SUPPLEMENTAL MATERIAL TO

Flame structure of a low-pressure laminar premixed and lightly

sooting acetylene flame and the effect of ethanol addition

T. Bierkandta. T.Kaspera*, E. Akyildiza, A. Lucassenb, P. Oßwaldc, M. Köhlerc, P. Hembergerd

a University of Duisburg-Essen, Germanyb Sandia National Laboratories, Livermore, California, USA

cDLR – Institute of Combustion Technology, Stuttgart 70569, GermanydMolecular Dynamics Group, Swiss Light Source, Paul Scherrer Institut, Villigen CH 5232, Switzerland

*Corresponding author: Tina Kasper:

Thermodynamics, Lotharstr. 1, 47057 Duisburg, Germany

phone: +49-203-379-1854, fax: +49-203-379-1250

Email: tina.kasper@uni-due.de

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Data reduction

Procedures for the evaluation of species mole fractions follow the specifications from Cool et al. [1].

The data reduction procedures for the ALS system were further refined and good summaries can be

found in [S2, S3]. Data reduction of the SLS mass spectra follows the same logic and a description

of the appropriate modifications can be found in [S4].

Flame species are identified by their exact masses and because of the high energy resolution by their

ionization energies and photoionization efficiency (PIE) or threshold photoelectron (TPE) spectra.

This is even possible for isomers. In spite of the good mass resolution, the spectra from the energy

and burner scans were numerically integrated for all nominal masses. Afterwards, the integrated

signal intensity is normalized to the number of averaged spectra (sweeps) and corrected of the

number of photons involved in the ionization process. The tendency of species to diffuse away from

the molecular beam results in mass discrimination effects. The correction of these mass

discrimination effects is effected from cold gas measurements with defined concentrations of H2,

CH4, C2H2, CO, Ar, CO2, Kr and Xe. Finally, the integrated signal intensities are corrected by a scan

factor which takes into account the overall detection efficiency between measurements, e.g. when the

measurements were performed at different photon energies. If required, a correction for 13C, 18O and

fragmentation patterns is performed.

The major species (H2, H2O, C2H2, CO, O2, Ar, CO2 and C2H5OH) mole fractions for the two flames

can be calculated from the signal intensities of high energy scans at 16.20 or 16.65 eV (ALS) and

16.4 eV (SLS), the flame conditions and the element balance for C, O and H. Furthermore, it is

necessary to know the photoionization cross section ratios between CO to CO2 and C2H2 to CO2 for

these energies or to calculate them from cold gas measurements. The mole fractions of all other

minority species are calculated by normalization to the argon signal according to:

S i(E)S Ar(E)

=MD i

MD Ar∙

PD i(E)PD Ar(E)

∙f i(E)

f Ar(E)∙

SW i

SW Ar∙

xs i( E)xsAr (E)

∙x i

x Ar

2

where MD is a mass discrimination factor, PD is the number of photons, f is an scan factor, SW is

the number of sweeps, xs the ionization cross section at the energy E, and x the mole fraction. It is

estimated from previous measurements that the error of the major species mole fractions is not

greater than 20 %. Errors of intermediate species are discussed in detail in [S3] and estimated to

range from factors of 0.5 to 3 dependent on cross section quality. The majority of cross sections was

obtained from the compilation in [S5] or estimated by analogy to known cross sections (e.g. C 10H4

and C11H4) when no measured or calculated values were available.

Many minority species can be precisely identified by their mass or ionization energy. It has to be

noted that compared to prior measurements with the flame machine at the ALS, the improved mass

resolution of the new mass spectrometer reduces accidental mass overlaps, e.g. overlapping signals

of ketene and propene for m/z = 42, and thus facilitates signal assignment and comparison to known

cross section data. Mass resolution of the mass spectrometer at the SLS is significantly smaller, so

we need two burner scans to separate isobaric species (e.g. CO and C2H4). From a burner scan at a

photon energy lower than the ionization energy of CO you can get the integrated signal of C2H4. This signal

can be extrapolated to higher energy, e.g. 14.35 eV where CO is present, when the photoionization cross

section or a calibration factor is known for both energies. Thus, the calculated signal of C 2H4 at 14.35 eV can

be subtracted from the measured signal of m/z = 28 (CO + C2H4) at 14.35 eV and we get the neat signal of

CO. However, here the focus will be on identification of species by their threshold photoelectron

spectra which show the ionization energy and further transition states of the molecule.

Fuel-rich conditions as employed in this study lead to a deposition of material on the sampling-probe

but a deterioration of signal-to-noise ratios was not a problem here. However, especially non-volatile

intermediates may have eluded detection.

The mole fractions of all other minority species are now available from argon as reference species. It

is estimated from previous measurements that the error of the major species mole fractions is not

greater than 20 %. For species with unmeasured photoionization cross sections, the accuracy may be

less.

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Table S1. List of combustion intermediates from measurements at the Advanced Light Source with their peak mole fractions, peak positions, photoionization cross sections, and energy at which the species were measured.

Mass Formula Species E [eV] xs [Mb] Reference neat acetylene flame ethanol-doped flamecross

section HAB [mm] xmax HAB [mm] xmax15 CH3 Methyl radical 10.60 6.25 [S6] 5 1.36E-03 5.5 1.94E-0316 CH4 Methane 13.20 7.92 [S7] 4.5 1.24E-03 5 1.50E-0327 C2H3 Vinyl radical 9.35 7.4 [S8] 5.5 8.62E-06 6 9.24E-0628 C2H4 Ethylene 10.60 3.5 [S12] 4.5 1.76E-03 5 4.31E-0329 C2H5 Ethyl radical 9.35 3.98 [S9] 7.5 8.82E-05 7 7.75E-0530 C2H6 Ethane 12.30 13.29 [S10] 3 5.72E-04 4.5 7.58E-0430 CH2O Formaldehyde 11.50 10.13 [S11] 2.5 3.44E-03 4 3.26E-0332 CH4O Methanol 11.50 9.53 [S12] 2.5 2.37E-04 3 3.81E-0434 H2O2 Hydrogen peroxide 11.50 9.2 [S5] 0.5 1.11E-04 0.5 1.19E-0438 C3H2 Triplet propargylenea 9.35 1.47 [S13] 6 4.88E-04 6.5 3.87E-0438 C3H2 Cyclopropenylidene39 C3H3 Propargyl radical 9.35 21.63 [S14] 5 8.04E-04 6 6.83E-0440 C3H4 Allene 9.80 1.14 [S15] 4.5 2.37E-04 5.5 2.13E-0440 C3H4 Propyne 10.60 28.22 [S12] 4 6.63E-04 5 6.20E-0441 C3H5 Allyl radial 9.35 5.65 [S16] 4 2.69E-05 5.5 3.60E-0542 C2H2O Ketene 10.60 22.52 [S17] 4.5 9.12E-04 5 1.09E-0342 C3H6 Propene 10.60 11.36 [S15] 4 1.55E-04 4 2.41E-0444 C2H4O Ethenol 9.80 4.29 [S15] 3 5.64E-05 5 3.60E-0444 C2H4O Acetaldehyde 10.60 8.06 [S15] 4 8.16E-05 4 2.18E-0350 C4H2 Diacetylene 10.60 23.65 [S12] 6.5 5.77E-03 7 5.40E-0351 C4H3 i-C4H3 radical 9.35 10 [S18] 5 1.60E-05 6 1.12E-0552 C4H4 1,2,3-Butatriene 9.35 2.3 [S5] 5 8.17E-05 6 7.69E-0552 C4H4 Vinylacetylene 9.80 15.75 [S12] 5 3.19E-04 5.5 3.62E-04

53 C4H5

But-1-yn-3-ylBut-2-yn-a-yl radicala,b 9.35 6.77 [S18] 4 1.11E-05 5 9.26E-06

53 C4H5 i-C4H554 C4H6 1,3-Butadiene 9.35 5.73 [S12] 4.5 1.16E-04 5 1.34E-04

4

58 Acetonec 9.80 5.5 [S12] 0.5 5.01E-03 0.5 5.28E-0362 C5H2 1,3-Pentadiynylide radical 9.35 4.26 [S5] 6 1.57E-05 6.5 1.05E-0563 C5H3 C5H3 isomers 9.35 10 [S19] 5.5 1.25E-04 6.5 8.80E-0564 C5H4 Ethynylallenea 9.35 4.05 [S5] 5 8.83E-05 6 7.67E-0564 C5H4 Pentatetraene64 C5H4 1,3-Pentadiyne 10.60 30 estimated 6 3.02E-05 6 1.55E-0565 C5H5 Cyclopentadienyl radical 9.35 4.34 [S19] 4.5 2.36E-05 5.5 2.09E-0566 C4H2O HCCCHCOa 9.35 10 estimated 5 6.88E-05 6 5.24E-0566 C4H2O H2CCCCO66 C5H6 1,3-Cyclopentadienea 9.35 14.12 [S19] 4 3.62E-05 5.5 3.26E-0566 C5H6 3-Penten-1-yne74 C6H2 1,3,5-Hexatriyne 9.80 14.79 [S5] 7 1.29E-03 7 1.11E-0376 C6H4 Benzyneb 9.35 19.91 [S5] 5.5 6.45E-05 6 5.04E-0576 C6H4 Hex-3-ene-1,5-diyne78 C6H6 Benzenea 9.35 6.74 [S12] 4.5 9.58E-05 5.5 7.69E-0578 C6H6 Fulvene80 C6H8 1,3-Cyclohexadiene 9.35 17.99 [S10] 3.5 3.25E-06 4.5 4.47E-0687 C7H3 9.35 10 estimated 5.5 9.33E-06 6.5 6.09E-0688 C7H4 1,3,5-Heptatriyne 9.35 4.77 [S5] 6 5.90E-05 6.5 4.43E-05

90 C7H6

5-Ethenylidene-1,3-cyclopentadiene 9.35 14.63 [S5] 5 7.88E-06 6 6.11E-06

92 C7H8 Toluene 9.35 14.63 [S20] 4.5 8.86E-06 5.5 6.60E-0694 C6H6O Phenol 9.35 17.79 [S21] 6.5 2.33E-05 7 1.43E-0598 C8H2 1,3,5,7-Octatetrayne 9.35 7.45 [S5] 6.5 5.84E-04 7 3.51E-04100 C8H4 1-Octene-3,5,7-triyne 9.35 7.93 [S5] 5.5 3.97E-05 6.5 2.87E-05100 C8H4 3-Octene-1,5,7-triyne102 C8H6 Phenylacetylene 9.35 24.72 [S20] 5 7.22E-06 6 5.85E-06112 C9H4 1,3,5,7-Nonantetrayne 9.35 6.76 [S5] 6 1.52E-05 6.5 8.74E-06116 C9H8 Indene 9.35 25.41 [S20] 4.5 2.62E-06 5.5 2.00E-06122 C10H2 1,3,5,7,9-Decapenatayne 9.35 10.51 [S5] 6.5 1.04E-04 7.5 5.24E-05124 C10H4 9.35 20 estimated 6 3.86E-06 7 2.27E-06126 C10H6 1,4-Diethynylbenzene 9.35 14.7 [S5] 5.5 2.12E-06 6 1.42E-06

5

128 C10H8 Naphthalene 9.35 18.2 [S5] 5 1.27E-06 5.5 8.88E-07136 C11H4 9.35 20 estimated 6.5 1.22E-06 7 9.10E-07146 C12H2 9.35 20 estimated 6.5 7.19E-06 7.5 2.98E-06170 C14H2 9.35 20 estimated 6.5 6.58E-07 7.5 3.72E-07

Notes: Cross sections from reference [S5] and [S18] are estimated values, amole fraction calculated for the dominant intermediate, bdistinction between isomers not possible because of close IEs, cacetone as contamination in acetylene.

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Figure S1. Temperature profiles and mole fraction profiles of the major species in the pure acetylene flame measured at the Swiss Light Source in comparison with modeling results. Symbols: experiment, lines: modeling.

Table S2. Adiabatic ionization energies of measured polyynes compared to previous studies.

Species IE [eV]a IE [eV]b IE [eV]c IE [eV]d IE [eV]C4H2 10.10 10.15 10.17 10.03 10.17e

C6H2 9.45 9.48 9.50 9.45 9.50f

C8H2 9.05 9.06 9.08 9.08 9.09g

C10H2 8.75 8.77 8.82 8.75C12H2 8.55 8.56 8.65C14H2 8.35 8.50

Notes: aMeasured values in our study, bLi et al. [S22], cHansen et al. [S23], dKaiser et al. [S24], eBieri et al. [S25], fBieri et al. [S26], gAllan et al. [S27].

The following figures (S2-S11) show a comparison of the mole fractions of more species to the

simulation results. The larger polyynes (S12) are not included in the chemistry model and shown

here to illustrate the nearly linear concentration decrease.

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Figure S2. Comparison of measured mole fraction profiles of methyl radical at the ALS with modeling results.

Figure S3. Comparison of measured mole fraction profiles of ethylene at the ALS with modeling results.

8

Figure S4. Comparison of measured mole fraction profiles of formaldehyde at the ALS with modeling results.

Figure S5. Comparison of measured mole fraction profiles of C3H2 at the ALS with modeling results.

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Figure S6. Comparison of measured mole fraction profiles of allyl radical at the ALS with modeling results.

Figure S7. Comparison of measured mole fraction profiles of ketene at the ALS with modeling results.

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Figure S8. Comparison of measured mole fraction profiles of propene at the ALS with modeling results.

Figure S9. Comparison of measured mole fraction profiles of diacetylene at the ALS with modeling results.

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Figure S10. Comparison of measured mole fraction profiles of C4H2O at the ALS with modeling results.

Figure S11. Comparison of measured mole fraction profiles of C6H2 at the ALS with modeling results.

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Figure S12. Comparison of measured mole fraction profiles of some higher polyynes at the ALS for the neat acetylene (solid symbols) and ethanol-blended (open symbols) flame.

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