Investigation in C6H6/O2/Ar and C6H6/C2H2/O2/Ar flames by
molecular beam mass spectrometry
V. Detilleux and J. Vandooren
[email protected]
CSTR – Laboratoire de Physico-Chimie de la Combustion
Université Catholique de Louvain – Place Louis Pasteur, 1
1348 Louvain-La-Neuve – Belgium
The combustion of hydrocarbons in rich flames leads to the formation of PAH
(Polycyclic Aromatic Hydrocarbons). Many PAH are know to be carcinogenic and
play an important role in the process of soot formation. Thus it is essential to
investigate the pathways by which they are formed, in order to inhibit their production.
Nowadays, three main sources of PAH production are suggested: the
cyclopentadienyl pathway1, the HACA mechanism2 and the biphenyl pathway3.
The aim of this work is to measure the structure of rich premixed flames of
benzene-oxygen-argon and benzene-acetylene-oxygen-argon, both with an identical
equivalence ratio of 2. Since benzene is an important precursor of PAH and
acetylene is supposed to be an essential intermediate in their formation, the analysis
and comparison of these flame structures will allow us to evaluate more precisely the
role of C2H2 in PAH production.
One dimensional benzene-oxygen-argon (11.5 mol % C6H6, 43.2 mol % O2
and 45.3 mol % Ar) and benzene-acetylene-oxygen-argon (10.7 mol % C6H6, 2.6 mol
% C2H2, 43.2 mol % O2 and 43.5 mol % Ar) flames at equivalence ratio of 2 were
stabilised at low pressure (45 mbar) on a flat flame burner. Gases sampling are
performed by a quartz cone, at different heights of the flame. Identification and
monitoring of chemical species were performed by molecular beam mass
spectrometry (MBMS). Every chemical species were analysed in similar conditions, in
both flames, in order to perform a reliable calibration and a direct comparison.
Hereby, some experimental mole fraction profiles are presented. Obviously,
the production of phenylacetylene (C8H6), naphthalene (C10H8), acenaphthylene
(C12H8) which are chemical species assumed to be produced by the HACA
mechanism is increased by the substitution of a part of benzene by acetylene.
With the help of the COSILAB4 software, by using the DIAS5;6 mechanism,
numerical simulations have been carried out to predict mole fraction profiles. The
experimental temperature profiles have been introduced in order to compare
experimental and calculated results, in similar heat transfer conditions.
The whole comparison, between the two flames and with simulated data, will
provide important clues about the role of C2H2 in reactions leading to the formation of
PAH.
Mole Fraction trends of C8H6 and C10H8
in C6H6/O2/Ar and C6H6/C2H2/O2/Ar flames,
with equivalence ratio of 2
2,50E-04
C8H6 in C6H6/O2/Ar
C10H8 in C6H6/O2/Ar
C8H6 in C6H6/C2H2/O2/Ar
C10H8 in C6H6/C2H2/O2/Ar
Mole Fraction
2,00E-04
1,50E-04
1,00E-04
5,00E-05
0,00E+00
0
0,2
0,4
0,6
0,8
1
1,2
1,4
Height Above Burner (cm)
Mole Fraction trends of C12H8
in C6H6/O2/Ar and C6H6/C2H2/O2/Ar flames,
with equivalence ratio of 2
1,80E-04
C8H6 in C6H6/O2/Ar
C8H6 in C6H6/C2H2/O2/Ar
1,60E-04
1,40E-04
Mole Fraction
1,20E-04
1,00E-04
8,00E-05
6,00E-05
4,00E-05
2,00E-05
0,00E+00
0
0,2
0,4
0,6
0,8
1
1,2
1,4
Height Above Burner (cm)
Mole fraction trends of C6H6, C2H2, O2 and Ar
in the C6H6/O2/Ar and C6H6/C2H2/O2/Ar flames,
with equivalence ratio of 2
4,50E-01
4,00E-01
3,50E-01
Mole Fraction
3,00E-01
Ar in C6H6/O2/Ar
C6H6 in C6H6/O2/Ar
O2 in C6H6/O2/Ar
C2H2 in C6H6/O2/Ar
2,50E-01
Ar in C6H6/C2H2/O2/Ar
C6H6 in C6H6/C2H2/O2/Ar
O2 in C6H6/C2H2/O2/Ar
C2H2 in C6H6/C2H2/O2/Ar
2,00E-01
1,50E-01
1,00E-01
5,00E-02
0,00E+00
0
0,5
1
1,5
2
2,5
Height Above Burner (cm)
1
2
3
4
5
6
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Université Catholique de Louvain, Belgium, 2003
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