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

2.2 Theory of Exhaust Gas Formation
Non-dimensional inter-droplet distance S/D0
Equivalent gas temperature for fuel C 10 H 22 T eq,C10 H 22
245 490 735 K
25.0
20.0
15.0
10.0
5.0
0.0
No flame spread,
pure vaporization
Mode I
Mode II
Mode III
Premixed flame
propagation
Autoignited
individual
droplet
combustion
Autoignited
droplet
array
combustion
0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
Non-dimensional gas temperature R s T ∞ /∆h v
Figure 2.5: Schematic of Flame Propagation Modes for Linear Droplet Arrays (reprinted
and adapted from Refs. [318, 456]). Experimental setups of the present study are
included in the plot and marked by hatched areas.
continues burning by itself without participating in group combustion. The
mode map, as depicted in Figure 2.5, is applicable to any kind of liquid hydrocarbon
fuel and combustion under atmospheric pressure [318, 446, 447, 456].
The droplet array setups of the present study are also indicated in Figure 2.5.
Setups without fuel pre-vaporization can be located in Mode I and II, whereas
setups with pre-vaporization are on the border of “no flame spread” and Mode
III. Due to pre-vaporization and the ensuing formation of a combustible gas
layer in the proximity of the droplets, this region becomes accessible to flame
propagation, offering some potential for NO x abatement (cf. Fig. 2.2).
2.2 Theory of Exhaust Gas Formation
There are a number of different emission sources of pollutant gases into the
atmosphere. Many of them are not of anthropogenic origin and might be
27