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

2.3 Kinetic Modeling
paring the combined mechanisms with the original C 10 H 22 mechanisms, with
the latter acting as reference in terms of Equations (2.26) and (2.27). The difference
(i.e. the relative error) was studied for temperature, velocity, fuel mass
fraction, and product species [298].
Laminar premixed flames were calculated at an equivalence ratio of φ = 0.6
to 1.4 in steps of 0.1. Laminar flame speed S L obtained with the Princeton
C 10 H 22 mechanism decreases by up to 0.4 % under near-stoichiometric conditions
and up to 1% at both φ= 0.6 and 1.4 as a consequence of adding the
NO x chemistry of Li and Williams [250] or the Leeds NO x kinetics [186]. Flame
speeds estimated with the combination “n-Decane (Aachen) + NO x (Li)” lie
0.3% below the original Aachen mechanism. By comparison, laminar flame
speed is similar for the Princeton and Aachen mechanism at φ = 0.7, but
the difference goes up to almost 30% at an equivalence ratio of φ = 1.4
(cf. Fig. 2.6).
Relative differences ǫ m (Eqs. (2.26) and (2.27)) were evaluated to analyze the
deviation in mass fraction Y between the combined and the original C 10 H 22
mechanisms. The mass fractions Y of C 10 H 22 , H 2 O, CO 2 , and CO were studied
in detail. Various calculations showed that neither fuel nor the NO x mechanism
has a significant influence on the absolute values of ǫ m . The values were
generally very small for ǫ m,abs and ǫ m,tot : The profile of the fuel C 10 H 22 was
modified by less than 0.4 %. The H 2 O fraction decreased by around 0.15 %,
while the CO 2 profile increased by 0.3 %. The formation of CO was reduced
by up to 4% under lean conditions, but the difference remained negligible for
stoichiometric and rich conditions. Furthermore, the mass fractions Y of OH
and CH x and the relevant radical pool for NO x formation were compared for
both the original and combined mechanisms. The relative differences ǫ m of
these NO x precursor species were consistently below 1%.
Counterflow diffusion flames performed in a similar manner to laminar premixed
flames, employing the mechanisms investigated. There was a comparable
agreement between the unmodified/original mechanism and combined
C 10 H 22 /NO x chemistry. The maximum relative difference ǫ m was 0.5 % for the
Princeton C 10 H 22 kinetics considering temperature, axial velocity, spreading
rate, and mass fractions of C 10 H 22 , O 2 , H 2 O, CO 2 , and CO. The respective value
for the Aachen C 10 H 22 mechanism was 0.8 %.
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