Influences of propylene/propyne addition on toluene pyrolysis in a single-pulse shock tube

To explore the potential interactions between toluene/benzyl and the common C-3 combustion intermediates, toluene-propylene and toluene-propyne co-pyrolysis is studied in the current work by taking neat toluene pyrolysis as a reference. Experiments are carried out at a nominal pressure of 20 bar over a temperature range of 1050-1700 K, using a single-pulse shock tube facility coupled to the gas chromatography-mass spectrometry speciation diagnostic technique. Temperature-dependent mole fraction profiles are obtained for numerous species ranging from small-molecule products to three-ring polycyclic aromatic hydrocarbons (PAHs). A kinetic model, which has been under development in our serial works, is extended by including the interplays between toluene/benzyl and propylene/propyne chemistry. The updated model can satisfactorily predict the measurements, regarding the absolute mole fractions as well as the variation trends brought by different initial fuel compositions. Increased reactivity is observed in the conversion of toluene with the presence of propylene or propyne, while the consumption rates of the studied C-3 fuels are barely influenced by toluene. Benzene formation is facilitated by the C-3+C-3 reactions introduced by the C-3 fuels. The pyrolysis of propylene (or propyne) significantly enhances the level of C-1-C-3 molecules/radicals that further react with aromatic species. For instance, the reactions of benzyl+propyne result in much higher mole fractions and lower speciation temperature windows of indene and naphthalene in toluene-propylene (or propyne) co-pyrolysis. The reactions with small hydrocarbons result in reduced levels of benzyl and other C-7 radicals in the reaction system in toluene- propylene (or propyne) co-pyrolysis. Consequently, for the PAHs which are mainly formed through C-7+C-7 reactions, such as bibenzyl and phenanthrene, the mole fractions are lowered by the addition of propylene (or propyne). Propyne has more obvious influences on the species pool of toluene pyrolysis than propylene, because the effective C-7-C-3 interactions are mostly through the reactions between toluene/benzyl and propyne/propargyl in both cases of toluene-propylene and toluene-propyne co-pyrolysis. (C) 2021 The Author(s). Published by Elsevier Inc. on behalf of The Combustion Institute.

Automated summary

The study explores the potential interactions between toluene/benzyl and common C-3 combustion intermediates through toluene-propylene and toluene-propyne co-pyrolysis. Experimental results show increased reactivity in the conversion of toluene with the presence of propylene or propyne. The updated kinetic model accurately predicts measurements and the variation trends brought by different initial fuel compositions. Impacts of propylene and propyne on the species pool of toluene pyrolysis are discussed, with propyne showing more obvious influences on the interactions between toluene/benzyl and propyne/propargyl.