Morphology and Raman Spectra of Engine-Emitted Particulates

Abstract

The morphology and nanostructure of soot from different engines were studied. The soot samples were collected from a 1.9 L Volkswagen light-duty diesel (LDD) engine for two different fuel types [ultralow sulfur diesel (ULSD) and B20] and six speed/load combinations, as well as from a heavy-duty engine using a pilot-ignited high-pressure direct-injection (HPDI) natural-gas combustion system for three different speed/load combinations. Transmission electron microscopy (TEM) was employed to investigate the soot morphology by using alternative fractal measurement methods. The fractal dimensions (D f) were computed from the scaling of the projected aggregate dimensions with the number of primary particles ("LW" method) and two-dimensional pair correlation functions. For the soot collected from the LDD, it was found that the fractal dimensions are independent of fuel type, while a higher engine load slightly decreased D f. The soot produced by the HPDI exhibited a similar correlation between D f and engine load. The fractal dimension of the engine-emitted soot was measured in a range of 1.70-1.85 and the fractal prefactor k fLW of 1.08-1.39. Raman spectroscopy was used to characterize the soot nanostructure based on the degree of microstructural disorder. The Raman spectral analysis was done using two-band ("G" at ∼1578 and "D" at ∼1340 cm −1) and five-band (G, D1, D2, D3, and D4 at about 1580, 1350, 1500, 1620, and 1200 cm −1 respectively) combinations. For the soot sampled from the LDD, the results from both methods showed that B20 soot exhibited a greater structural disorder. Likewise, the Raman analysis of the soot from both engines also showed that the increase in engine load condition caused increases in the degree of the structural order of soot. The use of either D/G ratio or D1 width cannot distinguish between the HPDI and the LDD soot. However, on a plot of D/G versus D1, the data fall into distinct clusters. This may indicate the importance of using more than two spectral parameters to characterize the soot samples. Supplementary materials are available for this article. Go to the publisher's online edition of Aerosol Science and Technology to view the free supplementary files.

Carbon Nanotube and Fullerene Emissions from Spark-Ignited Engines

“…By imaging regions of the grid away from the stagnation point, where the distance between particles is much greater than the particle diameter, we virtually eliminate the possibility of creating artificial agglomerates on the grid. This device has been used extensively for compression-ignition engine exhaust sampling (Soewono and Rogak 2011) and is similar in principle to that used by Rogak et al (1993). In an earlier study of engine soot using the same TPS, it was found that particle projected area equivalent diameter measurements from the TPS/TEM method were within 5% of the mobility diameter (Soewono and Rogak 2011).…”

“…Few studies (of diesel or gasoline engines) have examined more than several hundred aggregates, so rare CNT/FUL might be dismissed as contamination. After finding the CNT/FUL particles in autorickshaw emissions, we reanalyzed TPS/TEM images from an earlier study of diesel and NG compression-ignition engines (Soewono and Rogak 2011). Review of 600 images from that study (which used the same sampling methods as used in the present work) yielded only 3 possible FULs with the characteristic hollow core.…”

Raman spectroscopy and TEM characterization of solid particulate matter emitted from soot generators and aircraft turbine engines

“…The FWHMs of the D 1 and G bands, i.e., W(D 1 ) and W(G), have been used extensively in the literature to compare the graphitic structure of carbonaceous material (Wang et al 1990;Dippel et al 1999;Sadezky et al 2005;Knauer et al 2009;Soewono and Rogak 2011). Higher D 1 and G band FWHMs show higher levels of chemical heterogeneity and a lower degree of structural order (Knauer et al 2009).…”

The correlation of distribution of PM number emitted under actual conditions of operation by PC and HDV vehicles

“…Images of various aggregates of soot emitted for various loads of compression ignition engines in PC and HDD category vehicles made with the use of TEM technique [12]. Due to the standard complied by the engine, in literature we can distinguish between soot complying with Euro 2-4 [7,13,14].…”

“…2) and standards of emission of toxic components of exhaust gases complied by the engine [6,11,12]. The division of soot according to the last criterion is mainly ascribed to the change of generation of power systems with direct injection of fuel (change of such parameters as injection pressure, droplet size and dose division), optimization of combustion process as well as aftertreatment system (Tab.…”