An experimental and kinetic modeling investigation on a rich premixed n-propylbenzene flame at low pressure

A rich premixed flame of n-propylbenzene (1.79) was investigated at low pressure. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used to detect flame species including a lot of radicals, isomers and polycyclic aromatic hydrocarbons (PAHs) and measure their mole fraction profiles. A preliminary kinetic model of n-propylbenzene combustion was developed from recently reported toluene and ethylbenzene models [Y.Y. Li et al., Proc. Combust. Inst. 33 (2011) 593-600, 617-624] and validated by the experimental results. Rate constants of the important pathways of n-propylbenzene consumption, i.e. the H-abstraction reactions by H atom and the benzylic C-C bond dissociation, were calculated theoretically and included in this model. Based on the rate of production analysis and experimental observations, styrene, benzyl and benzene are confirmed as significant intermediates in the n-propylbenzene flame. For the formation pathways of PAHs, n-propylbenzene flame has a fuel specific pathway to form indene compared to smaller alkylbenzene, which increases the concentrations of indene and indenyl radical. It is concluded that high concentrations of important PAH precursors such as benzyl and indenyl radicals result in the enhanced PAHs formation in this flame compared with smaller alkylbenzenes.