel

摘要

This experimental work focuses on defining the detailed morphology of secondary emission products derived from the combustion of cerium (Ce) fuel-borne catalyst (FBC) doped with diesel fuel. Cerium is often used to promote the oxidation of diesel particulates collected in diesel aftertreatment systems, such as diesel particulate filters (DPFs). However, it is suspected that the secondary products could be emitted from the vehicle tailpipe without being effectively filtered by the aftertreatment systems. In this work, these secondary emissions were identified by means of a high-resolution transmission electron microscope (TEM), and their properties were examined in terms of morphology and chemistry. In preparation for fuel doping, a cerium-based aliphatic organic compound solution was mixed with a low-sulfur (110 ppm) diesel fuel at 50 ppm in terms of weight concentration. During combustion, particulate samples were collected from the exhaust manifolds of a 1.7-L, light-duty diesel engine by using a novel thermophoretic sampling system. The TEM and customized image processing/data acquisition systems are key instruments for the analysis of the morphology of particulate emissions. An energy dispersion X-ray spectrometer (EDXS) was used to analyze the chemistry of particulate emissions. Our analyses revealed that the Ce-FBC produced additional nano-particles beyond diesel particulates; the average size of nano-particles was found to be in a range of 3 to 4 nm in diameter under various engine operating conditions. The presence of such ceria nanoparticles was validated by an EDXS. The number concentration of ceria particles attached to soot aggregates apparently depended on the engine operating conditions. However, more ceria particles appeared to be present in the gaseous emission streams rather than were on the soot particles. With the use of Ce-FBC in fuel, the total mass of soot particles was found to decrease somewhat, while the total mass of particulate matter (PM) emissions, including ceria particles, was comparable with that in the case measured without use of Ce-FBC.