The Effect of Dual Injection on Combustor Emissions

The Effect of Dual Injection on Combustor Emissions
A Research Paper
Presented to the
Science Department
Eleanor Roosevelt High School
In Partial Fulfillment
Of the Requirements for
Research Practicum
By
Miles Robinson
May, 2013

i
Abstract: Effect of Dual Injection on Combustor Emissions
Miles Robinson May, 2013
Combustion is a series of chemical reactions that involves the burning of fuel
inside an engine to provide power to a system. In the process, combustion also emits
harmful gases into the environment such as carbon and nitrogen oxides. The mixing of
fuel and air that takes place in a combustor is not adequate resulting in hotspots (local
spot of high temperature). This increases the amount of pollutants formed. The standard
combustor has one air inlet and one fuel inlet. Altering the combustor design to allow for
two sets of air and fuel inlets has the potential to enhance mixing, reduce the frequency of
these hotspots and ultimately reduce harmful emissions.
The combustor was run with methane used as fuel at air-fuel equivalence ratios of
0.8, 0.7, 0.6, 0.5, and 0.4. Dual injection proved to be unsuccessful in lowering the
combustion emissions when tested using methane as fuel. A regression line was used to
test the correlation between the NO and CO emissions of single injection versus dual
injection. Strong R2
values indicate there is a significant increase in emissions of dual
injection.

ii
Acknowledgements
I would like to thank Dr. Ashwani K. Gupta for the internship opportunity at the
University of Maryland Combustion Laboratory. This internship has provided me with
valuable hands-on experience as well as an introduction into the broad field of
engineering. I would also like to thank Ahmed E. E. Khalil for his willing assistance
with anything and everything related to my project.

iii
Biographical Outline
Personal Data:
Name: Miles Robinson
Date of Birth: October 30, 1995
Place of Birth: Holy Cross Hospital, Silver Spring, MD
City of Residence: Bowie
College Attending: University of Maryland, College Park
Major: Aerospace Engineering
Academic Achievements:
 Full Banneker/Key Scholarship to the University of Maryland
 AP Scholar with Honor
 Outstanding Participant in the National Achievement Scholarship Program
Activities:
 National Honor Society
 Varsity Wrestling Team
 Varsity Football Team
 STEMS Mentoring Society

iv
Table of Contents
Abstract................................................................................................................................ i
Acknowledgements.............................................................................................................ii
Biographical Outline..........................................................................................................iii
Table of Contents............................................................................................................... iv
List of Tables and Figures................................................................................................... v
Chapter One ...................................................................................................................... 1
Chapter Two...................................................................................................................... 5
Introduction..................................................................................................................... 5
Emissions........................................................................................................................ 5
Carbon Monoxide ....................................................................................................... 5
Carbon Dioxide........................................................................................................... 6
Nitrogen Oxides.......................................................................................................... 6
Gas Turbines................................................................................................................... 7
The Combustor................................................................................................................ 7
Improving Combustion................................................................................................... 8
Air and Fuel Injection ..................................................................................................... 8
Swirl Flow....................................................................................................................... 9
Exit Arrangements .......................................................................................................... 9
Summary......................................................................................................................... 9
Chapter Three................................................................................................................. 11
Chapter Four................................................................................................................... 13
Chapter Five.................................................................................................................... 18
Literature Cited ................................................................................................................. 21

v
List of Tables and Figures
Figure 3.1: Dual Injection Combustor Diagram ............................................................... 11
Table 4.1: Trial #1 Emissions........................................................................................... 13
Table 4.2: Trial #2 Emissions........................................................................................... 14
Figure 4.1: NO and CO Emissions ................................................................................... 14
Figure 4.2: Single vs Dual Injection ................................................................................. 15
Figure 4.3: NO Emissions Single vs Dual ........................................................................ 16
Figure 4.4: CO Emissions: Single vs Dual ....................................................................... 17

Chapter One
The Problem and Its Setting
Introduction to the Problem
inside an engine to provide power to a system. In the process, combustion also emits
harmful gases into the environment such as carbon and nitrogen oxides (CO and NO).
Engineers and researchers are always looking for ways to make the combustion process
more efficient and less harmful to the environment. In a combustor, fuel and air are
mixed to allow for the combustion reaction to take place. However, the mixing of fuel
and air that takes place in a combustor is not adequate and it results in hotspots (local
spot of high temperature). This increases the amount of pollutants formed, especially
nitrogen oxides which are strong functions of the temperature. (Beer, 2012)
The emission of harmful pollutants is a big problem of the combustion process.
The standard combustor geometry is a cylinder with one air inlet and one fuel inlet
Altering the combustor design to allow for two sets of air and fuel inlets has the potential
to enhance mixing, reduce the frequency of these hotspots, and ultimately reduce harmful
emissions.

2
Statement of the Problem
The purpose of this experiment is to test how multiple inlets affect emissions from
a combustor. This research will aid in obtaining combustion characteristics for gas
turbine application. The performance of the combustor will be tested by experimentation
using methane as fuel. Flow rates of the fuel will be adjusted to determine the best ratio
of flow speed between the two injection points. The ultimate goal of this research is to
develop a combustor with ultra-low emissions to make the combustion process less
harmful to the environment.
Hypothesis
It is predicted that the presence of two separate injection points in the combustor
will enhance fuel-air mixing and reduce hotspots, therefore reducing the amount of CO
and NO that is released from the system. It is unclear whether adjusting the ratio of flow
rates between the injection points will have any effect on the system.
Variables and Limitations
Independent Variables
1. Combustor geometry: dual injection
2. Flow rates at injection points
Dependent Variables
1. Amount of gases emitted
a. CO
b. CO2

3
c. NO
d. O2
2. Temperature inside the combustion chamber
Control Treatments
1. Methane will be used as the fuel.
Regulated Conditions
Research will be conducted in the Combustion Laboratory in the J.M. Patterson
building; University of Maryland, 7950 Baltimore Avenue, College Park, MD 20742.
Limitations
1. The flow controllers used are not very precise, so measured flow rates may be slightly
different from actual flow rates.
Assumptions
1. Flow controllers are calibrated correctly to give fairly accurate measurements of flow
rates.
Statistical Analysis
A regression line will be used to compare emissions of carbon and nitrogen
oxides of single injection combustion to those of dual injection combustion.
Definition of Terms and Abbreviations
1. CO: carbon monoxide
2. CO2: carbon dioxide

4
3. Hotspot: local spot of high temperature inside a combustor that causes an increase in
harmful emissions
4. Injection point: the place at which the fuel-air mixing inside the combustor is initiated
5. NO: nitric oxide
6. NOx: This includes nitric oxide as well as any variations to the bonding structure of
the molecule. (NO, NO2, NO3)
7. Tex: Temperature inside the combustor

Chapter Two
The Review of the Related Literature
Introduction
inside an engine to provide power to a system. For example, one of the reactions that
take place in the burning of methane is:
CH4 + 2 O2 → CO2 + 2 H2O + energy
However, no combustion process is one hundred percent efficient so some reactants are
left over, including harmful pollutants such as carbon dioxide, carbon monoxide, and
various nitrogen oxides. The mixing of fuel and air that takes place in a combustor is not
entirely adequate, resulting in hotspots (local spot of high temperature). This increases
the amount of pollutants formed, especially nitrogen oxides which are strong functions of
the temperature. Engineers and researchers are always looking for ways to make the
combustion process more efficient and less harmful to the environment. (Beer, 2012)
Emissions
Carbon Monoxide
One of the harmful gases emitted during combustion is carbon monoxide (CO). It
is odorless, tasteless, and invisible, making it nearly impossible to detect without a carbon
monoxide alarm. Exposure to this gas can lead to carbon

6
monoxide poisoning with symptoms such as headache, nausea, drowsiness, and even
death if exposed to high levels. As there are about 150 deaths per year in the United
States due to carbon monoxide exposure, it is very important to limit CO emissions in
combustion. (U.S. Fire Administration, n.d.)
Carbon Dioxide
Carbon dioxide (CO2) is the primary gas emitted during combustion. Carbon
dioxide is naturally present in the air; however, human activities have greatly increased
the amount of CO2 in the atmosphere. These human activities include burning fossil
fuels for electricity generation and transportation. Since 1990, CO2 emissions have
increased by about 10% due to fossil fuel combustion. Plants naturally remove carbon
dioxide from the atmosphere, but with increased CO2 emissions, they cannot remove the
gas as fast as it is being emitted. It is important to reduce carbon dioxide emissions from
combustion because high levels of CO2 can cause climate change and lead to global
warming. (U.S. Environmental Protection Agency, n.d.)
Nitrogen Oxides
Combustion emits many different forms of nitrogen oxides including nitrous
oxide (N2O), nitric oxide (NO), and nitrogen dioxide (NO2). Nitrous oxide is very
harmful to the environment because there is no natural way to remove it from the
atmosphere. N2O stays in the air for about 120 years and has an impact on warming the
atmosphere that is nearly 300 times as great as that of carbon dioxide. (U.S.
Environmental Protection Agency, n.d.) NO and NO2 are more common products of
combustion. These forms of nitrogen oxide are highly reactive and can lead to smog,
acid rain, and deterioration in water quality. Reducing emissions of nitrogen oxides from

7
the combustion process is extremely vital because of their harmful environmental effects.
(Nitrogen oxide (nox) emissions, n.d.)
Gas Turbines
Combustion mechanics can be directly applied to gas turbines. A gas turbine is a
machine that converts fuel into mechanical energy or thrust, depending on the type of
energy needed. There are two main types of gas turbines: jet engines and industrial
turbines. Both of these types have three main parts: the compressor, the combustion
chamber, and the turbine. The gas is compressed in the compressor, heated in the
combustion chamber, and finally converted into mechanical work by the turbine. (Basics
of gas turbines, n.d.)
The Combustor
A combustor, or combustion chamber, is the part of a gas engine in which the
combustion takes place. The air and fuel mix together, allowing for combustion to occur.
The combustor is generally a cylindrical body with several openings to allow for air and
fuel to enter and products to exit. However, the combustor design is not limited to the
traditional cylindrical shape, as researchers have developed combustors with rectangular
prism geometries that do not have any negative drawbacks (Arghode, Gupta, Bryden,
2012).

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Improving Combustion
Emissions can be controlled in three separate phases of the combustion process:
the fuel can be treated before it is burned, the actual combustion process can be modified,
or the process can be cleaned up after the combustion takes place. The most promising
method is modifying the combustion process. Different techniques include altering the
injection points of air and fuel to the combustor, the use of fuel-gas recirculation, and
premixing the air and fuel before they are injected into the combustor. Altering the
combustion process has led to significant results. Using various methods to enhance the
combustor design, nitrogen oxide emissions have been reduced by up to 95% (Beér,
2012). Other ways to reduce emissions and enhance combustor performance include
developing sensors to monitor the reactions inside the combustor as well as developing
techniques to capture carbon dioxide and prevent it from being emitted to the
environment (Lieuwen, 2006).
Air and Fuel Injection
The injection of air and fuel into a combustor significantly affects the efficiency
of the combustion. Several methods of injection have been thoroughly tested. These
methods include premixing, in which air and fuel are mixed together prior to injection,
coaxial injection, in which the fuel line is inserted inside the air inlet, creating a coaxial
nozzle, and perpendicular injection, in which air and fuel are injected separately and
pointed perpendicular to each other. It was found that coaxial injection produces the
highest levels of nitrogen oxides. Separate air and fuel injection produced lower levels of
emissions. (Khalil, Gupta, Bryden, 2012) From experimentation, it has been concluded

9
that separate air and fuel injection allows for proper fuel-air mixing and produces the
lowest pollutants.
Swirl Flow
Swirl flow is a technique used to circulate the combustion products around and
back to the flame in the combustor for more efficient energy conversion. The more
reactants converted to energy, the lower the combustor emissions will be. The air is
injected tangent to the combustor so that it forms a swirling motion when it travels
through the cylinder and mixes with the fuel (Khalil, Gupta, 2011).
Exit Arrangements
Different exits for the product gases of combustion produce different levels of
emissions. Several types of exits include a normal exit (parallel to the air inlet), axial exit
(perpendicular to the air inlet), and an axial exit with an extended tube inside the
combustion chamber. It was determined that axial exit with an extended tube yields the
lowest emissions because the gases remain in the combustor longer, allowing more time
for the completion of the combustion process (Khalil, Gupta, 2011).
Summary
It has been found that altering combustor geometry is the most practical way to
reduce emissions and enhance the combustion process. Methods for improving
combustion include separate air and fuel injection, swirl flow inside the combustor, and
the use of an axial exit with an extended tube inside the combustor. All of these

10
adjustments have proven to be beneficial to the combustion process. However, the
process is not entirely efficient in all areas of the combustion chamber. Altering the
combustor design to allow for two sets of air and fuel inlets has the potential to enhance
mixing, reduce the frequency of these hotspots, and ultimately reduce harmful emissions
with a view to develop a combustor with ultra-low emissions for gas turbine application.

Chapter Three
Materials and Methods
Materials
1. Dual injection combustor
Figure 3.1
2. Methane (Airgas, Inc., Hyattsville, MD)
3. Propane torch
4. Exhaust vent
5. Gas analyzer (HORIBA, Kyoto, Japan)
6. Media gauges (SSI Technologies, Inc., Janesville, WI)
Air Inlet #1
Air Inlet #2
Fuel Inlet #2
Fuel Inlet #1

12
Methods
Prior to experimentation, preliminary data was collected to determine the
performance of a standard, dual injector. Combustor emissions were measured and
compared against this preliminary data. Emissions were measured at different air
temperatures and fuel-air pressure ratios. All data was recorded in the Combustion
Laboratory at the University of Maryland.
The combustor was secured into the test rig and all air and fuel lines were sealed
in order to prevent leakage of any air or fuel. The combustor was ignited with a propane
torch and air and fuel flow rates were increased to desired values. The combustor was
allowed to operate for thirty minutes before recording any data to ensure the combustor
was in steady state. Once steady state condition was reached, the air-fuel flow rate was
set to 0.8 using the media gauges. The combustor was allowed to run at this ratio for
about three to four minutes to allow for the reading on the gas analyzer to stabilize.
Emissions of NO, CO, CO2, and O2 were measured using the gas analyzer. This process
was repeated for pressure ratios of 0.7, 0.6, 0.5, and 0.4.
Data Collection & Analysis
After emissions data were collected, a regression line was used to plot emissions
from single injection combustion versus emissions from dual injection combustion.
Carbon and nitrogen oxides were compared separately. CO emissions from dual
injection were statistically compared to those of single injection. NOx emissions were
also statistically compared in the same way.

Chapter Four
Results
Data
Compared to single injection, the dual injection combustor did not produce lower
emissions as expected. Dual injection produced significantly higher emissions of
nitrogen oxides than single injection at all equivalence ratios except for 0.5. The dual
injection system recorded its lowest emissions at an air-fuel equivalence ratio of 0.6:
about 5ppm NO and 30ppm CO. Nitrogen oxide emissions decreased proportionally to
the equivalence ratio while carbon oxides decreased to a minimum at an equivalence ratio
of 0.6 and then began to increase again. Experiments with dual injection demonstrated
higher emissions than those demonstrated with single injection. For the same equivalence
ratio, NO emissions increased by about 20%, with minimal change in CO emissions.
Trial #1 0.8 0.7 0.6 0.5 0.4
NO (ppm) 98.50 36.80 11.90 4.60 2.60
CO (ppm) 179.00 63.00 33.00 61.00 800.00
CO2 (ppm) 11.08 9.56 8.09 6.70 5.30
O2 (ppm) 2.18 4.73 7.23 9.55 11.80
Tex 760K 724K 683K 636K 614K
Table 4.1: Emissions and temperature recorded at each equivalence ratio for the first trial.

14
Trial #2 0.8 0.7 0.6 0.5 0.4
NO (ppm) 96.50 37.10 11.70 4.70 2.40
CO (ppm) 175.00 62.00 36.00 59.00 800.00
CO2 (ppm) 11.03 9.56 8.11 6.70 5.30
O2 (ppm) 2.24 4.72 7.19 9.56 11.85
Tex 762K 729K 683K 640K 617K
Table 4.2: Emissions and temperature recorded at each equivalence ratio for the second
trial.
Figure 4.1: Emissions of NO and CO at each equivalence ratio tested.
1
10
100
1000
0
5
10
15
20
25
0.3 0.4 0.5 0.6 0.7 0.8 0.9
CO@15%O2(PPM)
NO@15%O2(PPM)
Equivalence Ratio
NO and CO Emissions
NO
CO

15
Figure 4.2: NO emissions using dual injection compared to the results from single
injection.
Data Anaylsis
Dual injection was shown to be unsuccessful in lowering the combustion
emissions when tested using methane as fuel. A regression line was used to test the
correlation between the NO and CO emissions of single injection versus dual injection.
Strong R2
values indicate there is a significant increase in emissions of dual injection.
0
5
10
15
20
25
30
35
40
0.4 0.5 0.6 0.7 0.8 0.9
NO@15%O2(PPM)
Equivalence Ratio
Single vs. Dual Injection
Single Injection
Dual Injection

16
Figure 4.3
y = 2.0191x - 4.2894
R² = 0.9973
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
0.00 5.00 10.00 15.00 20.00 25.00
DualInjection(ppm)
Single Injection (ppm)
NO Emissions: Single vs Dual Injection
The linear regression line
suggests that NO
emissions of dual
injection are twice as
much as single injection.

17
Figure 4.4
y = -0.0423x2 + 4.49x - 43.31
R² = 0.9844
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00
DualInjection(ppm)
Single Injection (ppm)
CO Emissions: Single vs Dual Injection
The regression line suggests that
the CO emissions in dual
injection are directly proportional
to the square of the CO emissions
from single injection.

Chapter Five
Conclusions
Summary
In this study the effect of dual injection on combustor emissions was tested. The
purpose of this experimentation was to potentially enhance the combustion process,
making it more efficient and environmentally-friendly. Any positive findings could be
applied to gas turbines specifically in aircrafts. Enhanced combustion could result in
better fuel efficiency for such vehicles and even in automobiles as well.
Standard combustion involves the injection of air and fuel into a combustion
chamber to be mixed and turned into mechanical energy in order to power a system. Air
and fuel are generally injected at one point in the combustor. The proposed dual injection
system would involve the addition of a second air-fuel injection point which could
potentially enhance the mixing of air and fuel by distributing the reaction more evenly
throughout the combustor. The null hypothesis was that the dual injection system would
produce lower emissions of carbon and nitrogen oxides, thereby resulting in higher
efficiency of the combustion process. The alternative hypothesis was that the adjustment
would negatively affect the combustion process and increase emissions.
To test the performance of the dual injection system, the combustor was run with
methane used as fuel. Emissions of carbon monoxide, carbon dioxide, and nitrogen
oxides were measured using a gas analyzer. These emissions were compared to the

19
results from standard, single combustion in which methane was also used. There was no
statistical test used as the proposed design would either perform absolutely better or
absolutely worse compared to the original design.
Conclusions and Discussion
According to the data, the dual injection system was unsuccessful in enhancing
the mixing of air and fuel inside a combustor. The carbon oxide emissions of dual
injection were generally the same as demonstrated with single injection, but the
emissions of nitrogen oxides increased significantly; there was about a 20% increase in
nitrogen oxides overall. As a result, the null hypothesis of enhanced combustion due to
the presence of two separate injection points was rejected. This experiment proved that
dual injection negatively impacts the combustion process.
As seen in Figure 4.2, at an air-fuel equivalence ratio of 0.5 the dual injection
combustor produced fewer amounts of nitrogen oxides than single injection. However,
this finding is meaningless because very large amounts of carbon oxides were detected at
this ratio so the low nitrogen oxide levels were insignificant. The increase in overall
emissions suggests that there is an interaction between both injections jets leading to an
un-equal distribution in the flame region of the combustor.
Recommendations
The results of tests with dual injection can be taken into account when testing
other methods of improving combustion. It is important to note the negative interaction
between the two air-fuel injection points. The addition of even more inlets in the

20
combustor design can now be eliminated since this method proved to negatively impact
the system.
To avoid such unequal distribution, fuel flow rate distribution can be modified.
Instead of air and fuel being split evenly between both injection points, the amount of
fuel for each injector can be manipulated to control the strength of each reaction zone.
Such fuel variation has the potential to change the local equivalence ratio of the jet
affecting different flame characteristics such as flame speed.
Future Implications
Varying the fuel amount can impact the resulting emissions and the strength of
the reaction zone. Consequently, fuel variation can be used as means to control flame
characteristics and emissions to produce enhanced performance and lower emissions than
those demonstrated through single injection. This is of extreme importance for
combustion research as multiple injectors will be required to maintain adequate residence
time and injection velocities within the combustor.

21
Literature Cited
Arghode, V. K., Gupta, A. K., & Bryden, K. M. (2012). High intensity colorless
distributed combustion for ultra-low emissions and enhanced performance.
Applied Energy, 92, 822-830.
Basics of gas turbines. (n.d.). Retrieved from http://www.aerostudents.com/
files/gasTurbines/basicsOfGasTurbines.pdf
Beér, J. M. (2012). Combustion. In Access Science. McGraw-Hill Companies.
Retrieved from http://accessscience.com/
content.aspx?searchStr=combustion&id=150600
Khalil, A. E. E., Gupta, A. K., & Bryden, K. M. (2012). Mixture preparation
effects on distributed combustion for gas turbine applications. Journal of
Energy Resources Technology, 134
Khalil, A. E. E., & Gupta, A. K. (2011). Swirling distributed combustion for clean
energy conversion in gas turbine applications. Applied Energy, 88(11), 3685-3693
Khalil, A. E. E., & Gupta, A. K. (2011). Distributed swirl combustion for gas
turbine application. Applied Energy, 88(12), 4898-4907
Lieuwen , T., & Richards , G. (2006). Burning questions: Combustion research
prepares for the more complex fuel supply of the near future. Science in Context,
Retrieved from http://go.galegroup.com/ps/
i.do?id=GALE|A143341492&v=2.1&u=gree55358&it=r&p=GPS&sw=w
Nitrogen oxide (nox) emissions. (n.d.). Retrieved from http://www.a2gov.org/
government/publicservices/systems_planning/Environment/soe07/cleanair/Pages/
nox.aspx
U.S. Environmental Protection Agency, (n.d.). Overview of greenhouse gases.
Retrieved from website: http://www.epa.gov/climatechange/ghgemissions/
gases.html
U.S. Fire Administration, (n.d.). Exposing an invisible killer: The dangers of
carbon monoxide. Retrieved from website: http://www.usfa.fema.gov/
citizens/co/fswy17.shtm

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