Pollutant Formation During C6 Fuel Pyrolysis And Oxidation

Currently,coal combustion,mobile exhausts and industrial emissions appear to be three main sources of fine particle in China.Among them,mobile exhausts has increasing influence on air pollution,especially in large and medium-sized cities in China.Development of clean fuels has been raised lots of concerns.In addition,the effects of fuel molecular structure on pollutant generation and particle formation.In this paper,the hightemperature pyrolysis and oxidation of C6 fuel were studied by means of experiment and simulation,thereby the effect of fuel molecular structure on particle generation characteristics was systematically analyzed.Based on the flow reactor experimental platform,pyrolysis of fuels were carried out and six liquid fuels,i.e.,n-hexane,cyclohexane,1-hexene,cyclohexene,1,4-hexadiene and 1,4-cyclohexadiene were selected.The experiment was conducted under three temperatures(1000,1150 and 1300° C).The particles were measured by a Scanning Mobility Particle Sizer(SMPS).The kinetic simulation of fuel pyrolysis reaction was based on the plug flow reactor model of CHEMKIN software,which is divided into two parts: cracking reaction and oxidation reaction.The parameters of pyrolysis reaction simulation are set based on the experimental conditions.Oxidation simulation was carried out by setting three sets of equivalence ratios(0.5,1,and 1.5)within the temperature range from 500 to 1500° C,and products were analysed under different oxygen concentrations and temperature conditions.It is found that the particle concentration increases with the increase of the number of double bonds.The formation rate of fuel molecules containing a double bond was significantly related to the ring structure.At1150° C,the fuels with ring structure produced more particle in compared with linear chain hydrocarbon.This tendency is not obvious at low temperature condition,e.g.,1000° C and 1300° C.The number of double bonds of linear and cyclic hydrocarbons has a significant effect on the particle size distribution at 1300° C.The number concentration of particles produced by pyrolysis of hydrocarbon fuels increased with the increasing number of double bonds.As the temperature rising,the distinct between particle generated from the ring structure and the linear chain fuels was not significant.According to the simulation results of CHEMKIN,the composition of the product changed significantly with temperature,the abundance of hydrogen and acetylene increased significantly with increasing temperature,and the mole fraction of benzene and methane decreased with increasing temperature.From the perspective of fuel structure,benzene content was lower than that of chain hydrocarbons in the cracking of cyclic hydrocarbons and higher than that of alkanes in olefins,especially at 1150° C.At 1300° C,the acetylene production of cyclic hydrocarbons was significantly lower than that of chain hydrocarbons,and the production of olefins was higher than that of alkanes.The condition of high temperature and high oxygen concentration was benefit to the fuel oxidation.The effect of molecular structure on the particle formation was suppressed at high temperature environment.