Blending Effects of Nitrogenous Bio-Fuel on Soot and NOx Formation during Gasoline Combustion

Abstract

Bio-fuel plays an important role in addressing the issue of CO2 and pollutant emission during cocombustion with fossil fuels. In this work, the effects of nitrogenous bio-fuel on soot and NOx formation during gasoline combustion were numerically investigated. Three bio-fuels, modeled by mixtures of pyridine, ethyl acetate, and ethanol with different volume fractions of pyridine and named SIM1 (0%), SIM2 (0.5%), and SIM3 (1%), were adopted to investigate the formation of soot and NOx when coburning with gasoline. Two mechanisms, i.e., the Glarborg mechanism and the Okafor mechanism, were employed to study the difference in soot and NOx formation. Results showed that pyridine exhibited different effects on soot formation in different regions. Based on the Okafor mechanism, soot formation was suppressed at the height of z = 3–4 cm, while it was promoted at the height of z = 4.5–5.5 cm. However, a reverse trend was predicted by the Glarborg mechanism. Moreover, the peak soot volume fraction (SVF) calculated by the Okafor mechanism was obviously higher than that calculated by the Glarborg mechanism; the major reason for the inconsistency of SVF in the two mechanisms was that more C6H5CH3 reacted with OH radicals to form C6H5CH2 in the Glarborg mechanism, resulting in less C6H5CH3 forming benzene (A1). Along with the increase of the pyridine proportion in the bio-fuel, the concentrations of NO increased by 92.1 and 91.4% in both mechanisms, attributed to the pyrolysis of pyridine into HCN, which promoted the formation of NO precursors (N, NH, NCO, and HNO) and thus NO. The difference in NO formation between the two mechanisms was because the reaction rate of NO converted from NO precursors in the Glarborg mechanism was higher than that in the Okafor mechanism. The NO2 was converted from NO via the reaction of NO + HO2 = NO2 + OH, and it distributed in the region with a lower NO concentration.