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

3 Experiments on Droplet Array Combustion
ular pump that was used for evacuation of the exhaust gas sample cylinder
during the final preparatory steps. Also, the whole drop tower being under
evacuation could be employed as a backing pump here.
3.2 Measurement Techniques and Data Acquisition
The experimental measurements conducted within the study at hand can be
subdivided into direct, in-situ measurements and subsequent measurements.
However, regardless whether parabolic flight, drop tower, or sounding rocket
campaign, almost all physical parameters were recorded in-situ. Only the
quantification of the exhaust gas concentrations of interest needed to be split
into two steps: exhaust gas sampling and exhaust gas analysis.
3.2.1 Influence of Microgravity Environment
Since the effects of gravitational forces hamper most of the combustion
related processes, a vast number of fundamental studies have been conducted
under microgravity conditions since the early work of Kumagai et
al. [219, 222]. Particularly, laboratory scale experiments are compromised
by buoyant motion due to experimental setups of reduced size and the lack
of turbulence in comparison with full-scale industrial applications. Furthermore,
good temporal and spatial resolution are needed for the very specific
investigations.
As pointed out in Chapter 1.4, combustion naturally involves the production
of high-temperature gases and a decrease of density. Under “normal” gravity,
those local areas of low density trigger buoyant motion, and thus complicate
the execution and interpretation of experiments. However, under microgravity
conditions, interfering effects due to buoyancy are canceled out.
Consequently, the microgravity environment can contribute to a better understanding
of combustion phenomena, including the interaction of fluid
dynamics, scalar transport, thermodynamics, and chemical kinetics. From
the technical point of view, it is possible to control low-speed flows, purely
diffusive transport regimes, and large droplet diameters. For instance, the
fuel used in the study at hand (C 10 H 22 ) has a vapor density of 3.564 kg m −3
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