Experimental and modelling study of speciation and benzene formation pathways in premixed 1-hexene flames

Abstract

An existing detailed and broadly validated kinetic scheme is augmented to capture the flame chemistry of 1-hexene under stoichiometric and fuel rich conditions including benzene formation pathways. In addition, the speciation in a premixed stoichiometric 1-hexene flame (flat-flame McKenna-type burner) has been studied under a reduced pressure of 20-30 mbar applying flame-sampling molecular-beam time-offlight mass spectrometry and photoionization by tunable vacuum-ultraviolet synchrotron radiation. Mole fraction profiles of 40 different species have been measured and validated against the new detailed chemical reaction model consisting of 275 species and 3047 reversible elementary reactions. A good agreement of modelling results with the experimentally observed mole fraction profiles has been found under both stoichiometric and fuel rich conditions providing a sound basis for analyzing benzene formation pathways during 1-hexene combustion. The analysis clearly shows that benzene formation via the fulvene intermediate is a very important pathway for 1-hexene.

Comprehensive kinetic modeling and experimental study of a fuel-rich, premixed n-heptane flame

“…The pathways for benzene formation via fulvene were discussed in detail in a recent study on 1-hexene flame chemistry [52]. In that work the fulvene chemistry has been included and the thermodynamic data of several species including C 3 H 3 (propargyl), C 3 H 4 (allene), C 3 H 4 P (propyne), C 3 H 5 (allyl), C 3 H 6 , n-C 3 H 7 , and i-C 3 H 7 have been updated.…”

“…This means that many intermediate C 2 , C 3 , C 4 , and C 5 species are formed by various pathways. This complexity is an effect of the fuel molecule's size and very different to the much simpler flame chemistry of butane, butene isomers and even 1-hexene, which were studied with older versions of the kinetic model [29,30,52]. Among the various decomposition pathways, two main threads of C-atom mass flows may be distinguished.…”

“…Fulvene in turn is formed via recombination reactions such as C 5 H 3 + CH 3 ; C 3 H 3 + C 3 H 5 resulting in fulvene + 2H, C 3 H 3 + C 3 H 3 , and several minor pathways. As outlined in Section 3, the fulvene pathways were included in the kinetic model and critically validated in very recent work on the flame chemistry of 1-hexene [52]. In that study fulvene and benzene were distinguished by their different ionization energies applying synchrotron-based single-photon ionization.…”

Investigating repetitive reaction pathways for the formation of polycyclic aromatic hydrocarbons in combustion processes

“…It is evident that the predictive capabilities of the PAH sub-model rely on the accuracy of the description of the formation of the first aromatic ring. Already this first step in the overall soot formation process can be very complex: Normally, benzene is considered to be this first aromatic ring and its formation is generally described by reactions of resonantly stabilized radicals like propargyl (C 3 H 3 ), allyl (C 3 H 5 ), i-C 4 H 5 , and cyclopentadienyl (C 5 H 5 ) [5,[13][14][15][16][17][18][19]. However, precursors and reactions have been identified that can form aromatic species without passing through benzene, and it is therefore important to note that benzene is not necessarily the first aromatic ring [5,6].…”

The influence of i-butanol addition to the chemistry of premixed 1,3-butadiene flames

“…Furthermore, the fulvene chemistry was added as described in Ref. [27]. In total, 70 species and 273 reactions were newly incorporated.…”