Raman characteristics of PM emitted by a diesel engine equipped with a NTP reactor

PM emitted by a diesel engine equipped with a NTP reactor was sampled at different engine loads. Raman spectra change with engine loads and the oxidation processes were investigated. Furthermore, the relations of Raman parameters with oxidation behaviour and thermal kinetics were analysed. Results showed that Raman spectra were dependent on engine operating conditions, and plasma exerted a significant influence on the Raman spectra. The D and G peak positions in the Raman spectra shifted slightly for some PM aggregation samples due to the changes in C-H. The intensity ratio I-D/I-G of original spectra increased during the oxidation process compared with the nascent value. The intensity ratio I-D1/I-G obtained by curve-fitting method for PM-NTP was higher than raw PM and PM aggregation. However, the area ratio A(D3)/A(G) was the highest for raw PM due to partial oxidation of oxygen functional groups in the plasma zone for PM-NTP and PM aggregation. The crystallite width, calculated using I-D1/I-G, was similar to that found from HRTEM results. The temperature at 50% mass loss was inversely related with D3 FWHM, and the activation energy increased with G FWHM. Apparent oxidation rate constant at 50% mass loss showed positive correlation with D1 FWHM. (C) 2016 Elsevier Ltd. All rights reserved.