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

4.4 Modeling of Nitrogen Oxide Formation
4.4 Modeling of Nitrogen Oxide Formation
The fuel of choice for the present study is n-decane (C 10 H 22 ). This is due to the
fact that it resembles the combustion characteristics of kerosene and diesel
fuel best (see also Chap. 2.3) [49, 93, 297, 298, 340]. Soot formation is not
considered because of the exclusion of polyaromatic compounds. The employed
n-decane mechanism was developed by Zhao et al. [474] for oxidation
and pyrolysis. It is combined with the nitrogen oxide (NO x ) kinetics of Li and
Williams [250]. As shown in Chapter 2.3.3, this combined reaction mechanism
produces reliable results, and it shows a good convergence behavior at the
crucial evaluation of the species production rates. It includes a total number
of 99 species and 693 reaction equations. Humid air at ISO standard reference
conditions is taken as an oxidizer [190]. At a temperature of T = 288.15 K and
pressure of p = 101325 Pa, the relative humidity is ϕ=0.6.
Studying NO x emissions, the species mass fractions of NO and NO 2 are generally
considered. In order to quantify the NO x emissions, the emission index
EI NOx is used here (Eqs. (4.43) and (4.44)). It is the ratio between the weighted
NO x masses and the fuel mass m fuel , and it comes with the units g NOx /kg fuel
[370]. It is given in NO 2 equivalents in its standard form as
EI NOx =
and in its extended from as [297, 298]
EI NOx ,N 2 O=
m NO
M NO2
M NO
m NO
M NO2
M NO
+ m NO2
m fuel
, (4.43)
M
+ m NO2 + m
NO2
N2 O M N2 O
. (4.44)
m fuel
The total mass produced of any particular NO x species m is obtained by integration
of the respective species production rate ˙ω m . For nitric oxide (NO) for
instance, this is
m NO,tot =
∫ tend
∫ R∞
t 0 R
˙ω NO,tot 4πr 2 dr dt. (4.45)
Furthermore, two different approaches may be used for the calculation of
the fuel mass m fuel within the emission index, particularly in the case of par-
135