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

5.3 Influence of Ambient Preheating
increases as a result of the exponential temperature dependency of thermal
NO formation (cf. Chap. 2.2.3).
Recalling the results of Chapter 5.1, composition as well as temperature of the
droplet atmosphere have a significant impact on the overall NO x emissions.
For this reason, droplets burning in an atmosphere of air are compared with
droplets burning in exhaust at different initial temperatures T g ,0 (Fig. 5.17).
Here, droplet combustion is initiated by auto-ignition and no supplementary
ignition modeling needs to be employed. Even though this comparison is
of a rather academic nature, it adds to the understanding of NO x formation
in droplet combustion 5 . Numerical simulation allows an initialization of the
computational domains with identical temperatures for air and exhaust gas.
Here, the temperature T g ,0 roughly ranges from 1690 to 2240 K (cf. Fig. 5.2).
Since N 2 , O 2 , and H 2 O are the only species appearing in the air atmosphere
modeled, and as their concentration remains constant, temperature is the
only parameter that has to be varied within the initial conditions. For droplet
Emission index of NOx EINOx
10 3
10 2
Droplet NO x , air atmosphere
Total NO x , air atmosphere
Droplet NO x , exhaust gas atm.
Total NO x , exhaust gas atm.
g kg −1 Initial temperature T g,0
10 1
1600 1800 2000 2200 K
Figure 5.17: NO x Emissions for Droplets Burning in Atmospheres of Air and Exhaust. The
droplet-caused NO x emissions “Droplet NO x , exhaust gas atm.” are taken from
Figure 5.2 and included for comparison purposes.
5 NO x emissions in technical fuel sprays can be expected to be significantly lower than the ones of single droplets
burning in regular air atmosphere.
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