=Paper= {{Paper |id=Vol-452/paper-13 |storemode=property |title=Detailed chemical kinetic modelling of aromatic Diesel fuel components |pdfUrl=https://ceur-ws.org/Vol-452/paper13.pdf |volume=Vol-452 }} ==Detailed chemical kinetic modelling of aromatic Diesel fuel components== https://ceur-ws.org/Vol-452/paper13.pdf

Detailed Chemical Kinetic Modelling of Aromatic Diesel Fuel Components
R.P. Lindstedt*, V. Markaki and R.K. Robinson
Department of Mechanical Engineering
Imperial College London, Exhibition Road, London SW7 2AZ, UK

The ability to predict the inter-conversion of poly-aromatic hydrocarbons (PAHs) of different toxicities and emissions
of fine carbon-based particles from Diesel engines are of increasing relevance given their harmful effects. The matter
is complicated by the complexity of Diesel fuels and model fuel blends have to be used in numerical simulations of
practical engines. The use of aromatic fuel component(-s) in such blends provides a route towards the modulation of
the propensity of a fuel to produce such emissions provided the chemistry is sufficiently well understood. The cur-
rent work extends past efforts related to the oxidation of 1-methyl naphthalene, which has been identified as a poten-
tial key component of surrogate Diesel fuels. Specifically, 1-methyl naphthalene may be used to modulate sooting
tendencies and the methyl groups on aromatic rings (e.g. xylenes and tri-methyl benzenes) have also been identified
as important in the context of fuel reactivity.

Background been identified as a means of modulating the soot-
Past work on the oxidation of single-ring aro- ing propensity of surrogate Diesel fuels. The ap-
matics include the studies by Emdee et al. [1], plied detailed chemical reaction mechanism was
Lindstedt and Maurice [2] and Klotz et al. [3]. Stu- initially created from reaction classes derived from
dies of two-ringed structures are less prevalent. studies of the oxidation and pyrolysis of toluene,
However, Shaddix [4] investigated the oxidation of benzene and cyclo-pentadiene. Accurate thermo-
naphthalene and 1-methyl naphthalene under tur- dynamic data is particularly important given the
bulent flow reactor (TFR) conditions and Pitsch [5] large number of isomerisation reaction present in
proposed a kinetic mechanism for the oxidation detailed reaction sequences for PAH forma-
latter species. Lindstedt et al. [6] considered a wide tion/oxidation. As part of the present work, earlier
range of PAH formation paths and Dagaut and co- estimates, often obtained on the basis of variants
workers [7,8] studied the oxidation of m-xylene and of Benson's additivity method, were replaced by
1-methyl naphthalene under jet-stirred reactor data derived from quantum mechanical methods
(JSR) conditions. The chemistry of soot/PAH using Gaussian-03 (at the G3MP2B3 level) in
growth and oxidation tends to be slow compared to combination with density functional theory (DFT)
flow time-scales and detailed studies of turbulent analysis for internal rotations. The validation of the
flames are less prevalent. Lindstedt and Louloudi derived mechanism was achieved by comparison
[9] reported a study of the formation and oxidation with experimental data from jet stirred and turbu-
of soot in turbulent diffusion flames using a trans- lent flow reactors.
ported PDF method combined with the method of
moments and with a soot surface oxidation analo- Results and Discussion
gy based on naphthalene. The explicit functional The 1-methyl naphthalene chemistry was initial-
form of the latter was obtained using the systemat- ly tested under JSR conditions using data from
ic reduction technique of Peters (e.g. Peters and Mati et al. [8] for the conditions shown in Table 1.
Rogg [10]). The chemistry of naphthalene and The data is suitable for clarifying the decomposi-
indene were subsequently explored by Lindstedt et tion channels of the fuel and provides extensive
al. [11] in an effort to further evaluate the ability of information on stable species.
a fixed sectional method [12] to compute soot par-
ticle size distributions in the size range from < 1 nm Φ P (atm) T (K) O2 C11H10
to 100 nm. Critical reaction steps in the oxidation 0.5 1.0 1097-1290 0.0270 0.001
process were identified and subjected to detailed
investigations via quantum mechanical methods 1.0 1.0 1094-1400 0.0135 0.001
using Gaussian-03 [13] with rate constants deter- 1.5 1.0 1147-1440 0.0090 0.001
mined from the potential energy surfaces using
variable transition state theory and Rice-
Ramsperger-Kassel-Marcus/master equation ap- Table 1: Experimental and modelling conditions for the
proaches. The critical reaction paths included C9H7 oxidation of 1-methyl naphthalene in a jet-stirred reactor
+ HO2/O2 channels and the linkage of C5 and C6 [8]. The species concentrations correspond to mole
rings as part of the oxidation process [11]. The fractions.
current work further assesses the progress made
in the understanding of the associated reaction Shaddix [4] performed gas-phase sampling to
paths for two-ringed aromatics. In particular, atten- study the oxidation of 1-methyl naphthalene in a
tion is given to 1-methyl naphthalene which has TFR and obtained time-dependent concentration

* Corresponding author: p.lindstedt@imperial.ac.uk
Towards Clean Diesel Engines, TCDE 2009
profiles for major species under the conditions A rate analysis was performed at a temperature of
shown in Table 2. In the current study, computa- 1202 K to highlight key reaction pathways. The 1-
tions were performed corresponding to all the ex- methyl naphthalene oxidation is overall controlled
perimental conditions. The focal point of the cur- by reactions (1) to (4). Reaction (1) is the major
rent discussion is the ability of the developed me- consumption channel and contributes up to 25%.
chanism to reproduce the oxidation behaviour un- Reaction (4) is responsible for 23% of consumption
der fuel rich conditions, due to the importance to and reactions (2) and (3) contribute a further 16%
the formation of particulates. However, the ob- and 12% respectively. The 1-methyl naphthyl radi-
tained agreement was similar for fuel lean cases. cal, formed by the benzylic H removal (1), is partly
recycled back to C11H10 via H recombination. The
Φ P (atm) T (K) O2 C11H10 pathway leading to the 1-napthyl methoxy radical
1.0 1.0 1169 0.01485 0.0011 (C11H9O) is responsible for ~70% of the naphtha-
lene production.
1.5 1.0 1166 0.00990 0.0011
C11H10 + OH = C11H9 + H2O (1)
Table 2: Experimental and modelling conditions for the C11H10 + OH = C11H9P + H2O (2)
oxidation of 1-methyl naphthalene in a turbulent flow
reactor [4]. The species concentrations correspond to
C11H10 + O = C11H9O + H (3)
mole fractions. C11H10 + O = OC11H9 + H (4)

In contrast to other studies, the developed me- Methane is produced by reactions (5) and (6)
chanism does not feature any global reaction steps which contribute 67% and 22% respectively. The
and generally reasonable agreement was obtained rate of reaction (5) is increased by 21% and reac-
between computations and the experimental data tion (6) by 7% compared to the fuel lean case.
obtained by Mati et al. [8] as exemplified for fuel Reaction (7) is responsible for less than 2% of CH4
rich oxidation shown in Fig. 1. production.

C11H10 + CH3 = C11H9 + CH4 (5)
C11H10 + CH3 = C11H9P + CH4 (6)
CH3 + HO2 = CH4 + O2 (7)

The CH3 radical pool is predominantly formed via
reactions (8) and (9). Reaction (8) is responsible
for 80% of the methyl radical production and reac-
tion (9) contributes 15%. The consumption of the
methyl radical is strongly influenced by reactions
(5) and (6), which contribute 30% and 11% respec-
tively. The methyl radical recombination leading to
ethane (C2H6) formation contributes up to 26%,
compared to the lean case where it is responsible
for the 32% of the total CH3 consumption. It may
be noted that ethane levels are reproduced with
reasonable accuracy as shown in Fig. 1.
C9H7 + CH3 = C9H7CH3 (8)
C11H10 + H = C10H8 + CH3 (9)
The 1-methyl-4-napthoxy radical (OC11H9) leads
almost exclusively to the 1-methyl indenyl radical
(C9H6CH3), which in turn leads to benzofulvene
and 1-methyl indene (C9H7CH3) via H addition. The
former subsequently leads to naphthalene via
isomerisation reactions. The pathway is responsi-
ble for 5% of the total naphthalene production and
suggests that the linkage between C5 and C6 ring
structures [6] also prevails to some extent at lower
temperatures. The overall distribution between
single and two ring aromatics is reasonably well
reproduced as shown in Figs. 1 and 2.
Fig. 1: Major and intermediate species for 1-methyl
naphthalene oxidation in jet-stirred reactor. Φ = 1.5, P =
1 atm and T = 1147 - 1440 K. Circles are experimental
data [8] and the solid lines the current simulations.
Conclusions
The current work has shown that the break-
down products resulting from the oxidation of 1- References
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Fig. 2: Examples of concentration profiles of species
during 1-methyl nahpthalene oxidation in a flow reactor
(Φ = 1.0, P =1 atm, T = 1169 K). Circles are experimen-
tal data [4] and solid lines the current simulations.

Acknowledgement
The authors are grateful for the financial sup-
port of EOARD under award FA8655-06-1-3052
and BP Global Fuels Ltd.