Influence of n-Butanol Addition on C<sub>3</sub>H<sub>3</sub> Formation in n-Butane Combustion
<sec> —The effects of different n-butanol blending ratios (R<sub>b</sub>) on the formation of propargyl radical (C<sub>3</sub>H<sub>3</sub>), 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<sub>b</sub> varying from 0 to 1.0. The results show that under the investigated conditions, the peak value of the mole fraction of C<sub>3</sub>H<sub>3</sub> decreases non-linearly with the increase of R<sub>b</sub>. Due to the interaction between combustion products of n-butane and n-butanol during the combustion process, the actual peak mole fraction of C<sub>3</sub>H<sub>3</sub> 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<sub>4</sub>H<sub>9</sub>) and C<sub>4</sub>H<sub>8</sub>OH-3 (CH<sub>3</sub>–*CH–CH<sub>2</sub>–CH<sub>2</sub>–OH), which are the two major original sources of C<sub>3</sub>H<sub>3</sub>. For both n-butane and n-butanol, the main pathway of forming C<sub>3</sub>H<sub>3</sub> from propene (C<sub>3</sub>H<sub>6</sub>) is basically the same, which is C<sub>3</sub>H<sub>6</sub> → C<sub>3</sub>H<sub>5</sub>-a (symmetric allyl radical) → C<sub>3</sub>H<sub>4</sub>-a (allene) → C<sub>3</sub>H<sub>4</sub>-p (propyne) → C<sub>3</sub>H<sub>3</sub>. When R<sub>b</sub> ranges from 0.4 to 0.6, the deviation degrees of the peak mole fraction of the involved C<sub>3</sub> 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<sub>3</sub>H<sub>3</sub> can attribute to three reasons: (a) the increase of R<sub>b</sub> promotes the increase of the conversion ratios of n-butane to sC<sub>4</sub>H<sub>9</sub> and n-butanol to C<sub>4</sub>H<sub>8</sub>OH-3; (b) the contribution ratios of the reactions involved in the C<sub>3</sub>H<sub>5</sub>-a → C<sub>3</sub>H<sub>4</sub>-a → C<sub>3</sub>H<sub>4</sub>-p → C<sub>3</sub>H<sub>3</sub> pathway decrease with increasing R<sub>b</sub> (c) C<sub>3</sub>H<sub>5</sub>-t (tertiary allyl radical) → C<sub>3</sub>H<sub>4</sub>-p → C<sub>3</sub>H<sub>3</sub> is the secondary pathway for the formation of C<sub>3</sub>H<sub>3</sub>. With the increase of R<sub>b</sub>, the dependence of C<sub>3</sub>H<sub>4</sub>-p on C<sub>3</sub>H<sub>5</sub>-t increases and the conversion ratio of C<sub>3</sub>H<sub>5</sub>-t to C<sub>3</sub>H<sub>4</sub>-p increases. This study investigates the non-linear decrease of the mole fraction of C<sub>3</sub>H<sub>3</sub> 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. </sec>