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

3.1 Droplet Combustion Facility
ously mentioned techniques as possible. Figure 3.5 illustrates the procedure:
Fuel is dripped through fine glass tubes in order to accumulate as full-size
droplets at the intersections of crossed SiC fibers. The droplet diameter is
controlled by the amount of fuel supplied. After verification of a successful
droplet array generation, the droplet array holder is lifted up into the combustion
chamber (see Fig. 3.3). Mikami et al. [282] extensively report on this
droplet generation technique, also evaluating other existing techniques. The
present technique stands out due to its high reliability and reproducibility
characteristics. It is applicable to difficult experiment conditions, as for instance
droplet pre-vaporization experiments with highly volatile fuels. The
characteristics of the utilized technique may be summarized as follows [282]:
• High droplet sphericity with minimal deformation in fiber contact areas
• Wide range of droplet diameters achievable
• High success rate of droplet deployment on suspension fibers
• No droplet vibrations due to the droplet generation process
• No droplet drift during ignition and burning (self-stabilizing suspension)
• Rapid droplet generation process
• Capability of simultaneous multi-droplet generation for droplet arrays
• Compact droplet generation device
Due to the interaction of the droplet array generation device and the droplet
array holder, it is essential to verify the alignment of the glass tubes with their
corresponding suspension fibers (cf. Fig. 3.5). Preliminary tests under normal
gravity as well as microgravity conditions helped with this verification. Furthermore,
experience taught that a slight offset of the glass tube orifices from
the fiber intersections in the vertical and in the forward direction is favorable
for reliable droplet generation under both gravity conditions. A positive offset
within the range of 1 to 2mm is the optimum for these two directions, as it is
pictured in Figure 3.5. However, direct contact has to be secured in the lateral
direction in order to anchor the droplets successfully. In very rare cases,
a glass tube hits a SiC fiber without slipping off this unstable position, while
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