Quantitative high-resolution transmission electron microscopy nanostructure analysis of soot oxidized in diesel spray flame periphery

Abstract

In order to better understand the in-flame diesel soot oxidation processes, soot particles at the oxidation-dominant periphery of diesel spray flame were sampled via newly developed suck type soot sampler employing a high-speed solenoid valve, and their morphology and nanostructure were observed and analyzed via high-resolution transmission electron microscopy. A single-shot diesel flame for the soot sampling experiment was achieved in a constant-volume vessel under a diesel-like condition (9.5 kg/m3, 2.5 MPa, 1070 K, and 21%O2). Morphology of soot aggregates, inner-core/outer-shell structure of primary particles within the aggregates, and carbon crystallite nanostructures within the primary particles were compared between the soot aggregates sampled at the diesel flame core near the central axis and the oxidation-dominant flame periphery. The morphology observation and the inner-core/outer-shell structure characteristics obtained by newly employed concentricity analysis showed that the flame core soot exhibits graphitic primary particles with clear outlines and boundaries similarly observed for engine exhaust soot. Each primary particle contained a well-defined inner core surrounded by thick graphitic outer shell. On the contrary, the flame periphery soot exhibited smaller primary particles with unclear and lumpy outlines containing multiple obscured inner cores surrounded by thinner outer shell. The analysis of carbon crystallite nanostructures within the primary particles showed that the in-flame soot nanostructure shifts toward amorphous from the flame core to the periphery. On the contrary, the engine soot nanostructure in the literature shifts toward graphitic from the in-cylinder TDC to the exhaust, exhibiting the opposite trend with the in-flame soot. These results suggest that the engine exhaust soot has not experienced the rapid in-flame oxidation by OH radicals and is therefore considered not to be the remains of incomplete or partial oxidation, but the runaways escaped from the flame core to the exhaust without being attacked by the in-flame OH radicals.

Characterisation of soot agglomerates from engine oil and exhaust system for modern compression ignition engines

“…400 À Soot in exhaust 30 48À270 À Soot in engine oil 14 45À132 10À35 Soot in engine oil 11 150À500 35À45 Soot in engine oil 29 À 15À50 Soot in engine oil 6 . 400 À Soot inside cylinder 31 273-897 11.65 Soot inside cylinder 32 À 15…”

Review of morphological and chemical characteristics of particulates from compression ignition engines

“…The particles' size, shape, and microstructure are analyzed using a scanning electron microscope (SEM) and transmission electron microscopy (TEM). 362 Generally, engine operating conditions and fuel composition influence particulate morphology. 363 TEM is used to analyze the spherule (micro), aggregate (macro), and nanostructure (nano-scale) of particles.…”

“…363 TEM is used to analyze the spherule (micro), aggregate (macro), and nanostructure (nano-scale) of particles. 362 Energy-dispersive X-ray spectroscopy (EDS) identifies the organic substances and trace metals in the particles. 364 Sometimes, zero dilution is used to avoid soot condensation, nucleation of new particles, and aggregate breakup.…”

Soot particles in piston-top pool fires and exhaust at 5 and 15 MPa injection pressure in a gasoline direct-injection engine

“…1. From this HR-TEM image, the concentricity of carbon-layer fringes were calculated as recently reported in the bulk-gas sampling study focused on soot particles outside the pool fire [21], which effectively differentiates the inner core and outer shell region. The fringes of individual carbon layers were also processed to estimate the distance between fringe pairs (i.e., fringe separation, FS).…”