chemiluminescence analysis of vitiated conditions for methane …€¦ · chemiluminescence...

Chemiluminescence analysis of vitiated conditions forMethane and Propane flames

Nelson dos Santos Alves

Thesis to obtain the Master of Science Degree in

Mechanical Engineering

Supervisors: Prof. Edgar Caetano FernandesProf. Teodoro José Pereira Trindade

Examination Committee

Chairperson: Prof. Viriato Sérgio de Almeida SemiãoSupervisor: Prof. Edgar Caetano Fernandes

Member of the Committee: Prof. Patrícia de Carvalho Baptista

November 2016

To my parents

iii

Acknowledgments

First and foremost I would like to thank Prof. Edgar C. Fernandes for the opportunity of working together

with him. It has been my pleasure to be his student and I’m sure his teachings will guide me throughout

the years. Without his guidance and support none of this would be possible. You have become like a

mentor to me, thank you.

I would like to extend by gratitude to Prof. Teodoro Trindade who have been always present in each

step of the way. His guidance was invaluable throughout this work. Thank you for your support and

wisdom, you have a special place in my heart.

I also would like to acknowledge the friends I made at IN+, your help and criticism was precious

during the experiments.

My deepest gratitude goes to Andre Marvao, my colleague throughout this past years. His help and

companionship were crucial to get this far. You began as a colleague but you have grown into a friend. I

am deeply honoured to have come to know you.

And finally, I would like to express my appreciation to my family, in particular to my parents who

always supported me in my decisions, I really hope I have made you proud of me. One final note to my

soul mate Sara who was always present when I needed comfort. Words cannot express my gratitude.

To all who make me who I am today, thank you. This is for you.

v

Resumo

Nos ultimos anos tem existido um grande interesse no controlo do processo de combustao e nas

emissoes de NOx . Uma das tecnicas usadas para minimizar estas emissoes e a recirculacao de

gases de escape (EGR). A quimiluminescencia emergiu como uma tecnica promissora para controlo

de chamas e embora uma ligacao ja tenha sido estabelecida com o EGR, e necessario investigar a

influencia que algumas das consequencias do uso do EGR trazem a este fenomeno. Esta tese propoe-

se a estudar dois desses efeitos (temperatura e conteudo em CO2) nas emissoes de OH*, CH* e C∗2.

Com esse objectivo, foi projectada uma experiencia para estudar estes efeitos em chamas laminares de

pre-mistura de metano e propano (1000 ≤ Re ≤ 2000 ; 0.80 ≤ φ ≤ 1.30). A influencia da temperatura

e do CO2 e descrita e um modelo empırico e apresentado. Foi descoberto que embora o aumento

de temperatura leve a um aumento das emissoes de OH*, CH* e C∗2 (dependendo do radical pode

chegar a 50 % para ∆ T = 100 K), as variacoes observadas nos quocientes entre estes radicais e nas

fraccoes quimiluminescentes sao de modo geral desprezaveis. Por outro lado, o efeito de CO2 e mais

acentuado com as emissoes de radicais a diminuirem com a adicao de CO2 (ate 80% para o radical C∗2

para xCO2 = 0.30). Foram descobertas variacoes consideraveis nos quocientes entre radicais (ICH∗ /IC∗2

pode chegar a 5 vezes mais do que para a condicao de referencia). Os desvios observados para as

fraccoes quimiluminescentes nao excederam 74%.

Palavras-chave: Quimiluminescencia, Controlo da razao de equivalencia, Pre-aquecimento,

Adicao de CO2

vii

Abstract

Some of the concern put into combustion processes in the past years is related with combustion mon-

itoring and NOx emissions. One of the techniques used to deal with the later is the recirculation of

exhaust gases (EGR). Flame chemiluminescence emerged as a good technique to flame monitoring

and although a link with EGR was already established, investigations are still necessary regarding the

effects of EGR in flame chemiluminescence. This master thesis proposes the study of two of these

effects (temperature and CO2 content) on the emissions of OH*, CH* and C∗2. An experiment was de-

signed to study this effects on laminar premixed flames of methane and propane (1000 ≤ Re ≤ 2000

; 0.80 ≤ φ ≤ 1.30). The influence of temperature and CO2 content on flame chemiluminescence is

described and an empirical model to evaluate these effects is presented. It was found that although an

increase in temperature leads to an increase in the emissions of OH*, CH* and C∗2 (depending on the

radical can go up to 50 % for ∆ T = 100 K), the variations found for the ratios between this radicals and

the chemiluminescence fractions are in general negligible. On the other hand, the effect of CO2 is more

pronounced with the emissions decreasing with an increase in CO2 content (up to 80% for the radical C∗2

for xCO2 = 0.30). Considerable deviations (ICH∗ /IC∗2

can be 5 times higher than the value for its reference

condition) were found in the ratios between radicals. The deviations found for the chemiluminescence

fractions did not exceed 74%.

Keywords: Flame chemiluminescence, Equivalence ratio monitoring, Preheating, CO2 addition

ix

Contents

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Resumo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii

1 Introduction 1

1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 State of the art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Experimental Setup 5

2.1 Burner system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Premixed control system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3 Flame spectrum acquisition system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3 Methodology 13

3.1 Flame chemiluminescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 Temperature effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.3 CO2 effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4 Results 25

4.1 Morphological differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.2 The effect of temperature in the flame spectrum . . . . . . . . . . . . . . . . . . . . . . . . 27

4.3 Analysis of temperature on chemiluminescence relations . . . . . . . . . . . . . . . . . . 31

4.4 The effect of CO2 in the flame spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.5 Analysis of CO2 on chemiluminescence relations . . . . . . . . . . . . . . . . . . . . . . . 38

4.6 Combined effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

xi

5 Conclusions 43

5.1 Achievements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

References 45

A Conditions measured 49

xii

List of Tables

2.1 Range of gas flow rates used for all the conditions tested . . . . . . . . . . . . . . . . . . 7

2.2 Specifications of the gases used in the experiments. . . . . . . . . . . . . . . . . . . . . . 10

2.3 Spectrometer specification list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.1 Wavelengths range considered to the spectrum integration. . . . . . . . . . . . . . . . . . 16

3.2 Reactions considered to the formation of the radicals OH*, CH* and C∗2. . . . . . . . . . . 18

4.1 Values to be used with Eq.4.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.2 Coefficients for Eq.4.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.3 Values of β for methane and propane flames . . . . . . . . . . . . . . . . . . . . . . . . . 37

A.1 Conditions measured . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

xiii

List of Figures

2.1 Experimental rig schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Internal contours of the burner, designed by Eq. 2.1. . . . . . . . . . . . . . . . . . . . . . 6

2.3 Partial view of the burner and burner in situ . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.4 Specimen of flow controller used to formulate the gas premixture. . . . . . . . . . . . . . . 8

2.5 Spectrometer QE65000 and optical fiber QP400-2-SR-BX. . . . . . . . . . . . . . . . . . 11

3.1 Spectrum from a typical propane and methane flame at φ = 1.3 . . . . . . . . . . . . . . . 14

3.2 Typical spectrum with identification of ICO∗2, Ii and an example of radiation intensity of

neighbor species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.3 Spectrum of a propane flame at φ = 1.3 before and after the subtraction of ICO∗2

. . . . . . 15

3.4 Variation of flame temperature with the increase of xAr for a methane flame at φ = 1.0 . . 17

3.5 Temperature profiles of methane and propane flames at φ = 0.90 . . . . . . . . . . . . . . 18

3.6 Concentration profiles of radical OH for methane and propane flames at φ = 0.90 . . . . . 19

3.7 Concentration profiles of O2 for methane and propane flames at φ = 0.90 . . . . . . . . . 19

3.8 Concentration profiles of radical C for methane and propane flames at φ = 0.90 . . . . . . 20

3.9 Concentration profiles of radical C2H for methane and propane flames at φ = 0.90 . . . . 20

3.10 Concentration profiles of radical CH for methane and propane flames at φ = 0.90 . . . . . 21

3.11 Concentration profiles of radical CH2 for methane and propane flames at φ = 0.90 . . . . 21

3.12 Concentration profiles of radical H for methane and propane flames at φ = 0.90 . . . . . . 22

3.13 Concentration profiles of radical HCO for methane and propane flames at φ = 0.90 . . . . 22

3.14 Concentration profiles of radical O for methane and propane flames at φ = 0.90 . . . . . . 23

3.15 Variation of flame temperature with the increase of xCO2for a methane flame at φ = 1.0 . 24

4.1 Influence of temperature in the flame height for methane flames at φ = 0.90. . . . . . . . 25

4.2 Influence of temperature in the flame height for propane flames at φ = 0.90. . . . . . . . 26

4.3 Influence of CO2 content in the flame height for methane flames at φ = 1.20. . . . . . . . 26

4.4 Influence of CO2 content in the flame height for propane flames at φ = 1.20. . . . . . . . . 26

4.5 Dependence of flame height regarding temperature for a propane flame at φ = 0.9 and

CO2 content for methane flame at φ = 1.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.6 Influence of gas preheating and CO2 addition on the flame emission spectrum (CH4/air φ

= 1.30) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

xv

4.7 Normalized Intensity of OH*, CH*, C∗2 and CO∗

2 radicals emission in C3H8/N2/O2/Ar flames

at φ = 1.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.8 Dependency of parameter α of Eq.4.2 with φ for both propane and methane flames . . . . 30

4.9 Data validation between experimental and model predictions by Eq. 4.2 for methane and

propane flames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.10 Effect of temperature in the radiation intensity of the radicals OH*, CH* and C∗2 for methane

and propane flames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.11 Ternary diagram of methane and propane and the effect of temperature . . . . . . . . . . 33

4.12 Influence of temperature in the ratio of radicals for methane and propane flames . . . . . 33

4.13 Influence of temperature in the chemiluminescence fraction for methane and propane

flames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.14 Emission intensity of OH*,CH*, C∗2 and CO∗

2 radicals of a propane flame (φ = 1.20) . . . . 35

4.15 Variation of parameter β of Eq.4.5 with the equivalence ratio for propane and methane

flames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.16 Data validation of CO2 effect on flame chemiluminescence facing predictions by Eq.4.5

for methane and propane flames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.17 Effect of CO2 addition in the radiation intensity of the radicals OH*, CH* and C∗2 for

methane and propane flames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.18 Effect of CO2 addition on the ternary diagram for propane and methane flames . . . . . . 40

4.19 Effect of CO2 addition on the ratio of radicals for methane and propane flames . . . . . . 40

4.20 Influence of the addition of CO2 in the chemiluminescence fraction for methane and

propane flames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.21 Data validation of temperature and CO2 combined effects on flame chemiluminescence

facing predictions by Eq.4.6 for methane and propane flames . . . . . . . . . . . . . . . . 42

xvi

Nomenclature

Greek symbols

∆ Difference.

λ Wavelength.

φ Equivalence ratio.

Roman symbols

a, b, c... Fitting constants.

c0 Light velocity.

ei Uncertainty in quantity i.

fi Chemiluminescence fraction of species i.

h Planck constant.

I∗ Radiation intensity from excited species.

Iλ Signal in population units.

Ii Radiation intensity of species i.

IBB Radiation from black body emissions.

ni Quantity of species i.

Qmax Maximum capacity of flow meter.

Sλ Signal in energetic units.

Tad Adiabatic flame temperature.

v Frequency.

xi Fraction of species i.

Qi Flow rate of species i.

� Diameter.

xvii

Chapter 1

Introduction

In the past few years non-intrusive techniques to combustion monitoring such as the use of flame chemi-

luminescence have been developed. This technology allows to monitor combustion characteristics such

as the equivalence ratio in a simple, cheaper way than most traditional technologies.

This chapter is organized as follows. A brief motivation on the investigated topic is presented in

Section 1.1. Section 1.2 provides a review of some of the work done in the past years concerning this

technology. In Section 1.3 the objectives for this master thesis are presented. Section 1.4 ends this

chapter presenting the thesis outline.

1.1 Motivation

Since its first use, combustion has remained throughout the years as the most important controllable

energy source for mankind. Electrical power generation, industry and domestic applications, transporta-

tion, all of them make use of combustion processes to convert chemical energy in thermal energy or

propulsive force. Both methane and propane are widely used in this applications. For instance, the main

fuel for industrial purposes is natural gas which is a blend mainly constituted by CH4 and in smaller

quantities by high-order hydrocarbons such as C2H6. On the other hand, one of the main components

of LPG (liquefied petroleum gas) is propane. The importance of this fuels for everyday applications is

well established. These fuels are also important for research purposes. CH4 is the smallest hydrocar-

bon molecule thus representing the simplest alkane to study. On the other hand, C3H8 has the lightest

weight of the simple hydrocarbons that start to exhibit general features of chain processes. The study of

C3H8 can then give insight to more heavier, complicated molecules.

In the past few years a lot of concern was put in the environmental impact of combustion processes.

This concern lead to an interest in new and advanced technologies to achieve lower pollutants emissions

and higher energetic efficiency.

One of the main concerns of the past years and that remains nowadays is the emissions of NOx .

Some success was achieved with the introduction of techniques like the exhaust or flue gas recirculation

(EGR or FGR). This techniques lead to the preheating of the premixture, changes in O2 concentration

1

and the addition of gases like CO2.

One of the aspects to have in mind to achieve a more efficient combustion is the control of combustion

systems. Conventionally this control rely on monitoring the CO2 and/or O2 content of the exhaust gases,

having inherent time-lag efficiency limitations [1]. Other technologies are available such as the optical

exploitation of the electromagnetic spectrum namely the flame chemiluminescence phenomena [2]. This

techniques are non-intrusive so they may operate away from the extreme combustion conditions. Since

flame chemiluminescence is an inherent process to combustion it also provides instantaneous informa-

tion. A connection between EGR and flame chemiluminescence was already reported in the literature

[3] nevertheless more research has to be done in this field. The purpose of this master thesis is then to

explore the relation that some of the consequences of EGR (preheating and the addition of CO2) have

in the flame chemiluminescence monitor techniques for methane and propane flames.

1.2 State of the art

In the middle of the 20th century a work by Gaydon [4] linked light emission with the concentration of

specific radical species. Several radicals were further studied by Clark [5] who investigated the spectral

emission of the species : OH*, CH*, C∗2 and CO∗

2 on C3H8/air flames. As usual in combustion literature

the superscript (*) denotes an excited chemical species. In his work, he found a relation between the

emission ratio C∗2/CH* and fuel/air ratio being one of the first works relating flame chemiluminescence

to equivalence ratio monitoring. Orain and Hardalupas [6, 7] studied flame chemiluminescence on flat

flames for natural gas and propane flames. It was reported that the emission ratio OH*/CH* decreased

with the equivalence ratio being appointed as the elected parameter to control burning conditions. Other

work [8] reported the same result but for acetylene/oxygen flames. Several studies [9, 10, 5] have also

suggested intensity ratios of two chemiluminescence radicals as robust parameter for equivalence ratio

monitoring. The most used ratios are OH*/CH*, CH*/C∗2 and C∗

2/OH*. The robustness of these ratios

is related to their claimed independence on optical and geometrical system parameters [11], strain rate

[12] and fuel consumption rate [10].

A link between flame chemiluminescence and EGR applications was established by Gupta et al. [3].

Measures were made at different values of EGR using CO∗2 chemiluminescence in natural gas fired re-

ciprocating engines to estimate important engines parameters such as in-cylinder bulk gas temperature

and heat release rate. Since the use of EGR technology leads to differences in the combustion process

it is of importance to investigate the impact of those differences in flames. The effects of preheating

and CO2 dilution in flames has been widely studied. Zhen et al. [13] studied the effects of air preheat

on the combustion and heat transfer characteristics of premixed flames diluted by CO2 and N2. It was

reported that the dilution generally deteriorates flame stability, on the other hand the preheating of the

reactants showed a favorable effect in lean mixtures expanding the stability limit. It was suggested that

the adiabatic flame temperature increases linearly with the initial temperature of reactants.

Some works studied the effects of other conditions in flame chemiluminescence. Higgins et al.

studied the influence of pressure (0.25 − 2.5 MPa), equivalence ratio (0.66 − 0.86 ) and mass flow rate

2

on OH* [14] and CH* [15] chemiluminescence for CH4/air premixed laminar flames. It was reported

that the OH* and CH* chemiluminescence increases with the equivalence ratio and decreases with the

pressure. It was also showed that the equivalence ratio can be deducted knowing the airflow rate and the

pressure. Nori et al. [16] examined CH*, OH* and CO∗2 chemiluminescence in methane and mixtures

of H2/CO. It was found that the ratio CO∗2/OH* is weakly dependent on temperature and fuel dilution

for H2/CO blends while the ratio CH*/OH* is only a weak function of reactants preheating for methane

flames. The effect of local properties on chemiluminescence stoichiometry measurement was studied

by Armingon et al. [17]. It was showed that the ratio OH*/CH* has a non-negligible variation along

turbulent flames which suggested that the local properties of the flame may have an effect on flame

chemiluminescence. The newly found interest in syngas lead to studies regarding the application of

chemiluminescence techniques in flame monitoring for these type of fuels. A recent work by Armingol et

al. [18] studied the effect of fuel composition in flame chemiluminescence for CH4/CO2/H2/CO premixed

flames. It was reported that for high hydrogen content no CH* emission peak could be detected. Thus,

only the emissions from OH* and CO∗2 can be used for monitoring purposes in these kind of fuels. In

particular, the ratio OH*/CO∗2 was found to be a good alternative for equivalence ratio monitoring in a

limited range.

A particular problem of the use of emission ratios for flame monitoring is the necessity of using several

ratios when a wide range of equivalence ratios is used. A recent work [1] defined a new parameter for

flame monitoring. This new parameter, called chemiluminescence fraction, was reported to achieve a

broader application range than the emission ratios.

Flame monitoring assumed a great importance in the past few years due to the concerns about

sustainability and efficiency. Flame chemiluminescence has already show potential to be a dominant

technique in flame monitoring due to its simplicity, robustness and price. However, further investigation

is needed particularly in the effects that may disrupt the parameters that are traditionally used.

1.3 Objectives

From the literature reviewed, one can recognize that flame chemiluminescence was been widely studied

in the past few years. A link between flame chemiluminescence and EGR has already been established.

However, only a few works studied the effects of temperature and CO2 addition in flame chemilumi-

nescence and even those works are generally more related to the describing of the effects than the

quantification of them.

Subsequently, to fill this gap, the objective of this master thesis is the study and quantification of pre-

heating and CO2 addition effects on flame chemiluminescence. In order to do that, special attention was

paid to the parameters used in flame monitoring namely the use of emission ratios and chemilumines-

cence fractions. Besides, a model that allow to describe the effects of preheating and CO2 was pursued.

Additionally, the validity of the use of emission ratios and chemiluminescence fractions regarding these

effects was investigated.

3

1.4 Thesis Outline

This master thesis is organized as follows:

Chapter 2 describes the experimental setup used in the experiments. The equipment used is pre-

sented as well as the conditions in which the measures were made. Several pictures are showed to

ensure clarity.

Chapter 3 describes briefly the methodology followed in this work. Some concepts are explained

and a brief explanation of the chemiluminescence phenomena is presented. Some insight is given to

the techniques used as well as the validation for these techniques.

Chapter 4 is the bulk of this work and consists in the presentation and discussion of the results

obtained in the experiments. The chapter is divided in two main sections: The effect of temperature

and the effect of CO2 in flame spectrum. A photographic documentation of some of the flames used is

shown. A simple model to predict the effects of preheating and CO2 addition is presented. Validation

between the experimental results and the model is also presented. Each part of this chapter ends with

the quantification of the effects studied in the emission ratios and chemiluminescence fractions. A brief

overview in the ternary diagrams of methane and propane flames is also shown.

The thesis ends in Chapter 5 with an overview of the main conclusions as well as some suggestions

on future work.

4

Chapter 2

Experimental Setup

The experimental results presented in this master thesis were obtained from the experimental rig schematic

shown in Figure 2.1. The rig is composed by essentially three parts: the burner system, the premixed

control system and the flame spectrum acquisition system. The burner system comprises not only the

physical equipment necessary to stabilize a flame but also the conditions at which the gaseous premix-

ture arrives to the burner nozzle (flow uniformity, gas temperature, etc). This is described in Section 2.1.

Section 2.2 describes the gas premixture control system which corresponds to the characteristics of

the fuel/air mixture but also to the equipment necessary to control the premixture. The flame spectrum

acquisition system is described in Section 2.3 and comprises not only the spectrometer used and the

optical fiber but also the optical probe positioning.

Figure 2.1: Experimental rig schematic.

2.1 Burner system

The Bunsen burner assembly was designed to ensure a steady and fully developed gas flow on laminar

regime at the nozzle level. The burner is a circular open nozzle of 20 mm in diameter at the exit, with

a high area contraction ratio of Aratio = 25 between the entrance and exit section areas. Its aim is to

uniformly accelerate the flow in order to reduce the flow turbulence and non uniformities. The contraction

of the burner was designed based on the fifth polynomial equation given by [19]:

5

y = (−10ξ3 + 15ξ4 − 6ξ5)(yi − y0) + yi (2.1)

where ξ = z/L and z is the axial burner coordinate and L the length of the nozzle. y is the height at

position z, yi is the height of the contraction wall from the center line at inlet and y0 is the height of the

contraction wall from the center line at outlet. These can be seen in Figure 2.2.

Figure 2.2: Internal contours of the burner, designed by Eq. 2.1.

The burner assembly is entirely made of stainless steel 304 and comprises three sections of identical

length. Between each section there is a distribution plate made of low porosity sintered glass (ROBU �

100 mm×5 mm, ε ≤ 100 µm) with the aim of straightening the flow, breaking the gas radial and angular

velocity profiles. The bottom section has four tangential gas inlets equally distributed throughout the

chamber wall, the interior of which is filled with Raschig rings (� 5 mm) acting as a jet breaking and

spreading evenly the flow. The intermediate section is an open cylindrical chamber used to equalize

gas pressure all over the second sintered plate area. The outer section is the contraction zone, which is

responsible for the velocity equalization at the burner exit. Figure 2.3 show a partial view of the burner

and the burner in situ respectively.

Experiments were conducted controlling: fuel type (CH4/C3H8), premixture composition (N2/O2/Ar/CO2)

and equivalence ratio (φ). The tested fuel power ranged from 0.75 kW to 1.60 kW while the range of

Reynolds number was 1000 ≤ Re ≤ 2000. Due to limitations of the burner stability range it was not

possible to fix the fuel power for each fuel type thus, for each fuel, two fuel powers were used. One for

the leanest mixture and one to all other mixtures. The unburned gas mixture was formulated as com-

binations of CH4/C3H8/O2/N2/Ar/CO2 depending on the experiment with methane and propane altering.

The air was formulated in a volumetric base as 21 % O2 and 79 % N2. This mixture was used instead of

normal atmospheric air since the methodology used in this work required the control of the composition

of the inert gas (more details can be found in Chapter 3). The equivalence ratio was varied between

6

(a) View of the burner (b) Burner in situ

Figure 2.3: Partial view of the burner (a) and burner in situ (b).

φ = 0.8 and 1.3 with increments of 0.1. When CO2 was involved, the tests began at φ = 0.90. Data

repeatability was ensured by a set of measurements made in different days (typically half of the amount

of conditions measured), achieving a 5.7% of maximum signal span. Table A.1 presents the range of

conditions and the number of measurements (#). More details can be found in Appendix A.

Table 2.1: Range of gas flow rates in SLPM (Standard liters per minute, 298 K, 101.3 kPa) used for allthe conditions tested.

Fuel φ Power(kW) # Qfuel QN2QO2

QAr QCO2

0.80 0.75 10 1.234 [11.65 - 7.15] 3.095 [0 - 4.50] 00.90 1.25 11 2.056 [17.25 - 12.25] 4.586 [0 - 5.00] 01.00 1.25 8 2.056 [15.52 - 12.22] 4.127 [0 - 3.30] 01.10 1.25 9 2.056 [14.12 - 10.12] 3.753 [0 - 4.00] 01.20 1.25 10 2.056 [12.94 - 8.44] 3.440 [0 - 4.50] 0

CH4 1.30 1.25 10 2.056 [11.95 - 7.45] 3.175 [0 - 4.50] 0

0.90 1.25 11 2.056 [17.25 - 12.51] 4.586 [0 - 3.015] [0 - 1.725]1.00 1.25 11 2.056 [15.52 - 6.47] 4.127 [0 - 5.987] [0 - 3.074]1.10 1.25 9 2.056 [14.12 - 4.69] 3.753 [0 - 6.000] [0 - 3.431]1.20 1.25 11 2.056 [12.90 - 3.16] 3.440 [0 - 5.960] [0 - 3.818]1.30 1.25 12 2.056 [11.95 - 2.03] 3.175 [0 - 5.992] [0 - 3.918]

1.30 1.25 4 2.056 [4.5 - 1.5] 3.175 [4.581-7.581] 2.867

0.80 1.00 11 0.650 [15.57 - 10.57] 4.140 [0 - 5.00] 00.90 1.60 11 1.060 [22.52 - 17.52] 5.980 [0 - 5.00] 01.00 1.60 11 1.060 [20.27 - 15.27] 5.380 [0 - 5.00] 01.10 1.60 11 1.060 [18.42 - 13.42] 4.900 [0 - 5.00] 01.20 1.60 9 1.060 [16.89 - 12.89] 4.490 [0 - 4.00] 0

C3H8 1.30 1.60 7 1.060 [15.59 - 12.59] 4.140 [0 - 3.00] 0

0.90 1.60 8 1.060 [22.52 - 18.04] 5.980 [0 - 2.883] [0 - 1.575]1.00 1.60 7 1.060 [20.27 - 12.83] 5.380 [0 - 4.993] [0 - 2.419]1.10 1.60 9 1.060 [18.42 - 9.94] 4.900 [0 - 5.541] [0 - 2.949]1.20 1.60 11 1.060 [16.89 - 7.98] 4.490 [0 - 5.537] [0 - 3.378]1.30 1.60 11 1.060 [15.59 - 11.42] 4.140 [0 - 2.596] [0 - 1.557]

1.20 1.60 4 1.060 [12.37 - 9.37] 4.490 [2.829-5.829] 1.689

7

2.2 Premixed control system

The burner system requires the use of a gas flow control system to ensure stationary conditions in the

flame. Precision gas flow controllers (Alicat Scientific, Series 16) of maximum capacity of 20, 5 and

1 SLPM were used. In Figure 2.4 an example of one of this controllers can be seen. The controllers

were operated with FlowVision software package which enables not only the monitoring of the gas flow

rate but also the temperature and pressure of it.

Figure 2.4: Specimen of flow controller used to formulate the gas premixture.

The uncertainty on gas flow rate eQi , which is indicated by the manufacturer, is related with the actual

flow rate Qi (L/min) and the maximum device capacity Qmax by the following equation:

eQi = 0.008Qi + 0.002Qmax (2.2)

where the subscript i indicates the type of gas used. Since the equivalence ratio is a very important

parameter in this work, the evaluation of its uncertainty is crucial.

The equivalence ratio φ is defined as the ratio between quantities of fuel nfuel and air nair at actual

and stoichiometric proportions as expressed by Eq. 2.3.

φ =(nfuel/nair)

(nfuel/nair)st(2.3)

When the amount of air is the necessary for, theoretically, burn all the fuel it is said that the mixture

is stoichiometric and the value of φ is unitary. For values higher than one it is said that the mixture is a

rich mixture. On the other hand, values lower than one indicate the presence of a lean mixture.

In practical terms, the equivalence ratio is a function of proportions between flow rates of gases in

the mixture.

8

φ = f(Qfuel, QO2 , QN2 , ..., Qn) (2.4)

The uncertainty in the value of the equivalence ratio can then be derived by:

e2φ = (

dφ

dQfuel)2e2

fuel + (dφ

dQO2

)2e2O2

+ (dφ

dQN2

)2e2N2

+ ...+ (dφ

dQn)2e2

n (2.5)

where the subscript n represents the amount of other species considered in the formulation of the

air. The value of the uncertainties for the gases measured by flowmeters can be obtained by Eq. 2.2.

Only the analysis of the derivative terms is left to do. Assuming the same value for the densities at actual

and stoichiometric conditions, Eq. 2.3 can be written in the following way:

φ =Qfuel/Qair

(Qfuel/Qair)st(2.6)

The value of Qfuel/Qair for stoichiometric conditions is a constant Ki that depend on the fuel used

(0.1050 for methane and 0.0420 for propane). Expanding the flow rate of air one can obtain:

φ =1

Ki

QfuelQO2 +QN2 + ...+Qn

(2.7)

Two derivatives can then be obtained, one for the fuel and the other for the various species that

formulate the air (N2, O2, Ar, CO2, ...). The equations are given below:

dφ

dQfuel=

1

Ki

1

QN2+QO2

+ ...+Qn(2.8)

dφ

dQi= −Qfuel

Ki

1

(QN2 +QO2 + ...+Qn)2(2.9)

The value for the uncertainty in φ can then be obtained combining the previous equations. It follows

then:

eφ =

√(

1

Ki

1

QN2+QO2

+ ...+Qn)2e2

fuel + ...+ (−QfuelKi

1

(QN2+QO2

+ ...+Qn)2)2e2

n (2.10)

As an example, for a methane flame, φ = 0.8 , QCH4= 1.234 , QN2

= 11.65 and QO2= 3.095 SLPM

and the appropriated flowmeters one can obtain eφ = 0.0149. Considering all the experimentally tested

conditions, the uncertainty in the value of the equivalence ratio didn’t exceed 2.5 %.

All the gases used were bottled (Air Liquide). Their specifications can be found on Table 2.2

9

Table 2.2: Specifications of the gases used in the experiments.Gas Code Molecular weight (g/mol) Purity(%)

CH4 UN 1971 16.04 ≥ 99.995C3H8 UN 1978 44.10 ≥ 99.95

N2 UN 1066 28.01 ≥ 99.8O2 UN 1072 32.00 ≥ 99.5Ar UN 1006 39.95 ≥ 99.999

CO2 UN 1013 44.01 ≥ 99.7

2.3 Flame spectrum acquisition system

The flame spectrum acquisition system is comprised of a optical fiber and a spectrometer.

The optical fiber (Ocean Optics, QP400-2-SR-BX) is made in fused silica, has a length of 2 m and a

core diameter of 400 µm. The fiber yields an average acceptance angle of 25.4◦ and produces a conical

field of view. In order to have the flame the most possible inside the field of view having at the same time

a signal with low noise a compromise in its position was made. The fiber was placed radially at 20 cm of

the burner axis and at a height of 17 cm above the burner exit.

The optical fiber was connected to a high-sensitivity spectrometer by an entrance slit of 100 µm wide.

A summary of the specifications of the spectrometer (Ocean Optics, QE65000) is presented in Table

2.3.

Table 2.3: Spectrometer specification listFeature Spectrometer

Manufacturer Ocean OpticsBase part number QE65000 Pro

Detector Hamamatsu S7031-1006Array type Matrix CCD array

Pixels 1024×58Grating HC1 composite 300 lines/mm

Wavelength range 200-1100 nmEntrance slit 100 µm

Optical resolution < 3 nm

During the experiments the spectrometer was controlled by Ocean Optics SpectraSuit software. The

average flame signal of each test was acquired for 100 exposures and an integration time of 1 second

was selected in order to obtain an high signal to noise ratio. Electronic dark noise was removed from

every spectrum aquired. The average and standard deviation of each exposure was computed using

a Matlab code. The background signal (signal obtained in the absence of flame) was subtracted from

the average flame signal. The result corresponds to the spectral signal of the measuring condition. The

units of this signal are µJ/s/nm/cm2. However, since the photons have different energy depending on the

wavelength, during the course of this thesis the results will be usually presented in photons/s/nm/cm2

since there is a direct correspondence between the number of photons measured and the number of

radicals that are emitters. Denoting the first signal by Sλ and the second by Iλ the conversion can be

10

made by the following equation:

Iλ =λ

hc0Sλ (2.11)

where h is the Planck Constant, c0 the light velocity and λ the radiation wavelength. Figure 2.5 shows

the acquisition system comprised of the optical fiber and spectrometer.

Figure 2.5: Spectrometer QE65000 and optical fiber QP400-2-SR-BX.

11

Chapter 3

Methodology

The objective of this work is to quantify the flame chemiluminescence response to the increase in tem-

perature and to the addition of CO2. The methodology followed will be explained in this Chapter. Section

3.1 presents a brief overview of the chemiluminescence phenomena as well as the steps necessary to

access the desired information. Sections 3.2 and 3.3 describe the details in these experiments.

3.1 Flame chemiluminescence

Flame chemiluminescence is related to the emission of electronically excited species produced by chem-

ical reactions such as A + B C + D*. Species D* may then be destroyed by spontaneous emission (D*

→ D + hv) or collisional quenching (D* + M→ D + M) [11]. The second reaction is the one responsible

by the mission of light thus being the one important to this work. Flame monitoring using flame chemi-

luminescence is concerned with the behavior of several species that may emit light through the reaction

described before. In flame monitoring the species that are usually used are OH*, CH*, C∗2 and CO∗

2 [18].

The information that these species provide may be accessed through the flame spectrum. Figure 3.1

shows an example of a typical spectrum for both methane and propane flames.

The spectra present distinct features which is a indication that flame spectra may be used to access

information regarding the combustion process. The steps necessary to acquire a flame spectrum were

presented in Chapter 2. As one can see, the spectrum present three major peaks. The peaks corre-

spond to the emission by the radicals OH* (309 nm), CH* (430 nm) and C∗2 (515 nm). To each radical

corresponds a band system which consists in the range of wavelengths where the emission of light is

performed. All major chemiluminescence species for flame monitoring are located in the range from

225 nm to 575 nm thus the analysis will only focus on this wavelength range. Lower wavelengths are

affected by molecular oxygen absorption while in higher wavelengths the black body emissions can’t be

neglected [1]. Consider Figure 3.2 where an example of a typical spectrum is shown.

The narrow band radical emissions are superimposed to a wide band continuum (dashed line in

Figure 3.2). This emission is attributed to CO∗2 emitters [20]. This continuum emission was reported [1]

to extend roughly from 250 nm to 650 nm thus being important in the wavelength range considered. A

13

Figure 3.1: Spectrum from a typical propane (dashed line) and methane flame (solid line) at φ = 1.3.

Figure 3.2: Typical spectrum with identification of ICO∗2

(dashed line), Ii (gray area) and an example ofradiation intensity of neighbor species (forward slash).

raw spectral intensity I (photons/s/nm/cm2) can then be seen as roughly the sum of three contributions:

I = I∗ + ICO∗2

+ IBB (3.1)

where I∗ is the radiation intensity from excited radicals (not only OH*, CH* and C∗2 but all excited

14

species that emit light in the wavelength considered), ICO∗2

the radiation intensity from excited CO2*

molecules and IBB is the radiation from black body emissions. Since the latter, described by Planck’s

law, has a growing effect towards longer wavelengths particularly for the infrared region and the analysis

performed was limited at 575 nm this radiation is neglected, thus:

I ≈ I∗ + ICO∗2

(3.2)

ICO∗2

can be outlined using the equation [21]:

ICO∗2

= ξ. exp[− exp(−λ+ λ0

w)− (

λ− λ0

w) + 1] (3.3)

where ξ a scaling factor, λ the wavelength, λ0 the band head wavelength and w and extent parameter

related to the wide band length.

I∗ can then be accessed subtracting the CO∗2 contribution from the raw spectral signal. Figure 3.3

shows the differences in the flame spectrum before and after this subtraction was carried out.

Figure 3.3: Spectrum of a propane flame at φ = 1.3 before (solid line) and after (dashed line) thesubtraction of ICO∗

2.

The narrow bands chemiluminescence can be accessed by the spectrum integration over a certain

wavelength range. Table 3.1 shows the wavelength intervals used in this work. To access the radiation

intensity of the radicals (Ii), besides the subtraction of the CO∗2 wide band one has also to take into

account the radiation intensity of neighbor species (forward slash in Figure 3.2). Both constitute what is

called background contamination. To estimate the CO∗2 radiation Eq. 3.3 can be used. To estimate the

remaining of the background contamination a smooth line connecting the upper and lower limits of the

interval used is required (see Figure 3.2). Ii (gray area in Figure 3.2) can then be obtained subtracting

the neighbor radiation from I∗ in a certain wavelength range. For more details in this method, the reader

15

can see other works [22, 23].

Table 3.1: Wavelengths range considered to the spectrum integration.Band Wavelength range [nm]

OH* [275 300] , [300-335]

CH* [375-405] , [410-445]

C∗2 [455-480] , [490-525] , [525-570]

It is important to note that several of the results shown in this work are normalized by a value which

corresponds to the ”reference condition”. These conditions are explained when needed. This works

focus on relative changes instead of absolute ones in order to minimize the effect that the experimental

setup can have in the measures.

Since all the flames studied are conical laminar flames a good representation of each flame is given

by its height. In order to evaluate that, a Matlab program was created. The program computed the

height of the flame in each picture taken. Since several pictures of the same condition were taken, the

characteristic height of the flame is given by the average of the heights.

3.2 Temperature effect

In order to increase the temperature of the flame, argon was added to the gas premixture. Since the

specific heat capacity of argon is lower than the one of nitrogen, the same energy release by fuel com-

bustion will result in an higher flame temperature. Argon was injected and nitrogen withdrawn in the

same amount to ensure an equivalent air flow pattern to the flame and the same fuel-oxidizer concen-

tration. The relation between the argon concentration and the increase in adiabatic flame temperature

is described by a linear relation of the type:

∆Tad = kxAr (3.4)

where ∆Tad is the increase in flame temperature (K), xAr is a measure of Ar content in the N2/Ar

mixture (expressed in mol fraction) and k is a proportionality constant (K/mol fraction). An example of

the effect of argon addition can be seen in Figure 3.4.

Therefore, the higher the value of xAr in the mixture (being xAr = 0 the original mixture with 21 %

O2 and 79 % N2) the higher the flame temperature. The adiabatic flame temperatures were obtained

by numerical simulations using the Cantera solver package under adiabatic and equilibrium conditions

[24]. The GRI-Mech 3.0 detailed kinetics was used in the calculations, which consist of 325 elementary

chemical reactions with associated reaction rate coefficients and thermochemical parameters for the

53 species involved [25]. The numerical results obtained for CH4/air and C3H8/air flames are in close

agreements with published data [26]. A majorant of the uncertainty for the temperature was obtained. It

was considered the maximum and the minimum value of xAr. The maximum and the minimum values

for ∆T were then computed using Eq. 3.4. The maximum and minimum value of xAr are given by the

16

Figure 3.4: Variation of flame temperature with the increase of xAr for a methane flame at φ = 1.0obtained by numerical simulations using GRI-Mech 3.0.

following equations:

xAr,max =QAr + eAr

QN2,ini − eN2,ini(3.5)

xAr,min =QAr − eAr

QN2,ini + eN2,ini(3.6)

where Qi is the actual flow rate of species i, ei is the uncertainty in the flow rate of species i and the

subscript ini means the ”reference condition” that is the mixture with xAr = 0.

Despite being an inert gas, it is of relevance to ensure that the flame temperature alteration caused by

the substitution of nitrogen by argon leads to the same effect that of a preheating of the gas mixture. To

that analysis, concentration profiles of related chemical species throughout the flame front were used for

comparison. Investigations [1, 27, 28] reported that OH, O, CH, H, HCO, O2, C2H, C and CH2 among

others, are key species in the combustion process and also in the formation of chemiluminescence

species. The reactions involving these species are shown in Table 3.2.

The species profile were obtained through kinetics simulations in a one-dimensional flame of Can-

tera’s burner-stabilized code running over GRI-Mech 3.0. Two flames were tested: one with the air

mixture formulated as O2/N2/Ar and other as O2/N2 but with an higher initial temperature. The increase

in the initial temperature corresponds to the necessary temperature to ensure that the flame temperature

is equivalent to the one that its observed when argon is added to the mixture. Figure 3.5 show the tem-

perature profiles for both methane and propane flames while Figures 3.6–3.14 show the concentration

profiles of previously mentioned radicals for the same flames.

17

Table 3.2: Reactions considered to the formation of the radicals OH*, CH* and C∗2.

Number Reaction Ref

R1 O + H + M OH* + M [28]R2 CH + O2 OH* + CO [28]R3 HCO + O OH* + CO [1]

R4 C2 + OH CH* + CO [27]R5 C2H + O CH* + CO [27]R6 C2H + O2 CH* + CO2 [27]R7 C + H + M CH* + M [27]

R8 CH2 + C C∗2 + H2 [1]

(a) Methane (b) Propane

Figure 3.5: Temperature profiles of methane (a) and propane (b) flames at φ = 0.90 obtained throughGRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 while dashed lines corre-sponds to Fuel/N2/O2/Ar.

18


Figure 3.6: Concentration profiles of radical OH for methane (a) and propane (b) flames at φ = 0.90obtained through GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 whiledashed lines corresponds to Fuel/N2/O2/Ar.


Figure 3.7: Concentration profiles of O2 for methane (a) and propane (b) flames at φ = 0.90 obtainedthrough GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 while dashed linescorresponds to Fuel/N2/O2/Ar.

19


Figure 3.8: Concentration profiles of radical C for methane (a) and propane (b) flames at φ = 0.90obtained through GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 whiledashed lines corresponds to Fuel/N2/O2/Ar.


Figure 3.9: Concentration profiles of radical C2H for methane (a) and propane (b) flames at φ = 0.90obtained through GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 whiledashed lines corresponds to Fuel/N2/O2/Ar.

20


Figure 3.10: Concentration profiles of radical CH for methane (a) and propane (b) flames at φ = 0.90obtained through GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 whiledashed lines corresponds to Fuel/N2/O2/Ar.


Figure 3.11: Concentration profiles of radical CH2 for methane (a) and propane (b) flames at φ = 0.90obtained through GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 whiledashed lines corresponds to Fuel/N2/O2/Ar.

21


Figure 3.12: Concentration profiles of radical H for methane (a) and propane (b) flames at φ = 0.90obtained through GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 whiledashed lines corresponds to Fuel/N2/O2/Ar.


Figure 3.13: Concentration profiles of radical HCO for methane (a) and propane (b) flames at φ = 0.90obtained through GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 whiledashed lines corresponds to Fuel/N2/O2/Ar.

22


Figure 3.14: Concentration profiles of radical O for methane (a) and propane (b) flames at φ = 0.90obtained through GRI-Mech 3.0 simulations. Solid lines correspond to a mixture of Fuel/N2/O2 whiledashed lines corresponds to Fuel/N2/O2/Ar.

The flame temperature profile is roughly the same between the preheated and the Ar addition situ-

ation. Despite the different initial temperature, the flame temperature assumes the same value in both

cases, for methane and for propane flames. Regarding the concentration profiles, the concentration

integral through the flame was obtained. The deviations obtained (εi) were: εOH = 1.7 %, εO = 5.2 %,

εCH = 11.3 %, εH = 7.9 %, εHCO = 9.1 %, εO2= 0.2 %, εC2H = 19.1 %, εC = 15.2 % and εCH2

= 8.8 %

for methane flames. The values obtained for propane flames were: εOH = 1.9 %, εO = 4.5 %, εCH =

10.7 %10.7%, εH = 7.0 %, εHCO = 7.0 %, εO2 = 0.7 %, εC2H = 12.7 %, εC = 13.9 % and εCH2 = 8.2 %.

This may be attributed to the differences in the methods followed. The Ar addition situation requires

the substitution of N2 for Ar, however this is a volumetric operation, the differences in molecular weight

observed between N2 and Ar may help to explain the small deviations observed in the profiles. Other

possible explanation may reside in the differences at the preheating zone of the flame. Both cases as-

sume the same flame temperature, however due to the preheating observed in one of the flames, the

thermal gradients are different. It should be noted that the value of the preheating doesn’t correspond

to the same increase in flame temperature altough both are related by a linear relation [13, 29]. Never-

theless, the deviations found for all the radicals were very small. Since the concentration of species like

OH, O, H and CH that play a role as precursors of the excited radicals exhibit changes of few percent

stands to reason that in terms of flame chemiluminescence it is equivalent the addition of argon to the

mixture or making a preheating.

3.3 CO2 effect

The CO2 effect over flame chemiluminescence was studied in a similar way of the temperature effect

(replacing in equal amount the N2 by CO2). However, in this case there are two distinct effects. Besides

23

the alterations induced in the combustion kinetics, the addition of CO2 to the unburned gas mixture leads

to a decrease in the flame temperature following the relation:

∆Tad = ax2CO2

+ bxCO2(3.7)

where ∆Tad is the variation in the adiabatic temperature (K) above normal conditions, a (K/mol fraction2)

and b (K/mol fraction) are functions of the equivalence ratio and xCO2is a measure of the CO2 concen-

tration in the premixture and is defined as the amount of CO2 that replaces N2. An example of the

decrease in temperature with the addition of CO2 can be seen in Figure 3.15.

Figure 3.15: Variation of flame temperature with the increase of xCO2 for a methane flame at φ = 1.0obtained by numerical simulations using GRI-Mech 3.0.

A majorant of the uncertainty for xCO2 was obtained. Similarly with the temperature effect it was

considered the maximum and the minimum value of xCO2 . The maximum and minimum value of xCO2

are given by the following equations:

xCO2,max =QCO2

+ eCO2

QN2,ini − eN2,ini(3.8)

xCO2,min =QCO2

− eCO2

QN2,ini + eN2,ini(3.9)

where Qi is the actual flow rate of species i, ei is the uncertainty in the flow rate of species i and the

subscript ini means the ”reference condition” that is the mixture with xCO2 = 0.

In order to isolate the effect of CO2 over combustion kinetics it was necessary to correct the flame

temperature by the addition of argon. This was possible due to the addition of argon and the corre-

sponding withdrawn of nitrogen (see Eq. 3.4).

24

Chapter 4

Results

Previous chapters presented the details of the experimental rig and the methodology followed in order

to study the effects previously mentioned. The results obtained will be presented in this Chapter. The

Chapter is organized as follow: Section 4.1 presents the morphological differences observed in the

flame when its temperature is increased and when the CO2 concentration is increased. Several pictures

are presented for clarity. An empirical expression relating temperature and CO2 concentration with the

height of the flame is presented. The effect of temperature in the flame spectrum is presented in Section

4.2. The main results are presented and an empirical model is showed. The agreement between the

model and the experimental data is investigated. The effects of temperature in the chemiluminescence

relations are presented in Section 4.3. Sections 4.4 and 4.5 are very similar with Sections 4.2 and 4.3,

being organized in the same way with the difference that the effect studied is not the temperature but the

CO2 concentration. This chapter ends with Section 4.6 where the models presented in previous sections

are combined and its agreement with experimental data regarding the combined effects of temperature

and CO2 concentration is investigated.

4.1 Morphological differences

The increase in temperature and the addition of CO2 lead to several differences in the flame spectrum

but also changes in the aspect of the flame. To quantify these changes, several pictures of different

flames were taken. Figures 4.1– 4.4 show some of these differences.

Figure 4.1: Influence of temperature in the flame height for methane flames at φ = 0.90.

25

Figure 4.2: Influence of temperature in the flame height for propane flames at φ = 0.90.

Figure 4.3: Influence of CO2 content in the flame height for methane flames at φ = 1.20.

Figure 4.4: Influence of CO2 content in the flame height for propane flames at φ = 1.20.

It can be seen that an increase in temperature leads to a decrease in flame height which is related

with the increase in the flame speed. Another effect observed is the increase in the luminosity emitted

by the flame. On the other hand, the increase in CO2 content lead to an increase in flame height which

can be explained by the decrease in the flame speed. It is also possible to see that when the content

of CO2 is increased, the flame gradually changes its shade of blue. An example of the dependence

between the flame height and the effects studied in this work is shown in Figure 4.5.

26

(a) Temperature effect (b) CO2 effect

Figure 4.5: Dependence of flame height regarding temperature (a) for a propane flame at φ = 0.9 andCO2 content (b) for methane flame at φ = 1.2.

The influence of temperature and CO2 in the flame height can be described by the generic linear

equation:

h = mx+ b (4.1)

where h is the flame height in milimeters, m and b are fitting parameters and x can be the value

of the increment in temperature (K) or the mol fraction of CO2 in the premixture. Table 4.1 shows the

parameters for the set of flames studied in this work.

As can be seen, the slope is not the same for all conditions and varies with the equivalence ratio. The

value of b represent the height of the flame at the reference condition of ∆T = 0 and xCO2 = 0. Although

the flame height is supposed to be constant for a given condition, in practice the flame oscillates a

bit which can be attributed to resonance in the burner. Since the flame height was computed through

the analysis of pictures, the value obtained depend of the position that the flame was occupying in the

moment the picture was taken. Thus, the values for the correlations presented should not be seen as

absolute values but as characteristic ones.

4.2 The effect of temperature in the flame spectrum

Figure 4.6b) shows an example of the emission spectrum of a typical CH4/O2/N2/ CO2/Ar flame as well

as the radicals more used in flame chemiluminescence monitoring [18].

In Figure 4.6c) one can see the effect of temperature on the flame chemiluminescence (it should be

noted that the contribution from CO∗2 is already subtracted). The temperature has an upward effect in

the flame emission. However, a distinct behavior has been noticed by the chemiluminescence radicals.

27

Table 4.1: Values to be used with Eq.4.1.Effect Fuel φ m b

0.8 -0.071 29.30.9 -0.072 35.9

CH4 1.0 -0.080 30.51.1 -0.069 28.71.2 -0.077 32.0

Temperature 1.3 -0.106 41.2

0.8 -0.047 30.80.9 -0.066 39.2

C3H8 1.0 -0.056 32.91.1 -0.056 31.21.2 -0.062 30.71.3 -0.071 35.5

0.9 0.738 35.91.0 0.419 30.5

CH4 1.1 0.422 28.71.2 0.360 32.0

CO2 1.3 0.249 41.2

0.9 0.884 39.21.0 0.692 32.9

C3H8 1.1 0.366 31.21.2 0.301 30.71.3 0.274 35.5

Figure 4.6: Influence of gas preheating and CO2 addition on the flame emission spectrum (CH4/air φ =1.30). The ∆T is the increase above normal flame temperature and xCO2 is the fraction of N2 substitutedby CO2.

28

These behavior can be seen in Figure 4.7 that shows the emission intensity of radicals OH*, CH* and

C∗2 as well as the radical CO∗

2 normalized by Ii at ∆T = 0 K. It should be noted that the uncertainty

associated with the radiation intensity is very small in all measures thus not being showed since its

representation in size is similar to the symbols presented in the figures.

Figure 4.7: Normalized Intensity of OH*, CH*, C∗2 and CO∗

2 radicals emission in C3H8/N2/O2/Ar flamesat φ = 1.10. ∆T corresponds to the increase in the flame temperature when compared with the corre-spondent temperature of a C3H8/N2/O2 flame.

Identical behavior occurs for both methane and propane flames along the tested equivalence ratios

following for the radicals the empirical expression:

IiIi,0

= eαi∆T (4.2)

in which Ii is the emission intensity of the radical i, Ii,0 is the reference value measured at ∆T = 0 K,

αi is a characteristic constant (K−1) and ∆T is the increase in the flame temperature (K). This model can

be used to describe the emissions of the radicals OH*, CH*, C∗2 and even CO∗

2 when there is an increase

in flame temperature. The characteristic constant αi can be seen as a measure of the proportionality

between an increment in temperature and the response in chemiluminescence radiation and translates

in a single value how the chemiluminescence phenomena is affected by the temperature. Figure 4.8

shows the variation of the characteristic constant α with the equivalence ratio for methane and propane

flames. For clarity, the error bar was omitted in the figures.

The effect of temperature is similar in the radicals CH* and C∗2 with the effect being maximum near φ

= 0.90 while for the radical OH* the effect is maximum near stoichiometry. The radical CO∗2 presents a

maximum near φ = 1.0 for methane flames and φ = 1.10 for propane flames. This was expected since

an increase in temperature leads to an increase in the reaction rate of the radicals [17, 1]. The radical

29

Figure 4.8: Dependency of parameter α of Eq.4.2 with φ for both propane (white symbols) and methaneflames (black symbols).

OH* seems to be more sensible to temperature than the others since the value of its characteristic

constant has a greater variation along the range of equivalence ratios studied. There seems to be little

difference in the behavior of the radicals between methane and propane flames. Since the focus of this

work is the chemiluminescence of OH*, CH* and C∗2 no further development will be made concerning

the CO∗2 emissions. An adjust of the values of α with the equivalence ratio was made. The relation can

be described by the following equation.

α = exp(a+ bφ+ cφ2 + dφ3) (4.3)

In which a, b, c and d are empirical coefficients which were determined (see Table 4.2) for both

methane and propane flames but also for the three radicals considered in this work.

Table 4.2: Coefficients for Eq.4.3 with α expressed in K−1.Fuel Radical a b c d R2

OH* -55.0319 126.6722 -105.6683 28.5915 0.9983CH4 CH* -48.2879 126.1876 -123.3160 39.3663 0.9522

C∗2 -138.2150 383.5241 -364.0750 112.7917 0.9997

OH* -42.7255 88.3156 -66.7524 15.7561 0.9855C3H8 CH* -38.3690 94.4864 -90.1900 28.1390 0.8317

C∗2 -28.1360 63.6768 -59.8683 17.9765 0.8017

The behavior of IOH∗, ICH∗ and IC∗2

when there is a preheating of the mixture can be predicted using

a simple model combining Eqs. 4.2 and 4.3. Figure 4.9 shows the agreement between the experimental

data (all equivalence ratios and both fuels) and the values predicted by this simple model.

The agreement is quite good for both methane and propane flames flames which shows that the

30

Figure 4.9: Data validation between experimental and model predictions by Eq. 4.2 for methane (blacksymbols) and propane (white symbols) flames ( OH*, CH*, C2*)

model proposed by Eqs. 4.2 and 4.3 can be used with good results for both propane and methane

flames in the range of conditions studied in this work.

Figure 4.10 summarize the effect of preheating in the radiation intensity of the radicals considered.

As one can see, the increase in temperature leads to a shift in the base curve (∆T = 0) for all radicals.

The intensity increase rate due to the temperature is not the same for all radicals. IOH∗ presents a

maximum for φ around stoichiometry for both methane and propane flames. ICH∗ presents a maximum

beyond φ = 1.3 for methane flames while propane has his maximum around 1.2. For IC∗2

there is no

data in this work for equivalence ratios higher than 1.3, however a previous work [1] suggested that its

maximum is around φ = 1.3 for methane flames and φ = 1.4 for propane flames. The data shows that the

radical OH* is the most sensible to temperature followed by the radical CH*. Propane seems also to be

more sensible to temperature than methane. In fact, for a typical equivalence ratio φ = 1.0 it was found

that for methane flames ∆IOH∗/∆T is around 1.1× 108 while ∆ICH∗/∆T is around 0.048× 108 and

∆IC∗2/∆T = 0.024× 108 photons/s/cm2/K. On the other hand, for propane flames the values obtained

were 2.5× 108, 0.54× 108 and 0.32× 108 photons/s/cm2/K for IOH∗ , ICH∗ and IC∗2

respectively. This

behavior shows agreement with the meaning of the characteristic constant α since the radicals that

have a higher value for α are also the ones where the increase in the radiation intensity is higher.

4.3 Analysis of temperature on chemiluminescence relations

It has been showed [1] the existence of a characteristic relation between the emissions of OH*, CH* and

C∗2 radicals, which is related with the hydrocarbon fuel composition. In Figure 4.11 is possible to see

31

(a) OH* (b) CH*

(c) C2*

Figure 4.10: Effect of temperature in the radiation intensity of the radicals OH* (a), CH* (b) and C∗2 (c)

for methane and propane flames

the ternary diagram that corresponds to the fuels that were studied in this work. The ternary diagram

is a tool that represents relative dependencies between variables. One can see that in the range of

temperatures considered (∆T = 100 K) there seems to be no influence in the baseline of each fuel thus

indicating that it is still possible to identify methane and propane flames by their ternary diagram even if

there is a preheating of the mixture.

One application of flame chemiluminescence is the estimation of the equivalence ratio using the ratio

of radical radiation intensities as been showed by previous works [30, 31, 6, 32]. The ratios IOH∗/ICH∗

and ICH∗/IC∗2

are usually used for lean mixtures while the ratio IC∗2/IOH∗ is more suitable for rich mixtures

[1, 32]. In this work, the focus is the differences that an increase in temperature will cause. To evaluate

that effect Figure 4.12 is shown below.

This figure show what happens to the value of the ratio between radicals when an increase in temper-

ature of 100 degrees is observed (white symbols). One can see that the general tendency is maintained.

32

Figure 4.11: Ternary diagram of methane and propane and the effect of temperature. Black symbolscorresponds to the reference condition while white symbols correspond to an increase of 100 K in theflame temperature.

(a) Methane flames (b) Propane flames

Figure 4.12: Influence of temperature in the ratio of radicals for methane (a) and propane (b) flames.The white symbols correspond to a variation of 100 K in the flame temperature.

For methane flames, the ratio IOH∗/ICH∗ has an higher variation with the temperature than the other two

with a maximum deviation of 25%. The ratios ICH∗/IC∗2

and IC∗2/IOH∗ are roughly invariant with the

temperature.

A similar analysis can be made for propane flames. Once again, the ratio with higher variation

with the temperature is IOH∗/ICH∗ with a maximum deviation of 27%. Similarly with methane flames,

the ratios ICH∗/IC∗2

and IC∗2/IOH∗ seem to be less affected by the temperature. These results are in

33

agreement with the previous analysis of the characteristic constant α since the ratio with higher devi-

ation correspond to the one involving the radicals OH* and CH* which are the ones more sensible to

temperature according with the data showed in Figure 4.8.

Since the objective is to find a ratio that is less sensible to temperature variations it follows that for

both methane and propane flames the ratio ICH∗/IC∗2

is more suitable for equivalence ratio evaluation in

lean mixtures while the ratio IC∗2/IOH∗ continues as the most adequate ratio for rich mixtures.

The use of the ratio of radicals is not the only way to monitor the equivalence ratio using flame

chemiluminescence. A previous work [1] introduced the concept of chemiluminescence fraction fi as

the ratio between an individual radical emission and the sum of all chemiluminescence. In the particular

case of i = OH∗,CH∗ and C∗2 the fi is defined as:

fi =I∗i

IOH∗ + ICH∗ + IC∗2

(4.4)

It was reported that the equivalence ratio can be monitored with high accuracy between φ = 0.80

and φ = 1.3 using the fractions fOH∗ and fC∗2. The influence of temperature was studied in the values of

these two fractions. The results are presented in Figure 4.13.


Figure 4.13: Influence of temperature in the chemiluminescence fraction for methane (a) and propaneflames (b). The white symbols correspond to a variation of 100 K in the flame temperature.

It was found that for fOH∗ and an increment of 100 K the maximum deviation was 0.049 for methane

flames and 0.072 for propane flames. For fC∗2

the maximum deviation observed was 0.039 for methane

flames and 0.052 for propane flames. The main advantage of using a chemiluminescence fraction in-

stead of a ratio of radicals its the broader application range of the first. Since the deviations observed for

the fractions are in general smaller than the ones observed for the ratios, chemiluminescence fractions

are preferable to use to monitor the equivalence ratio when the flame is preheated. These conclusion

stands for both methane and propane flames.

34

4.4 The effect of CO2 in the flame spectrum

Figure 4.6a) shows the effect in the flame spectrum when CO2 is added in the mixture. The ”reference

condition” defined as xCO2= 0 corresponds to a gas premixture without the CO2 addition while xCO2

= 1

correspond to a blend without N2, having instead the same volumetric flow in CO2. As one can see, the

increase in the CO2 content leads to differences in the emission spectrum. Observing the peaks of the

radicals OH*, CH*, C∗2 it is visible that a decrease in the radiation intensity occurs when the concentration

of CO2 increases in the flame. The integration along the wavelengths described in Table 3.1 was carried

out for all the equivalence ratios studied and for both methane and propane flames. Figure 4.14 shows

the behavior of the radiation intensity of the three radicals focused in this work, as well as the radical

CO∗2, with the increase in CO2 concentration for a particular flame. The values are normalized by the

reference condition (xCO2 = 0).

Figure 4.14: Emission intensity of OH*,CH*, C∗2 and CO∗

2 radicals of a propane flame (φ = 1.20) withdifferent CO2 content in gas premixture.

The radical CO∗2 presents an increase in its intensity which is different from the behavior of the other

radicals. The addition of CO2 seems to increase the concentration of precursor species (like CO) in the

formation of CO∗2 which may explain the increasing in the radiation intensity observed. However, since

the focus of this work is in the radicals OH*,CH* and C∗2 no further development will be made concerning

CO∗2 emissions. There is a clear reduction of the radiation intensities of the three radicals studied. This

reduction is higher for the radical C∗2 than it is for the radicals OH* and CH*. This behavior was observed

for both methane and propane flames but also for all the equivalence ratios tested which was similar to

what was found before for the temperature effect. In order to investigate this phenomenon numerical

simulations were carried out involving a detailed combustion mechanism.

The influence of CO2 was investigated in the rate of three reactions usually indicated as responsible

35

for the formation of the species OH*, CH* and C∗2. The reaction considered for OH* was HCO + O

OH* + CO. It was found that an increase of 5% in CO2 content in gas premixture at φ = 0.90 causes

a decrease of 13% (propane flames) and 15% (methane flames) in the reaction extent. For the radical

CH* one of the the reactions usually indicated to its formation is C2H + O CH* + CO, the decrease

observed was 15% for propane flames and almost three orders of magnitude less for methane flames

(both at φ = 0.9). The formation of C∗2 can be attributed to the reaction CH2 + C C∗

2 + H2, it was found

that the reaction speed of this reaction decreases by 26% with the addition of 5% of CO2 for propane

flames and 32% for methane flames (φ = 0.9). It should be noted that the reactions presented aren’t the

only ones that produce the excited radicals thus, for instance, the greater decrease observed for ICH∗

in methane flames don’t necessary mean that the effect of CO2 in the emissions of this radical is higher

than in propane flames. It only means that for this particular reaction and for this equivalence ratio it is.

The reduction in the radicals emission observed seems associated with the decrease in concen-

tration of several species necessary to the chemiluminescence reactions. The chemical effect of CO2

addition was studied in previous works [33, 34]. Their main conclusion was that the addition of CO2

exercises its influence mainly through the reaction CO2 + H CO + OH which leads to a decrease of

the concentration of the radical H. Liu et al. [34] indicated in their work that the most important chain

branching reaction is H + O2 O + OH which leads to a decrease in the concentrations of the radicals

O and OH. Another explanation was proposed by Cong and Dagout [35]. These authors suggested that

the decrease in concentration of the radical H leads to a decrease in the fuel consumption rate via the

competition with the H-abstraction reaction CH4 + H CH3 + H2. This inhibition disrupts the combustion

since all the reactions that follow are also inhibited. It follows then that the addition of CO2 to the gas

premixture leads to a decrease in concentrations of three key radicals to chemiluminescence reactions

which leads to the observed reductions in the emissions of radicals OH* and CH*, as reported in Figure

4.14. The reduction in the rate of reaction that leads to C∗2 formation, seems to justify the decrease in

C∗2 emissions although no additional information was found in the literature.

It was then investigated the possibility of finding a single law (similarly to the one found for the

temperature effect) to model de data obtained. It was found that the radiation intensity of the radicals

follows the same empirical expression given by Eq. 4.2 having instead of the increment in temperature,

the value of xCO2. The equation is then:

IiIi,0

= eβixCO2 (4.5)

in which Ii is the radiation intensity of the radical i, Ii,0 is the reference value of that radical measured

at xCO2= 0, βi is a constant (mol fraction−1) and xCO2

is a measure of the CO2 content (mol fraction).

This model can be used to describe the emissions of the radicals OH*, CH* and C∗2 regarding the effect

of CO2. The parameter β assumes an analog meaning of α, describing the proportionality between the

addition of CO2 and the decrease in radiation intensity. The higher its absolute value the higher the

decrease in the radiation intensity. Figure 4.15 shows the value of β for several equivalence ratios and

for both methane and propane flames.

36

Figure 4.15: Variation of parameter β of Eq.4.5 with the equivalence ratio for propane (white symbols)and methane (white symbols) flames.

It can be seen in flames of both fuels a similar behavior of the parameter β being roughly independent

on the equivalence ratio. The emissions of radicals OH*, CH* are aligned having and identical β while the

one for C∗2 emissions has a much higher absolute value. Since the behavior of β is roughly independent

on the equivalence ratio, a characteristic value for each type of radiation is proposed. These values are

presented in Table 4.3.

Table 4.3: Values of β expressed in mol fraction−1 for methane and propane flames.Fuel Radical β

OH* -1.294CH4 CH* -0.810

C∗2 -6.354

OH* -1.235C3H8 CH* -0.967

C∗2 -5.285

The effect of an increase in CO2 concentration in the radiation intensity of the radicals OH*, CH*

and C∗2 can then be predicted recurring to Eq. 4.5 and the values of Table 4.3. Figure 4.16 faces the

experimental flame emission data and the predictions by the model (Eq. 4.5) for both propane and

methane flames.

The agreement is remarkable indicating that Eq. 4.5 describes numerically the phenomena. Fig-

ure 4.17 summarize the effect of the addition of CO2 representing three levels of CO2 content in the

premixture.

There is a clear reduction of the radiation intensity with the increase of CO2 concentration, how-

37

Figure 4.16: Data validation of CO2 effect on flame chemiluminescence facing predictions by Eq.4.5 formethane (black symbols) and propane (white symbols) flames ( OH*, CH*, C2*).

ever this decrease is independent on the equivalence ratio which is characterized by the constant value

of β. Despite the increase in CO2 concentration, the φ at which the intensity is maximum is unal-

tered. For stoichiometric conditions it was found that ∆IOH∗/∆xCO2= −2.2× 108, ∆ICH∗/∆xCO2

=

−0.13× 108 and ∆IC∗2/∆xCO2 = −0.24× 108 photons/s/cm2/mol fraction for methane flames. The val-

ues for propane are : ∆IOH∗/∆xCO2= −4.4× 108, ∆ICH∗/∆xCO2

= −1.5× 108 and ∆IC∗2/∆xCO2

=

−4.4× 108 photons/s/cm2/mol fraction. The data shows that, in general, the radical C∗2 is the most sen-

sible to the addition of CO2. The effect is greater for propane flames than methane flames which is in

agreement with the value of its characteristic β.

4.5 Analysis of CO2 on chemiluminescence relations

A ternary diagram facing the chemiluminescence of OH*, CH* and C∗2 under the effect of CO2 addition

is shown in Figure 4.18.

The increasing CO2 concentration in the flame leads to a shift toward higher CH* fraction of the refer-

ence line at xCO2 = 0. However, contrary to what happened with the effect of temperature, the expected

shift is pronounced enough to render useless the identification of the fuel by the ternary diagram since

mixtures of fuel with CO2 are in fact a different fuel.

It is of relevance to verify if the ratio of radicals chemiluminescence can still be used to estimate

the equivalence ratio. The effect of CO2 content on the ratio of radicals for both methane and propane

flames is shown in Figure 4.19.

The effect of CO2 concentration is more pronounced than the effect of temperature. Contrary to what

38

(a) OH* (b) CH*

(c) C∗2

Figure 4.17: Effect of CO2 addition in the radiation intensity of the radicals OH* (a), CH* (b) and C∗2 (c)

for methane and propane flames

was shown with the latest, here the reference line shifts greatly in particular for IC∗2/IOH∗ and ICH∗/IC∗

2.

Since the decrease in the C∗2 intensity is higher than the other radicals, it was expected that the ratios

involving the radical C∗2 were more affected. However, due to the similarity in the curves, the monitoring

of the flame equivalence ratio is still possible, as long as the necessary correction is made in the transfer

function used. It was found that the ratio IOH∗/ICH∗ decreases with the addition of CO2 and presents

a deviation of 14% for methane flames and 8% for propane flames being the ratio with less deviation

relatively to the reference condition. The ratio IC∗2/IOH∗ decreases with the addition of CO2 and presents

a deviation from the reference condition of 78% for methane and 70% for propane flames. The value of

the ratio ICH∗/IC∗2

increases with the addition of CO2 and its value is about five times larger than the one

at the reference condition for methane flames and about 4 times larger for propane flames. It follows

that for monitoring purposes the transfer function I∗i = f(φ) has to be corrected when CO2 exists in the

39

Figure 4.18: Effect of CO2 addition on the ternary diagram for propane and methane flames. Blacksymbols correspond to the reference condition while white symbols correspond to an increase in CO2 of30 %.


Figure 4.19: Effect of CO2 addition on the ratio of radicals for methane (a) and propane (b) flames.

premixture.

An analysis of the addition of CO2 in the chemiluminescence fractions was performed. The results

are shown in Figure 4.20 .

The maximum deviation found for the fraction fOH∗ was 0.19 for methane flames and 0.13 for propane

flames with the effect of CO2 addition being higher in rich flames and similar in both methane and

propane flames. The fraction fC∗2

presents a maximum shift of 0.29 for methane flames along the range

40


Figure 4.20: Influence of the addition of CO2 in the chemiluminescence fraction for methane (a) andpropane (b) flames.

of equivalence ratio studied and 0.30 for propane flames. Once again, the presence of CO2 causes

great deviations in the reference flame chemiluminescence. This leads to the necessity of correcting the

intensity signals for equivalence ratio monitoring. However, comparing the intensity signals deviations

when chemiluminescence fractions and ratios are used one can conclude that the latter is preferable, at

least in lean flames, since the ratio IOH∗/ICH∗ has a lower shift than any of the fractions presented in

this work. Despite this, chemiluminescence fractions have a broader application range thus the choice

depends on the application.

4.6 Combined effects

A separated view on the effects of temperature and CO2 concentration on the flame emission spectrum

was already presented. In a generic combustion situation, both effects may be simultaneously present.

Assuming that both effects are independent the model describing the effect of temperature can be added

with the one for CO2 addition, obtaining a combined formulation:

IiIi,0

= eαi∆T+βixCO2 (4.6)

Figure 4.21 shows the agreement between the experimental data obtained from an independent set

of measures including both effects and the numerical values predicted by the combined model.

As one can see, the full model gives fair results for the OH* and CH* emissions. The results for

the radical C∗2 have a higher deviation. The kinetics of C∗

2 is the less studied of these three radicals,

some unknown effect which were not considered in this work may be the cause for the poor agreement

between the model and the experimental data obtained. The results indicate that the temperature effect

41

Figure 4.21: Data validation of temperature and CO2 combined effects on flame chemiluminescencefacing predictions by Eq.4.6 for methane (black symbols) and propane (white symbols) flames ( OH*,

CH*, C∗2).

and the addition of CO2 are not strictly independent effects thus it is necessary to introduce into the

formulation the interactions between the temperature effect and the addition of CO2. Future work is

necessary to continue to validate the model and to enhance it particularly for predictions of C∗2 radiation.

42

Chapter 5

Conclusions

The work performed throughout this master thesis lead to several conclusions regarding the application

of flame chemiluminescence in flame monitoring. However, there is still room to improve. This Chapter

is organized in two sections. An overview of the main achievements of this thesis is presented in Section

5.1. The chapter ends with Section 5.2 where some ideas for future work are pointed out.

5.1 Achievements

In this thesis, the effects of temperature and CO2 content on flame chemiluminescence were investigated

for both methane and propane flames.

The work was divided in two main branches: the effect of temperature and the effect of CO2 content.

An evaluation of the morphological differences on the flame was presented. It was showed that the flame

height decreases linearly with the flame temperature ( with a maximum of 0.1 mm/K ) and increases

linearly with the CO2 content (maximum of 0.9 mm/mol fraction).

The analysis proceeded with the effects on flame chemiluminescence. It was showed that while the

radiation intensity of the radicals OH*, CH* and C∗2 increase with increasing flame temperature the effect

is the opposite when CO2 is added to the mixture. As an example, for a methane flame (φ = 1.0) the

emissions of the radical OH* increase 54% with an increase of 100 K while for a content of 30% CO2

the emissions decrease 32%. An empirical model for the temperature effect (Ii/Ii,0 = exp(α∆T )) and

the effect of CO2 (Ii/Ii,0 = exp(βxCO2)) and its agreement with the experimental data was showed. The

model propose the definition of a characteristic constant α, β which is a measure of the proportionality

between the effect considered and the radiation intensity. It was found that the value of α is a function

of the equivalence ratio and a possible equation to define the dependence was presented. On the other

hand, β was found to be roughly invariant with the equivalence ratio.

The analysis was extended to chemiluminescence relations, namely ternary diagrams, ratios be-

tween radicals and chemiluminescence fractions. An analysis of the ternary diagram showed that, for

the range of temperatures considered the effect of temperature is negligible while the addition of CO2

leads to a pronounced shift of the reference line. Observing the ratios between radicals, it was con-

43

cluded that the ratios ICH∗/IC∗2

and IC∗2/IOH∗ don’t appear to be sensible to temperature variations

while the ratio IOH∗/ICH∗ presents a considerable variation (maximum of 25%). It follows then that the

ratio ICH∗/IC∗2

is preferable to equivalence ratio evaluation in lean mixtures while the ratio IC∗2/IOH∗

remained as the most adequate for rich mixtures. The addition of CO2 lead to high deviations from

the reference condition in the ratios IC∗2/IOH∗ and ICH∗/IC∗

2. Although the deviations observed were

high (almost 5 times higher for ICH∗/IC∗2

), the reference line seems to only shift from its initial position

which seems to mean that as long as the transfer function I∗i = f(φ) is corrected, an identification of the

equivalence ratio is still possible.

An analysis of the chemiluminescence fractions was also performed with the results indicating a low

dependence on temperature following that chemiluminescence fractions should be preferred over ratios

since the former have a broader range of application. On the other hand, these fractions seem to be

considerably affected by the addition of CO2, having been found a maximum deviation of 48%. Due

to the broader range of application of the chemiluminescence fractions, in the case of CO2 addition

the choice of what parameter to use for equivalence ratio evaluation should depend on the application.

Nevertheless it was found that for the case of CO2 addition the ratio IOH∗/ICH∗ seem to be more reliable,

at least for lean flames, that any of the chemiluminescence fractions presented.

The final part of the thesis was the validation of the full model for the effects of temperature and

CO2 simultaneously. The results showed that the model presented gives fair predictions although some

improvement should be made particularly for C∗2 emissions.

5.2 Future Work

In this master thesis some of the effects of EGR techniques were studied in flame chemilumescence.

Although the results obtained were satisfactory, further improvements could be made in order to enhance

the effectiveness of flame chemiluminescence in flame monitoring. Some suggestions are presented

next.

• The analysis should be extended to a broader range of equivalence ratios particularly for more

lean mixtures. The increasing energetic needs of nowadays society lead to the need of obtaining

more efficient processes from which combustion is an important one hence the interest in lean

flames. The extended analysis should complement the work already done and give more tools to

the proliferation of chemiluminescence techniques to flame monitoring.

• Investigations could be performed in biogas to validate the results concerning the addition of CO2.

Additionally, adjustments should be made to the model proposed to enhance its capabilities to

predict C∗2 emissions in flames with the addition of CO2.

44

References

[1] T. J. P. Trindade. Chemiluminescence Spectral Identity of Premixed Methane and Propane Flames.

PhD thesis, Universidade de Lisboa Instituto Superior Tecnico, 2015.

[2] J. Ballester and T. Garcia-Armingol. Diagnostic techniques for the monitoring and control of practical

flames. Progress in Energy and Combustion Science, 36(4):375 – 411, 2010.

[3] S. B. Gupta, B. P. Bihari, M. S. Biruduganti, R. R. Sekar, and J. Zigan. On use of co2 chemilu-

minescence for combustion metrics in natural gas fired reciprocating engines. Proceedings of the

Combustion Institute, (33):3131–3139, 2011.

[4] A. G. Gaydon. The Spectroscopy of Flames. London: Chapman & Hall, 1974.

[5] T. P. Clark. Studies of oh, co, ch, and c2 radiation from laminar and turbulent propane-air and

ethylene-air flames. Technical Report 4266, National Advisory Comitee for Aeronautics, June 1958.

[6] M. Orain and Y. Hardalupas. Effect of fuel type on equivalence ratio measurements using chemilu-

minescence in premixed flames. Comptes Rendus Mecanique, (338):241–254, 2010.

[7] Y. Hardalupas and M. Orain. Local measurements of the time-dependent heat release rate and

equivalence ratio using chemiluminescent emission from a flame. Combustion and Flame, (139):

188 – 207, 2004.

[8] A. K. Sandrowitz, J. M. Cooke, and N. G. Glumac. Flame emission spectroscopy for equivalence

ratio monitoring. Applied Spectroscopy, 52(5):658 – 662, 1998.

[9] T. Chou and D. J. Patterson. In-cylinder measurement of mixture maldistribution in a l-head engine.

Combustion and Flame, (101):45 – 57, 1995.

[10] M. R. Morrel, J. M. Seitzman, M. Wilensky, E. Lubarsky, J. Lee, and B. Zinn. Interpretation of

optical emissions for sensors in liquid fueled combustors. In 39th Aerospace Sciences Meeting and

& Exhibit, January 2001.

[11] N. Docquier and S. Candel. Combustion control and sensors: a review. Progress in Energy and

Combustion Science, (28):107–150, 2002.

[12] C. Panoutsos, Y. Hardalupas, and A. Taylor. Numerical evaluation of equivalence ratio measure-

ment using oh and ch chemiluminescence in premixed and non-premixed methane–air flames.

Combustion and Flame, (156):273 – 291, 2009.

45

[13] H. Zhen, J. Miao, C. Leung, C. Cheung, and Z. Huang. A study on the effects of air preheat on the

combustion and heat transfer characteristics of bunsen flames. Fuel, (184):50–58, 2016.

[14] B. Higgins, M. McQuay, F. Lacas, J. Rolon, N. Darabiha, and S. Candel. Systematic measurements

of oh chemiluminescence for fuel-lean, high-pressure, premixed, laminar flames. Fuel, (80):67 –

74, 2001.

[15] B. Higgins, M. McQuay, F. Lacas, and S. Candel. An experimental study on the effect of pressure

and strain rate on ch chemiluminescence of premixed ffuel-lean methane/air flames. Fuel, (80):

1583 – 1591, 2001.

[16] V. N. Nori and J. M. Seitzman. Chemiluminescence measurements and modeling in syngas,

methane and jet-a fueled combustors. In 45th AIAA Aerospace Sciences Meeting and Exhibit,

January 2007.

[17] T. Garcia-Armingol, Y. Hardalupas, A. Taylor, and J. Ballester. Effect of local flame properties on

chemiluminescence-based stoichiometry measurement. Experimental Thermal and Fluid Science,

(53):93–103, 2014.

[18] T. Garcia-Armingol and J. Ballester. Influence of fuel composition on chemiluminescence emission

in premixed flames of ch4/co2/h2/co blends. International Journal of Hydrogen Energy, (39):20255–

20265, 2014.

[19] R.Metha and P.Bradshaw. Design rules for small low-speed wind tunnels. Aeronautical Journal

(Royal Aeronautical Society), 73:443 – 449, 1979.

[20] E. Petersen, M. Kopp, and N. Donato. Assessement of current chemiluminescence kinetics models

at engine conditions. In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition,

pages 817 – 825, 2011.

[21] D. Guyot, F. Guethe, B. Schuermans, A. Lacarelle, and C. O. Paschereit. Ch*/oh* chemilumines-

cence response of an atmospheric premixed flame under varying operating conditions. In Proceed-

ings of ASME Turbo Expo 2010: Power for Land, Sea and Air, pages 933 – 944, June 2010.

[22] T. S. Cheng, C.-Y. Wu, Y.-H. Li, and Y.-C. Chao. Chemiluminescence measurements of local equiv-

alence ratio in a partially premixed flame. Combustion Science and Technology, (178):1821–1841,

2006.

[23] V. N. Nori and J. M. Seitzman. Ch* chemiluminescence modeling for combustion diagnostics.

Proceedings of the Combustion Institute, (32):895–903, 2009.

[24] D.Goodwin. Cantera: An object-oriented software toolkit for chemical kinetics, thermodynamics

and transport processes. URL http : //code.google.com/p/cantera, 2009.

[25] G. P. Smith, D. M. Golden, M. Frenklach, N. W. Moriarty, B. Eiteneer, M. Goldenberg, C. T. Bow-

man, R. K. Hanson, S. Song, W. C. Gardiner, V. V. L. Jr., and Z. Qin. Gri-mech 3.0. URL

http : //www.me.berkeley.edu/grimech.

46

[26] B. Lewis and G. von Elbe. Combustion, Flames and Explosions of Gases. Academic Press, 1987.

[27] J. M. Hall, J. de Vries, A. R. Amadio, and E. L. Petersen. Towards a kinetics model of ch chemilu-

minescence. In 43rd AIAA Aerospace Sciences Meeting and Exhibit, January 2005.

[28] J. M. Hall and E. L. Petersen. An optimized kinetics model for oh chemiluminescence at high

temperatures and atmospheric pressures. International Journal of Chemical Kinetics, 38(12):714 –

724, 2006.

[29] M. Lalovic, Z. Radovic, and N. Jaukovic. Flame temperature as a function of the combustion condi-

tions of gaseous gases. Materials and Technology, 40(3), 2006.

[30] Y. K. Jeong, C. H. Jeon, and Y. J. Chang. Evaluation of the equivalence ratio of the reacting

mixture using intensity ratio of chemiluminescence in laminar partially premixed ch4-air flames.

Experimental Thermal and Fluid Science, (30):663–673, 2006.

[31] T. Muruganandam, B.-H. Kim, M. Morrell, V. Nori, M. Patel, B. Romig, and J. Seitzman. Optical

equivalence ratio sensors for gas turbine combustors. Proceedings of the Combustion Institute,

(30):1601–1609, 2005.

[32] J. Kojima, Y. Ikeda, and T. Nakajima. Spatially resolved measurements of oh*, ch* and c2* chemi-

luminescence in the reaction zone of laminar methane/air premixed flames. Proceedings of the

Combustion Institute, 28(2):1757 – 1764, 2000.

[33] M. Han, Y. Ai, Z. Chen, and W. Kong. Laminar flame speeds of h2/co with co2 dilution at normal

and elevated pressures and temperatures. Fuel, (148):32–38, 2015.

[34] F. Liu, H. Guo, and G. J. Smallwood. The chemical effect of co2 replacement of n2 in air on the

burning velocity of ch4 and h2 premixed flames. Combustion and Flame, (133):495–497, 2003.

[35] T. L. Cong and P. Dagaut. Experimental and detailed kinetic modeling of the oxidation of methane

and methane/syngas mixtures and effect of carbon dioxide addition. Combustion Science and

Technology, 180(10 - 11):2046 – 2091, 2008.

47

Appendix A

Conditions measured

The complete list of conditions measured during the experiments is listed below.

Table A.1: Conditions measured

Fuel φ Power(kW) Qfuel QN2QO2

QAr QCO2

0.80 0.75 1.234 11.65 3.095 0 0

0.80 0.75 1.234 11.15 3.095 0.5 0

0.80 0.75 1.234 10.65 3.095 1.0 0

0.80 0.75 1.234 10.15 3.095 1.5 0

0.80 0.75 1.234 9.65 3.095 2.0 0

0.80 0.75 1.234 9.15 3.095 2.5 0

0.80 0.75 1.234 8.65 3.095 3.0 0

0.80 0.75 1.234 8.15 3.095 3.5 0

0.80 0.75 1.234 7.65 3.095 4.0 0

0.80 0.75 1.234 7.15 3.095 4.5 0

0.90 1.25 2.056 17.25 4.586 0 0

CH4 0.90 1.25 2.056 16.75 4.586 0.5 0

0.90 1.25 2.056 16.25 4.586 1.0 0

0.90 1.25 2.056 15.75 4.586 1.5 0

0.90 1.25 2.056 15.25 4.586 2.0 0

0.90 1.25 2.056 14.75 4.586 2.5 0

0.90 1.25 2.056 14.25 4.586 3.0 0

0.90 1.25 2.056 13.75 4.586 3.5 0

0.90 1.25 2.056 13.25 4.586 4.0 0

0.90 1.25 2.056 12.75 4.586 4.5 0

0.90 1.25 2.056 12.25 4.586 5.0 0

1.00 1.25 2.056 15.52 4.127 0 0

1.00 1.25 2.056 15.02 4.127 0.5 0

49

1.00 1.25 2.056 14.52 4.127 1.0 0

1.00 1.25 2.056 14.02 4.127 1.5 0

1.00 1.25 2.056 13.52 4.127 2.0 0

1.00 1.25 2.056 13.02 4.127 2.5 0

1.00 1.25 2.056 12.52 4.127 3.0 0

1.00 1.25 2.056 12.22 4.127 3.3 0

1.10 1.25 2.056 14.12 3.753 0 0

1.10 1.25 2.056 13.62 3.753 0.5 0

1.10 1.25 2.056 13.12 3.753 1.0 0

1.10 1.25 2.056 12.62 3.753 1.5 0

1.10 1.25 2.056 12.12 3.753 2.0 0

1.10 1.25 2.056 11.62 3.753 2.5 0

1.10 1.25 2.056 11.12 3.753 3.0 0

1.10 1.25 2.056 10.62 3.753 3.5 0

1.10 1.25 2.056 10.12 3.753 4.0 0

1.20 1.25 2.056 12.94 3.440 0 0

1.20 1.25 2.056 12.44 3.440 0.5 0

CH4 1.20 1.25 2.056 11.94 3.440 1.0 0

1.20 1.25 2.056 11.44 3.440 1.5 0

1.20 1.25 2.056 10.94 3.440 2.0 0

1.20 1.25 2.056 10.44 3.440 2.5 0

1.20 1.25 2.056 9.94 3.440 3.0 0

1.20 1.25 2.056 9.44 3.440 3.5 0

1.20 1.25 2.056 8.94 3.440 4.0 0

1.20 1.25 2.056 8.44 3.440 4.5 0

1.30 1.25 2.056 11.95 3.175 0 0

1.30 1.25 2.056 11.45 3.175 0.5 0

1.30 1.25 2.056 10.95 3.175 1.0 0

1.30 1.25 2.056 10.45 3.175 1.5 0

1.30 1.25 2.056 9.95 3.175 2.0 0

1.30 1.25 2.056 9.45 3.175 2.5 0

1.30 1.25 2.056 8.95 3.175 3.0 0

1.30 1.25 2.056 8.45 3.175 3.5 0

1.30 1.25 2.056 7.95 3.175 4.0 0

1.30 1.25 2.056 7.45 3.175 4.5 0

0.90 1.25 2.056 17.25 4.586 0 0

0.90 1.25 2.056 16.77 4.586 0.309 0.173

0.90 1.25 2.056 16.29 4.586 0.617 0.345

0.90 1.25 2.056 15.81 4.586 0.922 0.518

50

0.90 1.25 2.056 15.34 4.586 1.226 0.690

0.90 1.25 2.056 14.86 4.586 1.529 0.863

0.90 1.25 2.056 14.39 4.586 1.830 1.035

0.90 1.25 2.056 13.92 4.586 2.129 1.208

0.90 1.25 2.056 13.45 4.586 2.426 1.380

0.90 1.25 2.056 12.98 4.586 2.721 1.553

0.90 1.25 2.056 12.51 4.586 3.015 1.725

1.00 1.25 2.056 15.52 4.127 0 0

1.00 1.25 2.056 14.57 4.127 0.642 0.311

1.00 1.25 2.056 13.63 4.127 1.276 0.621

1.00 1.25 2.056 12.69 4.127 1.901 0.932

1.00 1.25 2.056 11.77 4.127 2.518 1.242

1.00 1.25 2.056 10.85 4.127 3.126 1.553

1.00 1.25 2.056 9.94 4.127 3.726 1.863

1.00 1.25 2.056 9.03 4.127 4.318 2.174

1.00 1.25 2.056 8.14 4.127 4.901 2.484

1.00 1.25 2.056 7.26 4.127 5.476 2.795

CH4 1.00 1.25 2.056 6.47 4.127 5.987 3.074

1.10 1.25 2.056 14.12 3.753 0 0

1.10 1.25 2.056 12.93 3.753 0.767 0.424

1.10 1.25 2.056 11.74 3.753 1.527 0.847

1.10 1.25 2.056 10.57 3.753 2.280 1.271

1.10 1.25 2.056 9.40 3.753 3.025 1.694

1.10 1.25 2.056 8.24 3.753 3.763 2.118

1.10 1.25 2.056 7.09 3.753 4.493 2.541

1.10 1.25 2.056 5.94 3.753 5.214 2.965

1.10 1.25 2.056 4.69 3.753 6.000 3.431

1.20 1.25 2.056 12.90 3.440 0 0

1.20 1.25 2.056 11.90 3.440 0.66 0.388

1.20 1.25 2.056 10.90 3.440 1.308 0.776

1.20 1.25 2.056 9.83 3.440 1.944 1.165

1.20 1.25 2.056 8.82 3.440 2.567 1.553

1.20 1.25 2.056 7.82 3.440 3.178 1.941

1.20 1.25 2.056 6.84 3.440 3.776 2.329

1.20 1.25 2.056 5.86 3.440 4.363 2.718

1.20 1.25 2.056 4.90 3.440 4.938 3.106

1.20 1.25 2.056 3.95 3.440 5.50 3.494

1.20 1.25 2.056 3.16 3.440 5.96 3.818

1.30 1.25 2.056 11.95 3.175 0 0

51

1.30 1.25 2.056 10.90 3.175 0.639 0.358

1.30 1.25 2.056 9.97 3.175 1.257 0.717

1.30 1.25 2.056 9.01 3.175 1.856 1.075

1.30 1.25 2.056 8.07 3.175 2.436 1.433

1.30 1.25 2.056 7.15 3.175 2.998 1.792

1.30 1.25 2.056 6.25 3.175 3.542 2.150

1.30 1.25 2.056 5.37 3.175 4.070 2.508

1.30 1.25 2.056 4.50 3.175 4.581 2.867

1.30 1.25 2.056 3.64 3.175 5.077 3.225

1.30 1.25 2.056 2.80 3.175 5.557 3.583

1.30 1.25 2.056 2.03 3.175 5.992 3.918

1.30 1.25 2.056 4.5 3.175 4.581 2.867

CH4 1.30 1.25 2.056 3.5 3.175 5.581 2.867

1.30 1.25 2.056 2.5 3.175 6.581 2.867

1.30 1.25 2.056 1.5 3.175 7.581 2.867

0.80 1.00 0.650 15.57 4.140 0 0

0.80 1.00 0.650 15.07 4.140 0.5 0

0.80 1.00 0.650 14.57 4.140 1.0 0

0.80 1.00 0.650 14.07 4.140 1.5 0

0.80 1.00 0.650 13.57 4.140 2.0 0

0.80 1.00 0.650 13.07 4.140 2.5 0

0.80 1.00 0.650 12.57 4.140 3.0 0

0.80 1.00 0.650 12.07 4.140 3.5 0

0.80 1.00 0.650 11.57 4.140 4.0 0

0.80 1.00 0.650 11.07 4.140 4.5 0

0.80 1.00 0.650 10.57 4.140 5.0 0

0.90 1.60 1.060 22.52 5.980 0 0

C3H8 0.90 1.60 1.060 22.02 5.980 0.5 0

0.90 1.60 1.060 21.52 5.980 1.0 0

0.90 1.60 1.060 21.02 5.980 1.5 0

0.90 1.60 1.060 20.52 5.980 2.0 0

0.90 1.60 1.060 20.02 5.980 2.5 0

0.90 1.60 1.060 19.52 5.980 3.0 0

0.90 1.60 1.060 19.02 5.980 3.5 0

0.90 1.60 1.060 18.52 5.980 4.0 0

0.90 1.60 1.060 18.02 5.980 4.5 0

0.90 1.60 1.060 17.52 5.980 5.0 0

1.00 1.60 1.060 20.27 5.380 0 0

52

1.00 1.60 1.060 19.77 5.380 0.5 0

1.00 1.60 1.060 19.27 5.380 1.0 0

1.00 1.60 1.060 18.77 5.380 1.5 0

1.00 1.60 1.060 18.27 5.380 2.0 0

1.00 1.60 1.060 17.77 5.380 2.5 0

1.00 1.60 1.060 17.27 5.380 3.0 0

1.00 1.60 1.060 16.77 5.380 3.5 0

1.00 1.60 1.060 16.27 5.380 4.0 0

1.00 1.60 1.060 15.77 5.380 4.5 0

1.00 1.60 1.060 15.27 5.380 5.0 0

1.10 1.60 1.060 18.42 4.900 0 0

1.10 1.60 1.060 17.92 4.900 0.5 0

1.10 1.60 1.060 17.42 4.900 1.0 0

1.10 1.60 1.060 16.92 4.900 1.5 0

1.10 1.60 1.060 16.42 4.900 2.0 0

1.10 1.60 1.060 15.92 4.900 2.5 0

1.10 1.60 1.060 15.42 4.900 3.0 0

1.10 1.60 1.060 14.92 4.900 3.5 0

C3H8 1.10 1.60 1.060 14.42 4.900 4.0 0

1.10 1.60 1.060 13.92 4.900 4.5 0

1.10 1.60 1.060 13.42 4.900 5.0 0

1.20 1.60 1.060 16.89 4.490 0 0

1.20 1.60 1.060 16.39 4.490 0.5 0

1.20 1.60 1.060 15.89 4.490 1.0 0

1.20 1.60 1.060 15.39 4.490 1.5 0

1.20 1.60 1.060 14.89 4.490 2.0 0

1.20 1.60 1.060 14.39 4.490 2.5 0

1.20 1.60 1.060 13.89 4.490 3.0 0

1.20 1.60 1.060 13.39 4.490 3.5 0

1.20 1.60 1.060 12.89 4.490 4.0 0

1.30 1.60 1.060 15.59 4.140 0 0

1.30 1.60 1.060 15.09 4.140 0.5 0

1.30 1.60 1.060 14.59 4.140 1.0 0

1.30 1.60 1.060 14.09 4.140 1.5 0

1.30 1.60 1.060 13.59 4.140 2.0 0

1.30 1.60 1.060 13.09 4.140 2.5 0

1.30 1.60 1.060 12.59 4.140 3.0 0

0.90 1.60 1.060 22.52 5.980 0 0

0.90 1.60 1.060 19.94 5.980 1.66 0.9

53

0.90 1.60 1.060 19.62 5.980 1.865 1.012

0.90 1.60 1.060 19.30 5.980 2.070 1.125

0.90 1.60 1.060 18.99 5.980 2.274 1.237

0.90 1.60 1.060 18.67 5.980 2.477 1.350

0.90 1.60 1.060 18.35 5.980 2.680 1.462

0.90 1.60 1.060 18.04 5.980 2.883 1.575

1.00 1.60 1.060 20.27 5.380 0 0

1.00 1.60 1.060 18.97 5.380 0.865 0.405

1.00 1.60 1.060 17.71 5.380 1.717 0.810

1.00 1.60 1.060 16.47 5.380 2.558 1.214

1.00 1.60 1.060 15.23 5.380 3.388 1.619

1.00 1.60 1.060 14.01 5.380 4.206 2.024

1.00 1.60 1.060 12.83 5.380 4.993 2.419

1.10 1.60 1.060 18.42 4.900 0 0

1.10 1.60 1.060 17.36 4.900 0.707 0.369

1.10 1.60 1.060 16.29 4.900 1.410 0.737

1.10 1.60 1.060 15.22 4.900 2.109 1.106

1.10 1.60 1.060 14.15 4.900 2.804 1.475

1.10 1.60 1.060 13.10 4.900 3.494 1.843

1.10 1.60 1.060 12.04 4.900 4.181 2.212

C3H8 1.10 1.60 1.060 10.99 4.900 4.863 2.581

1.10 1.60 1.060 9.94 4.900 5.541 2.949

1.20 1.60 1.060 16.89 4.490 0 0

1.20 1.60 1.060 15.98 4.490 0.575 0.338

1.20 1.60 1.060 15.07 4.490 1.146 0.676

1.20 1.60 1.060 14.17 4.490 1.712 1.013

1.20 1.60 1.060 13.27 4.490 2.273 1.351

1.20 1.60 1.060 12.37 4.490 2.829 1.689

1.20 1.60 1.060 11.48 4.490 3.381 2.027

1.20 1.60 1.060 10.60 4.490 3.927 2.365

1.20 1.60 1.060 9.72 4.490 4.469 2.703

1.20 1.60 1.060 8.85 4.490 5.005 3.040

1.20 1.60 1.060 7.98 4.490 5.537 3.378

1.30 1.60 1.060 15.59 4.140 0 0

1.30 1.60 1.060 15.15 4.140 0.270 0.156

1.30 1.60 1.060 14.73 4.140 0.537 0.311

1.30 1.60 1.060 14.31 4.140 0.802 0.467

1.30 1.60 1.060 13.89 4.140 1.065 0.623

1.30 1.60 1.060 13.47 4.140 1.326 0.779

54

1.30 1.60 1.060 13.06 4.140 1.584 0.934

1.30 1.60 1.060 12.64 4.140 1.840 1.090

1.30 1.60 1.060 12.23 4.140 2.095 1.246

1.30 1.60 1.060 11.83 4.140 2.347 1.402

1.30 1.60 1.060 11.42 4.140 2.596 1.557

1.20 1.60 1.060 12.37 4.490 2.829 1.689

C3H8 1.20 1.60 1.060 11.37 4.490 3.829 1.689

1.20 1.60 1.060 10.37 4.490 4.829 1.689

1.20 1.60 1.060 9.37 4.490 5.829 1.689

55

chemiluminescence analysis of vitiated conditions for methane …€¦ · chemiluminescence...

Documents