Pyrolysis characteristics of particulate matter from diesel engine fueled with methanol/bio-diesel

Abstract: Diesel exhaust particle matter is the main source of air pollutants PM2.5. It is limited not only on the quality but also on the number. Therefore, the widespread use of clean alternative fuel in diesel engine is one of the effective ways to reduce particulate emission. Previous study reported the effects of methanol/biodiesel blending fuel on the volatilization, oxidation process parameters and kinetic parameters of particle matter emitted from diesel engine. The volatilization, oxidation process parameters of particle matter varied with the methanol/biodiesel blending ratio (100%, 5%, 10%, 15%) were measured by the TGA/DSCI thermal analyzer, manufactured by Mettler, Switzrland. The mass change curves of the particles in the surroundings of N2 and O2 were obtained by thermo-gravimetric analyzer. Further, the volatilization and oxidation features of the particles were studied according to the pyrolysis curves (TG/DTG), the characteristic temperature and activation energy of pyrolysis of particles were calculated by tangent method and Flynn-Wall-Ozawa (FWO) pyrolysis kinetics. The results showed that when the content of H2O in particle matter was increased from 2.6% to 3.5%, the quality of soluble organic fraction (SOF) in particle matter could be increased from 26.1% to 32.5%, the peak of mass change rate and the temperature of the peak of SOF would be increased with the increasing of the methanol ratio. In O2 surroundings, the derivative thermal gravimetry curves of particle matter under 4 kind of blending fuels showed that the change way of SOF was consistent with that in N2 surroundings, but the peak value in O2 atmosphere was obviously greater. The soot mass showed a decreasing trend with the increase of ratio of methanol, which was decreased from 70.3% to 63.8%. In addition, the peak of mass change rate of soot was increased and the temperature of the peak was decreased, which indicated that the particles were more easily oxidized. The initial combustion temperature of soot was decreased from 488 ℃ to 458 ℃. Meanwhile, the SOF initial combustion temperature and the burnout temperature were slightly lower, and the total time of pyrolysis reaction of particles was shortened. The activation energy of particle matter was reduced from 140.3 kJ/mol to 117.3 kJ/mol. In summary, the pyrolysis properties of the particles were enhanced and the thermo chemical reaction of particles was easily carried out. These results could provide a theoretical basis for the treatment of methanol/biodiesel combustion particulates, and it is helpful to the design and application of diesel particulate filter (DPF).