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Chemical transformations of nitrogen oxides while sampling combustion products

01 Jul 1977-Journal of the Air Pollution Control Association (Taylor & Francis Group)-Vol. 27, Iss: 7, pp 648-655

Abstract: The study reviews the sampling environments and chemical transformations of nitrogen oxides that may occur within probes and sample lines while sampling combustion products. Experimental data are presented for NO/sub x/ transformations in silica and 316 stainless steel tubing when sampling simulated combustion products in the presence of oxygen, carbon monoxide, and hydrogen. A temperature range of 25 to 400/sup 0/C is explored. In the absence of CO and H/sub 2/, 316 stainless steel is observed to promote the reduction of nitrogen dioxide to nitric oxide at temperatures in excess of 300/sup 0/C, and silica is found to be passive to chemical transformation. In the presence of CO, reduction of NO/sub 2/ to NO is observed in 316 stainless steel at temperatures in excess of 100/sup 0/C, and reduction of NO/sub 2/ to NO in silica is observed at 400/sup 0/C. In the presence of H/sub 2/, NO/sub 2/ is reduced to NO in 316 stainless steel at 200/sup 0/C and NO/sub x/ is removed at temperatures exceeding 200/sup 0/C. In silica, the presence of H/sub 2/ promotes the reduction of NO/sub 2/ to NO at 300/sup 0/C and the removal of NO/sub x/ above 300/sup 0/C.

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Title
Chemical transformations of nitrogen oxides while sampling combustion products
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Journal
Journal of the Air Pollution Control Association, 27(7)
ISSN
0002-2470
Authors
Samuelsen, GS
Harman, JN
Publication Date
1977
DOI
10.1080/00022470.1977.10470467
Copyright Information
This work is made available under the terms of a Creative Commons Attribution
License, availalbe at https://creativecommons.org/licenses/by/4.0/
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University of California

Chemical Transformations of Nitrogen Oxides
While Sampling Combustion Products
G.
S. Samuelsen and John N. Harman, III
University of California, Irvine, California
The present study reviews the sampling environments and chemical transformations of nitro-
gen oxides that may occur within probes and sample lines while sampling combustion products.
Experimental data are presented for NO
X
transformations in silica and 316 stainless steel tubing
when sampling simulated combustion products in the presence of oxygen, carbon monoxide,
and hydrogen. A temperature range of 25° to 400 °C is explored. In the absence of CO and H
2
,
316 stainless steel is observed to promote the reduction of nitrogen dioxide to nitric oxide at
temperatures in excess of 300°C, and silica is found to be passive to chemical transformation.
In the presence of CO, reduction of NO
2
to NO is observed in 316 stainless steel at temperatures
in excess of 100°C, and reduction of NO
2
to NO In silica is observed at 400°C. In the presence
of H
2
, NO
2
is reduced to NO in 316 stainless steel at 200°C and NO
X
is removed at temperatures
exceeding 200°C. In silica, the presence of H
2
promotes the reduction of NO
2
to NO at 300°C
and the removal of NO* above 300°C.
Measurement of the exhaust gas com-
position from anthropogenic sources
such as automobile engines, diesel en-
gines,
utility and industrial boilers,
furnaces, and gas turbine engines is re-
quired to evaluate system efficiency and
pollutant emission
levels.
Measurement
generally proceeds by extracting and
transporting a sample to instrumenta-
Dr. Samuelsen is Associate Profes-
sor of Mechanical and Environmen-
tal Engineering, School of Engineer-
ing, University of California, Irvine,
CA 92717. Mr. Harman recently re-
ceived the Master of Science degree
in Engineering at UCI. He currently
serves as a Senior Chemist at Beck-
man Instruments, Inc., Fullerton, CA
92634. The work was conducted at
the UCI Combustion Laboratory,
School of Engineering, University of
California, Irvine, CA 92717.
tion for quantitative analysis. To obtain
reliable data, it is necessary that the
analytical instrumentation receive a
sample that is chemically identical to
the composition existing at the point of
extraction.
Potential sample transformations
may be minimized by careful selection
of materials for the probe and sample
line.
However, careful selection requires
data relevant to the application, and
data are presently not plentiful for two
products of combustion especially sus-
ceptible to chemical transformation,
nitric oxide (NO) and nitrogen dioxide
(NO2).
This paper summarizes the
available information and presents re-
sults from an experiment designed to
assess the conditions for which chemical
transformation of nitrogen oxides oc-
curs.
Types of Transformation
Chemical transformation of nitrogen
oxides in probes and sample lines may
be of three general types:
NO Oxidation: NO
NO
2
NO*
conserved
NO
2
Reduction: NO
2
NOr conserved
NO*
Removal: NO, NO
2
N
2
NO
X
not conserved
An additional transformation path,
formation, involves the oxidation of
ni-
trogen containing species such as am-
monia (NH3). Because formation of
NO*
in probes and sample lines is gen-
erally limited to specialized conditions
(e.g. sample extraction from flue gases
into which ammonia has been injected
for NO
X
control, or from flames into
which nitrogen containing compounds
have been injected to study fuel bound
NO*
formation), formation reactions are
not separately identified.
The potential significance of the
transformation of nitrogen oxides rests
on the use of the emissions data. For
example, emission standards for nitro-
gen oxides are currently proposed or
648
Journal of the Air Pollution Control Association

Table I. Sampling conditions for nitrogen oxides.
Source
Internal com-
bustion engine
Diesel engine
Residential oil
burners
Boilers
Gas turbine
Flame research
Typical
NO
X
ppm
500-4000
500-1000'
1000-7000
700-2500
20-100
200-1000
25-800
1000-8000
25-200
10-8000
Sampling point
Combustion zone
Engine exhaust
Combustion zone
Engine exhaust
Flue gas
Combustion zone
Flue gas
Combustion zone
Engine exhaust
Within flame
Typical sampling
Temperature °C
1300-2400
200-500
700-2500
200-500
100-300
100-1600
100-300
1300-2700
400-1500
700-2500
; environment
Atmosphere
Reducing
Reducing
Reducing and
Oxidizing
Oxidizing
Oxidizing
Reducing and
Oxidizing
Oxidizing
Reducing and
Oxidizing
Oxidizing
Reducing and
Oxidizing
References
Examples of
NO
X
probing
42,43
3,5
44
4
45
7,8
1,46,47
11
25,48,49,
50,
51
52,
53, 54,
55,
56,57
Prior studies
relevant to
possible NO
X
transformations
14
14
14
15,
16, 17
14
11,
14
15,
16, 17
promulgated in terms of nitrogen oxides,
NO*.
1-5
As a result, the enforcement of
emission standards is not compromised
by the occurrence of NO oxidation or
NO2 reduction reactions in the probe or
sample line so long as total oxides of
ni-
trogen are conserved. However, emis-
sions data biased by NO
X
removal re-
actions are unacceptable as the basis for
any emissions standard, control strate-
gy, or enforcement action.
In addition to conserving NO
X
, the
influence of NO oxidation and NO2 re-
duction reactions in probes and sample
lines warrants increased attention as
well. For example:
1.
Assessment of
local
air quality im-
pact
The NO/NO2 emission ratio is impor-
tant in assessing local air quality impact
from major sources. Ambiguity regard-
ing the NO/NO2 emission ratio from
combustion sources presently precludes
consideration of the impacts of NO and
NO2 emissions on areas in proximity to
the source.
2.
Assessment of plume visibility im-
pact
The NO/NO2 emission ratio is impor-
tant in the prediction of plume visibility
from power plants.
6
The ambiguity re-
garding the NO/NO2 emission ratio
from power plants presently precludes
a full assessment of air quality and
plume visibility impact, and compro-
mises attempts to validate visibility
impact models.
3.
Regional oxidant modeling
The prediction of local formation and
removal rates for oxidant requires spa-
tial and temporal emission inventories
for both NO and NO2. Ambiguity re-
garding the NO/NO2 emission ratio
from mobile and stationary sources
contributes to the limitations of regional
oxidant models and compromises efforts
to validate these models.
4.
Flame studies
The local concentrations of both NO
and NO2 within flames are required to
assess the chemical kinetic mechanisms
responsible for the formation of NO
X
.
Questions attendant to transformation
of NO and NO2 in sample probes pres-
ently limit the utility of fundamental
studies that address NO and NO2 for-
mation in combustion flows.
Sampling Conditions
Table I
is
a summary of the conditions
typically encountered when measuring
combustion product composition. Note
the wide variation of temperature and
species concentration. The tempera-
tures encountered (at the point of sam-
ple extraction) divide into three general
groups:
Temperature
Group
moderate
high
very high
Temperature
Range
25°-600°C
600°-1200°C
1200°-2500°C
Moderate temperature probing
(25°-600°C) is the most frequently en-
countered. Examples include flue and
exhaust gas sampling from stationary
and mobile sources. High temperature
probing is experienced in combustion
research, especially in studies of secon-
dary (post flame) combustion processes.
Very high temperature probing is com-
mon in flame research. Although flame
research has historically been conducted
in laboratory systems (premixed flames,
diffusion flames, shock tubes, stirred
reactors, and plug flow reactors), com-
bustion zones in practical combustion
systems are now being probed as
well.
7
-
8
The function of the sample probe is to
extract and cool the sample to a final
temperature. (For high and very high
temperature probing, rapid expansion
of the sample at the probe tip is em-
ployed to terminate active reactions.)
The final temperature is typically con-
trolled (150° to 200°C) to prevent con-
densation of water and hydrocarbons.
The function of the sample line is to
maintain the final temperature and
transport the sample to the analytical
instrumentation.
Chemical transformations of nitrogen
oxides in the temperature range 25° to
600° C are of special interest since (1)
moderate temperature probing (25° to
600°C) is the most frequently encoun-
tered, and (2) regardless of the temper-
ature at the point of extraction, the
sample will typically have an extended
residence time (seconds) at the final
temperature (150° to 200° C) while
undergoing transport to the analytical
instrumentation.
Available Information
A few general reviews of NO* sam-
pling problems are available to assist in
the design of sampling systems.
9
"
13
Additional information is available from
a limited number of specialized com-
bustion-related studies,
14
^
17
from
studies conducted to evaluate converter
materials for chemiluminescent oxides
of nitrogen analyzers,
18
"
20
and from
studies conducted to explore the cata-
lytic oxidation of
CO
in automobile ex-
haust by O
2
and NO.
21
-
23
July 1977 Volume 27, No. 7
649

Table
II. Homogeneous reactions.
Reference*
1
Transformation
Reaction COMB CONV
OTHER
NO Oxidation (1) 2 NO + 0
2
2 NO
2
9,14 58
NO
2
Reduction
(2) 2 NO
2
*•
2 NO + O
2
19 59
(3) NO
2
+
O
»-NO +
O
2
17
NO
x
Removal (4)
b
NO + CH >-CHO + N 31,32
a
COMB:
Combustion Related Study
CONV: Converter Related Study
b
CH:
Hydrocarbon
Summaries of the transformation re-
actions that may be active
in
probes and
sample lines are presented in Tables
II,
III,
and
IV
for
homogeneous, heteroge-
neous,
and
catalytic reactions, respec-
tively. (Catalytic reactions may be either
homogeneous
or
heterogeneous
but are
separately grouped here
for
convenience
of presentation.)
A
review
of
the reac-
tions
is
available.
24
The work
of
Halstead, Nation,
and
Turner
14
is the most definitive study
of
chemical transformations
of
NO*
when
sampling combustion products.
Com-
bustion products were sampled from
a
"Tunnel Mixing Burner" operating
on
natural
gas
and
air.
Two probe materials
(stainless
steel,
210
cm long
X 6
mm I.D.,
and silica tubing, 210
cm
long X
4 mm
I.D.) were evaluated
for
lean
and
rich
burn conditions. The temperature
at
the
probe inlet, measured with suction
py-
rometry, varied between 800°
and
1700°C. The temperature
of
the sample
at
the
outlet
was
near ambient.
The
sample probe residence time
was
esti-
mated
to
be 4 seconds. Lean fire condi-
tions produced
no
change
in
NO
X
con-
centrations
for
either
the
stainless steel
or silica tubing. Changes were observed
for rich fire with
the
stainless steel
probe.
In
particular,
the
NO
X
concen-
tration decreased
in
excess
of
90%.
No
effect
was
observed
for the
silica.
Al-
though
the
results suggest that impor-
tant chemical transformation occurs
when sampling fuel rich combustion
products with stainless steel, important
questions remain unanswered.
For ex-
ample,
the
extent
to
which
the
various
reducing species (e.g. CO, H2,
and hy-
drocarbons) participate
in
the reduction
and removal reactions cannot
be as-
sessed.
In
addition,
the
temperature
gradient along the probe length prevents
assessment
of
the sample conditions
at
which
the
reduction
and
removal reac-
tions were activated.
A
second study of note is reported by
Few, Bryson,
and
McGregor.
25
Nitric
oxide
was
measured at the exhaust plane
of
a gas
turbine combustor using
two
methods—conventional probing and
an
optical technique.
The NO
concentra-
tions measured optically ranged from
3
to
6
fold higher than those measured
by
conventional probing. Although
im-
portant questions remain unanswered
(e.g.
the
concentration
of
NO2
and re-
ducing species
at the
exhaust plane,
validation
of the
measurement
of
transmissivity,
and the
inlet pressure
conditions
and
sensitivity of the chem-
iluminescent analyzer),
the
results
re-
inforce the probability that
NO*
may be
removed within probes and sample lines
under conditions encountered
in
prac-
tice.
Experimental
An adequate accounting
of NO*
transformations requires that experi-
ments
be
conducted
to
identify
(1) the
conditions
for
which chemical trans-
formations occur,
and
(2)
the
extent
to
which they occur.
An experimental study has been
ini-
tiated
to
assess NO* transformations
that may be encountered when sampling
exhaust gas from practical combustion
devices that operate air-rich
(e.g.
boilers,
diesel engines,
and
gas turbine engines)
and fuel-rich (e.g. automobile engines).
A
schematic of the experimental system
is shown
in
Figure
1.
The experimental
system is designed to simulate the actual
conditions experienced
in
sampling
gaseous combustion products from
the
variety of
sources
shown in Table
I.
Test
parameters include carrier gas compo-
sition, concentration
and
composition of
the dopant gases, temperature,
and
probe material.
A carrier gas simulating
the
primary
combustion products
is
selected from
one of three prepared sources of
0,1,
and
5%
O
2
,
12% CO
2
,
and
balance
N
2
. The
carrier
gas
flow,
4 1/min, is
doped with
NO
and NO2
metered from high
con-
centration source cylinders by means of
porous sintered metal flow restrictors.
Additional species are introduced
in an
identical manner. After doping,
the
carrier
gas
enters
a
silica preheat oven
that raises
the gas
temperature
to the
desired probe test temperature. From
Table
III. Heterogeneous reaction.
Transformation Reaction
COMB
Reference
a
CONV
OTHER
NO
Oxidation
NO
2
Reduction
NO
V
Removal
(5)NO+O
(6)
NO
2
+ metal
(7)NO
2
+ C
(8)
NO
2
wall
NO,
wall
•*- metal oxide
+ NO
wall
-+-
CO +
NO
wall
(9)
(10)NO + C
NO,
condensate
absorbed
adsorbed
absorbed
1
x,
17
34
33
9, 12, 14
34
12,37
wall
(11)NO+ metal-
(12) NO
2
+metal
wall
wall
metal oxide + - N
metal oxide + -r N
20
20,60
20
29
29
35,36
a
COMB:
Combustion Related Study
CONV: Converter Related Study
650
Journal
of
the
Air
Pollution Control Association

Table
IV.
Catalytic
reactions.
Transformation
A'O
Oxidation
NO
2
Reduction
NO
x
Removal
Reaction
(13)N0+
| 0
2
-
\ i'ij 1MVJ
2
»
(15) NO + CO *•
(16) 5H
2
+ 2 NO-
NO
2
NO + A O
2
CO
2
+
-i N
2
2NH
3
+ 2 H
2
O
COMB
9
10
9, 14
Reference
a
CONV
18,
19,20,
34,38
CAT
21,22,
23
30, 39,
40,41
a
COMB:
Combustion Related Study
CONV:
Converter Related Study
CAT:
Catalyst Study
this point, the doped carrier gas enters
the test probe.
A
test probe oven is used
to maintain the temperature of the
doped carrier gas at the test tempera-
ture.
Test probe materials tested include
4.6 mm I.D. 316 stainless steel and silica
glass (Vycor, Corning Glass
Works).
The
length of each test probe is 2 m. The
residence time of the doped carrier gas
in the test probe is approximately \
sec.
The gas temperature within the test
probe is incrementally varied from 25°
to 400°C. Temperatures of the gas
stream (T2 and T3) are measured with
insulated platinum resistance ther-
mometers centered in the probe bore at
the inlet and outlet of the test probe.
The oven temperature is also recorded
by a thermocouple located adjacent to
the outer diameter of the test probe.
The NO and NO
2
input levels to the
test probe (sample point
2)
are chosen to
be 500 ppm and 75 ppm respectively.
These levels simulate a NO concentra-
tion selected as representative from
Table I, and a
NO2
concentration which
may be encountered in combustion
source effluents.
The present paper reports on chemi-
cal transformations that occur in the
presence and absence of
O2,
CO,
and H2.
Oxygen levels are taken to be 0, 1, and
5%;
CO levels are taken to be 0, 100,
1000,
and 2500 ppm; and hydrogen lev-
els are taken to be 0, 0.5, and 3.0%.
Gas composition is measured at
sample points 2 and 3 to assess the ex-
tent of NO and NO2 transformation
within the 2 m test probe. Gas compo-
sition is also measured at sample point
1 to assess whether chemical transfor-
mation occurs in the preheat oven.
Sample lines leading from points 1, 2,
and 3 are short, equidistant, and made
of 6.4 mm (V
4
in.) O.D. TFE Teflon.
Screening tests using varying lengths of
the TFE Teflon were conducted to as-
sure that
NO2
adsorption was not a sig-
nificant factor in the present experi-
ment.
Analysis of
NO
and NO
X
is conducted
with a Beckman Model 951H chemilu-
minescent oxides of nitrogen analyzer.
NO2 is determined by the difference
between the measured NO
X
and NO
concentrations. The (carbon) converter
efficiency is tested following the proce-
dure outlined in the Federal Register.
3
Carbon monoxide and H
2
concentra-
tions are measured using a Beckman
Model 315BL nondispersive infrared
analyzer, and a Beckman Model 7C
thermal conductivity analyzer respec-
tively.
Results
The results are presented in Figure 2
for oxidizing mixtures. Results for mix-
tures with
CO
are presented in Figure 3.
Results for mixtures with H2 are pre-
sented in Figure
4.
The percent change
of NO and NO2 represents the percent
change in concentration between sample
points 2 and 3 except where otherwise
noted. In the figures, points above the
horizontal temperature scale identify
those cases for which total NO
X
is con-
served. In such cases, changes in NO
concentration are proportional to
changes in NO
2
concentration. Points
below the horizontal temperature scale
identify those cases for which
NO*
is
not
conserved. The temperature shown is
the gas temperature (maintained uni-
form) at sample points 2 and
3.
The re-
sults reported are summarized from
earlier presentations.
24
-
26
-
27
Oxygen
The results for silica are presented in
Figure 2a. No significant transformation
is observed over the temperature range
and the residence time studied.
316 stainless steel (Figure 2b) cata-
lytically reduces NO2 to NO at gas
temperatures in excess of 300° C. The
conversion of NO2 to NO at elevated
temperatures is consistent with the re-
sults of a variety of chemiluminescent
analyzer converter studies (Table IV).
At temperatures below the catalytically
active temperature, no significant
change is observed.
Carbon Monoxide
The results for silica are presented in
Figure 3a. No significant transformation
is observed at temperatures up to and
including
300°C.
At
400°C,
reduction
of
NO2 to NO occurs.
The results for 316 stainless steel are
presented in Figure 3b. NO
2
reduction
is observed at 200°C and above. The
reduction is more pronounced at the
elevated levels of
CO
concentration.
The exposure history of the stainless
steel test probe is observed to alter the
degree of NO* transformation. Tem-
perature cycling and prolonged exposure
to one condition stabilizes the repro-
Resistance
thermometers
Test
Sample probe/
Rotameter
Sample
Carrier
U
12%
CO
2
0,1,5%0
2
bal N
2
NO/NOx
analyzer
Figure 1. Experimental system.
Three-way
valves
July 1977 Volume 27, No. 7
651

Citations
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Journal ArticleDOI
Abstract: The measurement techniques for delineating fuel-air mixing and transport in gas turbine combustion, as well as examples of representative results, are provided in this overview. The summary is broken into applications for gaseous fuels and liquid fuels since many diagnostics which are specific to the phase of the fuel have been developed. Many possible methods for assessing the general mixing have been developed, but not all have been applied to practical systems either under scaled or under actual conditions. With respect to gaseous mixing processes, planar laser-induced fluorescence (PLIF) based on acetone is now starting to be successfully applied to actual systems and conditions. In spray-fired systems, the need to discriminate between phases leads to considerable complication in delineating fuel-air mixing. Methods that focus on the discrete phase have successfully provided details relative to the droplets. These include phase Doppler interferometry (PDI), which is becoming ubiquitous in application to practical devices and under practical conditions. PDI is typically being applied to quantify droplet sizes, although the volume flux, which is relevant to fuel-air mixing, in practical systems is also being reported. In addition, PLIF strategies that focus upon the behaviour of the droplets are now being developed. However, PLIF strategies that can discriminate between phases either in the fuel or with respect to the liquid fuel and combustion air are also being developed. In terms of characterizing the vector fields associated with the mixing process, laser anemometry (LA), although it is tedious to apply, has proven reliable even in the presence of droplets. Newer methods such as DPIV and FRS have seen only limited application in practical systems but appear promising. In terms of scalar fields, LIF and PLIF have also been applied successfully to these systems, and examples of the measurements of concentrations of various radical species such as OH are found throughout the literature.

42 citations


01 Jan 2012-
Abstract: This study contributes to the topic of nitrogen oxide (NOx) formation at the level of single droplet and droplet array combustion The results show that the trade-off between ambient temperature and available oxygen determines the NOx formation of droplets burning in hot exhaust gas The degree of droplet vaporization has an effect on flame stabilization around the droplet and on NOx formation In the ignition model, the NOx production rate turns out to be very sensitive against the ignition position

12 citations


Cites background from "Chemical transformations of nitroge..."

  • ...Stainless steel tubing is found to promote chemical transformation when sampling fuel-rich combustion products [122, 371]....

    [...]

  • ...Potential sampling artifacts were minimized by a careful selection of materials for the entire sampling equipment [293, 371]....

    [...]

  • ...Three general types of chemical transformation of these nitrogen oxides prevail in probes and sample lines [136, 217, 266, 371]:...

    [...]

  • ...For instance, local concentrations of NO and NO2 are required to assess the chemical mechanisms responsible for the formation of NOx [56, 183, 371, 374]....

    [...]

  • ...Chromium, nickel, and copper, for instance, are well-known to be active catalysts, and it can be concluded that untreated stainless steel is not an adequate material for gas sampling equipment [122, 136, 145, 179, 247, 371, 387]....

    [...]


Book ChapterDOI
M. V. Heitor1, A. L. N. Moreira1Institutions (1)
01 Jan 1992-
Abstract: This paper presents a review of the capabilities of probe techniques for combustion diagnostic and outlines the most significant sources of error inherent to their use. The emphasis of the search is on measurements of temperature and on those of major species and ion concentrations in combusting environments, and attention is focused to elucidate the importance of probe measurements to improve understanding of turbulent combustion.

9 citations



Proceedings ArticleDOI
R. James Rollbuhler1Institutions (1)
01 Jan 1991-
Abstract: Future aeropropulsion gas turbine combustion requirements call for operating at very high inlet temperatures, pressures, and large temperature rises. At the same time, the combustion process is to have minimum pollution effects on the environment. Aircraft gas turbine engines utilize liquid hydrocarbon fuels which are difficult to uniformly atomize and mix with combustion air. An approach for minimizing fuel related problems is to transform the liquid fuel into gaseous form prior to the completion of the combustion process. Experimentally obtained results are presented for vaporizing and partially oxidizing a liquid hydrocarbon fuel into burnable gaseous components. The presented experimental data show that 1200 to 1300 K reaction product gas, rich in hydrogen, carbon monoxide, and light-end hydrocarbons, is formed when flowing 0.3 to 0.6 fuel to air mixes through a catalyst reactor. The reaction temperatures are kept low enough that nitrogen oxides and carbon particles (soot) do not form. Results are reported for tests using different catalyst types and configurations, mass flowrates, input temperatures, and fuel to air ratios.

5 citations


References
More filters

Journal ArticleDOI
C.P. Fenimore1Institutions (1)
01 Jan 1971-
Abstract: The formation was followed by probing flames of ethylene, methane, or propane with N2-O2 mixtures. The known kinetic laws of the well-understood N2-O2-NO system (limited by the rate of the reaction O+N2→N+NO) described the growth of nitric oxide in the post-flame gas, after hydrocarbons were consumed, but could not describe a faster, transient formation of nitric oxide in the primary reaction zone. The transient formation did not occur in hydrogen or carbon monoxide flames, and therefore, may involve an attack of carbon or hydrocarbon radicals on nitrogen molecules (e.g., CH+N2→HCN+N). At atmospheric pressure, the transient formation gave its greatest yield in flames containing 1.3 to 1.4 times the stoichiometric amount of fuel. Its yield increased somewhat with pressure, particularly in fuel-lean flames, so that at 3 atmos pressure the nitric oxide formed quickly in the primary reaction zone was about the same in flames of 0.8 as of 1.4 mixture strength. The transient formation possessed a relatively weak temperature dependence. Extrapolating the measurements, one can suggest that the new mechanism may contribute significantly to the emission of nitrogen oxides from a gas turbine, but the major contribution occurs by the known mechanism of the N2-O2 system.

733 citations


Journal ArticleDOI
Mordecai Shelef1, K. Otto1, Haren S. Gandhi1Institutions (1)
Abstract: The oxidation of CO by NO and by O 2 has been studied on a number of supported transition metal oxide catalysts. On supported chromia the oxidation of CO by NO is faster than by O 2 ; however, with mixtures of NO and O 2 the reaction is selective towards O 2 . The application of continuous mass-spectrometer monitoring to the study of surface state changes in chromia catalysts is outlined. The method was extended to determine the oxidation state of the surface in situ during reaction. In the oxidation-reduction cycle involving alternate passage of HeCO and HeO 2 mixtures at 500 °, the majority of the surface atoms undergo a change of oxidation state from Cr 6+ to Cr 2+ . The extent of this change diminishes with decreasing temperature. Mixtures of He and NO oxidize the surface of supported chromia to a lesser extent than HeO 2 . During the CONO reaction the average surface oxidation state is lower than in the presence of oxygen. A tentative explanation is offered for the selectivity for oxygen over nitric oxide in the oxidation-reduction reactions on commonly employed catalysts.

183 citations


Journal ArticleDOI
Abstract: A prototype instrument monitoring ozone or nitric oxide has been used for photochemical smog studies in the laboratory and the atmosphere. The principle of the detector is based on the chemiluminescent reaction

63 citations


Journal ArticleDOI
J.D. Allen1Institutions (1)

57 citations


Journal ArticleDOI
Francesco Pompei1, John B. Heywood1Institutions (1)
Abstract: Nonuniformities and rates of mixing are found to play an important role in determining emissions of carbon monoxide and nitric oxide from a kerosene-fueled atmospheric-pressure burner. Nonuniformaties are allowed for by assuming that burnt gas eddies have a normal distribution of equivalence ratios about the mean value. Mixedness is characterized by the ratio of the standard deviation of this distribution to the mean value and is related to combustor operating variables. A simple one-dimensional flow model is coupled with the mixing model to predict the variation of CO and NO concentrations with atomizing pressure and distance along the burner. The data obtained agree with the predictions and show clear mixing effects on both CO and NO concentration levels.

54 citations


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