Mid-IR Absorption Cross-Section Measurements of
Hydrocarbons
Thesis by
Majed Abdullah Alrefae
In Partial Fulfillment of the Requirements
For the Degree of
Masters of Science
King Abdullah University of Science and Technology
Thuwal, Kingdom of Saudi Arabia
May 2013
2
The thesis of Majed Abdullah Alrefae is approved by the examination committee.
Committee Chairperson (Thesis Supervisor) [Dr. Aamir Farooq]
Committee Member [Dr. Suk Hu Chung]
Committee Member [Dr. William Roberts]
King Abdullah University of Science and Technology
May 2013
3
© 2013
Majed Abdullah Alrefae
All Rights Reserved
4
ABSTRACT
Mid-IR Absorption Cross-Section Measurements of Hydrocarbons
Majed Abdullah Alrefae
Laser diagnostics are fast-response, non-intrusive and species-specific tools perfectly
applicable for studying combustion processes. Quantitative measurements of species
concentration and temperature require spectroscopic data to be well-known at
combustion-relevant conditions. Absorption cross-section is an important spectroscopic
quantity and has direct relation to the species concentration. In this work, the
absorption cross-sections of basic hydrocarbons are measured using Fourier Transform
Infrared (FTIR) spectrometer, tunable Difference Frequency Generation laser and fixed
wavelength helium-neon laser. The studied species are methane, methanol, acetylene,
ethylene, ethane, ethanol, propylene, propane, 1-butene, n-butane, n-pentane, nhexane, and n-heptane.
The Fourier Transform Infrared (FTIR) spectrometer is used for the measurements of the
absorption cross-sections and the integrated band intensities of the 13 hydrocarbons.
The spectral region of the spectra is 2800 – 3400 cm-1 (2.9 – 3.6 µm) and the
temperature range is 673 – 1100 K. These valuable data provide huge opportunities to
select interference-free wavelengths for measuring time-histories of a specific species in
a shock tube or other combustion systems. Such measurements can allow
5
developing/improving chemical kinetics mechanisms by experimentally determining
reaction rates.
The Difference Frequency Generation (DFG) laser is a narrow line-width, tunable laser in
the 3.35 – 3.53 µm wavelength region which contains strong absorption features for
most hydrocarbons due to the fundamental C-H vibrating stretch. The absorption crosssections of propylene are measured at seven different wavelengths using the DFG laser.
The temperature range is 296 – 460 K which is reached using a Reflex Cell. The DFG laser
is very attractive for kinetic studies in the shock tube because of its fast time response
and the potential possibility of making species-specific measurements.
The Fixed wavelength helium-neon (HeNe) laser at 3.39 µm is used to measure the
absorption cross-section of the fuels mentioned above. The dependence on
temperature, pressure and bath gas (helium, argon and nitrogen) is also examined. The
temperature and pressure ranges of this study are 296 – 800 K and 250 – 1000 Torr,
respectively. These are the first measured cross-sections at HeNe laser wavelength that
are applicable at combustion-relevant conditions.
6
ACKNOWLEDGEMENTS
Studying at KAUST has provided me tremendous opportunities that immensely
contribute to my life. This is mainly because of the trust, support and encouragement
from my advisor, Prof. Aamir Farooq. Prof. Farooq helped me a lot in developing my
research skills through his close monitoring during my whole master degree. This work
couldn’t have been done without his guidance, suggestions and motivation.
I would like to thank Professor Suk Hu Chung and Professor William Roberts for their
valued inputs and suggestions during the review of my thesis. Special thanks to Dr.
Ettouhami Es-sbbar who helped me in setting up the experiments and discussing the
results obtained. Also, I would like to thank my colleagues in the lab: Kyle Owen, Bilal
Sajid, Tamour Javed, Awad Alquaity and Ehson Fawad. We enjoyed working together
and sharing our thoughts about our research projects and other aspects of life.
This thesis is dedicated to my mother, my wife and my daughter who supported me a lot
during my study at KAUST. My mother was so patient and understandable if I couldn’t
visit her for some time despite the fact that she is just 200 km from KAUST. My wife and
my daughter have prepared the environment for my success and we have enjoyed the
life at KAUST a lot.
7
TABLE OF CONTENTS
LIST OF FIGURES ..............................................................................................................................................9
LIST OF TABLES ..............................................................................................................................................12
1
2
3
4
Introduction ..........................................................................................................................................14
1.1
Motivation ...................................................................................................................................14
1.2
Organization of the Thesis ...........................................................................................................15
Absorption Cross-section Theory .........................................................................................................17
2.1
Absorption, Scattering and Transmission ....................................................................................17
2.2
The Beer-Lambert Law .................................................................................................................19
2.3
Integrated Band Intensity ............................................................................................................22
Experimental Setups for Measuring Absorption Cross-sections ..........................................................24
3.1
Helium-Neon (HeNe) Laser ..........................................................................................................25
3.2
Difference Frequency generation Laser .......................................................................................26
3.3
The FTIR Spectrometer ................................................................................................................29
3.4
Preparation of the Gas/Liquid Mixtures ......................................................................................31
3.5
Common Mode Rejection Strategy ..............................................................................................34
3.6
Decomposition Temperature Simulation.....................................................................................36
3.7
Uncertainty Analysis ....................................................................................................................39
Absorption Cross-section of Hydrocarbons at 3.392 µm ......................................................................42
4.1
Literature Review .........................................................................................................................42
4.2
Absorption Cross-sections of Methane .......................................................................................45
8
5
6
7
4.3
Absorption Cross-sections of Other Alkanes ...............................................................................48
4.4
Absorption Cross-sections of Alkenes..........................................................................................54
4.5
Absorption Cross-Sections of Alcohol ..........................................................................................57
4.6
Absorption Cross-sections Comparison .......................................................................................58
Absorption Cross-section of Propylene using DFG Laser ......................................................................61
5.1
Literature Review .........................................................................................................................61
5.2
Phase-Matching Conditions .........................................................................................................62
5.3
The Cross-sections of Propylene ..................................................................................................63
Hydrocarbon Spectra using FTIR Spectrometer....................................................................................68
6.1
Literature Review .........................................................................................................................68
6.2
Mid-IR Spectra of Alkanes ............................................................................................................71
6.3
Mid-IR Spectra of Alkenes and alkyne .........................................................................................79
6.4
Mid-IR Spectra of Alcohol ............................................................................................................84
Conclusion and Future Work ................................................................................................................89
7.1
Summary ......................................................................................................................................89
7.2
Future Work .................................................................................................................................91
REFERENCES ..................................................................................................................................................93
9
LIST OF FIGURES
Figure ‎2.1: The possible interaction modes between a beam and a molecule. ............................................17
Figure ‎2.2: Absorption transition for a molecule. .........................................................................................18
Figure ‎2.3: Schematic of an absorption experiment. ....................................................................................19
Figure ‎3.1: The experimental setup for measuring the cross-sections using HeNe Laser. ............................25
Figure ‎3.2: Two near-IR sources are combined in the PNNL crystal to produce a tunable mid-IR Laser. .....27
Figure ‎3.3: Phase-matching conditions for DFG laser with Pump wavelength of 1074 nm. (Source:
Novawave [6]) ...............................................................................................................................................28
Figure ‎3.4: The setup for the DFG laser using Reflex Cell. .............................................................................29
Figure ‎3.5: FTIR experimental setup for high temperature spectra measurements . ...................................31
Figure ‎3.6: The mixing vessel and its manifold used for mixture preparation. .............................................32
2
Figure ‎3.7: Cross-sections (in cm /molecule) of methane with nitrogen at different mole fractions. .........33
Figure ‎3.8: Common mode rejection scheme of the HeNe laser, with propylene as a sample. ...................35
Figure ‎3.9: Common Mode Rejection of the DFG Laser, Unit 113. ...............................................................35
Figure ‎3.10: Common Mode Rejection of the DFG Laser, Unit 114. .............................................................36
Figure ‎3.11: Pyrolysis of methane, ethylene, n-butane and n-hexane..........................................................38
Figure ‎3.12: Offset signals due to the noise from the furnace emission. ......................................................39
Figure ‎3.13: Reduced noise using an iris to block the emission from the furnace. .......................................40
Figure ‎4.1: Methane cross-section at 1 atm (X = 1% - 3%). ...........................................................................45
Figure ‎4.2: Locations of the rotational line of methane (P7) from HITRAN and the centerline of the HeNe
laser ...............................................................................................................................................................46
Figure ‎4.3: Pressure dependent absorption cross-sections of methane with Ar, He and N2 as bath gases at
T = 296 K. .......................................................................................................................................................47
Figure ‎4.4: Locations of the HeNe laser centerline for ethane, propane and n-butane at 296 K. ................48
Figure ‎4.5: The cross-section of ethane at 1 atm (X= 10 %). .........................................................................49
10
Figure ‎4.6: Propane absorption cross-section at 1 atm (X = 1%). .................................................................50
Figure ‎4.7: Absorption cross-section of n-butane at 1 atm (X = 5%). ............................................................51
Figure ‎4.8: n-pentane cross-section at 1 atm (X =2 %). .................................................................................52
Figure ‎4.9: The cross-section of n-hexane at 1 atm (X~ 1.25 %). ..................................................................53
Figure ‎4.10: Measured cross-section of n-heptane at 1 atm (X ~ 0.6 %). .....................................................54
Figure ‎4.11: Ethylene cross-section at 1 atm (X= 50 %). ...............................................................................55
Figure ‎4.12: Cross-section of propylene at 1 atm (X= 10 %). ........................................................................56
Figure ‎4.13: 1-butene cross-section at 1 atm (X= 5 %). .................................................................................56
Figure ‎4.14: Methanol cross-section at 1 atm (X = 2.5 %). ............................................................................57
Figure ‎4.15: Cross-section of ethanol at 1 atm (X= 1.15 %). .........................................................................58
Figure ‎4.16: The cross-section of the studied hydrocarbons at 1 atm and 296 K with 3 different bath gases.
X is the mole fraction of the hydrocarbon. ...................................................................................................59
Figure ‎4.17: The cross-section of the studied hydrocarbons at 1 atm and 773 K with 3 different bath
gases. X is the mole fraction of the hydrocarbon. .........................................................................................60
Figure ‎5.1: Absorption cross-sections of propylene at the seven locations. .................................................64
-1
Figure ‎5.2: The FTIR and DFG cross-sections of propylene over the 2850 – 2975 cm range at three
different temperatures: (a) 296 K, (b) 343 K and (c) 383 K. The symbols show the results obtained by the
DFG system. (Permission is taken from the author) .....................................................................................65
-1
Figure ‎5.3: The cross-sections from the DFG laser and the FTIR at 2950.87 cm . ........................................66
-1
Figure ‎5.4: The cross-sections from the DFG laser and the FTIR at 2867.91 cm . ........................................67
Figure ‎6.1: The spectra of methane in the mid-IR showing the origin of the band and the P,Q and R
branches. .......................................................................................................................................................71
Figure ‎6.2: Cross-section of Ethane at 1 atm (X ~ 10 %). ...............................................................................73
Figure ‎6.3 Propane cross-section at 1 atm (X ~ 10 %). ..................................................................................74
Figure ‎6.4: Cross-section of n-butane at high temperatures. .......................................................................75
Figure ‎6.5: n-pentane spectra at high temperatures. ...................................................................................76
11
Figure ‎6.6: Cross-section of n-hexane at high temperatures. .......................................................................77
Figure ‎6.7: n-heptane spectra in the mid-IR at high temperatures. ..............................................................78
Figure ‎6.8: The spectra of the studied alkanes at 673 K................................................................................79
Figure ‎6.9: Cross-sections of acetylene at ~ 400 Torr ( X ~ 18 %)..................................................................80
Figure ‎6.10: Cross-section of ethylene at 1 atm (X ~ 40 %). ..........................................................................81
Figure ‎6.11: Propylene cross-sections at high temperatures. .......................................................................82
Figure ‎6.12: Mid-IR spectra of 1-butene at high temperatures. ...................................................................83
Figure ‎6.13: Comparison between the spectra of the studied alkenes at 673 K. ..........................................84
Figure ‎6.14: The cross-sections of methanol at high temperatures..............................................................85
Figure ‎6.15: The spectra of ethanol at elavated temperatures. ...................................................................86
Figure ‎6.16: The integrated band intensities of the studied hydrocarbons. .................................................87
Figure ‎6.17: The relations of the integrated band intensities for the studied hydrocarbons. ......................88
12
LIST OF TABLES
Table ‎3.1: Summary of lasers specifications used in this work. ....................................................................24
Table ‎3.2: Specifications for the two DFG laser systems. ..............................................................................27
Table ‎3.3: FTIR settings used in this study.....................................................................................................30
Table ‎3.4: Fast decomposition temperatures of the fuels with the correspnding chemical mechanisms. ...37
Table ‎4.1: The measured cross-sections of hydrocarbons with helium, argon and nitrogen as bath gases at
296 K and 1 atm with uncertainty of the measurements and the purities of the hydrocarbons. ................44
Table ‎5.1: Phase-Matching conditions for the selected wavelengths in this study. .....................................63
Table ‎6.1: The mole fraction, maximum temperature as well as the calculated integrated band intensity of
the studied hydrocarbons compared to Sharpe et al. ...................................................................................70
Table ‎6.2: Integrated band intensities of methane at different temperatures compared to Sharpe et al.
and Klingbeil. .................................................................................................................................................72
Table ‎6.3: Integrated band intensities of ethane at different temperatures compared to Sharpe et al. and
Klingbeil. ........................................................................................................................................................73
Table ‎6.4: Integrated band intensities of propane at different temperatures compared to Sharpe et al. ...74
Table ‎6.5: Integrated band intensities of n-butane compared with Sharpe et al. ........................................75
Table ‎6.6: Integrated band intensities of n-pentane at different temperatures compared to Sharpe et al.
and Klingbeil et al. .........................................................................................................................................76
Table ‎6.7: Integrated band intensities of n-hexane compared to Sharpe et al. ............................................77
Table ‎6.8: Integrated band intensities of n-heptane at different temperatures compared to Sharpe et al.
and Klingbeil et al. .........................................................................................................................................78
Table ‎6.9: Integrated band intensities of acetylene at different temperatures agree with Sharpe et al. ....80
Table ‎6.10: Integrated band intensities of ethylene at different temperatures compared to Sharpe et al.
and Klingbeil. .................................................................................................................................................81
13
Table ‎6.11: Integrated band intensities of propylene at different temperatures compared to Es-sebar et
al.[52], Sharpe et al. and Klingbeil et al. ........................................................................................................82
Table ‎6.12: Integrated band intensities of 1-butene at different temperatures compared to Sharpe et al.,
Es-sebar et al. and Klingbeil. ..........................................................................................................................83
Table ‎6.13: Integrated band intensities of methanol at different temperatures compared to Sharpe et al.
.......................................................................................................................................................................85
Table ‎6.14: Integrated band intensities of ethanol at different temperatures compared to Sharpe et al.
and Klingbeil. .................................................................................................................................................86
14
Chapter 1
1 Introduction
1.1 Motivation
Hydrocarbons are the main sources of fuels for combustion applications ranging from
power plants, automobiles to airplanes. The study and understanding of the behavior of
fuels are important to reduce their consumptions, the pollutant emissions and hence
increase the overall efficiency. Laser diagnostics are valuable tools to non-intrusively
measure concentrations, temperature and the velocity of the reacting flows [1].Their
fast-time response and the high measurement accuracy make this technique very
suitable for combustion study in shock tubes, pulse detonation engines and rapid
compression machines [1]. Therefore, the optical parameters like absorption crosssections, line strength of the transition, and the line-shape functions must be well
studied. Because of the mixing of lines and the large vibrational modes of most of the
hydrocarbons, the absorption cross-sections are preferred. Also, the absorption crosssections of the hydrocarbons are very strong at mid-IR, because of the fundamental C-H
vibrational modes at this region. Furthermore, the products of the combustion, such as
CO2, H2O have no interference with the hydrocarbons at the mid-IR region, and so
provide greater sensitivities.
There is little study of the absorption cross-sections of the hydrocarbons at high
temperatures. So, one of the primary objectives of this thesis is to measure the Mid-IR
15
absorption cross-sections of several basic hydrocarbons to temperature up to 1100 K.
Also, the dependence of the absorption cross-sections on bath gas and pressure is
studied at fixed wavelength. This thesis provides the first detail spectra of several
hydrocarbons using FTIR for temperatures typical of combustion environments. These
spectra are important to select wavelength locations at which only one strong species is
absorbing. Finally, these data can be utilized to validate and improve chemical models
important for combustion applications.
1.2 Organization of the Thesis
Three laser sources: Helium-Neon laser, Difference Frequency Generation (DFG) laser
and Fourier Transform IR (FTIR) spectrometer are used in this work to measure the midIR absorption cross-sections of hydrocarbons. This thesis contains introduction,
conclusion and five chapters.
Chapter 2 explains the absorption theory as well as the Beer- Lambert Law. It describes
the relation between the decrease of the spectrally narrow radiation intensity light
passing through absorbing species to absorption cross-section of the species, the path
length and the concentration. The relation of the absorption cross-sections with the line
strength as well as the line-shape function is discussed to understand the dependence
on temperature, pressure and bath gas. The concept of the integrated band intensity is
then introduced, to be used for the spectra obtained from the FTIR.
16
Chapter 3 summarizes the three experimental setups implemented to measure the
absorption cross-sections. Two static cells are used in this thesis: Reflex cell for DFG
laser work and Quarts cell placed inside a furnace for HeNe laser and FTIR
measurements. Also, the uncertainty analysis of these measurements is discussed and
found to be less than 5 %.
In Chapter 4, the absorption cross-sections at 3.392 µm of 12 hydrocarbons
representing alkanes, alkenes and alcohols groups are measured using a fixed
wavelength helium-neon laser. The dependence on temperature, pressure and bath gas
(helium, argon and nitrogen) is examined. The temperature and pressure ranges are 296
– 800 K and 250 – 1000 Torr, respectively.
The measured absorption cross-section of propylene (C3H6) in temperature 296 – 460 K
by Difference Frequency Generation (DFG) laser is presented in Chapter 5. Propylene is
an unsaturated hydrocarbon and considered one of the important intermediate species
in combustion. The phase-matching condition of the DFG laser at the selected seven
wavelengths is explained.
Chapter 6 shows the spectra of many hydrocarbons in the 2500 – 3400 cm-1 region at
high temperatures obtained from the FTIR. The absorption cross-sections and the
integrated band intensities are described for these hydrocarbons.
17
Chapter 2
2 Absorption Cross-section Theory
2.1 Absorption, Scattering and Transmission
When a beam of a collimated light at frequency ν passes through a uniform gas sample,
the gas molecule will absorb, scatter or transmit the light, Figure 2.1. The probabilities
for all of these cases are summed to 1:
Absorption + Scattering + Transmission = 1
(1)
Figure ‎2.1: The possible interaction modes between a beam and a molecule.
In the mid-IR, scattering can be neglected and so either absorption or transmission can
occur. For the molecule to absorb the laser and excite to the higher energy level, the
18
energy of the light should be the same as the difference between the initial and the
excited energy levels of the molecule, equivalent to Plank’s Law:
(2)
Where h is the Plank’s constant,
collimated light and
, ν is the frequency of the
represents the energy difference of the photon corresponding
to the molecular transition (absorption here) between the two quantum states, Figure
2.2.
Figure ‎2.2: Absorption transition for a molecule.
For the mid-IR region the internal energy change
is the sum of the rotational and
vibrational energy since the change occurs in the rotational and vibrational quantum
numbers [2].
19
2.2 The Beer-Lambert Law
The Beer-Lambert’s Law describes the relation between the absorbance of
monochromic light passing through a uniform medium with the path length, as follow:
( )
Where
signal,
the absorbance of the light is,
(3)
is the reference signal, is the transmitted
is the absorption cross-section in cm2/molecule (or cm2/mole), n is the
concentration of the gas in cm-3 and L is the optical path length in cm, Figure 2.3. The
absorption cross-sections can be also written in cm2/mole through multiplying by the
Avogadro’s number: 6.022 * 1023 molecule/mole.
Figure ‎2.3: Schematic of an absorption experiment.
The absorption cross-section is the probability of the molecule to absorb the light at
frequency ν (the effective area of the molecule). If the gas is assumed to be ideal, the
concentration can be written as:
(4)
20
Where k is the Boltzmann’s constant,
K, P and T are the pressure
and the temperature of the gas, respectively. Therefore, the absorption cross-section in
terms of pressure, temperature, absorbance, and the path length is:
(5)
To define the parameters on which the absorption cross-sections depend, other form of
the Beer’s Law is used in terms of line strength and the line-shape function, as follow:
(6)
So, the absorption cross-sections in terms of the above parameters are found by
equating Equations (3) and (6) to get:
(7)
The line strength is a fundamental quantity depends on the Einstein’s Coefficients and
the number of molecules in the ground state of the molecule at that transition. The line
strength
for a specific transition
reference-temperature line strength
frequency
at temperature
, the partition function
and the transition lower state energy
( )
{
can be determined from
[
(
}]
, the transition
:
)] [
{
(8)
}]
[
21
The line-shape function accounts for the uncertainty of the energy levels that lead to
broader line. The main two line broadening mechanisms are Doppler and Collisional
broadenings. Doppler Broadening is important at high temperature and low pressure.
The Doppler Broadening is described by Gaussian line-shape which at the line center
(
):
(9)
The Doppler full width at half maximum (FWHM)
is given in terms of the linecenter
frequency, the temperature in K and the molcular weight of the species in g/mol, as:
(10)
Collisional (Pressure) Broadening is important at high pressure and low temperature.
This is a function of the pressure, and the collisional broadening coefficients for the
absorbing species and a collisional partner. It follows a Lorentzian line-shape function
which is at the line center (
):
(11)
The collisional full width at half maximum (FWHM)
is a function of the total
pressure, the mole fraction of each species and the collisional broadening
∑
(12)
, as:
22
The dependence of the absorption cross-section on the bath gas is due mainly to the
pressure broadening; i.e.
. From Equation (7), the absorption cross-sections
inversely related to the collisional broadening coefficients. Also, these coefficients
depend on temperature and so the bath gas dependence behaves differently as
temperature changes.
2.3 Integrated Band Intensity
The infrared spectra of a molecule occur when there is a rovibrational transition which is
due to the change in the vibrational quantum number as well as in the rotational
quantum number when the molecules absorb a photon. In IR, it is commonly accepted
to use the band strength which represents many lines of different ground and excited
vibrational quantum numbers.
The integrated band intensity is the integration of the absorption cross-sections over
the whole band, for example the 2800 – 3400 cm-1 band in this work. The integrated
band intensity is independent on temperature since the temperature will spread the
band because of populating new rotational lines [3, 4]. The integrated band intensity
over frequency in cm-1 can be given by:
∫
∫
(13)
The integrated band intensity will depend on temperatures higher than the
characteristic vibrational temperature written as:
23
(14)
Where h is the Planck’s constant, c is the speed of light, is the characteristic vibrational
frequency and k is the Boltzmann constant. In the 2800 – 3400 cm-1 band (2.9 to 4.0 µm)
the characteristic temperature is ~ 4000 K which is much higher than the maximum
temperature in this study (1200 K) [3].
24
Chapter 3
3 Experimental Setups for Measuring Absorption Cross-sections
Table 3.1 summarizes the laser systems used to measure the absorption cross-sections of the
hydrocarbons in this thesis.
Laser
Manufacturer
Spectral Range
Resolution
Temperature
(Model)
(cm-1)
(cm-1)
Range (K)
0.08 and 0.6
296 – 1150
0.0001
296 – 460
0.01
296 – 1100
Fourier
Transform IR
Bruker (Vertex V 80)
Spectrometer
Difference
Frequency
Generation (DFG)
Laser
Helium Neon
(HeNe) Laser
Thermo Fisher
Scientific (Novawave,
IRIS 1000)
Newport
700 to 6000
(1.6 to 14.3 µm)
2832 – 2985
(3.35 -3.53 µm)
2947.909
(3.392 µm)
Table ‎3.1: Summary of lasers specifications used in this work.
For the three laser systems, three experimental setups are used with similar components: laser
source, laser detector and different optics to direct and focus the laser. Two different cells
containing the sample are used: Reflex Cell and Quartz Cell.
25
3.1 Helium-Neon (HeNe) Laser
The experimental setup for direct absorption measurements of hydrocarbons cross-sections
using HeNe Laser is shown in Figure 3.1.
Figure ‎3.1: The experimental setup for measuring the cross-sections using HeNe Laser.
Helium Neon (HeNe) laser (2.0 mW, Newport, R-32172) is used as the light source. Its center
wavenumber was measured by Bristol Spectrum Analyzer (721) and found to be near 2947.909
cm-1 as suggested by Mallard and Gardiner [5]. The line-width (FWHM) of the HeNe laser is 0.01
cm-1 which is less than that of the absorbing species [6]. Common Mode Rejection (CMR) is
used to minimize the intensity fluctuation of the laser. The CaF2 Beam Splitter is used to direct
50 % of the laser beam to the detector 1 (Vigo Systems, PVMI-3TE-10.6, 2mm x 2mm active
area) while the rest is transmitted to the detector 2 (Vigo Systems, PVMI-3TE-10.6, 2mmx2mm
active area). An iris is used before each detector to eliminate the noise from the furnace
emission, and another one is used after the HeNe laser to block any emission coming from the
furnace and to avoid detectors saturation.
26
The quartz cell is placed in a furnace (BlueBird) where the 7.747 cm long test section is in a
uniform temperature profile. The other two sections are evacuated to have no temperature
gradients at the ends of the tube furnace. Four fused silica windows are placed at inclined angle
to block unwanted interference fringes. To measure the temperature of the test gas, four Ktype thermocouples (Omega) are equally spaced along the test section. The temperature
difference between the four thermocouples has a maximum value of < 1.5%.
The mixture enters the cell through a valve and its pressure is monitored by 1,000-Torr
Baratron capacitance gauge (MKS 620A). The vacuum sections are also monitored by 200-Torr
Baratron capacitance gauges (MKS 620A). The accuracy of both gauges is ± 0.12 % of reading.
The cell is evacuated using a vacuum pump to less than 0.1 mTorr.
The measurements of the absorption cross-sections start by recording the baseline signal when
the test cell is under vacuum. The mixture is then introduced to the cell up to the required
pressure and the transmitted signal is finally recorded. The sampling rate of both signals is 2.5 *
106 samples/second while the number of samples is 10,000 which are recorded in 0.02 sec.
After the test, the cell is evacuated and the signal remains the same when using the Common
Mode Rejection.
3.2 Difference Frequency generation Laser
Two tunable mid-IR Difference Frequency Generation (DFG) laser systems (Novawave IRIS 1000
[7]) were used to measure the cross-sections of propylene (C3H6) as a function of temperature.
The specifications of the two systems are summarized in Table 3.2.
27
Unit
Wavelength Range
Central Wavelength
Pump Wavelength
113
3.350-3.440 µm
3.395 µm
1.064 µm
114
3.440-3.530 µm
3.485 µm
1.074 µm
Table ‎3.2: Specifications for the two DFG laser systems.
To produce mid-IR light, the pump laser operating at 1064 nm (1074 nm for the other system) is
combined with near-IR distributed feedback (DFB) diode lasers in a periodically poled lithium
niobate (PPLN) crystal, Figure 3.2. This nonlinear wavelength-mixing result in a mid-IR tunable
beam with frequency, as follow:
(15)
Figure ‎3.2: Two near-IR sources are combined in the PNNL crystal to produce a tunable mid-IR Laser.
There are five DFB diode lasers for each unit, and they are interchangeable to produce the
required output laser wavelength. Each DFB is able to be tuned to ~ 10 nm by selecting the right
conditions for phase-matching in order to have higher output power, Figure 3.3.
28
Figure ‎3.3: Phase-matching conditions for DFG laser with Pump wavelength of 1074 nm. (Source:
Novawave [6])
The output power is weak (~ 600 µW) and to have this power two parameters are needed to be
set correctly: the signal current and the PPLN temperature. The signal current is between 60007000 mA while the PPLN temperature range is 10 – 80 oC. The spectral line-width of the
resulting mid-IR light is about 0.0001 cm-1 which is very narrow and will be very suitable for
trace gas detection.
The schematic of the experimental setup for measuring propylene using DFG laser is shown in
Figure 3.4. Common-mode rejection (CMR) scheme is also used to account for the intensity
variation of the laser. The output wavelength of the mid-IR DFG is measured using a Spectrum
Analyzer (Bristol Instruments 721 B). The laser intensity was measured using photo-detectors
supplied by Vigo Systems (PVMI-3TE-10.6, 2mm x 2mm active area). As in the case for HeNe
laser setup, the temperature of the gas is monitored using K-type thermocouples. Before each
29
measurement, the absorption cell was evacuated to pressure lower than 0.01 Torr. Two MKS
Baratron capacitance manometers (20 and 1000 Torr range) were used for measuring the gas
pressure. Measurements of the propylene cross-sections were performed at seven
wavenumbers between 2850 and 2975 cm-1.
Figure ‎3.4: The setup for the DFG laser using Reflex Cell.
3.3 The FTIR Spectrometer
The Fourier Transform Infrared (FTIR) spectrometer is a valuable device used to obtain the
spectral information for a sample over a wide range of wavelength [8]. In this work, the FTIR
spectrometer used is made by Bruker, model VERTEX 80V. It has a Globar MIR source to
produce broadband beam which is modulated through Michelson interferometer. This
modulated beam is transmitted throughout the heated cell and finally is detected by a DigiTect
30
DLaTGS detector. The detector signal is then converted through a dual-channel A/D converter
and finally processed and analyzed by OPUS (a software for Bruker’s FTIR) to display the
absorbance over a range of wavenumbers. The range of wavenumber of this FTIR is from 400 to
8000 cm-1 with resolution of 0.08 cm-1. First, the reference signal is recorded when the cell is
evacuated then the sample is introduced and finally the transmitted signal is recorded. The
number of scanning of both signals is 50 scans, and at high temperatures the number of
scanning is 10 scans to reduce the test time. Table 3.3 lists the settings of the FTIR in this study.
The interferograms were corrected with the Mertz phase function. To calibrate the FTIR
wavenumbers, spectra of CO gas were recorded and compared with the CO lines from the
HITRAN database [9].
-1
Resolution
0.08 (or 0.6) cm
Beamsplitter
Potassium Bromide (KBr)
FTIR input aperture
2.5 mm
Detector
DLaTGS
Light Source
Globar (Mid-Infrared)
FT phase correction, zero fill
Mertz, 2 x zero-filling
Table ‎3.3: FTIR settings used in this study.
To measure the spectra of the hydrocarbons at high temperature (670 – 1200 K), quarts cell is
used in the furnace, as in the HeNe laser setup. The schematic of the experimental setup of the
FTIR measurements at high temperatures is shown in Figure 3.5.
31
Figure ‎3.5: FTIR experimental setup for high temperature spectra measurements .
3.4 Preparation of the Gas/Liquid Mixtures
In this work, a mixing vessel with three stirrers is used to prepare mixtures of the hydrocarbons
with a bath gas (argon, helium and nitrogen). It is connected to the test cell through a manifold,
Figure 3.6. The manifold is designed to easily fill the vessel with the hydrocarbon and the bath
gas separately, monitor the pressure and finally transport the mixture to the test cell.
32
Figure ‎3.6: The mixing vessel and its manifold used for mixture preparation.
To perfectly prepare a mixture, the following procedure is followed to ensure accurate mole
fraction calculation. The mixing vessel and the manifold are first evacuated using a vacuum
pump to pressure less than 0.1 mTorr using a rotary pump (Varian DS 102). Secondly, the fuel
enters the vessel slowly till the required pressure reached, and then the valve between the
vessel and the manifold is closed and evacuated. In the case of liquid fuels, they are freezed by
liquid nitrogen to extract the air from the fuel flask. The pressure of the fuel is monitored using
100 Torr Baratron capacitance gauges (MKS 620A) with accuracy of ± 0.12 % of the reading.
After reaching the required fuel pressure, the vessel is closed and the manifold is evacuated.
Thirdly, some amount of the bath gas is used to purge the manifold, and then evacuated.
33
Fourthly, when the pressure of the manifold reaches 0.1 mTorr, the bath gas is filled to higher
pressure than the fuel in the vessel and then the valve is opened. The pressure in the system is
monitored using 10,000 Baratron capacitance gauges (MKS 620A) for the total mixture pressure
with accuracy of ± 0.12 % of the reading. Finally, the mixture is blended using a magnetic stirrer
for 30 minutes. Before using the mixture, some amount of the mixture is pumped out to
remove any unmixed gaseous near the dead zones. In some cases where small volume of
mixture is required, a mixing cylinder (from Swagelok) is used to prepare the mixture and kept
for 24 hours before use. To ensure no condensation of the fuel, the absorption cross-section of
methane at different mole fractions were measured, and the same values of the cross-sections
we obtained, as shown in Figure 3.7.
XMethane= 1%
Cross Section (cm2)
2.00E-018
XMethane= 0.5%
T= 296 K
L= 15 cm
Bath gas: Nitrogen
1.50E-018
1.00E-018
5.00E-019
300
400
500
600
P (Torr)
Figure ‎3.7: Cross-sections (in cm2/molecule) of methane with nitrogen at different mole fractions.
34
3.5 Common Mode Rejection Strategy
It is found that the intensity of HeNe laser and the DFG laser fluctuate over time. In order to
have accurate measurements of the absorption cross-sections, the absorbance
should be
well known. Common mode rejection strategy is the best way to largely eliminate the effect of
this intensity variation. For this, a CaF2 Beam Splitter is used to direct 50 % of the laser to the
detector 2, while the rest goes through the cell to the detector 1, Figures 3.1 and 3.4. The
absorbance now will be given as:
(
Where
)
(16)
is the reference signal , is the transmitted signal, both from the Detector 1,
the signal of the CMR during recording the transmitted signal ,
during recording the reference signal
is
is the signal of the CMR
both from the Detector 2. If the laser intensity doesn’t
change over time, the value of the absorbance will be the same as before, since
and
will cancel out in the above equation.
The laser intensity of the HeNe laser over time is shown in Figure 3.8. There is a great
improvement of the signal when divided by the CMR. This will lead to more accurate
measurements.
35
Signal
CMR
Ratio
2.5
Signal (V)
2.0
1.5
Io/ICMR
I/ICMR
100 Torr
23 oC
L = 7.747 cm
45% of C3H6 in N2
1.0
0.5
0.0
0
500
1000
1500
2000
Time (Sec)
Figure ‎3.8: Common mode rejection scheme of the HeNe laser, with propylene as a sample.
Figure 3.9 and 3.10 show the intensity of the two DFG laser systems over time measured by the
two detectors. These fluctuations are eliminated by taking the ration of the two detectors
).
4.0
T= 296 K
P = 760 Torr
3.5
Detector 1, I1
DFG Laser
Unit 113
Detector 2, I2
Ratio, I2/I1
3.0
Detector 1 (V)
(
2.5
2.0
Laser Fluctuation is eliminated
1.5
1.0
0.5
0.0
0
200
400
600
800
1000
Time (Sec)
Figure ‎3.9: Common Mode Rejection of the DFG Laser, Unit 113.
36
4.0
T= 296 K
P = 760 Torr
3.5
DFG Laser
Unit 114
Signal, I2
Ratio, I2/I1
3.0
Reference (V)
Reference, I1
2.5
2.0
Huge Laser Fluctuation
1.5
Laser Fluctuation is eliminated
1.0
0.5
0.0
0
500
1000
1500
2000
2500
3000
Time (Sec)
Figure ‎3.10: Common Mode Rejection of the DFG Laser, Unit 114.
3.6 Decomposition Temperature Simulation
For accurately measuring the absorption cross-sections of the hydrocarbons at higher
temperatures, thermal decomposition should not take place. To know the temperatures at
which fast decomposition occur, simulations using ChemKin Pro are done using applicable
chemical kinetic mechanisms. These mechanisms are n-butane, n-heptane and ethanol
developed by Marinov et al. [10] Seiser et al. [11] and Marinov [12], respectively. The
decomposition temperatures of the studied hydrocarbons are listed in Table 3.4.
37
Hydrocarbon
Mechanism
Tfast-decomp. (K)
Methane
1,120
Ethane
773
Marinov et al. [10]
Propane
773
n-Butane
773
n-Pentane
773
n-Hexane
Seiser et al. [11]
773
n-Heptane
773
Acetylene
923
Ethylene
923
Marinov et al. [10]
Propylene
920
1-Butene
773
Methanol
773
Marinov [12]
Ethanol
773
Table ‎3.4: Fast decomposition temperatures of the fuels with the correspnding chemical
mechanisms.
As examples, the simulated mole fractions of methane, n-butane, n-hexane and ethylene over
longer time than the experiment are shown Figure 3.11. In this work, the resident time is kept
below the time when fast decomposition starts.
38
0.45
0.12
0.40
0.10
0.08
773 K
923 K
1123 K
0.06
0.04
XCH4 ~ 10 %
Mole Fraction, C2H4
Mole Fraction, CH4
0.35
0.30
773 K
923 K
1023 K
0.25
0.20
0.15
XC2H4 ~ 40 %
0.10
0.02
0.05
0.00
0.00
0
100
200
300
400
500
0
600
100
200
300
400
500
0.06
0.12
0.05
0.10
773 K
923 K
Mole Fraction, n-hexane
Mole Fraction, n-butane
Xhexane ~ 0.9 %
0.04
0.03
773 K
923 K
0.02
0.01
600
Time (Sec)
Time (sec)
Xbutane ~ 5 %
0.08
0.06
0.04
0.02
0.00
0.00
0
20
40
60
80
100
120
Time (Sec)
0
100
200
300
400
500
600
Time (Sec)
Figure ‎3.11: Pyrolysis of methane, ethylene, n-butane and n-hexane.
Flow measurements are implemented to have shorter residence time than the decomposition
time to perform the experiments at high temperatures. The mixture flows into the system by
controlling the inlet and the outlet valves. The flow experiment is used during the
measurements of the hydrocarbon spectra in the FTIR to measure the spectra at high at 920
and 1,100 K. The number of scans for the signal laser is reduced to 7 scans to minimize the test
time while having higher signal-to-noise ratio.
39
3.7 Uncertainty Analysis
The uncertainty analysis is estimated to know the accuracies of the measured absorption crosssections and the integrated band intensity. As per Equations (5) and (13), the absorption crosssections and the integrated band intensity are function of five measurable parameters:
absorbance, mole fraction, temperature, pressure and path length.
The uncertainty in absorbance is reduced by subtracting the offsets of the two detectors which
are mainly due to the emission from the furnace, Figure 3.12. The noise is reduced by using an
iris that allows the beam to penetrate through only. Huge decrease on the noise due to the
furnace emission is achieved using this technique, Figure 3.13.
1.4
1.2
I_off (V)
1.0
0.8
0.6
0.4
0.2
0.0
300
350
400
450
500
T (K)
Figure ‎3.12: Offset signals due to the noise from the furnace emission.
40
0.15
Offset (V)
0.10
0.05
Offset
0.00
200
300
400
500
600
700
T (C)
Figure ‎3.13: Reduced noise using an iris to block the emission from the furnace.
Also, the accuracy of the absorbance is improved by using common mode rejection since laser
intensity fluctuates over time. Most of the absorbance in this study is between 0.2 and 2, by
choosing appropriate mole fraction, to have higher SNR. As per the previous discussion, the
uncertainty on the absorbance is taken from the standard deviation of the recorded data.
The second source of uncertainty is the mole fraction of the fuel which is determined by
dividing the partial pressure of the fuel by the total pressure. The uncertainty of the two
baratrons used is ± 0.12 % of the reading. No leak is expected from the system, and so the main
uncertainty on the mole fraction is from the two pressure values. For liquid fuels (i.e. npentane) more caution is taken to eliminate the effect of adsorption by employing fuel pressure
of 50 % less than their vapor pressures at 296 K.
41
The uncertainty due to temperature comes from the temperature profile in the test section at
equilibrium. The mean value of the four thermocouples is used as the gas temperature.
The uncertainty of the test pressure is ±0.12% of the reading. Before recording any
measurement, care is taken to have constant pressure during the test time. The last parameter
that affects the measured cross-section is the path length which uncertainty mainly due to the
expansion of the two windows with temperature.
The overall uncertainty of the absorption cross-section is given by:
√( )
(
)
( )
( )
( )
(17)
For the integrated band intensity, the overall uncertainty is given by:
√( )
(
)
( )
( )
( )
(18)
In this work, the uncertainty of the absorption cross-section is less than 5%, and the
repeatability of the values is achieved within the estimated uncertainty by repeating the
experiments at the same conditions.
42
Chapter 4
4 Absorption Cross-section of Hydrocarbons at 3.392 µm
4.1 Literature Review
The absorption cross-section of hydrocarbons at 3.392 µm have been widely studied and used
in different laser diagnostic configurations. MacDonald et al. [13, 14] used IR HeNe laser
absorption at 3.392 µm to measure the fuel concentration in the pyrolysis of n-dodecane,
methylcyclohexane (MCH), and iso-cetane as well as RP-1 in a heated high-pressure shock tube.
Davidson et al. [15, 16] measured the concentrations of n- heptane and n-dodecane during
oxidations of n-heptane and n-dodecane, respectively. Haylette et al. [17] used IR HeNe laser to
measure the concentration of hexadecane in an aerosol shock tube. Boettcher et al. [18]
measured the concentration of hexane in low temperature hexane-air combustion to
understand the effect of heating rate. Sato and Hidaka [19] used HeNe laser to measure the
decay of acetone CH-compound formation rates in acetone pyrolysis and oxidation using a
shock tube. Tomita et al. [20] measured the concentration of the fuel near the spark plug in
spark ignition engines using a HeNe laser with a wavelength of 3.39 μm.
Inexpensive Helium Neon (HeNe) laser at 3.392 µm was previously used to find the absorption
cross-section of hydrocarbons. Olson et al. [21] reported the absorptivity of methane,
acetylene, ethylene, ethane, propane, n-butane and n-pentane in the temperature range of
300-2000 K using a shock tube. Mallard and Gardiner [5] studied the absorptivity of methane
from 300 to 2400 K using a shock tube. Tsuboi et al. [22] measured the molar extinction
43
coefficients of different hydrocarbons in the range of 292-1100 K using a shock tube. However,
the uncertainty in their measurements is about 20 %. Perrin and Hartmann [23] measured the
absorptivity of methane in the temperature range 290-800 K and then reported the calculated
absorptivity till 3000 K. Drallmeier [24] measured room temperature (296 K) absorption
coefficient of hydrocarbon species belong to paraffin, olefins and aromatics. The dependence of
absorption cross-sections on temperature and pressure at 3.39 µm was investigated by
Klingbeil et al. [6] for several hydrocarbons. The temperature range of the study was from 298
to 673 K and the pressure was from 500 to 2000 Torr. Mevel et al. [25] reported the absorption
cross-sections of 21 liquid hydrocarbons in temperature range of 303-413 K and then try to
relate the absorption cross-section of a species to the chemical structure.
In this work, the absorption cross-sections at 3.392 µm of methane, methanol, ethylene,
ethanol, ethane, propylene, propane, 1-butene, n-butane, n-pentane, n-hexane, and n-heptane
are studied. The temperature ranges from 296 to 800 K while the pressure is from 250 to 1000
Torr. The dependence of the absorption cross-sections on bath gas is reported for argon,
helium and nitrogen.
Table 4.1 shows the measured absorption cross-sections for the studied hydrocarbons at 296 K
with the three bath gases: argon, helium and nitrogen. Also, the table provides the purity of the
hydrocarbons, with the uncertainty of the measured values.
44
Absorption Cross-section (m2/mol)
Hydrocarbon Chemical Group Uncertainty, % Purity, %
Helium
Argon
Nitrogen
Methane
Alkane
3.9
99.999
26.4484
22.20117
20.76141
Ethane
Alkane
4.1
99.990
10.26926
10.1732
10.09835
Propane
Alkane
3.3
99.990
20.81252
19.9858
19.90691
n-Butane
Alkane
3.7
99.990
29.88516
29.80701
29.78105
n-Pentane
Alkane
4.1
98.000
33.67208
33.26361
33.09925
n-Hexane
Alkane
4.2
99.000
38.92369
38.98385
38.65275
n-Heptane
Alkane
4.3
95.000
44.03889
44.43525
44.15146
Ethylene
Alkene
3.1
99.950
0.44509
0.44265
0.43726
Propylene
Alkene
5.0
99.990
5.68903
5.68969
5.59279
1-Butene
Alkene
3.5
99.500
9.36804
9.39906
9.33582
Methanol
Alcohol
3.6
99.800
8.63045
8.53274
7.70099
Ethanol
Alcohol
4.0
99.800
6.7298
6.47772
6.2841
Table ‎4.1: The measured cross-sections of hydrocarbons with helium, argon and nitrogen as bath
gases at 296 K and 1 atm with uncertainty of the measurements and the purities of the
hydrocarbons.
45
4.2 Absorption Cross-sections of Methane
The cross-sections of methane (CH4) with helium, argon and nitrogen were measured at 3.392
µm in temperature range of 296-1045 K and pressure range of 200-1000 Torr, Figure 4.1. The
measured cross-sections agree with the available data. Perrin et al. calculated the crosssections beyond 800 K, and they also agree well with the measurements. The effect of
temperature is to reduce the absorption cross-section of methane because the number of
population in the ground state is reduced.
Absorption Cross Section (m2/mol)
30
This Work (with He)
This Work (with Ar)
This Work (with N2)
Klingbeil 2006
Perrin 1989
HITRAN 2008
25
20
15
10
5
0
200
300
400
500
600
700
800
900
1000 1100
Temperature (K)
Figure ‎4.1: Methane cross-section at 1 atm (X = 1% - 3%).
46
The line center of this rotational transition (P7) is 2947.9121 cm-1, whereas the center line of
the HeNe laser is 2947.909 cm-1, Figure 4.2.
1.0
0.9
T = 296 K
XCH4=1%
0.8
L = 7.747 cm
100 Torr
400 Torr
200 Torr
Absorbance
0.7
0.6
Laser Center line
o=2947.909 cm-1
P(7) center line
=2947.9121 cm-1
0.5
0.4
0.3
0.2
0.1
0.0
2947.86
2947.88
2947.90
2947.92
2947.94
2947.96
-1
Wavenumber (cm )
Figure ‎4.2: Locations of the rotational line of methane (P7) from HITRAN and the centerline of the
HeNe laser
The cross-sections of methane show dependence on the bath gas with highest values with
helium, then argon and lastly nitrogen, Figure 4.3. This trend is observed because the
collisional-broadening coefficient inversely related to the absorption cross-section. At this
transition (P7), the collisional-broadening coefficients of nitrogen and argon are 0.06302,
0.05621 cm-1/atm, respectively [26]. At 296 K, the pressure broadening of helium is less than
argon and nitrogen but at different wavelength from the HeNe laser [27].
47
80
N2
He
Ar
Methane
X~ 1%
T = 296 K
Cross Section (m2/mole)
70
60
50
40
30
20
10
0
200
400
600
800
1000
Pressure (Torr)
Figure ‎4.3: Pressure dependent absorption cross-sections of methane with Ar, He and N2 as bath
gases at T = 296 K.
The effect of the bath gas changes with temperature as expected, since the collisional
broadening coefficients are also temperature dependent. The absorption cross-sections of
methane are almost independent on bath gas in the range of 450 – 850 K. In the temperature
region from 850 to 1055 K, the cross-sections are the highest for argon then He and finally N2.
The cross-sections of methane depend on pressure, especially at lower pressures where the
cross-sections of methane are higher because of the Dicke Narrowing [26]. The cross-sections
tend to asymptotic value as pressure increases as shown also by Klingbeil et al. Finally, as
temperature increases, the dependence of cross-sections on pressure in minimized.
48
4.3 Absorption Cross-sections of Other Alkanes
The absorption cross-sections of five other alkanes are measured in temperature range of 296 –
800 K and pressure of 450 – 950 Torr. Although the methane cross-section at 3.392 µm is due
to one rotational line, the contribution to the absorption cross-sections of other alkanes is from
several mixed rotational lines, Figure 4.4. Therefore, the cross-sections are pressure
independent except for ethane and propane which show little pressure dependence. Also, their
dependence on bath gas is weaker than methane, because their higher molecular weights and
their broader spectral structures. The dependence on the bath gas decreases as the number of
C-H increases, but their behavior is similar to methane. The cross-sections of these
hydrocarbons increase as the number of C-H bonds increase.
Absorption Cross Section (m2/mole)
40
Ethane, Harrison et al. 2010
Propane, Harrison and Bernath 2010
n-Butane, FTIR
35
30
Laser Center line
o=2947.909 cm-1
25
20
15
10
5
0
2947.0
2947.5
2948.0
2948.5
2949.0
2949.5
2950.0
-1
Wavenumber (cm )
Figure ‎4.4: Locations of the HeNe laser centerline for ethane, propane and n-butane at 296 K.
49
The cross-sections of these alkanes show little dependence on temperature as presented in
previous studies. The centerline of the HeNe laser is neither in one of the bands to show huge
decrease in their absorptivity nor in their wings to increase it as temperature increases. The
temperature of the experiment is limited by the decomposition temperature of these species.
The measured cross-sections of ethane (C2H6) agree with Harrison and Bernath [28], Olson et al.
and Tsuboi et al. Figure 4.5. The uncertainty of the Tsuboi measurements is about 20 %. The
cross-sections are almost constant in the studied temperature range, 296-800 K.
Absorption Cross Section (m2/mole)
14
This Work (with He)
This Work (with Ar)
This Work (with N2)
Harrison 2010
Tsuboi 1985
Olson 1978
13
12
11
10
9
8
7
6
300
400
500
600
700
800
Temperature (K)
Figure ‎4.5: The cross-section of ethane at 1 atm (X= 10 %).
The dependence on the bath gas is weaker than methane since the mole fraction is high and
the spectrum is broad. The pressure broadening coefficients of nitrogen, argon and helium
reported by Blass et al. [29] at 12 µm are 0.090, 0.068 and 0.069, respectively. It appears that
50
the pressure broadening for the monoatomic inert gases, argon and helium, are similar, so their
cross-section is almost equal. The same behavior is noticed in the whole temperature ranges.
However, the pressure broadening of nitrogen, the diatomic gas, is higher and therefore its
cross-sections are lower at 296 and 387 K.
The absorption cross-sections of propane (C3H8) are in good agreement with Harrison et al. [30]
Klingebil et al., Tsuboi et al. and Olson et al., Figure 4.6. As ethane, the cross-section of propane
has little dependence on temperature and pressure. The pressure broadening coefficients at
296 K for nitrogen and helium at 784 cm-1 are 0.119 and 0.105, respectively [31].
30
This Wrok (with N2)
This Wrok (with Ar)
This Wrok (with He)
Harrison and Bernath 2010
Klingbeil 2006
Tsuboi 1985
Olson 1978
Absorption Cross Section (m2/mole)
28
26
24
22
20
18
16
14
12
10
300
400
500
600
700
800
Temperature (K)
Figure ‎4.6: Propane absorption cross-section at 1 atm (X = 1%).
The measured absorption cross-sections of n-butane, n-hexane, n-pentane and n-heptane are
show in Figures 4.7 to 4.10. Our n-butane (n-C4H10) data agree well with Olson et al., and show
little dependence on bath gas. However, since no available data for the pressure broadening
51
coefficients, it is apparent that the same trend of low molecule hydrocarbons is followed by nbutane. That is the nitrogen has the highest pressure coefficient and hence the broadest line,
followed by argon and lastly by helium.
Absorption Cross Section (m2/mole)
34
This Work (with He)
This Work (with Ar)
This Work (with N2)
Olson 1978
32
30
28
26
24
22
20
18
16
300
400
500
600
700
800
900
Temperature (K)
Figure ‎4.7: Absorption cross-section of n-butane at 1 atm (X = 5%).
The cross-sections of n-pentane (n-C5H12) agree with Mevel et al. while Tsuboi et al. and Olson
et al. have little higher cross-sections (a difference of 6 %). As for n-butane, the cross-sections
of n-pentane have little dependence on bath gas as well as on temperature. Also, it can be
concluded that nitrogen has the highest pressure broadening then argon and helium. More
interestingly, their order is the same in the range of 296 to 780 K, which indicate that their
temperature exponents are almost similar.
52
Absorption Cross Section (m2/mole)
38
This Work (with He)
This Work (with Ar)
This Work (with N2)
Mevel 2012
Tsuboi 1985
Olson 1978
36
34
32
30
28
26
24
300
400
500
600
700
800
Temperature (K)
Figure ‎4.8: n-pentane cross-section at 1 atm (X =2 %).
The measured cross-sections of n-hexane (n-C6H14) is 3.5 % above the values of Drallmeier et al.
and are 2.5 % and 5.8 % below the report cross-sections by Mevel et al. and Tsuboi et al.,
respectively. As in the case of butane and pentane, the cross-section of hexane has little
dependence on the bath gas with the same behavior of them. However, the cross-sections with
nitrogen are the highest in temperature ranges of 473 to 680 K indicating that its pressure
broadening is the lowest in this temperature range.
53
Absorption Cross Section (m2/mole)
46
This Work (with He)
This Work (with Ar)
This Work (with N2)
Mevel 2012
Drallmeier 2003
Tsuboi 1985
44
42
40
38
36
34
32
300
400
500
600
700
800
Temperature (K)
Figure ‎4.9: The cross-section of n-hexane at 1 atm (X~ 1.25 %).
The n-heptane (n-C7H16) absorption cross-sections are studied a lot due to its importance in
combustion environments. In this study, the measured cross-sections of heptane agree well
with Mevel et al., Sharpe et al. [32], are 16 % above Drallmeier et al. Drallmeier reported some
pressure dependence of the measured absorption cross-sections whereas they are
independent on pressure on other measurements. Our values are 5.0 % and 4.5 % below the
report cross-sections by Klingbeil et al. and Tsuboi et al., respectively. Since the molecular
weight of n- heptane is the largest, the influence of the bath gas on its cross-section is the least.
54
50
Absorption Cross Section (m2/mole)
48
46
44
42
40
This Work (with He)
This Work (with Ar)
This Work (with N2)
Mevel 2012
Klingbeil 2006
Sharpe 2004
Drallmeier 2003
Tsuboi 1985
38
36
34
32
30
300
400
500
600
700
800
Temperature (K)
Figure ‎4.10: Measured cross-section of n-heptane at 1 atm (X ~ 0.6 %).
4.4 Absorption Cross-sections of Alkenes
The absorption cross-sections of ethylene, propylene, and 1-butene are measured at 3.392 µm
with three different bath gases: argon, helium and nitrogen. The temperature ranges from 296
to 785 K, except for ethylene and propylene the maximum temperature is extended to 885 K.
The absorption cross-sections of these fuels are much less than that of alkanes because of the
decrease on the C-H bonds. No pressure dependence in the pressure range of 400 to 1000 Torr
was observed, except for ethylene which shows little pressure dependence. Since the
absorption is weak for these fuels, their mole fractions are increased to have large absorbance.
The cross-sections of the fuels mixed with helium have the highest values for all temperature
55
range, which indicate that their pressure broadening coefficients are the lowest in the studied
temperature range.
The cross-sections of ethylene (C2H4) increase with temperatures which agree with Klingbeil et
al., Figure 4.11. Since the absorption of ethylene is weak at HeNe laser wavelength, the mole
fraction is increased to have enough absorbance. Even with this high mole fraction, there is
little dependence on the bath gas. The broadening coefficients at 949.113 cm-1 for nitrogen,
argon and helium are 0.0687, 0.0557 and 0.0493 cm-1 atm-1, respectively [33]. Regardless of the
difference on the wavelength, the absorption cross-sections at HeNe laser wavelength are the
highest for helium, then argon and nitrogen. This indicates that the line with nitrogen is broader
while it is the narrower with helium in the studied temperature range.
Absorption Cross Section (m2 /mol)
1.0
0.9
0.8
0.7
0.6
0.5
This Work (with He)
This Work (with Ar)
This Work (with N2)
Klingbeil 2006
0.4
0.3
300
400
500
600
700
800
900
Temperature (K)
Figure ‎4.11: Ethylene cross-section at 1 atm (X= 50 %).
56
The absorption cross-sections of propylene (C3H6) have little dependence on temperature in the
studied temperature range, Figure 4.12.
Absorption Cross Section (m2/mole)
7.0
This Work (with He)
This Work (with Ar)
This Work (with N2)
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
200
300
400
500
600
700
800
900
Temperature (K)
Figure ‎4.12: Cross-section of propylene at 1 atm (X= 10 %).
The absorption cross-sections of 1-butene (1-C4H8) cross-sections are almost constant in the
range 296-780 K, Figure 4.13.
Absorption Cross Section (m2/mole)
12.0
This Work (with He)
This Work (with Ar)
This Work (with N2)
11.5
11.0
10.5
10.0
9.5
9.0
8.5
8.0
300
400
500
600
700
800
T (K)
Figure ‎4.13: 1-butene cross-section at 1 atm (X= 5 %).
57
Both propylene and 1-butene have no dependence on the bath gas, because of their broad
spectra.
4.5 Absorption Cross-Sections of Alcohol
The measured cross-sections of methanol (CH3OH) agree well with Tsuboi et al, Figure 4.14. The
cross-sections are independent on temperature from 470 to 785 K. However, they depend on
the bath gas in the temperature range 296 – 585 K. It has the highest value with helium then
argon and finally nitrogen which result in having nitrogen as the broader line.
Absorption Cross Section (m2/mole)
12
This Work (with He)
This Work (with Ar)
This Work (with N2)
Tsuboi 1985
11
10
9
8
7
6
5
4
3
2
300
400
500
600
700
800
Temperature (K)
Figure ‎4.14: Methanol cross-section at 1 atm (X = 2.5 %).
The ethanol (CH3CH2OH) cross-sections are obtained in temperature range of 296-780 K, Figure
4.15. The measurements agree well with Tsuboi et al. and Mevel et al. and show little
58
dependence on temperature in the range of 296 - 573 K. It shows less bath gas dependence
than methanol since it molecular weight is higher.
Absorption Cross Section (m2/mole)
12
This Work (with He)
This Work (with Ar)
This Work (with N2)
Mevel 2012
Tsuboi 1984
10
8
6
4
300
400
500
600
700
800
Temperature (K)
Figure ‎4.15: Cross-section of ethanol at 1 atm (X= 1.15 %).
4.6 Absorption Cross-sections Comparison
The studied fuels belong to three different chemical groups: alkanes, alkenes and alcohol. The
cross-sections at the HeNe laser wavelength for the alkanes are the highest, followed by
alcohols and lastly by alkenes. For alkanes, the absorption cross-sections are almost linearly
dependent on the C-H bonds, except for methane which shows higher values than ethane and
propane. Similar results are observed for alkenes with lower magnitude of their absorption
cross-sections. For alcohol, ethanol has higher absorption cross-sections than methanol except
at 296 and 385 K.
59
Figure 4.16 and 4.17 compare the cross-sections of the hydrocarbons with different bath gas at
296 and 773 K, respectively.
Absorption Cross Section (m2/mole)
50
45
He
Ar
N2
X~0.5 %
40
X~1.25 %
35
T = 296 K
P = 760 Torr
X~2 %
X~5 %
30
X~1 %
25
X~1 %
20
15
X~10 %
10
X~5 %
X~2.5 %
X~2.5 %
X~10 %
5
X~ 50 %
0
CH4
C2H6
C3H8 C4H10 C5H12 C6H14 C7H16 C2H4
C3H6 1-C4H8 CH3OHC2H5OH
Compound
Figure ‎4.16: The cross-section of the studied hydrocarbons at 1 atm and 296 K with 3 different bath
gases. X is the mole fraction of the hydrocarbon.
60
Absorption Cross Section (m2/mole)
45
He
Ar
N2
X~ 0.5 %
40
X~1.25 %
35
30
T ~ 773 K
P = 760 Torr
X~2 %
X~5 %
25
20
X~1 %
15
X~3 %
10
X~5 %
X~10 %
X~2.5 %
X~10 %
5
X~2.5 %
X~50 %
0
CH4
C2H6
C3H8 C4H10 C5H12 C6H14 C7H16 C2H4
C3H6 1-C4H8 CH3OHC2H5OH
Compound
Figure ‎4.17: The cross-section of the studied hydrocarbons at 1 atm and 773 K with 3 different bath
gases. X is the mole fraction of the hydrocarbon.
The absorption cross-sections of small hydrocarbons; methane, methanol and ethylene show
dependence on that bath gas (helium, nitrogen and argon). They show similar behavior in the
ranges of temperature and pressure in this thesis. The effect of helium is to increase the crosssections since it has the lowest pressure broadening coefficient. Argon has lower pressure
broadening coefficient compared to nitrogen in most temperature ranges, so it has the higher
absorption cross-sections. Nitrogen, on the other hand, has the smallest absorption crosssections because of its highest pressure broadening coefficient.
61
Chapter 5
5 Absorption Cross-section of Propylene using DFG Laser
5.1 Literature Review
Difference Frequency Generation (DFG) lasers have been developed to produce tunable mid-IR
lasers [34, 35]. The first continuous DFG laser was made in 1974 by mixing argon and tunable
dye lasers in LiNbO3 to produce laser in the region of 2.2 – 2.4 µm [36]. It was demonstrated to
detect water vapor, ammonia, methane, and nitrous oxide. After that, there has been a lot of
advances for the DFG laser [7].
The applications of DFG laser for combustion applications are very promising because of the
strong C-H stretch in the range of the DFG laser. Also, the DFG laser is tunable and has very
narrow linewidth which allow accurate detection of a specific species with free-interference
from others. Klingbeil et al. used a tunable DFG to measure species concentrations of MCH,
during its decomposition in a shock tube [37]. They also measured the vapor concentration of
n-dodecane using differential absorption technique in a shock-heated evaporating aerosol.
Furthermore, Klingbeil et al. used two-wavelength DFG laser to simultaneously measure the
temperature and n-heptane concentrations in a shock tube [38]. Porter et al. developed a midIR laser techniques using DFG laser to measure the vapor phase concentration of n-decane as
well as the liquid fuel film thickness of n-dodecane [39]. The DFG laser was used by Pyan et al.
to measure the concentration of gasoline and the temperature of the gas in internal
combustion engines [40]. Finally, DFG laser was used to detect methane concentration in shock
62
tube during the pyrolysis of 1-butanol [41], n-butane and n-heptane pyrolysis [42] and dimethyl
ether (DME) pyrolysis [43]. Van Helden et al. used DFG laser for probing methane, ethane,
acetylene and ethylene plasmas [44].
In this work, DFG laser in the region of 2850 – 2975 cm-1 is used to find the cross-sections of
propylene from 296 to 440 K. Seven wavelengths are chosen in this study, and the measured
quantities are compared to the FTIR results.
5.2 Phase-Matching Conditions
As stated in Section 3.2, the DFG laser power is very weak i.e. 600 µW, and it has to be phasematched in order to achieve this power. Phase-matching occurs when the interacting waves
from the two NIR lasers are in phase during their travel in the nonlinear crystal [35]. The phasematching can be adjusted by either altering the signal laser wavelength (replaceable DFBs) or
the temperature of the PPLN crystal. The wavelength can be changed by changing either
current or temperature of the signal. Since the PPLN temperature changes relatively slowly, the
signal laser is initially selected to find the optimal phase-matching condition, and then
iteratively adjust the PPLN and signal laser together to achieve the desired mid-IR wavelength.
To find the optimal condition, the signal laser temperature is simply adjusted up or down in 1 oC
increments while watching the output power.
In this study, seven wavelengths are selected to find the cross-sections of propylene. These
wavelengths are spread along the range of the two units, and chosen for peak locations as well
63
as valleys in the propylene spectra. The phase-matching conditions of the seven wavelengths
are listed in Table 5.1.
Wavelength (cm-1)
DFG
Unit
PPLN Temp.
(oC)
Signal Temp.
(oC)
Signal Current
(mA)
Set Current
(mA)
2854.83
114
33.0
40.0
250
7,500
2867.91
114
50.0
32.1
219
6,200
2915.67
113
21.7
27.3
200
7000
2918.38
113
24.0
34.2
200
7000
2931.45
113
34.0
30.7
200
6,200
2931.69
113
30.9
35.0
209
6,200
2950.87
113
49.7
40.0
228
7,000
Table ‎5.1: Phase-Matching conditions for the selected wavelengths in this study.
5.3 The Cross-sections of Propylene
The cross-sections of propylene (C3H6) at the selected wavelengths are shown in Figure 5.1. At
each individual wavenumber, a series of measurements were performed at four pressures and
the cross-sections obtained at the various pressures were averaged with standard deviation of
less than 5% of the mean value.
64
Absorption CrossSection (cm2/molecule)
2.00E-019
2931.49 cm-1
2931.67 cm-1
2867.91 cm-1
2854.83 cm-1
2950.87 cm-1
2915.67 cm-1
2918.38 cm-1
1.50E-019
1.00E-019
5.00E-020
0.00E+000
280
300
320
340
360
380
400
420
440
Temperature (K)
Figure ‎5.1: Absorption cross-sections of propylene at the seven locations.
The cross-sections of propylene change with temperature depending on wavelength of the DFG
laser. For the peaks positions (2931.49, 2950.87, 2967.91 and 2931.67 cm-1) the absorption
cross-sections decrease as the temperature increase because the number of population in the
ground state decreases. However, for the valley at 2854.83 cm-1, the cross-sections increase as
the temperature increase because of more population at higher temperatures. Two locations
(2915.67 and 2918.38 cm-1) show constant cross-sections over the studied temperature range.
Their locations are neither in the peak nor in the valley, so their absorption cross-sections
independent on temperature. The IR absorption cross-sections of propylene obtained by FTIR
are compared with the DFG laser system at the three temperatures, Figure 5.2.
2
-19
5.0x10
-20
2.0x10
-19
1.5x10
-19
1.0x10
-19
5.0x10
-20
2.0x10
-19
1.5x10
-19
1.0x10
-19
5.0x10
-20
0.0
2850
2915.67 cm
-1
2918.38 cm
-1
0.0
2850
2867.91 cm
-1
0.0
2850
-1
1.0x10
(a) 296 K
2931.69 cm
-19
-1
1.5x10
2931.45 cm
-19
-1
2.0x10
2854.83 cm
C3H6 cross-section, cm /molecule
65
-1
2950.87 cm
2875
2900
2925
2950
2975
2925
2950
2975
2950
2975
(b) 343 K
2875
2900
(c) 389 K
2875
2900
2925
Wavenumber, cm
-1
Figure ‎5.2: The FTIR and DFG cross-sections of propylene over the 2850 – 2975 cm-1 range at three
different temperatures: (a) 296 K, (b) 343 K and (c) 383 K. The symbols show the results obtained by
the DFG system. (Permission is taken from the author)
The results from the FTIR and DFG measurements are in good agreement with a maximum
difference of about 10 %. One reason is that, the spectral resolution of the FTIR measurements
is 0.08 cm-1 while it is about 0.0001 cm-1 for the DFG laser.
For example, the FTIR couldn’t capture the peak at 2950.87 cm-1 in especially at low
temperatures, Figure 5.3. This could conclude that the linewidth of the propylene at this
wavelength is higher than the FTIR resolution at 296 K. However, at higher temperature the
66
line-width of the propylene increases as in Equation (10), and hence the difference between the
measured values from DFG and FTIR is smaller.
Absorption Cross Section (cm2/molecule)
2.50E-019
DFG
FTIR
 = 2950.87 cm-1
2.00E-019
1.50E-019
1.00E-019
5.00E-020
280
300
320
340
360
380
400
420
440
Temperature (K)
Figure ‎5.3: The cross-sections from the DFG laser and the FTIR at 2950.87 cm-1.
On the other hand, at other wavelengths the cross-sections are the same for the DFG laser and
the FTIR because the FTIR resolution is sufficient to resolve the spectra. For example, at
2867.91 cm-1 the absorption cross-sections from the DFG laser agree well with the ones from
the FTIR, Figure 5.4.
67
Absorption Cross Section (cm2/molecule)
5.50E-020
DFG
FTIR
5.00E-020
 = 2867.91 cm-1
4.50E-020
4.00E-020
3.50E-020
3.00E-020
2.50E-020
2.00E-020
280
300
320
340
360
380
400
Temperature (K)
Figure ‎5.4: The cross-sections from the DFG laser and the FTIR at 2867.91 cm-1.
68
Chapter 6
6 Hydrocarbon Spectra using FTIR Spectrometer
6.1 Literature Review
The IR spectrum of a species is measured using the Fourier Transform Infrared (FTIR)
spectrometer. It is important for researchers in the combustion field because it helps in
selecting free-interference wavelength for laser diagnostics. FTIR was used to select the best
wavelength for methane detection in a shock tube during n-heptane pyrolysis [45]. Klingbeil et
al. used FTIR to measure n-heptane spectra as a function of temperature to select the best two
wavelengths to sensitively measure the temperature and concentration in a shock tube [38].
Therefore, the temperature-dependent spectra of important species in combustion
environment (i.e. methane and ethylene) are required to select candidate wavelength for laser
diagnostics application. Klingebiel et al. reported the spectra of twelve hydrocarbons in
temperature range of 298 – 773 K [46]. The spectral range is 2500–3400 cm−1 with 1 cm−1
resolution. Es-sabbar et al. measured the IR spectra as well as the VUV spectra of 1-butene in
temperature range of 296 – 529 K [9]. Etzkorn et al. measured the UV and IR cross-sections of
24 aromatic hydrocarbons at [47]. From HITRAN database, the infrared absorption crosssections of ethane at 296 K is reported by Harrison et al. [28]. Also, Harrison and Bernath
measured the infrared absorption cross-section of propane at 296 K [30].
69
There are many worldwide database for hydrocarbons spectra, such as HITRAN (HighResolution Transmission Molecular Absorption Database) [48], NIST (National Institution of
Standard and Technology) [49] and PNNL (Pacific Northwest National Laboratory) [32]. The
HITRAN database contains the spectral parameters for 39 low molecular-weight gases, as well
as the infrared absorption cross-sections of 40 other molecules at low temperatures. The NIST
and the PNNL databases provide the absorption cross-sections of many species, but at low
temperature (up to 50 oC). Therefore, the cross-sections of hydrocarbons at high temperatures
are crucial and should be known for combustion applications.
In this study, the spectra of methane, methanol, acetylene, ethylene, ethane, ethanol,
propylene, 1-butene, propane, n-butane, n-pentane, n-hexane and n-heptane are measured.
The studied spectral region is at the fundamental region (2800 – 3400 cm-1, or 2.9 - 3.7 µm)
with spectral resolution of 0.6 cm-1. The temperature varies from 673 to 1100 K which is the
temperature at which fast pyrolysis of most hydrocarbons occurs. The integrated band intensity
which is independent on temperature is also calculated in this region. Table 6.1 compares the
integrated band intensities for the studied hydrocarbons found in this work to that from Sharpe
et al. Also, the mole fraction of the studied fuels and the estimated uncertainties of the
measured integrated band intensity are included.
70
Hydrocarbon
Chemical
Group
Uncertainty,
%
Tmax (K)
Integrated Band Intensity in the
range 2800-3400 cm-1
(x10-17 cm2/molecule.cm)
This Work
Sharpe et al.
(298 K)
Methane
Alkane
4.2
1,120
1.02
1.10
Ethane
Alkane
4.3
1,055
2.77
2.84
Propane
Alkane
3.6
1,055
3.99
3.99
n-Butane
Alkane
3.7
921
4.99
5.00
n-Pentane
Alkane
5.3
920
5.87
6.02
n-Hexane
Alkane
5.2
920
6.83
7.00
n-Heptane
Alkane
5.5
920
7.94
7.99
Acetylene
Alkyne
4.8
1,055
1.14
1.19
Ethylene
Alkene
3.1
1,055
0.70
0.69
Propylene
Alkene
4.7
1,055
1.58
1.68
1-Butene
Alkene
3.3
923
2.70
2.81
Methanol
Alcohol
3.6
1,040
2.00
2.04
Ethanol
Alcohol
4.0
1,040
2.20
2.20
Table ‎6.1: The mole fraction, maximum temperature as well as the calculated integrated band
intensity of the studied hydrocarbons compared to Sharpe et al.
71
6.2 Mid-IR Spectra of Alkanes
The spectra of normal alkanes in the mid-IR are measured in temperature range of 673 to 1100
K. The spectra show dependence on temperature result in a decrease of their peaks with
increase of their wings. Methane spectra are narrow because of the contribution from the
rotational lines whereas the spectra are broad for high molecular weight alkanes, such ethane.
The integrated band intensities are also measured and found to increase as the number of the
C-H bond increases.
The spectra methane with the assignment of its fundamental frequency in the IR region (v3 =
3020.3 cm-1) is shown in Figure 6.1.
Absorption Cross Section (cm2/molecule)
2.00E-018
673 K
773 K
921 K
1060 K
1120 K
1.50E-018
1.00E-018
Q-branch
5.00E-019
R-branch
P-branch 3
0.00E+000
2800
2900
3000
3100
3200
3300
3400
Wavenumber (cm-1)
Figure ‎6.1: The spectra of methane in the mid-IR showing the origin of the band and the P,Q and R
branches.
72
For methane, there are four IR fundamental frequencies but only two are actives: ν3 at 3020.3
cm-1 and ν4 at 1306.2 cm-1 [2]. The ν3 band has three branches: P, Q and R. As temperature
increases, higher rotational levels are populated that result in new rotational lines. The Rbranch has the highest potential for performing methane-time histories for combustion
applications because of their highest absorption cross-sections.
The integrated band intensity of methane is obtained and compared to Sharpe et al. and
Klingbeil [50], Table 6.2. Our measured intensities over the studied range of temperature show
good agreement with the available literature.
T (K)
673
773
921
1060
1120
This Work
9.32 E-18
1.04 E-18
9.32 E -18
1.15 E -17
1.12 E -17
Sharpe et al. (298 K)
Klingbeil (298 K)
1.10 E-17
1.18 E-17
Table ‎6.2: Integrated band intensities of methane at different temperatures compared to Sharpe et
al. and Klingbeil.
Ethane spectrum is broad and has some rotational fine lines near the fundamental band ν 7,
Figure 6.2. Ethane has two fundamental frequencies in the infrared region ν 7 and ν5 centers of
2995.5 and 2895.5 cm-1, respectively [2]. The effects of temperature are to decrease the peak
and increase the wings with minimizing the fine rotational lines at the ν 7. The highest
temperature spectrum was smoothed since there was some noise near the two wings.
However, the integrated band intensity at 1055 K has little changes and is comparable to the
other temperatures and available data, Table 6.3.
73
Absorption Cross Section (cm2/molecule)
3.50E-019
673 K
773 K
921 K
1055 K
7
3.00E-019
2.50E-019
2.00E-019
5
1.50E-019
1.00E-019
5.00E-020
0.00E+000
2800
2900
3000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.2: Cross-section of Ethane at 1 atm (X ~ 10 %).
T (K)
673
773
921
1055
This Work
2.87 E-17
2.84 E-17
2.78 E -17
2.69 E -17
Sharpe et al. (298 K)
Klingbeil (298 K)
2.84 E-17
2.81 E-17
Table ‎6.3: Integrated band intensities of ethane at different temperatures compared to Sharpe et al.
and Klingbeil.
The spectra of propane are also broader, Figure 6.3, with two strong bands: ν15 and ν22 at 2885
and 2980 cm-1, respectively [2]. At higher temperature, the peaks of the two bands decrease
but the two sides are increased since higher levels are populated.
74
Absorption Cross Section (cm2/molecule)
5.00E-019
15
676 K
772 K
921 K
4.00E-019
22
3.00E-019
2.00E-019
1.00E-019
0.00E+000
2800
2900
3000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.3 Propane cross-section at 1 atm (X ~ 10 %).
Table 6.4 shows the integrated band intensity of propane which agrees with Sharpe et al. with a
difference of less than
1.5 %.
T (K)
676
772
921
This Work
3.95 E-17
3.96 E-17
4.05 E -17
Sharpe et al. (298 K)
3.99 E-17
Table ‎6.4: Integrated band intensities of propane at different temperatures compared to Sharpe et
al.
75
N-butane spectrum has a peak at 2960 cm-1, and its cross-section decreases as the temperature
increases due to depopulation, Figure 6.4. The integrated band intensities are in agreement
Absorption Cross Section (cm2/molecule)
with Sharpe et al., Table 6.5.
6.00E-019
669 K
781 K
920 K
5.00E-019
4.00E-019
3.00E-019
2.00E-019
1.00E-019
0.00E+000
2800
2900
3000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.4: Cross-section of n-butane at high temperatures.
T (K)
669
781
920
This Work
5.02 E-17
4.91 E-17
5.04 E-17
Sharpe et al. (298 K)
5.00 E-17
Table ‎6.5: Integrated band intensities of n-butane compared with Sharpe et al.
Figure 6.5 shows n-pentane spectrum where the peak absorption occurs at 2954 cm-1. The
same temperature effects are noticed on n-pentane spectra with decreasing of the peak and
increasing of the sides. The integrated band intensities of n-pentane is presented in Table 6.6
and have difference of less than 4 % and 3 % with Sharpe et al. and Klingbeil et al. respectively.
Absorption Cross Section (cm2/molecule)
76
7.00E-019
670 K
781 K
921 K
6.00E-019
5.00E-019
4.00E-019
3.00E-019
2.00E-019
1.00E-019
0.00E+000
2800
2900
3000
3100
3200
3300
3400
Wavenumber (cm-1)
Figure ‎6.5: n-pentane spectra at high temperatures.
T (K)
670
781
921
This Work
5.91 E-17
5.84 E-17
5.86 E-17
Sharpe et al. (298 K)
Klingbeil et al. (298 K)
6.12 E-17
6.02 E-17
Table ‎6.6: Integrated band intensities of n-pentane at different temperatures compared to Sharpe et
al. and Klingbeil et al.
N-hexane spectrum has similar shape as n-butane and n-pentane, but with peak absorption at
2935 cm-1, Figure 6.6. The measured integrated band intensities are shown in Table 6.7 and
have a difference of less than 3 % with Sharpe et al.
Absorption Cross Section (cm2/molecule)
77
8.00E-019
766 K
863 K
920 K
6.00E-019
4.00E-019
2.00E-019
0.00E+000
2800
2900
3000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.6: Cross-section of n-hexane at high temperatures.
T (K)
766
863
920
This work
6.85 E-17
6.80 E-17
6.84 E-17
Sharpe et al. (298 K)
7.00 E-17
Table ‎6.7: Integrated band intensities of n-hexane compared to Sharpe et al.
Figure 6.7 presents the cross-sections of n-heptane in the range of 2800 – 3400 cm-1. The
dependence on temperature is similar to the previous alkanes. The integrated band intensities
in this spectral range are also measured and agree well with Sharpe et al. and Klingbeil et al.,
Table 6.8.
Absorption Cross Section (cm2/molecule)
78
1.00E-018
682 K
776 K
925 K
8.00E-019
6.00E-019
4.00E-019
2.00E-019
0.00E+000
2800
2900
3000
3100
3200
-1
Wavenumber (cm )
Figure ‎6.7: n-heptane spectra in the mid-IR at high temperatures.
T (K)
682
776
925
This Work
8.03 E-17
7.95 E-17
8.04 E-17
Sharpe et al. (298 K)
Klingbeil et al. (298 K)
7.99 E-17
7.99 E-17
Table ‎6.8: Integrated band intensities of n-heptane at different temperatures compared to Sharpe et
al. and Klingbeil et al.
The spectra of the above studied alkanes at 673 K are compiled in Figure 6.8 to see the effects
of increasing the C-H bond on the spectrum. First, the structure of the spectra moves from fine
lines for methane to broad one for n-butane and heavier hydrocarbons. The structure of ethane
and propane combine the fine structure like methane as well as broad spectra like n-butane.
Therefore, since small alkanes have less vibrational modes, their rotational lines have more
79
tendencies to be isolated. Second, the peak position of the spectra propagates to lower
wavenumbers as the number of C-H increases.
Absorption cross section (cm2/molecule)
2.00E-018
n-heptane
n-hexane
n-pentane
n-butane
propane
ethane
methane
1.50E-018
The peak position
1.00E-018
T ~ 673 K
5.00E-019
0.00E+000
2800
2900
3000
3100
3200
3300
3400
Wavenumber (cm-1)
Figure ‎6.8: The spectra of the studied alkanes at 673 K.
6.3 Mid-IR Spectra of Alkenes and alkyne
Alkenes and alkynes are important hydrocarbons result from incomplete combustion and play
major industrial rules. One alkyne: acetylene and three alkenes: ethylene, propylene and 1butene are studied to determine the mid-IR spectra at high temperatures. The absorption
cross-sections of these hydrocarbons are measured in temperature range of 673 – 1100 K.
80
The spectrum of acetylene is measured in the range of 3100 – 3400 cm-1 at temperatures of
673, 773, 922 and 1055 K, Figure 6.9. This band is the fundamental ν3 which has an origin at
3287 cm-1 and P- and R-branch [51]. As in methane, the R-branch has higher absorption
magnitude compared to the P-branch.
Absorption Cross Section (cm2/molecule)
3.75E-019
3.00E-019
R-branch
673 K
773 K
923 K
1055 K
P-branch
2.25E-019

1.50E-019
7.50E-020
0.00E+000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.9: Cross-sections of acetylene at ~ 400 Torr ( X ~ 18 %).
The integrated band intensities of acetylene are measured at different temperatures, and they
fairly agree with Sharpe et al., Table 6.9.
T (K)
673
773
923
1055
This Work
1.17 E-17
1.15 E-17
1.22 E-17
1.03 E-17
Sharpe et al. (298 K)
1.19 E-17
Table ‎6.9: Integrated band intensities of acetylene at different temperatures agree with Sharpe et al.
81
Figure 6.10 shows ethylene spectra at different temperatures. The two fundamental bands are
ν11 and ν9 at 2989.5 and 3105.5 cm-1, respectively [2]. As the temperature increases, the fine-
Absorption Cross Section (cm2/molecule)
structure lines decreases while the spectrum base increases.
1.20E-019
673 K
773 K
920 K
1055 K
1.00E-019
11
8.00E-020
9
6.00E-020
4.00E-020
2.00E-020
0.00E+000
2900
3000
3100
3200
3300
-1
Wavenumber (cm )
Figure ‎6.10: Cross-section of ethylene at 1 atm (X ~ 40 %).
The integrated band intensities are measured from the spectra and their values agree with
Sharpe et al., Table 6.10.
T (K)
673
773
920
1055
This Work
6.92 E-18
6.98 E-18
6.94 E-18
7.07 E-18
Sharpe et al. (298 K)
Klingbeil (298 K)
6.92 E-18
7.20 E-18
Table ‎6.10: Integrated band intensities of ethylene at different temperatures compared to Sharpe et
al. and Klingbeil.
82
The spectra of propylene at higher temperatures are measured in the spectra region of 2800 –
3400 cm-1, Figure 6.11. There are four fundamental bands in the studied region which are 1, 3,
Absorption Cross Section (cm2/molecule)
5, 15 with peak positions at 3091, 2991, 2931 and 2952 cm-1, respectively [2].
1.20E-019

675 K
773 K
920 K
1.00E-019
8.00E-020


6.00E-020
4.00E-020
2.00E-020
0.00E+000
2800
2900
3000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.11: Propylene cross-sections at high temperatures.
The integrated band intensities agree with the available data with difference of less than 6 %,
Table 6.11.
T (K)
766
863
920
This Work
1.60 E-17
1.58 E-17
1.68 E-17
PNNL (298 K)
Es-sebbar (298 K)
Klingbeil (298 K)
1.68 E-17
1.63 E-17
1.66 E-17
Table ‎6.11: Integrated band intensities of propylene at different temperatures compared to Es-sebar
et al.[52], Sharpe et al. and Klingbeil et al.
The spectra of 1-butene at four temperature values are plotted in Figure 6.12 and the
absorption at the peak at 2960 cm-1 decreases as the temperature increases.
Absorption Cross Section (cm2/molecule)
83
2.50E-019
673 K
779 K
925 K
2.00E-019
1.50E-019
1.00E-019
5.00E-020
0.00E+000
2900
3000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.12: Mid-IR spectra of 1-butene at high temperatures.
The integrated band intensities are calculated from the spectra and found to be in agreement
with the available data, Table 6.12.
T (K)
673
779
925
This Work
2.74 E-17
2.73 E-17
2.74 E-17
Sharpe et al. (298 K)
Es-sebbar et al. (298 K)
Klingbeil (298 K)
2.81 E-17
2.75 E-17
2.81 E-17
Table ‎6.12: Integrated band intensities of 1-butene at different temperatures compared to Sharpe et
al., Es-sebar et al. and Klingbeil.
Figure 6.13 contains the spectra for alkene: ethylene, propylene and 1-butene at 673 K. The
same conclusions for the trends of these alkenes can be made as the behavior of alkanes. The
absorption cross-sections increase as the molecular weight increases. Also, the ethylene
spectrum has fine structure whereas the spectra of propylene and 1-butene are broad.
84
Absorption cross section (cm2/molecule)
2.50E-019
ethylene
propylene
1-butene
2.00E-019
T ~ 673 K
1.50E-019
1.00E-019
5.00E-020
0.00E+000
2800
2900
3000
3100
3200
3300
3400
Wavenumber (cm-1)
Figure ‎6.13: Comparison between the spectra of the studied alkenes at 673 K.
6.4 Mid-IR Spectra of Alcohol
Alcohols are organic compound having OH bond connected to the C atom. They have different
properties than alkanes and alkenes, but they still interact with light at mid-IR region because
of the C-H bonds. High temperature spectra of methanol and ethanol are measured in 2800 –
3400 cm-1 at high temperatures.
The spectra of methanol at high temperatures are shown in Figure 6.14. There are four peaks in
this region which are ν2, ν3+ν6 ν5, 2ν6 and ν2 with values of 2844, 2914, 2949 and 2977 cm-1,
respectively [2]. The integrated band intensities in 2750 - 3400 cm-1 band are calculated and
found in good agreement with Sharpe et al, Table 6.13.
Absoprtion Cross Section (cm2/molecule)
85
1.60E-019

1.40E-019
+
1.20E-019
676 K
783 K
923 K


1.00E-019
8.00E-020
6.00E-020
4.00E-020
2.00E-020
0.00E+000
2800
2900
3000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.14: The cross-sections of methanol at high temperatures.
T (K)
676
778
923
This Work
2.06 E-17
2.02 E-17
2.04 E-17
Sharpe et al. (298 K)
2.04 E-17
Table ‎6.13: Integrated band intensities of methanol at different temperatures compared to Sharpe
et al.
Figure 6.15 presents the spectra of ethanol at 669, 775 and 920 K in the spectral range of 2800
– 3400 cm-1. The absorption peak occurs at 2953 cm-1 and the peak decreases as the
temperature increases. The integrated band intensities of ethanol are obtained at 669 and 775
K, and found to have a difference of less than 3 % compared to Sharpe et al, Table 6.14.
Absorption Cross-Section (cm2/molecule)
86
669 K
778 K
920 K
1.60E-019
1.20E-019
8.00E-020
4.00E-020
0.00E+000
2800
2900
3000
3100
3200
3300
3400
-1
Wavenumber (cm )
Figure ‎6.15: The spectra of ethanol at elavated temperatures.
T (K)
669
778
920
This Work
2.22 E-17
2.04 E-17
1.90 E -17
Sharpe et al. (298 K)
Klingbeil (298 K)
2.20 E-17
2.07 E-17
Table ‎6.14: Integrated band intensities of ethanol at different temperatures compared to Sharpe et
al. and Klingbeil.
Figure 6.16 presents the integrated band intensities of the studied fuels. The integrated band
intensity increases with the number of the C-H bond, because the spectra at this region are
primarily due to the C-H stretching vibration.
9.00E-017
8.00E-017
7.00E-017
6.00E-017
5.00E-017
4.00E-017
3.00E-017
2.00E-017
1.00E-017
ethanol
methanol
1-butene
propylene
ethylene
acetylene
heptane
hexane
pentane
butane
propane
ethane
0.00E+000
methane
Integrated Band Intensity (cm2 molecule-1cm-1)
87
Compound
Figure ‎6.16: The integrated band intensities of the studied hydrocarbons.
For alkanes and alkene, the increase of the band intensity is almost linear with the number of
the C-H bonds, except for methane, Figure 6.17. The slope for this linear relation is 5.0 E-17.
However, for alcohol, the integrated band intensities of methanol and ethanol are almost
similar which indicate that the C-H bond in alcohol is saturated.
Integrated Band Intensity (cm2 molecule-1cm-1)
88
8.00E-017
Alkane
Methane
Alkene
Alcohol
Acetylene
6.00E-017
S=NC-H5.035E-17
4.00E-017
S=NC-H1.7E-17
2.00E-017
S=NC-H5.005E-17
0.00E+000
0
2
4
6
8
10
12
14
16
Number of C-H Bonds
Figure ‎6.17: The relations of the integrated band intensities for the studied hydrocarbons.
The relations between the number of the C-H bonds and the integrated band intensities can be
used to predict/check the spectra of blended fuels [46].
89
Chapter 7
7 Conclusion and Future Work
7.1 Summary
The absorption cross-sections of 13 hydrocarbons are measured at high temperatures in the
mid-IR region. The temperature ranges from 296 to 1100 K while the pressure is from 300 to
1000 Torr. Three laser systems were used in the experiment for obtaining the absorption crosssections of methane, methanol, acetylene, ethylene, ethane, ethanol, propylene, propane, 1butene, n-butane, n-pentane, n-hexane and n-heptane.
The first part of this thesis focuses on measuring the absorption cross-sections at 3.39 µm using
HeNe laser for 12 hydrocarbons representing different chemical groups: alkanes, alkenes and
alcohols. The quartz cell placed in the furnace allows the measurement temperatures to vary
from 296 K till the decomposition temperature of the species which is below 1,100 K. While
methane shows strong temperature and pressure dependence, the other hydrocarbons
experience weak temperature dependence and little/no pressure dependence. Three
perturbers: helium, argon and nitrogen, are selected to know the effect of the bath gas on the
absorption cross-sections. The absorption cross-sections depend on the bath gas for methane,
ethylene and methanol gases. The absorption cross-sections of the fuel with helium have higher
values because of the low pressure broadening coefficients for helium, followed by argon and
lastly by nitrogen. On the contrary, higher molecular weight fuels have little dependence on the
bath gas. This study explains the relation between the pressure broadening coefficient and the
90
absorption cross-sections. For alkanes, the absorption cross-sections are higher than alkenes
and alcohols because of higher number of C-H bonds. The cross-sections of alkanes, alkenes
and alcohol increase as the molecular weight increases in the studied temperature ranges
except for alcohol (methanol and ethanol) in temperatures less than 400 K. This study extends
the absorption cross-sections at 3.39 µm to higher temperatures similar to those in practical
combustions environments.
Due to the advancements in the DFG systems, a tunable mid-IR laser is made based on the
difference of two collimated lights on a PPLN crystal. At KAUST, two units of a DFG laser are
available with tenability region of 3.35 to 3.53 µm. The DFG laser is utilized to measure the
cross-sections of propylene at seven different wavelengths. The dependence of these crosssections on temperature is studied from 296 to 460 K. For peak positions, the cross-sections
decrease as temperature rises due to depopulation of the ground energy levels. On the other
hand, the cross-sections at the valleys slightly increase as the temperature increases. A
comparison with absorption cross-sections obtained from the FTIR is made, and found to be
similar to the ones measured by the DFG laser except at one location. The line-width of this
location is narrow, and FTIR resolution is not sufficient to resolve this peak. Therefore, its
absorption cross-sections obtained from the DFG laser are higher than FTIR, because the high
resolution (narrow line-width) of the DFG laser.
The spectra of 13 hydrocarbons are measured using FTIR spectrometer IR range. The range of
the spectra is 2800 – 3400 cm-1 with resolution of 0.6 cm-1. The temperature range of these
measured spectra is 673 – 1,100 K which is typical for combustion applications. These are
91
considered the first data for these hydrocarbons taken at high temperatures. The dependence
on temperature is almost similar for the studied hydrocarbons. As temperature increases, more
energy levels are populated and so new lines are introduced for small hydrocarbons, i.e.
methane, while the wings of the broad spectra increase, i.e. propane. One the other hand, the
absorption at the peaks of the spectra decrease since less population is at the ground energy
levels decrease. Although the spectra exhibit some changes at different temperatures, the
integrated band intensity in the 2800 – 3400 cm-1 range is constant. This parameter is
calculated from the measured spectra and compared to available literature. The integrated
band intensity increases linearly as the number of the C-H increases. Alkanes and alkenes have
similar slope while it’s almost flat for alcohol.
7.2 Future Work
These high temperatures measured cross-sections will be the basis for future kinetic study in
the shock tube. HeNe laser has high potential to measure the decay of the hydrocarbons during
pyrolysis/oxidation in the shock tube. Also, the HeNe laser will be used to confirm the mole
fraction of a fuel in a mixture before performing experiments in the shock tube and the rapid
compression machine. This will decrease the uncertainty in the mole fraction, especially for
liquid fuels.
The DFG system has a narrow line-width (~ 0.0001 cm-1) and can be applied to in-situ
measurement of propylene or any hydrocarbons in systems requiring rapid time response. Also,
the DFG laser is tunable which makes it more species-specific than HeNe laser which has strong
92
interference from other hydrocarbons. The DFG laser will be the tool for determining timehistories of a species in the shock tube for improving kinetics models. Furthermore, the DFG
laser will be used to obtain spectroscopic parameters, such as: line strength and pressure
broadening coefficients of a species. These parameters are important for remote sensing,
environmental monitoring as well as combustion applications.
The FTIR spectrometer can be used to measure the spectra of other species which have not
been studied at elevated temperature. Also, since the spectral range of this study is limited by
the transmission of the Fused Silica windows, the Reflex cell with ZnSe windows can be used to
measure the spectra at spectral range of 700 – 7000 cm-1 to temperatures up to 623 K. This will
result in building a database that will serve in selecting wavelengths that are interference-free.
Furthermore, the FTIR range can be extended to cover the UV range (400 – 700 cm-1). This will
help in studying the spectra in the UV range of different species which have strong absorption
at this range.
93
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
Hanson, R.K., Applications of quantitative laser sensors to kinetics, propulsion and practical energy
systems. Proceedings of the Combustion Institute, 2011. 33(1): p. 1-40.
Herzberg, G., Molecular Spectra And Molecular Structure: Infrared and Raman Spectra of Polyatomic
Molecules. Vol. II. 1991, Malabar, Florida 32950: Krieger Publishing Company. 660.
Penner, S.S., Quantitative Molecular Spectroscopy and Gas Emissivities. 1959, Reading, MA: AddisonWesley Publishing Company, Inc.
Edwards, D.K. and W.A. Menard, Comparison of Models for Correlation of Total Band Absorption. Appl.
Opt., 1964. 3(5): p. 621-625.
Mallard, W.G. and W.C. Gardiner Jr, Absorption of the 3.39 μm He-Ne laser line by methane from 300 to
2400 K. Journal of Quantitative Spectroscopy and Radiative Transfer, 1978. 20(2): p. 135-149.
Klingbeil, A.E., J.B. Jeffries, and R.K. Hanson, Temperature- and pressure-dependent absorption cross
sections of gaseous hydrocarbons at 3.39 µm. Measurement Science and Technology, 2006. 17(7): p.
1950.
; Available from: http://www.novawavetech.com/.
How an FTIR Works, in Fundamentals of Fourier Transform Infrared Spectroscopy, Second Edition. 2011,
CRC Press. p. 19-53.
Es-sebbar, E.-t., Y. Benilan, and A. Farooq, Temperature-dependent absorption cross-section
measurements of 1-butene (1-C4H8) in VUV and IR. Journal of Quantitative Spectroscopy and Radiative
Transfer, 2013. 115(0): p. 1-12.
Marinov, N.M., et al., Aromatic and polycyclic aromatic hydrocarbon formation in a laminar premixed nbutane flame. Combustion and Flame, 1998. 114(1-2): p. 192-213.
Seiser, R., et al., Extinction and autoignition of n-heptane in counterflow configuration. Symposium
(International) on Combustion, 2000. 28(2): p. 2029-2036.
Marinov, N.M., A Detailed Chemical Kinetic Model for High Temperature Ethanol Oxidation. International
Journal of Chemical Kinetics, 1999. 31(2-3): p. 183-220.
MacDonald, M.E., et al., Fuel and Ethylene Measurements during n-dodecane, methylcyclohexane, and isocetane pyrolysis in shock tubes. Fuel, 2012.
MacDonald, M.E., et al., Formulation of an RP-1 pyrolysis surrogate from shock tube measurements of fuel
and ethylene time histories. Fuel, 2012.
Davidson, D.F., et al., Multi-species time-history measurements during n-dodecane oxidation behind
reflected shock waves. Proceedings of the Combustion Institute, 2011. 33(1): p. 151-157.
Davidson, D.F., et al., Multi-species time-history measurements during n-heptane oxidation behind
reflected shock waves. Combustion and Flame, 2010. 157(10): p. 1899-1905.
Haylett, D.R., et al., OH and C2H4 species time-histories during hexadecane and diesel ignition behind
reflected shock waves. Proceedings of the Combustion Institute, 2011. 33(1): p. 167-173.
Boettcher, P.A., et al., The effect of heating rates on low temperature hexane air combustion. Fuel, 2012.
96(0): p. 392-403.
Sato, K. and Y. Hidaka, Shock-tube and modeling study of acetone pyrolysis and oxidation. Combustion and
Flame, 2000. 122(3): p. 291-311.
Tomita, E., et al., In situ fuel concentration measurement near spark plug in spark-ignition engines by 3.39
μm infrared laser absorption method. Proceedings of the Combustion Institute, 2002. 29(1): p. 735-741.
Olson, D.B., W.G. Mallard, and W.C. Gardiner Jr, HIGH TEMPERATURE ABSORPTION OF THE 3. 39 mu m
He-Ne LASER LINE BY SMALL HYDROCARBONS. Applied Spectroscopy, 1978. 32(5): p. 489-493.
Takao Tsuboi, K.I., Yutaka Tsunoda, Akihito Isobe and Koh-ichi Nagaya Light absorption by hydrocarbon
molecules at 3.392 µm of He-Ne laser. Japan. J. Appl. Phys., 1985. 24(1): p. 8-13.
Perrin, M.Y. and J.M. Hartmann, High temperature absorption of the 3.39 μm He-Ne Laser line by
Methane. Journal of Quantitative Spectroscopy and Radiative Transfer, 1989. 42(6): p. 459-464.
Drallmeier, J.A., Hydrocarbon absorption coefficients at the 3.39-μm He-Ne laser transition. Applied
Optics, 2003. 42(6): p. 979-982.
94
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
Mével, R., P.A. Boettcher, and J.E. Shepherd, Absorption cross section at 3.39&#xa0;μm of alkanes,
aromatics and substituted hydrocarbons. Chemical Physics Letters, 2012. 531(0): p. 22-27.
Pine, A.S., N2 and Ar broadening and line mixing in the P and R branches of the v3 band of CH4. Journal of
Quantitative Spectroscopy and Radiative Transfer, 1997. 57(2): p. 157-176.
Varanasi, P. and S. Chudamani, The temperature dependence of lineshifts, linewidths and line intensities of
methane at low temperatures. Journal of Quantitative Spectroscopy and Radiative Transfer, 1990. 43(1):
p. 1-11.
Harrison, J.J., N.D.C. Allen, and P.F. Bernath, Infrared absorption cross sections for ethane (C2H6) in the
3&#xa0;μm region. Journal of Quantitative Spectroscopy and Radiative Transfer, 2010. 111(3): p. 357-363.
Blass, W.E., G.W. Halsey, and D.E. Jennings, Self- and foreign-gas broadening of ethane lines determined
from diode laser measurements at 12 μm. Journal of Quantitative Spectroscopy and Radiative Transfer,
1987. 38(3): p. 183-184.
Harrison, J.J. and P.F. Bernath, Infrared absorption cross sections for propane (C3H8) in the 3&#xa0;μm
region. Journal of Quantitative Spectroscopy and Radiative Transfer, 2010. 111(9): p. 1282-1288.
Nadler, S. and D.E. Jennings, Foreign-gas pressure broadening parameters of propane near 748 cm-1.
Journal of Quantitative Spectroscopy and Radiative Transfer, 1989. 42(5): p. 399-403.
Sharpe, S.W., et al., Gas-phase databases for quantitative infrared spectroscopy. Applied Spectroscopy,
2004. 58(12): p. 1452-1461.
Reuter, D.C. and J.M. Sirota, Absolute intensities and foreign gas broadening coefficients of the
111,10←112,10 and 180,18←181,18 lines in the v7 band of C2H4. Journal of Quantitative Spectroscopy
and Radiative Transfer, 1993. 50(5): p. 477-482.
Richter, D. and P. Weibring, Ultra-high precision mid-IR spectrometer I: Design and analysis of an optical
fiber pumped difference-frequency generation source. Applied Physics B: Lasers and Optics, 2006. 82(3): p.
479-486.
Chen, W., et al., Continuous-wave mid-infrared laser sources based on difference frequency generation.
Comptes Rendus Physique, 2007. 8(10): p. 1129-1150.
Pine, A.S., DOPPLER-LIMITED MOLECULAR SPECTROSCOPY BY DIFFERENCE-FREQUENCY MIXING. J Opt Soc
Am, 1974. 64(12): p. 1683-1690.
Klingbeil, A.E., J.B. Jeffries, and R.K. Hanson. Tunable mid-IR laser absorption sensor for time-resolved
hydrocarbon fuel measurements. 2007.
Klingbeil, A.E., et al. Two-wavelength mid-IR absorption diagnostic for simultaneous measurement of
temperature and hydrocarbon fuel concentration. 2009.
Porter, J.M., J.B. Jeffries, and R.K. Hanson, Mid-infrared laser-absorption diagnostic for vapor-phase fuel
mole fraction and liquid fuel film thickness. Applied Physics B: Lasers and Optics, 2011. 102(2): p. 345-355.
Pyun, S.H., et al., Two-color-absorption sensor for time-resolved measurements of gasoline concentration
and temperature. Applied Optics, 2009. 48(33): p. 6492-6500.
Stranic, I., et al., Multi-species measurements in 1-butanol pyrolysis behind reflected shock waves.
Combustion and Flame, 2012. 159(11): p. 3242-3250.
Pyun, S.H., et al., Methane and ethylene time-history measurements in n-butane and n-heptane pyrolysis
behind reflected shock waves. Fuel, 2013.
Pyun, S.H., et al., Shock tube measurements of methane, ethylene and carbon monoxide time-histories in
DME pyrolysis. Combustion and Flame, 2013. 160(4): p. 747-754.
Van Helden, J.H., et al., A 3 μm difference frequency laser source for probing hydrocarbon plasmas. Journal
of Physics D: Applied Physics, 2011. 44(12).
Pyun, S.H., et al., Interference-free mid-IR laser absorption detection of methane. Measurement Science
and Technology, 2011. 22(2): p. 025303.
Klingbeil, A.E., J.B. Jeffries, and R.K. Hanson, Temperature-dependent mid-IR absorption spectra of
gaseous hydrocarbons. Journal of Quantitative Spectroscopy and Radiative Transfer, 2007. 107(3): p. 407420.
Etzkorn, T., et al., Gas-phase absorption cross sections of 24 monocyclic aromatic hydrocarbons in the UV
and IR spectral ranges. Atmospheric Environment, 1999. 33(4): p. 525-540.
Rothman, L.S., et al., The HITRAN 2008 molecular spectroscopic database. Journal of Quantitative
Spectroscopy and Radiative Transfer, 2009. 110(9-10): p. 533-572.
95
49.
50.
51.
52.
Chu, P.M., et al., The NIST quantitative infrared database. Journal of Research of the National Institute of
Standards and Technology, 1999. 104(1): p. 59-81.
Klingbeil, A.E., MID-IR laser absorption diagnostics for hydrocarbon vapor sensing in harsh environments,
in Mechanical Engineering 2007, Stanford University.
Lafferty, W.J. and R.J. Thibault, High resolution infrared spectra of C212H2, C12C13H2, and C213H2.
Journal of Molecular Spectroscopy, 1964. 14(1–4): p. 79-96.
Et-touhami Es-sebbar, M.A., Aamir Farooq, Infrared cross-sections and integrated band intensities of
propylene: Temperature-dependent studies, 2013, King Abdullah University of Science and Technology
(KAUST).