<div>
<p>Combustion
will likely continue to be utilized over the next century to meet the world’s
energy needs. As increasingly stringent
requirements on emissions, particularly of oxides of nitrogen (NO and NO<sub>2</sub>)
are imposed on power plants due to their harmful effects on the environment,
advanced combustor strategies to limit NO<sub>X</sub> productions are needed. One such advanced concept involves axially
staging the fuel to create a distributed combustion system. The fundamental problem for staged combustion
involves the injection of a reacting jet into crossflow. This canonical problem is modified for this
dissertation through injection of a reacting premixed natural gas and air jet into
a compressible vitiated crossflow with negligible swirl. In addition, the experimental efforts for
this work were conducted at elevated inlet air temperature and combustor
pressure.</p><p>The
development and performance of a perforated plate burner (PPB) to provide
vitiated crossflow and operating using premixed natural gas (NG) and air at
engine-relevant conditions is discussed.
A significant benefit of using burners with simplified flow fields, such
as the PPB, for experimental studies in the laboratory is the potential for
decoupling the complex fluid dynamics in typical combustors from the chemical
kinetics. The stable operation of the
PPB within a high-pressure test rig was validated: successful ignition,
effective use of redlines for flashback mitigation, and long duration
steady-state operation in both piloted and non-piloted modes were all
observed. Exhaust gas emissions measured
using a Fourier-transform infrared (FTIR) spectrometer showed very good
performance of the PPB in terms of the combustion efficiency and low levels of
NO<sub>X</sub><i> </i>in non-piloted
operation that were generally within 3 ppm.</p><p>Emissions
measurements of the premixed reacting jet in vitiated crossflow were obtained
for a variety of conditions and a significant NO<sub>X</sub> reduction was
achieved when the staged combustor exit Mach number was increased and the axial
residence time was decreased. Based on
this preliminary investigation, a test matrix was developed to independently
vary the exit Mach number for a constant axial residence time by using modular
rig hardware to change the length of the axial combustor. Up to 70% reduction in NO<sub>X</sub>
produced by the axial stage was observed when the combustor exit Mach number
was increased from about 0.26 to 0.66 at a constant residence time of 1.4
ms. NO<sub>X</sub> reduction based on
variation in the Mach number and at a constant residence time has not been
previously reported in the literature to the best of our knowledge. This decrease in NO<sub>X</sub> is
hypothesized to be due to the lower static temperature of a compressible flow
and potentially better mixing of the jet with the crossflow due to the
interaction occurring at high speeds.</p><p>Based on the strong effect of Mach number for NO<sub>X</sub>
reduction even at a constant residence time, further investigation using
laser-based diagnostics is needed to provide insight on physical processes
controlling this phenomenon. An
optically-accessible secondary combustion zone was developed and fabricated to
study the flame position and structure of reacting jets injected into a
high-speed vitiated crossflow. The
windowed combustor was capable of long-duration, steady-state operation despite
a trifecta of: elevated pressures, high combustion gas temperatures, and
high-speed reacting flows. High-speed
imaging using OH* and CH* chemiluminescence was used to validate operation of
the optically-accessible secondary combustion zone.</p><p>High-repetition-rate
(1 – 10 kHz) planar laser-induced fluorescence (PLIF) imaging of OH and CH were
performed on both premixed NG-air reacting jets and premixed NG-hydrogen-air
reacting jets to investigate the flame structure of the reacting jet within a
high-speed crossflow. OH-PLIF was performed in the A-X electronic system using
excitation at near 283 nm in the (vʹ = 1, v″ = 0) band and near 311 nm in the (vʹ = 0, v″ = 0) band. The crossflow velocity and equivalence ratio were
observed to have a strong impact on the stabilization of the reacting jet
flame. Additional insight on the stabilization mechanism was obtained using 50
kHz OH* chemiluminescence imaging. CH-PLIF was
performed in the C-X electronic system using R-branch excitation near 311 nm in
the (vʹ =
0, v″=
0) band. The CH-PLIF images
indicated local stoichiometric regions near the leeward side of jet injection
and in regions where significant interaction of the fuel rich jet with the vitiated
crossflow is expected. In addition, the CH-PLIF images showed
evidence of broken, thickened, non-premixed reaction layers.<br></p></div>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12205805 |
| Date | 29 April 2020 |
| Creators | Neil Rodrigues (8774093) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY-NC-SA 4.0 |
| Relation | https://figshare.com/articles/Reacting_Jets_in_Compressible_Vitiated_Crossflow_with_Negligible_Swirl/12205805 |
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