Global NOx Measurements in Turbulent Nitrogen-Diluted Hydrogen Jet Flames Page: 3 of 10
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2. Experimental Apparatus
The combustor used for all of the atmospheric pressure
measurements in this study is shown to scale in Figure 1.
Ultra high purity hydrogen and nitrogen are individually
metered from gas cylinders to the fuel tube using separate
mass flow controllers. The fuel tubes are made from 1/8"
OD stainless steel tubing with varying wall thicknesses,
each tapered to a thin lip at the jet exit, with measured jet
exit diameters of 0.84 mm, 1.45 mm, and 2.12 mm.
Another mass flow controller delivers high purity air to
the coflow air apparatus, consisting of a packed bed of
copper beads overlaid with a stack of wire mesh screens.
In all cases, the coflow air is supplied at an equivalence
ratio of (D = 0.5 or 0.33, and its velocity calculated to be
less than 0.25% of the fuel jet velocity.
The combustion chamber is made from an 8" Pyrex
cylinder whose wall temperature is monitored with
externally mounted thermocouples. The cylinder can be
internally cooled via ambient air flow through eight 1/2"
holes around the base of the combustion chamber, though
these holes were sealed for all experiments in this study,
as cooling was deemed unnecessary.
The top of the combustion chamber is fitted with an
aluminum cap to direct the exhaust to an overhead vent.
To prevent NOx profiles at the exhaust, a mixing baffle
composed of three wire mesh screens is suspended from
the aluminum cap by three heavy gauge wires. A gas
sampling probe draws well-mixed combustion products
through a heated sample line to a NOx converter,
followed by an ice bath and desiccant trap to remove any
To NOx. 02
8' Dia Py'rex
Figure 1: Experimental apparatus
for atmospheric pressure NOx
water vapor from the gas sample. The gas is then analyzed by Rosemount NGA2000 NOx and
oxygen analyzers. Global NOx measurements, XNOx,measured, are then corrected to 15% oxygen,
XNOx@1502, using the measured oxygen content in the exhaust gas, X02,measured, as follows :
X NOx@15%02 X NOxmeasured
0.21 - X02,measured
Corrected NOx @ 15% 02 can also be converted to an emission index using :
EINO - XNOx@15%o2 Nprod@15%02 MNO2 (3)
1000 NH2 MH2
where Nprod@15%O2/NH2 is the total moles of dry combustion products containing 15% oxygen, per
mole of hydrogen burned, and MNO2 and MH2 are the molecular weights of NO2 and H2,
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Weiland, N.T. & Strakey, P.A. Global NOx Measurements in Turbulent Nitrogen-Diluted Hydrogen Jet Flames, article, March 1, 2007; (digital.library.unt.edu/ark:/67531/metadc882648/m1/3/: accessed August 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.