Temperature Measurements in an Ethylene-Air-Opposed 

Flow Diffusion Flame 

by Matthew S. Kurman, John M. Densmore, Chol-Bum M. Kweon, 

and Kevin L. McNesby 

ARL-TR-5870 January 2012 

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Army Research Laboratory 

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ARL-TR-5870 January 2012 

Temperature Measurements in an Ethylene-Air-Opposed 

Flow Diffusion Flame 

Matthew S. Kurman 

Oak Ridge Associated Universities 

John M. Densmore 

Lawrence Livermore National Laboratory 

Chol-Bum M. Kweon 

Vehicle Technology Directorate, ARL 

Kevin L. McNesby 

Weapons and Materials Research Directorate, ARL 

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Temperature Measurements in an Ethylene-Air-Opposed Flow Diffusion Flame 

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14. ABSTRACT 

To support the advancement of chemical kinetic models for soot, temperature measurements were conducted on an ethylene 

(C2H4)/air-opposed flow diffusion flame at atmospheric pressure. This detailed study compares temperature measurements 

acquired from a single high-speed color camera optical pyrometer to thermocouple measurements and Cantera simulations for 

opposed flow diffusion flames. Unlike thermocouples, optical pyrometry provides a nonintrusive technique to experimentally 

measure flame temperature. A soot surface temperature of ~2000 K at a flame position ~2 mm above the fuel duct was 

acquired from the optical pyrometer. A maximum centerline flame temperature of 1898 K at 3.70 mm above the fuel duct was 

obtained from the thermocouple measurements. In addition, chemical kinetic modeling was conducted with Cantera and results 

predicted intermediate species produced during combustion and a maximum centerline flame temperature of 2077 K at 3.79 

mm from the fuel duct. The results presented in this report can be used to validate and refine chemical kinetic models for soot, 

which ultimately can lead to advanced power-generating systems.

15. SUBJECT TERMS

optical pyrometry, thermocouple measurements, ethylene, soot, combustion 

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Matthew S. Kurman 

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iii 

Contents 

List of Figures iv

List of Tables iv

Acknowledgments v

1. Summary 1

2. Introduction 1

3. Background 2

4. Experiment and Modeling 4

5. Results and Discussion 9

6. Conclusions 13

7. References 15

List of Symbols, Abbreviations, and Acronyms 17

Distribution List 20
iv 

List of Figures 

Figure 1. Soot and NOx regions within an equivalence ratio/temperature plane showing 

conventional diesel and different low-temperature combustion processes. ...............................3

Figure 2. Schematic of the opposed flow diffusion flame burner with an enlarged view of the 

reaction zone. x and r are axial and radial directions, respectively. Vx and Vr are 

velocities in the axial and radial directions, respectively. .........................................................4

Figure 3. Camera setup for acquiring images of opposed flow diffusion flames. ..........................5

Figure 4. Photograph of the camera setup showing various components. ......................................6

Figure 5. Photograph of the thermocouple setup showing various components. ...........................8

Figure 6. (a) Picture of the C2H4/air-opposed flow diffusion flame. (b) Reconstructed image 

showing the surface temperature of the C2H4 flame. The incorrect temperature in the 

blue region is caused by discrete emission. .............................................................................10

Figure 7. Comparison of the Cantera simulation with the results of the pyrometry and 

thermocouple temperature measurements. The blue and red regions represent locations 

of visible light produced from the flame. .................................................................................11

Figure 8. Simulation results from Cantera showing intermediate species produced during 

combustion, temperature profile, and local equivalence ratio. The multiplication factors 

are listed in parentheses. ..........................................................................................................12

Figure 9. Representation of soot and NOx regions within an equivalence ratio/temperature 

plane showing Cantera simulations for different pressures. ....................................................13

List of Tables 

Table 1. Initial conditions for the Cantera simulation. The mass flux of the fuel and oxidizer 

corresponds to the flow rates of the experiment and dimensions of the burner. .......................9
v 

Acknowledgments 

This research was supported in part by an appointment to the U.S. Army Research Laboratory 

Postdoctoral Fellowship Program administered by the Oak Ridge Associated Universities 

through a contract (W911QX-04-C-0129) with the U.S. Army Research Laboratory. Burner 

development was supported in part by the Strategic Environmental Research and Development 

Program of the Department of Defense. Lawrence Livermore National Laboratory is operated by 

Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National 

Nuclear Security Administration, under contract DE-AC52-07NA27344.
vi 

INTENTIONALLY LEFT BLANK. 
1 

1. Summary 

Optical pyrometry and thermocouple temperature measurements were conducted on an ethylene 

(C2H4)/air-opposed flow diffusion flame at atmospheric pressure. The optical pyrometry results 

showed a soot surface temperature of ~2000 K at a flame position ~2 mm above the fuel duct. 

The pyrometry method shows an accurate temperature measurement where soot incandescence 

occurs. A centerline temperature profile based on thermocouple measurements (not corrected for 

emissivity) was reported with a maximum flame temperature of 1898 K at 3.70 mm above the 

fuel duct. Chemical kinetic modeling of the flame was conducted with Cantera. The results 

indicated that acetylene (C2H2), and benzene (C6H6), are formed in the red/orange sooting region 

of the flame, and methylidyne (CH) and hydroxyl (OH) are formed in the blue colored region. 

The modeling results predicted a maximum centerline temperature of 2077 K at 3.79 mm from 

the fuel duct. The experimental temperature results of this study can be used to validate and 

refine the chemical kinetic models, which can ultimately be used to develop and advance current 

power system designs. 

2. Introduction 

Understanding soot temperature and production can lead to the design and development of power 

systems that are more fuel efficient and produce less harmful emissions. In addition, the average 

time between failures of power systems can be increased if soot is reduced during combustion. 

JP-8 and Jet A, which are aviation fuels primarily used in military and commercial gas turbines, 

respectively, can contain aromatic hydrocarbons (Edwards and Maurice, 2001). These 

aromatics, which are considered as soot precursors, can form polycyclic aromatic hydrocarbons 

(PAHs) during combustion. Based on specification MIL-DTL-83133G (2010), up to 25% 

volume of JP-8 composition can be aromatic hydrocarbons. An important aspect of concealing a 

vehicle is reducing the plume caused by soot and incomplete combustion, which is visible during 

acceleration and high-load conditions. Soot not only indicates incomplete combustion and loss 

of efficiency, it is also a health concern. Precursors to soot, such as C6H6 pose many health risks 

(Glass et al., 2003; IARC, 1987; Rinsky et al., 1989). A focus of this study is measuring the 

temperature of a sooting C2H4/air flame. 
2 

3. Background 

Soot is primarily produced from fuel-rich flames where particles can interact with one another 

and agglomerate to larger structures. The initial step in soot production is fuel decomposition 

followed by the formation of the first aromatic ring (Turns, 2000). Aliphatic fuels contain no 

aromatics; therefore, forming the first aromatic ring structure is the basis of soot production. 

Hydrocarbons that contain aromatics readily produce soot since they contain an initial supply of 

cyclic aromatic structures. Once the first aromatic ring is formed, other aromatic compounds can 

combine and grow to form larger molecular structures, PAHs, leading to the production of soot 

particles. A production pathway for soot can be formed by combining propargyl (C3H3) radicals, 

which are resonantly stable, to form the cyclic ring structure of C6H6 (Miller et al., 1992). 

Results also showed that self-combining C3H3 radicals were responsible for producing phenyl, 

which also contains a cyclic ring structure. Once an aromatic is formed, a repetition of two 

primary reactions can proceed to form soot. These reactions are shown in equations 1 and 2: 

 Ai + H →Ai- + H2, (1) 

and 

 Ai- + C2H2 →products, (2) 

where Ai is a parent aromatic and Ai- is the radical of the aromatic hydrocarbon. Equation 1 

proceeds with a hydrogen atom abstraction from the parent aromatic to form an aromatic radical 

and hydrogen (H2). C2H2 then attaches to the aromatic radical to form polycyclic products. 

Equations 1 and 2 can then repeat and continue to form larger aromatic ring structures and 

ultimately soot (Frenklach, 2002). 

To investigate soot production, it is important to understand what operating conditions, such as 

equivalence ratio and temperature, promote soot formation during combustion. Figure 1 is a plot 

from Kook et al. (2005), showing an equivalence ratio and temperature plane with modeling 

calculations from Kitamura et al. (2002), involving n-heptane (C7H16), combustion at a pressure 

of 6 MPa, and a reaction time of 2 ms. A main sooting region occurs above an equivalence ratio 

of ~2, whereas a region containing nitrogen oxides (NOx) occurs at leaner equivalence ratios and 

higher temperatures. The behavior of a fuel element of a conventional diesel process is also 

shown in figure 1. An interesting observation shown in figure 1 is that there is a trade-off 

between soot and NOx production. If soot is decreased by lowering the equivalence ratio, the 

flame temperature increases and more NOx is produced. If NOx is reduced by increasing the 

equivalence ratio, the flame temperature lowers and soot production increases. Figure 1 also 

shows two different low-temperature combustion paths. A typical homogeneous charge 

compression ignition path, where the fuel/oxidizer is well mixed before combustion 
3 

Figure 1. Soot and NOx regions within an equivalence ratio/temperature plane showing 

conventional diesel and different low-temperature combustion processes 

(Kook et al., 2005). 

occurs, is represented by the black arrows. The other combustion pathway, represented by gray 

arrows, occurs when lean equivalence ratios are attained by the continuation of high rates of 

mixing after premixed burning has started. A comparison of the low-temperature combustion 

processes to the conventional diesel process on the equivalence ratio/temperature plane reveals 

that soot and NOx production are reduced when low-temperature combustion occurs. 

C2H4 was chosen as a fuel for this study because of its abundance found during the combustion 

process of conventional fuels. During the oxidation of aliphatic hydrocarbons, such as 

n-dodecane (C12H26), n-decane (C10H22), and C7H16, C2H4 is an intermediate species (Ciajolo and 

D’Anna, 1998; Kurman et al., 2011; Olchanski et al., 2006). The oxidation process of 

hydrocarbons includes many intermediate species. As the molecular weight of a hydrocarbon 

increases, the number of intermediate species also increases. The increase in intermediate 

species makes studying the combustion chemistry of higher-molecular-weight hydrocarbons a 

challenging task. Therefore, understanding the combustion processes involved in the oxidation 

of C2H4 is a foundation to understanding the combustion of higher-molecular-weight 

hydrocarbons, which are used as practical fuels in power systems. 
4 

4. Experiment and Modeling 

Flame studies were conducted with an opposed flow diffusion flame burner constructed out of 

304 stainless steel. Opposed flow flame configurations are of interest to the combustion 

community because the configuration may be modeled as a one-dimensional (1-D) problem, and 

residence times can be readily adjusted (Turns, 2000). Additionally, this configuration allows 

for a comprehensive examination of different flame regimes. A detailed schematic of the burner 

and reaction zone is shown in figure 2. The burner is capable of operating at elevated and 

subatmospheric pressure conditions. However, for the experiments described in this study, the 

burner was operated at 1 atm. The burner includes an oxidizer and a fuel duct, each with a 

diameter of 16 mm. A 25.4-mm-diameter nitrogen (N2) duct surrounds both the oxidizer and 

fuel ducts. The oxidizer and fuel ducts are arranged in a counter-flow configuration, with a duct 

separation of 6 mm. The compressed gases used for the flame studies consisted of C2H4 (purity 

of 99.9%) as fuel, air (zero grade) as oxidizer, and N2 (purity of 99.999%). A multigas flow 

controller (MKS Instruments) was used to control the mass flow rates during the experiment. 

Oxidizer

Fuel N2

N2 N2

N2

Stagnation 

Plane x

r

vr vx

Oxidizer

Fuel

N2

N2

Exhaust 

Vacuum

Figure 2. Schematic of the opposed flow diffusion flame burner with an enlarged view of the 

reaction zone. x and r are axial and radial directions, respectively. Vx and Vr are velocities 

in the axial and radial directions, respectively. 
5 

To acquire a stabilized flame, a pilot light was inserted between the oxidizer and fuel ducts prior 

to commencing fuel and oxidizer flow. Once inserted, the flow rates were adjusted to 2.5 

standard liters per minute (SLPM) for C2H4, 2.0 SLPM for air, and 2.0 SLPM for N2 shroud on 

the fuel duct. The calculated strain rate on the oxidizer side of the flame (i.e., 2 a ) was 123 s-1, 

which is defined by equation 3: 

2

2

1 , ox f f

ox ox

V V

a

L V





 

   

 

 (3) 

where Vox , L , Vf ,  f , and ox are the oxidizer velocity, duct separation, fuel velocity, fuel 

density, and oxidizer density, respectively (Seshadri and Williams, 1978). Once gas flow started, 

the burner would light and the opposed flow diffusion flame would be visible. To ensure that the 

flame was stabilized, measurements were not taken for ~5 min after ignition. Water was allowed 

to flow through the upper assembly of the burner, near the exhaust, for cooling. A vacuum pump 

extracted the exhaust from the burner chamber. Figure 3 shows a representation of the opposed 

flow diffusion flame. A visible blue region is present when the fuel diffuses into the oxidizer 

stream and stoichiometric combustion occurs. A visible red/orange region is present where 

fuel-rich combustion/fuel pyrolysis occurs. The blue region is attributed to light emission from 

CH and diatomic carbon (C2) radicals, whereas the red/orange region is associated with soot 

incandescence. 

Opposed Flow 

Diffusion 

Flame

Oxidizer

Fuel N2

N2 N2

N2

Phantom v5.1c Camera Nikon Nikkor 

Lens

KG3 IR Filter

Figure 3. Camera setup for acquiring images of opposed flow diffusion flames. 
6 

Flame imaging was conducted with a Phantom v5.1c high-speed color camera manufactured by 

Vision Research Inc. Figure 3 also shows the camera setup used to image an opposed flow 

diffusion flame. A photograph of the experimental setup is shown in figure 4. The camera uses 

an 8-bit complementary metal oxide semiconductor (CMOS) imaging sensor with 1024 × 1024 

pixels. At full resolution, the camera is capable of capturing 1200 frames per second (fps). 

However, during the flame studies presented here, the sample rate was 10 fps to compensate for 

low light levels from the flame. The camera is coupled to a Nikon AF Nikkor 24-85 mm 

f/2.8-4D IF lens, which has a macro mode feature. To ensure near-infrared (IR) radiation was 

blocked from reaching the CMOS image sensor, a Schott KG3 IR cutoff filter was placed 

between the lens and flame. 

Phantom v5.1c

Camera

Opposed Flow Burner

Nikon Lens

IR cutoff filter

Figure 4. Photograph of the camera setup showing various components. 

Pyrometry temperature measurements were accomplished using the Phantom v5.1c color camera. 

Using the light collected through a color filter array, a ratio of the green to red channels can be 

used to calculate the temperature of a flame. A gray body assumption, in which the variance in 

emissivity with wavelength is assumed to be constant, is also used in calculating the temperature. 

Additionally, errors in temperature measurements occur when discrete emission, such as C2 or 

CH emission, is present in either spectral region used for the pyrometer measurement. 
7 

Interpretation of the pyrometry temperature measurements depends on the optical thickness of 

the flame. The camera images light from the surface of an optically thick flame. In such a 

flame, light from the interior of the flame is absorbed before it reaches the surface, and the 

interior flame temperature is not measured. In optically thin flames, light from the interior 

reaches the surface of the flame and is imaged by the camera. The measured temperature of an 

optically thin flame is a spatial average across the optical path. 

Planck’s law states that the spectral radiance, I , of a blackbody is dependent on the emissivity, 

 , wavelength,  , and temperature, T , where h is the Planck constant, c is the speed of light, 

and k is the Boltzmann constant, as shown in equation 4: 



2

5

2 ,, . ( 1) hc kThc IT T

e



  

   (4) 

An analytical expression for the raw digital number from each sensor pixel is shown in equation 5, 

       Dx, y  i

Addt   S   i  d , (5) 

where Dx, y is the digital number from pixel ( x, y ),  i is the gain of the camera electronics, 

Ad is the area of a pixel, d is the solid angle subtended by the pixel, t is the exposure time, 

    is the transmission through the lens, S is the input spectral radiation,  i   is the color 

filter response for each channel, and the subscript i indicates the color filter (red, green, blue) of 

the pixel. A full color image is produced by using the raw image data and a simple mean filter 

(Densmore et al., 2011). To acquire a ratio of two color channels, equations 4 and 5 can be 

combined as shown in equation 6: 

   

  

, . ,

g g

r r

Green IT d

Red IT d  



   

    (6) 

Once the gain of the electronics (i.e., calibration factor) is calculated, a calibration curve can be 

established and unknown temperatures can be determined. Additional details of the two-colorratio method used in this study have been described elsewhere (Densmore et al., 2011). 

Thermocouple temperature measurements were conducted with an uncoated 0.051-mm-diameter 

Pt-Pt/10% Rh thermocouple. Each leg of the thermocouple was inserted through an alumina 

(Al2O3) tube to add support, and the legs were wired to a miniature ceramic connector. Once 

constructed, the thermocouple assembly was attached to a 3-axis (0.001-mm-resolution 

adjustment) translation stage for movement within the flame. A photograph of the thermocouple 

setup is shown in figure 5. 
8 

Thermocouple Meter

3‐axis Translation Stage

Thermocouple

Opposed Flow Burner

Figure 5. Photograph of the thermocouple setup showing various components. 

Initially, the procedure to record the flame temperature was to insert and move the thermocouple 

from the lower fuel duct through the flame to the upper air duct. However, soot would 

accumulate on the thermocouple junction and cause inaccurate temperature readings. To prevent 

soot buildup on the junction, a new method was used. The new method consisted of inserting the 

thermocouple into the centerline of the flame, recording the temperature, and immediately 

removing the thermocouple. Dwell time of the thermocouple in the flame region was ~2 s. 

Once removed from the flame, the thermocouple was inspected for soot deposits. If soot 

deposits were found, they were removed by burning them off with an external flame source. To 

acquire a centerline temperature map of the flame, the vertical stage height was adjusted, and the 

insertion procedure was repeated. For the results presented in this study, the temperature 

measurements in the sooting region of the flame are an average of four experiments with a 

maximum error in the measurements of 20 K, based on ±1 standard deviation. The nonsooting 

region data are from one experiment. 

Chemical kinetic modeling was performed using the Appel, Bockhorn, and Frenklach (ABF) 

mechanism, which contains 101 species, 544 reactions, and associated thermodynamic and 

transport files (Appel et al., 2000). The ABF mechanism was developed for soot formation and 

does not contain NOx chemistry. The ABF mechanism has been validated with ethane (C2H6),
9 

C2H4, and C2H2 as fuels, and it predicts major, minor, and aromatic species up to pyrene 

(C16H10). Cantera, which is an open source, multiplatform software code used to study 

combustion behavior, was used in conjunction with the programming language Python to 

execute the ABF mechanism (Goodwin, 2011). The modeling effort was conducted with a 1-D 

counter-flow flame object to simulate the opposed flow burner configuration. Initial conditions 

for the model simulation are shown in table 1. Initial grid spacing between the inlets for the 

simulation was set to 0.0, 0.06, 0.12, 0.18, 0.24, 0.30, 0.36, 0.48, 0.6 cm. After a Newton 

iteration was successfully converged, grid refinement was enabled and new grid points were 

inserted to continue with the simulation. The relative and absolute steady-state tolerances for 

convergence were set to 1.0 × 10-5 and 1.0 × 10-9, respectively, and the relative and absolute 

tolerances for time stepping were set to 1.0 × 10-4 and 1.0 × 10-9, respectively. A 2.67-GHz Intel 

Core* i5 processor with a 32-bit Windows operating system showed that the computational time 

for convergence to occur was 90 s with a total final grid count of 162. 

Table 1. Initial conditions for the Cantera simulation. The 

mass flux of the fuel and oxidizer corresponds to 

the flow rates of the experiment and dimensions of 

the burner. 

Parameter Setting 

Pressure 1 atm 

Fuel and oxidizer temperature 300 K 

Mass flux fuel (C2H4) 0.24 kg/m2/s 

Mass flux oxidizer (air) 0.20 kg/m2/s 

Duct separation 0.6 cm 

5. Results and Discussion 

A photograph of the C2H4/air-opposed flow diffusion flame at 1-atm pressure is shown in figure 

6a. A notable characteristic of the opposed flow configuration is that two separate flame regions 

can be observed as the blue and red colors in the flame. The blue region is associated with 

emission from CH and C2, whereas the red region is associated with soot incandescence. Figure 

6b shows the surface temperature acquired from the pyrometry temperature measurement 

technique. The surface temperature of the C2H4/air in the sooting red/orange region of the flame 

is ~2000 K. As previously mentioned, the pyrometry technique is valid only when the gray body 

assumption holds and when discrete emission is minimal. Therefore, the temperature 

measurements in the blue region with emission from CH and C2 are incorrect.

 *

Intel Core is a registered trademark of Intel Corporation. 
10 

Tem

perature (K)

(a)

(b)

Figure 6. (a) Picture of the C2H4/air-opposed flow diffusion flame. (b) Reconstructed image showing the 

surface temperature of the C2H4 flame. The incorrect temperature in the blue region is caused by 

discrete emission. 

Figure 7 shows a comparison of the pyrometry and thermocouple measurements, and a 

simulation calculated using Cantera. The pyrometry temperature measurements are a surface 

edge temperature ranging from the lower fuel duct to the upper air duct. In a plane located 

~2 mm above the fuel duct (normal to the centerline between ducts), soot incandescence is 

present with a measured temperature of ~2000 K. The soot surface temperature increases as the 

fuel diffuses into the air stream. However, as mentioned previously, the pyrometry temperature 

measurements are erroneous in regions of the flame where discrete emission is present. The 

invalid temperatures caused by discrete emission between ~2.4 and 3.3 mm from the fuel duct 

are shown in figure 7. Additionally, discrepancies between the thermocouple measurements and 

pyrometer measurements of the surface temperature can also be caused by discrete emission. 

Further work needs to be performed to assure discrete emission is not affecting the pyrometry 

temperature measurements near the surface of the sooting region. The error in the pyrometer 

temperature measurements is approximately ±100 K. This error is from the uncertainty in the 

spectral transmission through the optical components and measured signal to noise. 

Thermocouple temperature measurements are shown in figure 7. The temperature measurements 

between 2.20 and 3.20 mm above the fuel duct (i.e., sooting region) are an average of four 

experiments. Based on ±1 standard deviation of the measured temperatures, the maximum error 

in the measurements is 20 K. The thermocouple temperature measurements above 3.20 mm are 

from one experiment. The first measurement was 2.20 mm above the fuel duct with a 

temperature of 802 K. The temperature increased throughout the sooting region, moving toward 

the oxidizer duct, to a maximum temperature of 1898 K at 3.70 mm above the fuel duct. In this 

region, the flame appeared blue. Beyond 3.70 mm, toward the air duct, the flame temperature 
11 

Figure 7. Comparison of the Cantera simulation with the results of the pyrometry and thermocouple 

temperature measurements. The blue and red regions represent locations of visible light 

produced from the flame. 

decreased. Temperature measurements were taken up to 5.20 mm from the fuel duct. The 

arrangement of the thermocouple assembly prevented further measurements nearer to the air 

duct. However, it was expected that the temperature would decrease, as no flame was present in 

this region. 

Similar experiments were performed by Olten and Senkan (1999) at atmospheric pressure with 

opposed-flow C2H4 diffusion flames. However, the calculated strain rate and duct separation for 

their study was 37.7 s-1 and 15 mm, respectively. Their thermocouple temperature measurements 

were recorded throughout the range of the fuel and oxidizer duct, and a maximum temperature of 

1850 K was recorded. The thermocouple measurements by Olten and Senkan did not include 

corrections for radiation loss, similar to the results presented in this study. The radiation 

correction was left to the reader since additional uncertainties in the measured temperature can 

be introduced. A similar temperature profile was shown by the results of Olten and Senkan and 

the results presented in this study. 

Figure 8 shows simulation results from executing the ABF mechanism with Cantera. The 

temperature increases at ~1.5 mm from the fuel duct. The temperature continues to increase 

throughout the red/orange sooting region of the flame until a maximum temperature of 2077 K at 

3.79 mm is reached. The temperature then decreases toward the air duct. Concentration profiles 

of intermediate species produced during the combustion event are also shown in figure 8. The 

modeling simulation captures the two distinct regions, which were experimentally observed with 
12 

the opposed flow flame. Throughout the red/orange regime, soot incandescence is responsible 

for the color of the flame. The Cantera simulation shows the formation of soot precursors, such 

as C2H2 and C6H6. The local equivalence ratio is also shown in figure 8. The maximum 

production of soot precursors occurs at local equivalence ratios >1, which indicates that soot is 

formed in the fuel-rich region of the opposed flow flame. Additionally, the simulation shows the 

formation of CH and OH in the high-temperature regime where the blue color of the flame is 

observed. Simulations of a similar opposed flow diffusion flame system using the CHEMKIN 

software package conducted by McNesby et al. (2005) showed nearly identical results, as those 

predicted by Cantera in this study. 

Figure 8. Simulation results from Cantera showing intermediate species produced during combustion, 

temperature profile, and local equivalence ratio. The multiplication factors are listed in parentheses. 

Figure 9 shows a representation of figure 1, which is from Kook et al. (2005). In addition to the 

soot region, NOx region, and typical diesel combustion pathway, figure 9 also shows the results 

of the Cantera calculation for local equivalence ratio with a C2H4/air flame at different pressures. 

The modeling results show that as pressure increases, the flame temperature also increases, thus 

moving the pathway toward the higher temperature NOx region. However, the modeling effort 

does not include heat loss from soot radiation, which, if included, would cause the flame 

temperature to decrease as pressure increases. Each simulation at a different pressure yields a 

combustion pathway that lies in the sooting region. Therefore, using an opposed flow flame 

burner is an effective way to examine soot formation regions in a flame. 
13 

Figure 9. Representation of soot and NOx regions within an equivalence ratio/temperature 

plane showing Cantera simulations for different pressures. 

6. Conclusions 

Temperature measurements of a C2H4/air-opposed flow diffusion flame were recorded 

experimentally by both optical pyrometry and thermocouple techniques. Optical pyrometry is a 

nonintrusive method for determining flame temperatures and does not interfere with the 

combustion chemistry of the flame. The pyrometry technique allows for an accurate temperature 

measurement only in regions of the flame where soot incandescence is occurring. In other 

regions of the flame where discrete emission is observed, the pyrometry temperature 

measurements are invalid. The Cantera modeling results predicted the temperature profile of the 

opposed flow flame, and the results from the thermocouple measurements showed a general 

trend. Additionally, the intermediate species responsible for soot production and the distinct 

color regions of the flame were also predicted by Cantera. 

To our knowledge, this is the first detailed study comparing temperature measurements acquired 

from a single high-speed color camera pyrometer to thermocouple measurements and Cantera 

simulations for opposed flow diffusion flames. However, digital single lens reflex still-frame 

cameras have been reported as coflow flame pyrometers (Kuhn et al., 2011). The development 
14 

of a high-speed color camera as a pyrometer may allow scientists to investigate flame 

temperatures during dynamic events, such as flame extinguishment, turbulence, and rapid 

changes in fuel/oxidizer composition. Overall, the research results presented in this study will 

help to refine and validate chemical kinetic models for soot, which ultimately can lead to cleaner 

burning and more fuel-efficient power systems. 
15 

7. References 

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Chemistry and Physics. Laminar Premixed Flames of C2 Hydrocarbons. Combustion and 

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iso-Octane. Combustion and Flame 1998, 112 (4), 617–622. 

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Imaging Pyrometry. Applied Optics 2011, 50 (17), 2659–2665. 

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Glass, D.; Gray, C.; Jolley, D.; Gibbons, C.; Sim, M.; Fritschi, L.; Adams, G.; Bisby, J.; 

Manuell, R. Leukemia Risk Associated With Low-Level Benzene Exposure. Epidemiology

2003, 14 (5), 569–577. 

Goodwin, D.; Cantera, G. Suite of Object-Oriented Software Tools for Problems Involving 

Chemical Kinetics, Thermodynamics, and/or Transport Processes. http://code.google. 

com/p/cantera (accessed 8 August 2011). 

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Kitamura, T.; Ito, T.; Senda, J.; Fujimoto, H. Mechanism of Smokeless Diesel Combustion With 

Oxygenated Fuels Based on the Dependence of the Equivalence Ratio and Temperature on 

Soot Particle Formation. International Journal of Engine Research 2002, 3 (4), 223–248. 

Kook, S.; Bae, C.; Miles, P. C.; Choi, D.; Pickett, L. M. The Influence of Charge Dilution and 

Injection Timing on Low-Temperature Diesel Combustion and Emissions. Society of 

Automotive Engineers (SAE) International, 2005-01-3837, 2005.

Kuhn, P. B.; Ma, B.; Connelly, B. C.; Smooke, M. D.; Long, M. B. Soot and Thin-Filament 

Pyrometry Using a Color Digital Camera. Proceedings of the Combustion Institute 2011, 33

(1), 743–750. 
16 

Kurman, M. S.; Natelson, R. H.; Cernansky, N. P.; Miller, D. L. Speciation of the Reaction 

Intermediates From n-Dodecane Oxidation in the Low Temperature Regime. Proceedings of 

the Combustion Institute 2011, 33 (1), 159–166. 

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Experimental and Computational Studies of Oxidizer and Fuel Side Addition of Ethanol to 

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17 

List of Symbols, Abbreviations, and Acronyms 

1-D one dimensional 

2 a strain rate on the oxidizer side of flame 

Ad area of pixel 

ABF Appel, Bockhorn, and Frenklach 

atm atmosphere 

c speed of light 

C2 diatomic carbon 

C2H2 acetylene 

C2H4 ethylene 

C2H6 ethane 

C3H3 propargyl 

C6H6 benzene 

C7H16 n-heptane 

C10H22 n-decane 

C12H26 n-dodecane 

C16H10 pyrene 

CH methylidyne 

cm centimeter 

CMOS complementary metal oxide semiconductor 

D measured signal from camera 

 emissivity 
18 

fps frames per second 

GHz gigahertz 

h Planck constant 

H2 hydrogen 

i(subscript) color filter of a pixel

I spectral radiance 

IR infrared 

k Boltzmann constant 

K Kelvin 

kg kilogram 

 wavelength

L duct separation

m meter 

mm millimeter 

MPa megapascal 

ms millisecond 

N2 nitrogen 

OH hydroxyl 

PAH polycyclic aromatic hydrocarbon 

 f fuel density

ox oxidizer density 

Pt platinum 

Rh rhodium
19 

 i gain of camera electronics 

s second

S   input spectral radiation 

SLPM standard liters per minute 

t exposure time 

T temperature 

    transmission through lens 

Vf fuel velocity

Vox oxidizer velocity 

d solid angle subtended by pixel 

 i   color filter response of each channel
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