Exploring fuel molecular structure effects on the pyrolysis chemistry of branched hexenes

Abstract

3,3-Dimethyl-1-butene (NEC6D3) and 2,3-dimethyl-2-butene (XC6D2) are representative branched alkene components in gasoline. This work experimentally investigated the pyrolysis of NEC6D3 and XC6D2 in a flow reactor (T = 950–1350 K, P = 0.04 atm) and a jet-stirred reactor (T = 730–1000 K, P = 1 atm) using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC). A pyrolysis model of branched hexenes was proposed and validated against the new experimental data. The combined experimental observations and modeling analyses provide insights into the predominant fuel decomposition pathways and specific formation pathways of products under pyrolysis conditions. NEC6D3 exhibits a much higher reactivity than XC6D2 due to the existence of allylic CC bonds. Unimolecular decomposition reactions play the most crucial role in NEC6D3 decomposition, while in XC6D2 pyrolysis, fuel consumption is dominated by H-abstraction reactions and the H-assisted isomerization reaction. Fuel-specific pathways can remarkably influence the formation of pyrolysis products, especially the key C1C2 products, isomer pairs and dialkenes. Furthermore, the reactions involving propargyl radical dominate the formation of fulvene and aromatic products in the pyrolysis of both fuels, leading to more abundant production of C6 and larger cyclic products in XC6D2 pyrolysis.