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

3 Experiments on Droplet Array
Combustion
Emissions of nitrogen oxides (NO x ) in sprays are a complex and crucial topic.
Current scientific knowledge about NO x formation in sprays is based on research
of droplet combustion, since a droplet can be regarded as the primary
element of a spray. Single droplets, droplet arrays, and droplet matrices have
therefore been investigated experimentally by various researchers and research
groups to acquire a basic understanding of the fundamental processes
involved in spray combustion [6, 27, 29, 47, 48, 59, 75–77, 101, 102, 105, 121,
141, 151, 152, 161–164, 170, 192, 202, 203, 207, 212, 221–223, 228, 237, 239, 267–
270, 278–280, 282, 283, 292, 307–309, 312, 317–319, 327, 329, 352, 353, 357, 392,
394, 412–415, 425, 431–433, 444, 465, 467, 470]. Law [234] and Kono et al. [216]
review state of the art and recent advances in this research field. As far as the
present thesis is concerned, Chapters 2.1.3 and 2.2.3 provide the theoretical
framework on droplet combustion and NO x formation, respectively.
This chapter presents the experimental setup for the combustion of an n-
decane droplet array under microgravity conditions as utilized within the
studies contributing to this thesis. The setup accounts for undisturbed burning
characteristics and a representative NO x formation. Different droplet
regimes were investigated in order to enhance the understanding of the physical
and chemical processes of combustion, such as vaporization, transport,
chemical kinetics, and their interaction. The pre-vaporization rate Ψ of
the liquid droplets, mainly realized by the adjustable pre-vaporization time,
was the main experiment parameter. The microgravity environment was
needed for uniform and idealized experiment conditions during the entire
process of droplet vaporization and combustion, particularly the extended
pre-vaporization periods (cf. Figs. 1.1 and 1.2). It allowed an experiment conduction
without the effect of natural convection, which causes difficulties
apart from the complexity inherent to combustion itself.
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