The effect of methyl pentanoate addition on the structure of premixed fuel-rich n-heptane/toluene flame at atmospheric pressure

The effect of adding methyl pentanoate (MP) on the species pool in a rich premixed flame fueled by n-heptane/toluene blend (7/3 by volume of liquids) at atmospheric pressure is investigated. The emphasis of this work is on the effect of MP on the concentrations of intermediates, which are precursors of polycyclic aromatic hydrocarbons (PAH), in order to understand the processes responsible for reduction of concentration of PAH when biodiesel is added to diesel fuel in combustion devices. Two premixed fuel-rich n-heptane/toluene/O{cyrillic}₂/Ar (2.29/1.36/21.36/75%) and n-heptane/toluene/MP/O{cyrillic}₂/Ar (1.26/0.75/2.00/21.355/75%, 50% of liquid MP in liquid fuel mixture of n-heptane and toluene) fuel-rich flames with the same equivalence ratio ϕ=1.75 were stabilized on a flat burner at 1atm. Molecular beam mass spectrometric measurements of mole fraction profiles of reactants, the major products and many intermediate species were performed. The experimental profiles were compared with those calculated using a detailed chemical kinetic mechanism, which was a combination of two detailed mechanisms proposed earlier in the literature for combustion of n-heptane/iso-octane/toluene mixture and for MP oxidation, respectively. Addition of MP was found to reduce mole fractions of many intermediates, which play an important role in formation of PAH, specifically, benzene, cyclopentadienyl, acetylene, propargyl, and vinylacetylene. Analysis of the reaction pathways responsible for formation of naphthalene, a typical representative of small PAH, was performed in order to elucidate the chemical effect of MP addition on its formation. To ascertain the effect of MP addition on the primary reactions of consumption of n-heptane and toluene, the analysis of the relative contributions of these reactions to the total rate of consumption of the fuels was carried out.