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

5 Results
16
g kg −1
Emission index of NOx EINOx
12
8
4
Ignition fixed,
heat sink fixed
Ignition variable,
heat sink at fixed position
Ignition variable,
heat sink at fixed distance
0
0.0 0.2 0.4 0.6 0.8 1.0
Pre-vaporization rate Ψ
Figure 5.5: Emission Index of NO x for Different Ignition Approaches. The emission index
EI NOx is related to the initial droplet mass m fuel,0 and shown as a function of prevaporization
rate Ψ (cf. Fig. 5.3 and B.2). The initial droplet diameter, before prevaporization,
is set to D 0 = 100µm [297].
position and expansion of the heat extraction volume V ex is marginal with regard
to flame position and relative NO x production. This is due to the larger
radial distance of r m,ex , the overall wide stretch of V ex , and the low values of the
volumetric heat sink ˙q v [297]. Figure 5.5 opposes the emission indices EI NOx
calculated for the investigated methods of heat introduction and extraction to
one another. Squares depict emissions for the case of heat introduction and
extraction at the constant positions r m,in = 0.8×10 −3 m and r m,ex = 1.4×10 −3 m,
respectively. Circles show emissions for an ignition at φ r = 0.5 and a fixed
heat extraction at r m,ex = 1.4×10 −3 m (“ignition variable, heat sink at fixed position”).
Triangles also indicate emissions for an ignition position at φ r = 0.5
but a fixed heat extraction distance from this φ r -position (“ignition variable,
heat sink at fixed distance”) [297].
A large difference emerges in the absolute values of EI NOx for the two different
ignition approaches (Fig. 5.5). The emissions are significantly higher for the
spatially variable ignition (φ r = 0.5), and an increase of fuel pre-vaporization
results in continuous NO x reduction. A significant NO x reduction seems to be
feasible in the range of Ψ = 0.15 to 0.6. However, the real potential for NO x
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