Influence of n -Butanol Addition on C 3 H 3 Formation in n -Butane Combustion

The effects of different n -butanol blending ratios ( R b ) on the formation of propargyl radical (C 3 H 3 ), an important benzene precursor, during the combustion of n -butanol/ n -butane blends are studied. A detailed kinetic combustion model of n -butanol/ n -butane is developed and the premixed n -butanol/ n -butane flames are calculated at an equivalence ratio of 1.5, an initial pressure of 1.0 atm, and a temperature range from 800 to 2000 K in a perfectly stirred reactor (PSR), with R b varying from 0 to 1.0. The results show that under the investigated conditions, the peak value of the mole fraction of C 3 H 3 decreases non-linearly with the increase of R b . Due to the interaction between combustion products of n -butane and n -butanol during the combustion process, the actual peak mole fraction of C 3 H 3 is higher than the theoretical value. A rate of production (ROP) analysis reveals that the number of β-carbon atoms in the molecule of n -butane and n -butanol affects the efficiency of H-abstraction reactions in generating 2-butyl (sC 4 H 9 ) and C 4 H 8 OH-3 (CH 3 –*CH–CH 2 –CH 2 –OH), which are the two major original sources of C 3 H 3 . For both n -butane and n -butanol, the main pathway of forming C 3 H 3 from propene (C 3 H 6 ) is basically the same, which is C 3 H 6 → C 3 H 5 -a (symmetric allyl radical) → C 3 H 4 -a (allene) → C 3 H 4 -p (propyne) → C 3 H 3 . When R b ranges from 0.4 to 0.6, the deviation degrees of the peak mole fraction of the involved C 3 species reach a maximum, indicating that the interaction between the two fuels is the most significant. The non-linear decrease in the mole fraction of C 3 H 3 can attribute to three reasons: (a) the increase of R b promotes the increase of the conversion ratios of n -butane to sC 4 H 9 and n -butanol to C 4 H 8 OH-3; (b) the contribution ratios of the reactions involved in the C 3 H 5 -a → C 3 H 4 -a → C 3 H 4 -p → C 3 H 3 pathway decrease with increasing R b ; (c) C 3 H 5 -t (tertiary allyl radical) → C 3 H 4 -p → C 3 H 3 is the secondary pathway for the formation of C 3 H 3 . With the increase of R b , the dependence of C 3 H 4 -p on C 3 H 5 -t increases and the conversion ratio of C 3 H 5 -t to C 3 H 4 -p increases. This study investigates the non-linear decrease of the mole fraction of C 3 H 3 by revealing the interactions between n -butanol and n -butane during the combustion, which can help better understand the effect of n -butanol on the formation of benzene.