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

3.1 Droplet Combustion Facility
C
D
B
E
A
F
Figure 3.3: Droplet Array Lifting Devices. The droplet array holder is shown in its lower position,
as used during droplet generation with the combustion chamber closed
[196]. A: fuel-dosing pump with servo motor SM3, B: linear bearing with guidance
carriage, C: droplet array holder, D: gears, E: stepper motor SM2 for lifting,
F: fuel storage case.
3.1.1 Droplet Array Generation Device
In the 1980’s, Haggard Jr. and Kropp developed a distinct droplet generation
concept that was extensively used in drop tower and space flight experiments
throughout the following years [12, 76, 77, 79, 101, 161–163, 312, 394]. Its design
allows the generation of free droplets by two opposing fuel supply tubes.
These are slowly separated from one another, while forming a droplet of desired
diameter. The droplet is deployed via a final, rapid retraction. Even
though the droplet has a spherical shape and no negative effects on droplet
vaporization/burning have to be expected due to the absence of a droplet suspender,
this approach has some shortcomings: The probability of generating
a stationary droplet is low, and the droplet may not maintain its initial position
for the full burning period. As a result, the droplet could drift out of the
field of view of the observation system or even touch the combustion chamber
walls. Furthermore, it is impossible to generate a well-defined droplet
array, as for instance depicted by Figure 3.1 [234, 282, 393]. Avedisian et al.
[29] used a piezoelectric droplet generator propelling a continuous stream of
droplets on a parabolic trajectory. When the last droplet emerging from the
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