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

B.1 Experiment Operation Conditions for Droplet Array Combustion
produces as a link in an infinite droplet array. Nevertheless, gas exchange during
the combustion and gas sampling processes needs to be accounted for.
Since the sounding rocket flight of TEXUS-46 originally comprised only four
combustion cycles, a statistical evaluation of the procedures for gas sampling
and analysis became indispensable. Furthermore, diversification of the experiment
parameters was essential for the scientific output. Consequently,
parabolic flight and drop tower experiments were conducted as precursor experiments
to investigate the reference case for the sounding rocket experiments
as well as to gain additional knowledge about various technical aspects
of the experiment. 1
As mentioned above, the main focus of the study at hand was the degree of fuel
vaporization Ψ. The extended microgravity duration of sounding rocket flight
allowed to investigate larger values of Ψ compared to parabolic flight and
drop tower. However, further experiment parameters were studied within the
drop tower campaign to achieve a more complete understanding of droplet
combustion and NO x formation. They included the preheating temperature
T ∞ , initial droplet diameter D 0 , inter-droplet distance S, and total droplet
number N. Table B.1 gives an overview of all experiments conducted under
microgravity conditions. The reason for investigating such large droplets
(0.840 – 1.608 mm) was to provide large spatial and temporal scales, and thus
well-defined droplet combustion regimes. This approach in particular helped
to restrain the relative deviations within fuel vapor formation around the
droplets. Experimental errors in the initial droplet diameter D 0 and/or prevaporization
time t Ψ can be caused by the fuel-dosing pump, the fine glass
tubes, the ignition system, and the hysteresis of the system itself.
Precursor Experiments
Parabolic flight experiments typically provide a microgravity level of 1×10 −2 g 0
for approximately 20s. Major advantages of parabolic flight are direct access
to the experiment by the scientist, multiple experiment runs within one
campaign, absence of negative impact loads, minor restrictions in weight and
power consumption, and moderate costs. However, the aircraft can normally
1 In the meantime, Nomura et al. [318] and Oyagi et al. [327] were making efforts to investigate the combustion
of moving droplets and droplet clusters, which is the next step towards the systematic investigation of complex
sprays.
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