An overview of physical and chemical features of diesel exhaust particles

Diesel exhaust particles have a negative impact on both human health and the ecosystem. An adequate understanding of the physical and chemical characteristics of diesel exhaust particles is essential for both minimizing particles formation and optimizing particles oxidation. This paper systematically reviews the physicochemical characteristics of diesel exhaust particles. Firstly, the approaches to studying the characteristics of diesel exhaust particles are described and the main features of particulate matter (PM) such as particle size distributions, microstructure of aggregate particles, nanostructure of primary particle, chemical compositions of diesel particles and oxidation reactivity of diesel particles are discussed in this paper. Then, the effects of operating parameters containing engine speed, engine load, injection pressure, injection timing and exhaust gas recirculation (EGR) on each PM feature are summarized and discussed in detail. Subsequently, the relationships between PM features and its oxidation reactivity are exclusively reviewed. It can be concluded that soot oxidation reactivity is influenced by the combination of multiple properties of the emitted PM. Finally, concluding remarks are presented and further research recommendations are listed.