On the Formation of Nitrogen Oxides During the Combustion of ...

A Chemical Mechanisms
the reactions appearing in the particular field of application as accurately as
possible. The set of preselected species A also has to be chosen to fit the later
field of application, which is not trivial and requires a priori knowledge about
the overall reactions of the system.
Sun et al. [157, 256, 426] provide a set of tools along with their method to carry
out the whole process of kinetics reduction. The procedure implemented in
the PFA reduction tools uses a general method to capture species production
rates from a wide range of reaction phenomena. This method presumes that
all phenomena dominating reactions appear during ignition and extinction of
the flame. Ignition is modeled by a perfectly stirred, closed adiabatic reactor at
constant pressure, available in the software package Senkin [259, 348]. Here,
a homogeneous mixture is investigated at temperatures of T 0 ≥ 1000 K. The
ensuing species net production rates are captured at fixed time intervals until
the mixture ignites, with ignition delay time t ign being defined as
T (t ign )=T 0 + 400 K.
(A.15)
To obtain species production rates of the extinction phenomena, a perfectly
stirred reactor (PSR) is used. More precisely, this is an open, adiabatic constant
mass flow reactor at constant pressure. A mixture at low temperatures
is inserted into this reactor at a progressive rate with T in = 300K. Here, the
species production rates are captured while the mass flow rate is increased
until flame blowout. Finally, all species production rates from the Senkin and
PSR calculations are combined in one library. For execution of the actual PFA
method, values of ˙ω Al are taken from this library.
This set of PFA tools was employed to reduce the combined kinetics “n-
Decane (Princeton) + NO x (Li)” with an initial number of 99 species and 693
reactions. The goal was to deliberately provide and evaluate a reduction by
about one third. Thus, the threshold ε was trimmed to obtain a reduced mechanism
with 64 species. For the Senkin and PSR calculations, the initial mixture
properties were varied to obtain the optimum with respect to an application in
droplet combustion. As illustrated in Table A.1, these properties included the
range of equivalence ratios φ, range of temperatures T 0 , and different sets of
preselected species A. The species C 10 H 22 , N 2 , O 2 , CO 2 , and H 2 O were considered
to be essential for the combustion process in general and were therefore
preselected in any case. The different parameter sets were varied systematically:
Only one parameter was changed, while the two remaining ones were
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