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

3.2 Measurement Techniques and Data Acquisition
point of time of exhaust gas sampling on the basis of the known leakage rate
[338, 339].
Measurement of Temperature
Three thermocouples are installed in the combustion chamber in total, of
which one K-type (Ni-Cr/Ni-Al) thermocouple is attached to the inner combustion
chamber wall to control the preheating temperature at 500±1K within
a two-step (on/off) control approach. In doing so, the thermocouple monitors
a temperature range of 0 to 250 ◦ C with a sampling rate of 5Hz. Two
S-type (Pt10Rh/Pt) thermocouples directly measure the gas temperature inside
the combustion chamber in the range of 0 to 1250 ◦ C at 500 Hz [196]. The
platinum hot junction was selected here because of its stable temperaturevoltage
relationship and the exposition of the two measurement locations to
hot combustion gases. The downside is its lower sensitivity of approximately
10µV K −1 and its higher cost compared to other types. Apart from the recording
for scientific purposes, the output of the two S-type thermocouples is used
to trigger the exhaust gas sampling (Chap. 3.2.6) [390]. In addition, resistance
thermometers (Pt100) are used to monitor the ambient temperature inside the
DCU vacuum protection vessel. They are installed on the experiment deck,
close to the droplet array generation system, and in the proximity of the combustion
chamber. This information is also used for cold-junction compensation
of the three thermocouple inputs.
3.2.3 Optical Observation
The optical observation method is threefold:
• Observation of the droplet array generation by a color CCD camera
• Observation of the combustion sequence by a color CCD and a highspeed
camera
• Backlit observation of the droplet size by a monochrome CCD camera
Consequently, the camera system consists of four cameras, which are summarized
in Table 3.4. The cameras CCD1 and CCD2 are identical color cameras
83