Experimental And Kinetic Modeling Studies On Pyrolysis And Premixed Flames Of N-Hptane And Iso-Octane

In this dissertation, experimental,theoretical and kinetic studies have been carried on the pyrolysis and premixed flames of n-heptane and iso-octane at low pressure.In Chapter 1, the importance of fossil fuels and pollutants from fossil fuels combustion are illustrated. Then, n-heptane and iso-octane, two typical alkanes of which have been chosen as surrogates to study pyrolysis and combustion of fossil fuels. In the end of this chapter, the previous studies on the pyrolysis, oxidation and combustion of n-heptane and iso-octane are summarized.In the beginning of Chapter 2, the characteristic of synchrotron radiation, U10 and U14C beamlines, the equipments of pyrolysis and premixed flame are introduced. Next, the operations of pyrolysis and premixed flame and the analysis of experiment data are explained. In this section, the formulas for calculating the mole fractions of pyrolysis and premixed flame species are presented. And then, the theoretical methods used in this dissertation are briefly introduced. Finally, the history of CHEMKIN and the important parameters on CHEMKIN calculation are illustrated.In Chapter 3, about 23 pyrolysis species, including H₂,CH₃,CH₄,C₂H₂,C₂H₄,C₃H₃,aC₃H₄,pC₃H₄,aC₃H₅,C₃H₆,1-C₄H₈,1-C₅H₁₀,C₆H₆ and 1-C₆H₁₂, are observed from pyrolysis of n-heptane at low pressure. The structures of pyrolysis species are identified and the isomers are distinguished by measurements of photoionization efficiency spectra. Mole fraction profiles of pyrolysis species are measured at the selective photon energies near ionization thresholds. The unimolecular dissociation and H attack channels of n-heptane are calculated by CCSD(T) method. The dissociation energies of different C—C and C—H bonds are compared and the unimolecular dissociation rules of long-chain alkanes are summarized. Based on the experiment measurements and previous kinetic studies, a kinetic model of n-heptane pyrolysis are developed. Based on rate of product (ROP) analysis and sensitivity analysis, consumption channels of n-heptane, produce and consumption channels of C₂-C₆ alkenes are discussed .In chapter 4, four premixed n-heptane flames of different C/O ratio (C/O= XXXX) are carried out at low pressure. The structures of flame species are identified by measurements of photoionization efficiency spectra. Mole fraction profiles of flame species are evaluated from the spatial distributions of signals measured by scanning burner position at several selected photon energies. Based on kinetic model of n-heptane pyrolysis, a kinetic model of n-heptane flame is described. By ROP analysis, consumption channels of n-heptane, produce and consumption channels of C₂-C₆ alkenes are presented for the fuel-lean and fuel-rich flames, respectively.In chapter 5, about 25 pyrolysis species, including H₂,CH₃,CH₄,C₂H₂,C₂H₄,C₃H₃,aC₃H₄,pC₃H₄,aC₃H₅,C₃H₆,iC₄H₇,iC₄H₈,C₅H₆ and C₆H₆, are observed from pyrolysis of iso-octane at low pressure. With the same method of n-heptane pyrolysis, structures of pyrolysis species are identified, isomers are distinguished and mole fraction profiles are evaluated. The unimolecular dissociation and H attack channels of iso-octane are calculated by CCSD(T) method. The dissociation energies of different C—C and C—H bonds are compared. In this part, the dissociation channels of n-heptane and iso-octane are also summarized. Finally, the kinetic model of iso-octane pyrolysis is described. Based on ROP analysis and sensitivity analysis, consumption channels of iso-octane and produce and consumption channels of C₂H₄, C₃H₆ and iC₄H₈ are presented.In chapter 6, four premixed C/O ratio (C/O= XXXX) n-heptane flames are measured at low pressure. With the same method of n-heptane flames, the structures of flame species are identified, the isomers are distinguished and the mole fraction profiles are evaluated. Based on the kinetic model of iso-octane pyrolysis, the kinetic model of iso-octane flame is described. By ROP analysis, consumption channels of iso-octane, produce and consumption channels of C₂H₄, C₃H₆ and iC₄H₈ are presented in fuel-lean and fuel-rich flames, respectively. Finally, a combustion kinetic model including 205 species and 1031 reactions were presented, which can predict the low-pressure pyrolysis and combustion chemistry of n-heptane and iso-octane.