Linking operating conditions of a GDI engine to the nature and nanostructure of ultrafine soot particles

Sub-23 nm particulate emissions from internal combustion engines have become a topic of interest for research and legislative regulations in recent years. Many studies focused on electrical mobility measurements of soot particles, but few works employed additional techniques that do not rely on equivalent diameters. In this work, exhaust-sampled soot from a 1.0 L gasoline direct injection engine was analysed by transmission electron microscopy (TEM). Three operating conditions were assessed: 1500 rpm fast-idle, 1500 rpm with 40 Nm and 1750 rpm with 20 Nm brake torque. A distinct mode of sub-10 nm particulates was found equally distributed on some sections of the TEM grids for all three conditions. These particulates appeared to be stable under the electron beam, suggesting a non-volatile nature. Differential mobility spectrometer measurements with and without catalytic stripper suggested the presence of volatiles but also indicated high levels of solid sub-23 nm particulates. Furthermore, more fractal soot agglomerates consisting of several primary particles were also observed by TEM. The nanostructure of primary particles exhibited mainly core-shell nanostructures for all operating conditions. An additional amorphous layer was observed surrounding primary particles for 1500 rpm fast-idle. Amorphous particulates and crystalline regions in agglomerates were identified for 1750 rpm with 20 Nm brake torque. Fringe analysis of the nanostructures was conducted for all three samples, with preliminary findings indicating similar fringe lengths of ca. 1.04 nm and tortuosity values of around 1.16. (C) 2022 The Author(s). Published by Elsevier Inc. on behalf of The Combustion Institute.

Automated summary

This study analyzed sub-23 nm particulate emissions from internal combustion engines using techniques that do not rely on equivalent diameters. It found the presence of stable, non-volatile sub-10 nm particulates in the exhaust, as well as fractal soot agglomerates consisting of several primary particles. The primary particles exhibited mainly core-shell nanostructures, and additional amorphous layers or crystalline regions were observed under different operating conditions.