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

A Chemical Mechanisms
Another, very recent approach to reduce kinetics is the path flux analysis (PFA)
developed by Sun et al. [426]. The PFA method reduces a chemical mechanism
by removing species and reactions that have a minor influence on the conversion
of reactants to products. It is possible to specify certain target species, as
for instance the oxides of nitrogen, which are kept in the reduced mechanism
in any case. Since this is a promising approach to obtain a compact mechanism
that can also predict NO x formation, a sensitivity analysis was conducted
on this method, starting from the combination “n-Decane (Princeton) + NO x
(Li)” discussed in Chapter 2.3.3.
As a starting point it is necessary to consider a reacting system, such as a perfectly
stirred reactor, that is representative for the particular application. This
system is run with a number of elementary reactions and their associated net
reaction rates ˙ω m . The so-called flux of one species S m to another species S n
is the basis for finding the significance of species. The reduction process begins
with a set of preselected species A. The significance of all other species B
to the conversion of the preselected species is determined by the interaction
coefficient r AB . Using the total production fluxes P A and the total consumption
fluxes C A of a particular species A (Eqs. (A.5) and (A.6)), the PFA method
evaluates the interaction coefficient between the selected species A and any
other species B. The stoichiometric coefficient of species A in the l-th reaction
and the respective net production rate are represented by ν Al and ˙ω Al .
The number of elementary reactions is identified by L [426]:
L∑
P A = max(ν Al ˙ω Al ,0) ,
C A =
l=1
L∑
max(−ν Al ˙ω Al ,0).
l=1
(A.5)
(A.6)
The determination of the interaction coefficient r AB further requires the production
and consumption fluxes of A due to the presence of B:
L∑
P AB = max ( ν Al ˙ω Al δ l B ,0) ,
C AB =
l=1
L∑
max ( −ν Al ˙ω Al δ l B ,0) ,
l=1
(A.7)
(A.8)
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