| With the depletion of fossil fuel,the extremely urgent of environmental problems,and the gradual implementation of the carbon neutrality bill,searching a cleaner alternative fuel for fossil fuel has become a top priority for future development.The utilization of biomass energy has continued from the birth of human to today,and the progress of science and technology made it more clean and efficient.With its own carbon neutralization characteristics and advanced preparation technology,bio-oil are expected to replace some fossil fuels and be applied to various thermal equipment.Although the use of bio-oil can effectively alleviate the shortage of fossil energy,further attention and research on the emission characteristics of co-combustion of biofuels and fossil fuels are worthwhile.In this paper,the formation mechanisms of soot and NOx in gasoline flame blended bio-oil that with ethyl acetate and ethanol as model compounds were studied by numerical simulation.In addition,considering the trace nitrogenous compounds in bio-oil,pyridine was added to the model compounds of bio-oil to explore the mechanism of pyridine affecting soot and NOx formation.When the proportion of ethyl acetate in bio-oil increased from 0%to 75%,the peak flame temperature and peak NO concentration increased by 3.02%and 130%,respectively,while the peak soot volume fraction decreased by 74.5%.Both the temperature variation of the flame and the detailed formation path of NO indicated that the NO in the bio-oil/gasoline flame was produced by two pathways,named as thermal NO pathway and NO reburning cycle pathway,which the thermal NO pathway was dominant.When the proportion of ethyl acetate in bio-oil increased,the concentration of H radical are decreased,and the decreasd concentration of H radical inhibited the rate of reaction C6H5CH3+H<=>Al+CH3,resulting in the limitation of Al formation.The decrease of Al concentration inhibited the growth of PAH,soot nucleation and soot surface growth,which ultimately hinder soot formation and lead to a reduation in soot volume fraction.When the proportion of pyridine increased,the variation of soot volume fraction was limited,while the concentration of NOx has a significant growth trend,the results indicated that the addition of pyridine made the fuel-type NOx pathway dominant in the NOx formation process in bio-oil/gasoline flame.Comparing the difference of soot formation between Okafor mechanism and Glarborg mechanism,it can be found that the peak soot volume fraction in Okafor mechanism was significantly higher than that in Glarborg mechanism,it was mainly due to the fact that part of C6H5CH3 in Glarborg mechanism was consumed by OH radical,resulting in less C6H5CH3 used to formate Al in this mechanism.In pyridine-free conditions,the reaction rate constant of N+OH=NO+H in Glarborg mechanism was greater than that in Okafor mechanism.In pyridine-containing conditions,the integrated rate of NO formation from NO precursors in the Glarborg mechanism was higher than that in the Okafor mechanism.Therefore,the concentration of NOx in the Glarborg mechanism,which is dominant in both thermal NOx and fuel NOx,was naturally higher than that in the Okafor mechanism. |
