Effects of exhaust gas recirculation on the functional groups and oxidation characteristics of diesel particulate matter

The effects of EGR on the carbon-containing functional groups in PM were determined by X-ray absorption near-edge spectroscopy. A TG analyzer was used to determine the effects of EGR on the components and oxidative activity of PM. The results show that the use of EGR in the diesel engine had a minor influence on the types of carbon-containing functional groups in the PM; however, it did affect their relative contents. As the EGR rate increased, the aromatic and graphitized carbon contents of the PM gradually decreased, and the contents of the oxygen-containing and aliphatic C H functional groups increased, which strongly promoted the oxidative activity of the PM. The percentage of soot in the PM decreased with the use of EGR, while the percentages of water and volatile organic matter increased. In addition, the volatile emission temperature TSOF1 gradually decreased, and the trends in the initial volatile combustion temperature TSOF2, the soot ignition temperature Ti, and the burnout temperature Th were consistent with that in the volatile emission temperature. Both the combustion and burnout characteristic indices gradually increased as the EGR rate grows. Instead, the activation energy decreased dramatically, and the energy required for PM to react decreased with the increase of EGR rate.