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

3.2 Measurement Techniques and Data Acquisition
The acronym HSV stands for “High-Speed Video”. In the drop tower campaign,
a Kodak camera was employed for this purpose (Fig. 3.11, D) [110], whereas a
camera of NAC Image Technology was utilized in the sounding rocket experiments
[302]. Both high-speed cameras have a resolution of 510×484 pixel at
a frame rate of 500Hz. High-speed recording with each of these cameras was
started with the activation of the hot-wire igniter. In order to allow the necessary
optical access to the interior of the combustion chamber, it is equipped
with one window on each longitudinal side (Fig. 3.7, F). The window sizes are
optimized towards a minimum heat loss and a maximum field of view [196].
3.2.4 Exhaust Gas Analysis
A considerable number of measurement techniques are practical for the analysis
of combustion products. They include infrared and ultraviolet absorption
of electromagnetic radiation, mass spectroscopy, emission spectroscopy, various
chemical methods, and electrochemical methods. Sampling and analysis
systems can be classified in “cold/dry” and “hot/wet”. While a cold/dry
system consists of the sample probe, particulate matter filter, heated sample
line, moisture removal unit, and the analyzer itself, a hot/wet system forgoes
the moisture removal and directly measures the emission concentrations on
a wet basis. Besides, those techniques may also be grouped into “methods
by separation” and “methods without separation” [97, 136, 181, 275, 321, 390,
420, 440, 460].
Since the spatial distribution of the combustion products within the combustion
chamber was three-dimensional at any given time, it is evident that some
limitations are imposed on the interpretation of the exhaust gas samples obtained.
A concept combining gas sampling during the experimental phase
with a successive gas analysis on the ground was pursued here. In the case of
parabolic and sounding rocket flight, the sampling process took place during
the microgravity period, while it was enforced under normal gravity conditions
(i.e. after drop capsule deceleration) in the case of the drop tower experiments.
To perform the gas analysis in the particular laboratory environment,
the filled gas sample cylinders were physically removed from the DCU. The
surface coating discussed above helped in keeping the emission signature stable
until the analysis was performed (see Chap. 3.1.4). A combination of a FT-
IR (Fourier Transform Infrared) spectrometer and a chemiluminescent NO x
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