PAH formation and soot morphology in flames of C4 fuels

Abstract

In this work, we describe experimental studies on the formation of polycyclic aromatic hydrocarbons (PAH's) in opposed-flow atmospheric-pressure flames of n-butane, i-butane, i-butene, and i-butanol and on the morphology of nascent soot particles sampled from premixed atmospheric-pressure flames of the same fuels. To identify the major contributors to the molecular growth mechanism in opposed-flow flames, we employed flame-sampling molecular-beam mass spectrometry with electron ionization (EI) and in situ gas-chromatography (GC) with mass spectrometric detection. The EI and GC-EI mass spectra indicate that several pathways with different building blocks can contribute to molecular growth. Besides the commonly accepted hydrogen-abstraction-C 2 H 2 -addition steps, we found reactions of the methyl radical to be important steps. This observation is also supported by the complexity of the mass spectra which indicates that at least one of the building blocks is rather small. The importance of phenyl radicals as building blocks seems to be limited. We also sampled nascent soot particles from premixed atmospheric-pressure flames of the above mentioned fuels and used helium-ion microscopy to unravel the influence of the fuel structure on the morphology of the sampled particles. While differences in flame temperatures and residence times are known to influence the particle sizes, the observed different morphologies are likely due to slightly different C/O ratios and potentially the chemical nature of the fuel.

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

“…The flame conditions were identical to the ones reported in Ref. [49] and are provided here only as Supplementary Material. The fuels were chosen because their respective combustion chemistry are interesting research topics as outlined in Refs.…”

“…The experimental approach used to record the flame-sampled mass spectra has been detailed in Ref. [49]. In short, opposed-flow fuel-Ar/O 2 -Ar diffusion flames were established at atmospheric pressure between the two outlets of a home-built burner system [54] while regulating the respective gas flows with an absolute precision of ±0.5 % using calibrated mass flow controllers.…”

“…The present work is intended to shed further light on repetitive growth sequences in PAH formation chemistry and builds upon the studies of Panariello et al [37], Shukla and coworkers [38,39], and Schenk et al [49] in which repetitive sequences of acetylene and methyl additions were qualitatively identified as molecular-weight growth reactions via signal patterns in mass spectrometric experiments. This study elucidates the possibility of gaining information about the PAH growth process not just from the signal patterns but additionally from quantitative signal intensities.…”

PAH formation in counterflow non-premixed flames of butane and butanol isomers

“…9 (b). From the past studies [20,25,82] , it has been shown that in the formation of benzene ring the propargyl radical plays an important role. Therefore, the ranking of A 1 -ring formation (benzene, C 6 H 6 ) in Fig.…”

“…[16][17][18][19][20][21][22][23][24]. Recently, Schenk et al [25] have proposed the methyland phenyl-addition pathways of the PAH formation. In addition, the odd-carbon-atom pathways have been introduced as possible reaction routes of the incipient PAH formation, as the propargyl http://dx.doi.org/10.1016/j.combustflame.2016.05.009 0010-2180/© 2016 The Combustion Institute.…”