Effects of Lubricating Oil Additives on the Microphysical Properties of Diesel Exhaust Particulate Matter

ABSTRACT

In this work, experiments were performed on a diesel engine bench using different experimental fuels prepared by mixing diesel with three lubricating oil additives (LOAs), namely, an antioxidant, a detergent and a foam inhibitor. Diesel exhaust particulate matter (DEPM) samples were subsequently collected. The effects of the LOAs on the micromorphological and microstructural characteristics of the DEPM and its degree of graphitization were investigated using a combination of analytical methods (scanning electron microscopy, transmission electron microscopy and Raman spectroscopy) in conjunction with image processing software. The results showed the following: The DEPM diameter was determined by the polycyclic aromatic hydrocarbon (PAH) content of the fuel. Unburned PAHs caused the organic matter component of the DEPM to precipitate between the lamellae of its primary carbon particles (PCPs). The addition of the antioxidant to the fuel resulted in increased chemical heterogeneity of the DEPM. Furthermore, the D peak in the Raman spectrum of this DEPM had the highest intensity. The DEPM generated from combustion of the foam inhibitor-diesel fuel had the largest average PCP crystallite size; the addition of the foam inhibitor increased the degree of graphitization of the DEPM, and the graphite crystallites in this DEPM were the largest (4.65 nm). The DEPM generated from the combustion of the detergent-diesel fuel had the largest PCP interlayer spacing (mainly in the range of 0.42–0.44 nm). The LOAs did not significantly impact the C-C bond length in the DEPM graphite lattice.

GRAPHICAL ABSTRACT

KEYWORDS:

• Lubricating oil additive
• Particle micromorphology
• Particle microstructure characteristics
• Degree of graphitization of particles
• Raman spectra

Article highlights

1. The effects of lubricating oil additives on the micromorphological and microstructural characteristics and the degree of graphitization of diesel exhaust particulate matter (DEPM) were analyzed.

2. An increase in the cetane number of the fuel resulted in larger graphite crystallites in the DEPM.

3. As the polycyclic aromatic hydrocarbon content of the fuel increased, DEPM more easily adsorbed many intermediate products, resulting in increased chemical heterogeneity.

4. An increase in the heavy fraction content of the fuel increased the organic matter component of the DEPM between the lamellae of the primary carbon particles (PCPs) comprising the DEPM, resulting in increased PCP interlayer spacing.

Acknowledgments

The authors gratefully acknowledge financial support from National Natural Science Foundation of China (NSFC 51506011, 11802039), Natural Science Foundation of Jiangsu Province (BK20160406), Natural Science Research Project of Jiangsu Higher Education Institutions (15KJB470001, 18KJB470001) and Basic research project of Suzhou (SYG201515).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51506011,11802039]; Natural Science Foundation of Jiangsu Province [BK20160406]; Basic research project of Suzhou [SYG201515]; Natural Science Research Project of Jiangsu Higher Education Institutions [15KJB470001,18KJB470001].