60 Figure 3.7.1b NH
3
Gas Injection Nozzle.
3.7.2 Gas flow meter and pressure gauge.
A needle valve was used to control gas flow rate into the exhaust stream and a rotameter – type flow meter measured the rate. The reading on the flow meter was calibrated to ensure an
appropriate amount of NH
3
gas was injected. There were two floats available on the flow meter, a glass float and a stainless steel float. The glass float was more sensitive and less dense but was
limited to a maximum flow rate of 24 litres per minute. The stainless steel float was denser and suitable for higher flow rate while capable of measuring up to a maximum of 44 litres per minute.
To establish the gas flow rate, measurements must be taken by observing the position of the centre of the float on a graduated scale. The scale ranged from 0 to 150 mm at increments of 10 mm.
Readings were converted to flow rate using a calibration chart for air with the appropriate float as shown in appendix 3.7a and 3.7b. Flow rate was controlled using the dial at the bottom of the flow
meter. The pressure within the line was monitored by reading the pressure gauge. The gas flow
NH
3
Gas Out
Exhaust flow
60mm 1
st
instrumentation module
NH
3
Gas Inlet
61 meter readings were taken manually and the changes of flow rate were marked by pressing the
voltage signal trigger. The voltage signal trigger was a switch wired to the Froude Texcel data logger which helps to identify
the change of gas flow rate used. Therefore any changes of NOx and NH
3
levels were clearly visible and differentiated on the Texcel control panel. Actually, the measurements with gas flow meter as
shown in figure 3.7.2 were used only as a guide. The actual NH
3
mass flow was calculated from the measured ppm and exhaust flow rate.
Figure 3.7.2 Gas flow meter reading as a guide.
3.7.3 NH
3
gas experimental layout.
The 5 NH
3
gas was used and connected to the exhaust stream in the 1
st
instrumentation module. Stainless steel pipes were used due to the nature of NH
3
which has a tendency to stick on every surface especially on materials such as Teflon. The pressure in the line was fixed to 1 bar and a
vented safety valve was connected to the air extraction system on the roof of the engine test cell. A pressure gauge was connected to the flow meter and the pressure recorded throughout to ensure
gas flow rate can be accurately calculated. NH
3
gas setup is shown in figure 3.7.3
62 Figure 3.7.3 Schematic of NH
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