Impact of early injection on physicochemical characteristics of diesel soot particles

Abstract

The early injection is widely employed in advanced combustion technologies, which could substantially impact the engine particulate matter (PM) emissions. The primary objective of the present study was to investigate the effect of early injection on the diesel soot particle characteristics, so as to obtain comprehensive information when using a diesel particulate filter (DPF) for PM reduction. Three operating modes were employed, including P (-50 CA), P (-30 CA) and P (-10 CA), which were marked by the early injection timing. The main injection was adjusted such that three modes have similar combustion phases. The soot particles were produced from a heavy-duty diesel engine. Transmission electron microscopy (TEM) and Raman spectroscopy were used to analyze morphology, nanostructure and graphitization degree. Thermalgravimetric analysis (TGA) was done to quantify the volatile fraction content of particles, as well as the oxidation reactivity. Results showed that with early injection advanced, primary particle size became bigger with more disordered nanostructure and lower graphitization degree. Meanwhile, the advanced early injection resulted in relatively more organic carbon (OC) and higher oxidation reactivity of the produced soot particles because incomplete combustion caused by spray-wall impingement and suppressed in-cylinder PM oxidation process.