Abstract
Pyrolysis of three practical fuels, i.e., petroleum diesel (PD), diesel from direct coal liquefaction (DDCL), and diesel from indirect coal liquefaction (DICL) were conducted at temperatures from 950° to 1450 °C in a flow reactor. The effect of temperature and fuel components on soot formation were investigated through measurement of particle volatility, size distribution (PSD), and monocyclic/polycyclic aromatic hydrocarbon (MAH/PAH) profiles. DDCL and DICL were mainly composed of cycloalkane and paraffin, respectively, and both of them were almost free of aromatics compared with PD. Results showed that pyrolysis of DDCL produced the highest particle mass concentration and broadest PSDs, followed by PD and DICL, indicating that cyclic and aromatic components had a strong promote effect on sooting tendency. ∑PAH mass concentrations of practical fuels followed the same order of DDCL > PD > DICL as particle mass concentrations and PSDs, and DDCL formed the highest ∑PAHs at a lower temperature (1050 °C) compared to that of PD (1150 °C) and DICL (1250 °C), attributing to the different pyrolysis routes of these fuel components. The chemical kinetic simulation revealed that the fuel components mainly influenced benzene formation below 1150 °C, where nucleation effect was dominant in particle behaviors. For all tested fuels, 3–4 ring PAHs / alkyl PAHs exhibited the highest mass concentrations at the whole temperature range, suggesting a primary contribution to particle nucleation. The fraction of high molecular weight PAHs showed a rise-then-fall trend, and the decrease of corresponding fractions above 1250 °C could be ascribed to their accelerated conversion to soot. Particles and PAHs showed a high correlation at the whole temperature range for tested fuels, and two-stage pyrolysis related to temperature was verified by varieties of particle and PAH characteristics. According to analytical results obtained in this study, DICL has the potential to be applied in low-temperature-combustion engines to control particle and PAH emissions.
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