Experimental study of 1 atmosphere, rich, premixed n-heptane and iso-octane flames

Temperature and species mole fraction profiles have been measured in laminar premixed n-heptane/O-2/N-2 and iso-octane/O-2/N-2 flames. Both flames have been stabilized on a flat-flame burner, at atmospheric pressure. Species identification and concentration measurements have been performed by gas chromatography and GC-MS analysis of samples withdrawn locally by a quartz microprobe. Temperature profiles were measured by Pt-Pt 10%Rh thermocouples with radiative heat losses suppressed by the electrical compensation method. For both flames, the equivalence ratio was equal to 1.9 and a faint yellow luminosity due to soot particles was observed. The main objective of this work was to provide detailed experimental data on the nature and concentration of the intermediate species formed by consumption of a linear or highly branched fuel molecule. In addition to reactants and major products (CO, CO2, H-2, H2O), the mole fraction profiles of C-1(CH4), C-2(C2H2, C2H4, C2H6), C-3(allene, propyne, propene, propane), C-4(C4H2, C4H4, 1,2-C4H6, 1,3-C4H6, 1-butyne, butenes) C-5(pentadienes, methyl butenes, pentenes), C-6(hexenes, hexadienes, dimethyl butenes, methyl pentenes) and C-7 species (heptenes, dimethyl pentenes) have been measured. Marked differences in the nature of the C-4-C-7 are observed as a result of the change in the structure of the fuel molecule. On the other hand, the major products, C2 and C1 species exhibit very similar mole fraction profiles. Both benzene and allene are formed in higher concentrations in the iso-octane flame. This observation reinforces at least qualitatively the role of Cg species in the benzene formation mechanism. It also confirms the results of a comparative study of the structure of low pressure n-heptane and iso-octane flames previously performed in our laboratory (Doute et al., 1997).