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

A.2 Concepts of Kinetics Reduction
Table A.1: Accuracy of Reduced Mechanisms as Controlled by Path Flux Parameters.
Preselected path flux parameter: Equivalence ratio φ
Mech. ID Scope of φ ǫ NOx ,pre in % ǫ NOx ,diff in % ǫ tign in %
P1 1.00 4.22 17.14 0.81
P2 0.75, 1.00, 1.25 1.98 4.19 0.81
P3 0.60, 0.75, 0.90, 1.00, 1.10, 1.25, 1.40 1.98 4.19 0.81
Preselected path flux parameter: Temperature T 0 in K
Mech. ID Scope of T 0 ǫ NOx ,pre in % ǫ NOx ,diff in % ǫ tign in %
T1 1500, 1800 1.52 2.60 172.85
T2 1200, 1500, 1800, 2000 2.65 4.74 78.22
T3 1000, 1200, 1500, 1800, 2000, 2200 1.98 4.19 0.81
Preselected path flux parameter: NO x species
Mech. ID Scope of NO x species ǫ NOx ,pre in % ǫ NOx ,diff in % ǫ tign in %
S1 – 1.98 4.19 0.81
S2 NO 1.98 4.19 0.81
S3 NO, NO 2 , N 2 O 1.98 4.19 0.81
S4 Total NO x chemistry [250] 1.79 7.82 3.09
kept constant. For each of these parameter variations, a reduced mechanism
was calculated, at which the threshold ε was trimmed to retain a number of
64 species. Moreover, the integral of the local relative error ǫ (Eqs. (2.26) and
(2.27)) was used as a measure for the deviation between original and reduced
kinetics. Quality criteria were the NO x mass fractions in stoichiometric premixed
flames and diffusion flames, as well as ignition delay time. For preselection
of the parameter φ, a medium range of values (P2) is beneficial to reduce
errors (Tab. A.1). On the other hand, the range of the parameter T 0 turns
out to be very important. Preselection of the species N 2 alone is sufficient to
capture NO x kinetics (S1 to S3). Consequently, NO x formation must be a dominant
contributor for the production and consumption of N 2 . Hence, the final
reduced mechanism with 64 species and 443 reactions reproduces the emission
indices EI NOx of Figures 5.2 and 5.3 with a maximum relative error of 6.3%
and 7.0%, respectively.
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