Experimental investigation into the oxidation reactivity, morphology and graphitization of soot particles from diesel/n-octanol mixtures

Aiming to investigate the impacts of n-octanol addition on the oxidation reactivity, morphology and graphitization of diesel exhaust particles, soot samples were collected from a four-cylinder turbocharged diesel engine fueled with D100 (neat diesel fuel), DO15 (85% diesel and 15% n-octanol, V/V) and DO30 (70% diesel and 30% n-octanol, V/V). All tests were conducted at two engine speeds of 1370 and 2150 r/min under a fixed torque of 125 N·m. The soot properties were characterized by thermogravimetric analyzer (TGA), transmission electron microscopy (TEM) and Raman spectroscopy (RS). The higher volatile organic fraction content, lower soot oxidation temperatures and lower activation energy from TGA results indicated that both the increasing n-octanol concentration and engine speed enhanced the soot oxidation reactivity. Additionally, quantitative analysis of TEM images showed that the soot derived from DO30 had the smallest primary particle diameters and fractal dimension, followed by those of soot produced by DO15 and D100. The RS results demonstrated that the n-octanol addition and higher engine speed led to a larger D1-FWHM (D1-full width at half maximum), A_D1/A_T (area ratio of D1 band and the total spectral) and A_D3/A_T (area ratio of D3 band and the total spectral) as well as a smaller L_a (crystallite width), revealing a lower degree of graphitization. Furthermore, the correlations between characterization parameters of soot properties and reactivity were nonlinear.

Nanostructure and reactivity of soot particles from open burning of household solid waste

The main purpose of this work was to quantify and characterize chemically and morphologically the emission of soot particles from the open burning of several common solid waste including paperboard, wood, peel, chemical fiber, polyethylene (PE) and polyvinyl chloride (PVC). The experiment was conducted in a laboratory-scale open-burning combustor with a dilution sampling system to obtain soot particles. The thermogravimetric profiles (TGA) showed an increasing order of oxidation reactivity: PE > PVC > fiber > paper ≈ peel > wood. High resolution transmission electron microscopy (HRTEM) images revealed more detailed information about the morphology and the particle size of soot aggregates. Subsequent quantification of nanostructure by fringe analysis showed that plastics generated soot particles with the looser carbon layers with higher tortuosity compared to the three kind of biomass. Raman spectroscopy further confirms the observed differences. In addition, wood soot exhibited the highest content of C-OH group (17.5%) among the six samples (X-Ray photoelectron spectroscopy, XPS), whereas PE and PVC soot exhibited the highest absorption peaks of aliphatic C-H groups (Fourier transform infrared spectroscopy, FTIR). Comparative analysis revealed that the interlayer distance was more important on the evaluation of reactivity than soot morphologies. The present work concluded that the physiochemical characteristics of soot particles releasing during open burning are strongly depending on waste composition and provided new data for the understanding of soot emissions from open burning.