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

5 Results
6.0
g kg −1
Emission index of NOx EINOx
4.0
2.0
T ∞ = 500 K
T ∞ = 600 K
T ∞ = 700 K
0.0
0.0 0.2 0.4 0.6 0.8 1.0
Pre-vaporization rate Ψ
Figure 5.16: Impact of Ambient Preheating on NO x Abatement Potential due to Pre-
Vaporization by Referring to the Reacting Fuel Mass. The positions of heat introduction
and extraction are set to the constant values of r m,in = 0.8×10 −3 m and
r m,ex = 1.4×10 −3 m (cf. Fig. 5.3).
Emissions altogether are lower when relating the emission index EI NOx to the
initial droplet mass (Fig. 5.15) than to the reacting fuel (Fig. 5.16). Despite
the temperature difference of ∆T ∞ = 100 and 200K, pre-vaporization is capable
of compensating the increased NO x formation at Ψ= 0.5 and 0.8, respectively
(Fig. 5.15). This is essential, as temperature level and pre-vaporization
time are major design parameters that need to be weighed up against each
other in the layout of many combustion systems. Furthermore, with an increase
in T ∞ , the process of obtaining lower NO x emissions starts at lower degrees
of vaporization. This is due to an increased diffusive transport at those
higher temperature levels. As pointed out in Chapter 5.2, a certain amount
of gaseous, unburned fuel remains in the outer region of the gas atmosphere.
This fuel can be consumed in the further course of the combustion process
within a technical application. For a preheating temperature of T ∞ = 700K
and a pre-vaporization rate of Ψ = 0.8, this fuel amount rises up to 278 % of
the fuel consumed in the droplet flame. Figure 5.16 shows the NO x emissions
of the droplet after correcting the results for this influence. The trend is uniform
for all three temperature levels. The offset of the individual curves alone
180