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

3.2 Measurement Techniques and Data Acquisition
Table 3.9: Nominal Experiment Parameters for Droplet Arrays on TEXUS-46. The droplet
number is N = 5, and the non-dimensionless droplet spacing S = 18mm [195].
Pre-vaporization Droplet diameter Dimensionless
No. time t Ψ in s initial D 0 in mm ignition D ign in mm spacing ratio S/D ign
1 18 1.5 1.01 17.8
2 10 1.5 1.34 13.4
3 5 1.5 1.47 12.2
4 15 1.5 1.15 15.7
from repeated countdown holds during the final steps of the TEXUS launch
sequence. Apart from testing and validation, the experiments of the TEXNOX
drop tower campaign were destined to diversify the scientific output. Here,
the initial droplet diameter D 0 was varied in the range of 0.8 to 1.0mm, a dimensionless
spacing ratio S/D 0 of 4.5, 6.0, and 9.0 with 17, 13, and 9 droplets
was applied (Tab. 3.1), and preheating temperature T Ψ was set at 300, 400, 450,
and 500 K. The different amounts of pre-vaporization time t Ψ and preheating
temperature T Ψ were essential for the development of a flammable gas layer
around the droplets and for diversification [195–197, 208, 293, 294, 296].
Control of Droplet Lifting System
The droplet lifting system moves the droplet array holder 105 mm vertically
from its initial position to the end position inside the combustion chamber.
Stepper motor, gear system, and crank arms are adjusted for a quick
but smooth operation. The working time for covering the distance of 105 mm
was set to 2.0s for the TEXUS-46 sounding rocket flight but to 1350 ms for the
TEXNOX drop tower campaign due to the limited microgravity time. Furthermore,
the lift-up process was started 700ms before the drop capsule release
to extend the available time for droplet burnout within the drop tower experiments
(cf. Fig. 3.18). This approach split the process into two phases: a first
phase under normal gravity with the droplet array in ambient temperature
T ∞ and a second phase under microgravity with the droplet array exposed to
the preheated combustion chamber. Bringing forward the lift-up process further
is limited by the abrupt drop of surface tension during the temperature
101