Investigation of flame structure and stability for oxygen-enhanced combustion of low calorific value gases

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INVESTIGATION OF FLAME STRUCTURE AND

STABILITY FOR OXYGEN-ENHANCED COMBUSTION OF LOW CALORIFIC VALUE GASES

BISRAT YOSEPH GEBREYESUS

DEPARTMENT OF MECHANICAL ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY DELHI

OCTOBER – 2017

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INVESTIGATION OF FLAME STRUCTURE AND

STABILITY FOR OXYGEN-ENHANCED COMBUSTION OF LOW CALORIFIC VALUE GASES

by

BISRAT YOSEPH GEBREYESUS Department of Mechanical Engineering

Submitted

in fulfillment of the requirements of the degree of Doctor of Philosophy to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI NEW DELHI, INDIA

OCTOBER - 2017

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Dedicated to My Mother and Father

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CERTIFICATE

The thesis entitled “Investigation of Flame Structure and Stability for Oxygen-Enhanced Combustion of Low Calorific Value Gases” being submitted by Capt. Bisrat Yoseph to the Indian Institute of Technology Delhi for the award of the degree of Doctor of Philosophy, is a record of original bonafide research work carried out by him. He has worked under my guidance and supervision and has fulfilled the requirements for the submission of this thesis, which has attained the standard required for a Ph.D. degree of this Institute.

The results represented in this thesis have not been submitted elsewhere for the award of any degree or diploma.

Dr. Anjan Ray Professor, Department of Mechanical Engineering,

Indian Institute of Technology, Delhi

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ACKNOWLEDGMENTS

“Trust in the Lord with all your heart, and lean not on your understanding.

In all ways acknowledge Him, and He shall direct your paths” Proverbs 3: 5-6 The completion of the last six years work would not have been possible without the support that I received from God and many peoples. I would like to put on record my deepest gratitude to each and every one.

At the outset, I would like to express my ultimate praise to my Lord God, who relives His agape love through Jesus Christ and for providing me wisdom, peace, and inspiration to each of my days through Holy Spirit.

I would like to express my sincere gratitude to Professor Anjan Ray, who exposed me to the depths of the exciting field of combustion, for his continuous guidance, encouragement and imparting imminence knowledge throughout my study at Indian Institute of Technology, New Delhi. I had an absolute freedom to plan and execute my ideas without any pressure, along with the critical issues, which incented me to widen my research from various perspectives.

Besides my advisor, I am deeply indebted to my research committee: Prof. Sangeeta Kohli, Prof. M. R. Ravi, Dr. Murali Cholemari and Dr. Sawan S. Sinha for spending their time to set compressive exam, reading my reports and giving insightful suggestions during my research proposal and synopsis presentations.

I am also thankful to Ethiopia Defence University, College of Engineering, for giving permission to pursue my Ph.D. study and Ethiopia Ministry of Defence for providing financial support.

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ii ACKNOWLEDGMENTS

My sincere thanks also go to Dr. Vednath Mathur, Dr. Ratna Kishore (my seniors), Mr.

Mohan Kumar, Col. K.S.R Reddy, Mr. Pushan Sherma (pass out Mtech. and MS(R) graduates) Mr. Suvabrata Panja (internship), Mr. Abdul Rahman (Ph.D. Scholar) and Mr. Tesfay Molalgn (Ph.D. Scholar) for their invaluable contribution, technical assistance and thoughtful discussions during fabrication of experimental setup, conducting simulations and experiments.

Without their precious support, it would not be possible to conduct this research.

I thank all my colleagues and technical staffs in the Heat Transfer, Thermal Science, Fire, Combustion research laboratories and Central workshop. My thanks also go to Mr. Pradeep Kumar and his family members for their encouragement and sharing friendship.

Thanks is too small a word to express my heartfelt emotions to my beloved wife Debora Daniel. The love, patience, understanding and help bestowed on me by her eased my way to attain my goal. I express my sincere gratitude to her for giving encouragement during the toughest phases of my work, helping me a lot in proofreading and made me the father of a son. Big Sorry for my absence in the moments I should be with you.

And last but not least, my thanks are also due to my mother, brothers and sister for their encouragement and prayers. Especially for my late father who taught me to be patient while striving for any goals set in life.

New Delhi,

October, 2017 Bisrat Yoseph (Capt.)

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ABSTRACT

Low calorific value gas (LCVG) is a mixture of combustible gases (hydrogen, carbon monoxide and methane), inert gases (nitrogen and carbon dioxide) and non-hydrocarbon impurities (H2S, NH3, HCN, etc.) having a heating value below 7 MJ/m³. Identifying the best strategy for efficient burning of LCVG becomes inevitable to improve the efficiency of a system and reduction of emission of pollutants. In the present work, the non-premixed laminar flame structure and stability of LCVG fuel with co-flowing oxygen-enhanced oxidizer have been investigated experimentally and numerically.

The LCVG was modeled in the laboratory by mixing the nitrogen and methane gases while keeping the heating value below 7.2 MJ/m³ (≤ 20 % by vol. methane concentration level in the fuel stream). The oxidizer was modeled by mixing oxygen and nitrogen gases where the oxygen concentration level was varied from 21 to 100 % by volume. The flame length, width, lift-off height and radial and axial flame temperature distribution were measured and predicted under the influence of varying oxygen enrichment level, fuel dilution level, jet and co-flow velocities. Experimentally, the flame stability zones (anchored, lifted and blow-out regimes) were determined by identifying the critical fuel dilution and oxygen enhancement levels for fixed jet and co-flow velocities. Additionally, major species radial profiles at different flame heights and the LCVG-OEC flames leading edge structure were studied numerically.

When the oxygen enrichment level was decreased for fixed fuel composition, jet and co-flow velocities, the flame became longer, wider and increases its lift-off height. When the fuel dilution level was increased for fixed oxygen enhancement level, jet and co-flow velocities (decreasing the methane concentration level starting from 20 % by vol.), the flame length and width did not show appreciable change until the flame started lifting-off at 13 % by vol.

methane concentration level. Reduction of methane concentration level below 13 % by vol.

increases the lift-off height and flame base width and decreases the flame length considerably.

In the present work a fuel composition of 8 % CH4 - 92 % N2, which has 2.85 MJ/m³calorific value, was the lowest fuel dilution level at which the flame sustained without blow-out under pure oxygen co-flowing oxidizer.

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iv ABSTRACT When the jet velocity was increased for fixed fuel and oxidizer gas compositions and co-flow velocity, the flame length exhibited significant rise but the lift-off height and flame width remained constant except for very low flow ranges. When the co-flow velocity was increased for fixed fuel and oxidizer gas compositions and jet velocity, the flame length, width and lift-off height did not show significant changes. But at higher global equivalence ratio or lower co-flow velocity (V_CF 5cm s) ranges, the flame became sensitive to small perturbation and showed longer flame length since flame temperature decrease due to starvation of oxidizer.

Additionally, at lower oxygen enrichment levels (close to blow-out limits), the flame also showed lift-off tendency with increasing co-flow velocities. In order to determine the flame lift-off height, it was found that the maximum concentration of HO2 iso-contour defines the flame front position very well compared to the 1000 K isotherm which was used by other researchers. The LCVG-OEC flame edges (tri-brachial) structure was studied numerically using a combination of iso-contours of volumetric heat release rate, mass fraction of HO2, stoichiometric mixture fraction and 1000 K isotherm.

To conclude, the present work contributes to the fundamental knowledge in ongoing research activities and technology development for efficient burning of LCVG with oxygen- enhanced combustion mode in the non-premixed burner. Thus, the system efficiency can be improved by utilizing such waste gases as an alternative fuel and reduce the environmental pollution and global warming without flaring.

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सार

निम्न उष्मीय माि मूल्य (LCVG) ज्वलनशील गैसों (हाइड्रोजन, कार्बन मोनोऑक्साइड और मीथेन), जड़

गैस (नाइट्रोजन और कार्बन डाइऑक्साइड) और गैर-हाइड्रोकार्बन अशुद्धियों का द्धमश्रण है (H2S, NH3,

HCN, आदि।) एक ताप मूल्य नीचे है 7 MJ/m³. LCVG गैस को जलाने की सवोत्तम रणनीद्धत की पहचान करना, एक प्रणाली की िक्षता में सुधार और प्रिूषण के उत्सजबन में कमी के द्धलए अद्धनवायब हो जाता है।

वतबमान कायब में, अनमनित पटलीय ज्वाला की संरचिा एवं उसके स्थनयत्वा का सांनययक एवं प्रोगात्मक अध्यि ऑक्सीजि वर्धित , सह-प्रवाही ऑक्सीकारक की उपनस्तनथ में ककया गया है।

LCVG एलसीवीजी को नाइट्रोजन और मीथेन गैसों को द्धमलाकर प्रयोगशाला में तैयार दकया

गया था, जर्दक उष्मीय माि को 7.2 MJ/m³(≤ 20 % मीथेन सांद्रण स्तर) से नीचे रखा गया था।

ऑक्सीकारक ऑक्सीजन और नाइट्रोजन गैसों को द्धमलाकर द्धमद्धश्रत दकया गया था, जहाां ऑक्सीजन सांद्रण

स्तर की मात्रा 21 से 100 % तक बदली गयी थी । लौ की लांर्ाई, चौड़ाई, द्धलफ्ट-ऑफ की ऊांचाई और रेद्धडयल और अक्षीय लौ तापमान द्धवतरण को मापा गया और ऑद्धक्सजन सांवधबन स्तर, ईंधन तिुता के स्तर, जेट और सह-प्रवाह वेगों के प्रभाव के तहत प्रागुक्त की गई। प्रयोगात्मक रूप से, ज्वाला द्धस्थरता वाले क्षेत्र (नस्थर, द्धलफ्ट-ऑफ और वातगति प्रवृत्नत वाले) लौ में सह-प्रवाह वेग र्ढ़ने के साथ द्धलफ्ट-ऑफ प्रवृद्धत्त भी दिखाई

िेती है। लौ द्धलफ्ट-ऑफ ऊांचाई को द्धनधाबररत करने के द्धलए, यह पाया गया दक HO2 आईएसओ समोच्चकी

अद्धधकतम सांद्रण स्तर, लौ के सामने की द्धस्थद्धत को र्हुत अच्छी तरह से 1000 K समताप रेखा की तुलना में

पररभाद्धषत करता है द्धजसका उपयोग अन्य शोधकताबओं द्वारा दकया गया था। LCVG-OEC लौ प्रमुख धार सांरचना सांख्यात्मक रूप से अध्ययन दकया गया।

जर् ऑक्सीजन सांवधबन का स्तर द्धनद्धित ईंधन सांरचना, जेट और सह-प्रवाह वेग के द्धलए कम हो

गया, तो लौ अर् और अद्धधक हो गई और द्धलफ्ट-ऑफ की ऊांचाई र्ढ़ा िी जर् तय ऑक्सीजन वृद्धि स्तर, जेट और सह-प्रवाह वेग (वॉल्यूम से 20 % से शुरू होने वाले मीथेन सांद्रण स्तर को घटाने) के द्धलए ईंधन के

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vi सार

कमजोर पड़ने का स्तर र्ढ़ गया था, तो लौ की लांर्ाई और चौड़ाई लौटे जाने तक महत्वपूणब पररवतबन नहीं

दिखा पाई थी- वॉल्यूम से 13 % पर र्ांि मीथेन सांद्रण स्तर वॉल्यूम से मीथेन सांद्रण स्तर 13 % से नीचे

घटाना द्धलफ्ट-ऑफ ऊांचाई और लौ आधार चौड़ाई र्ढ़ जाती है और लौ की लांर्ाई काफी कम हो जाती है।

वतबमान कायब में 8% CH4 - 92 % N2 का ईंधन सांरचना है, द्धजसमें 2.85 MJ/m³कैलोरी मान हैं, यह सर्से

कम ईंधन कमजोर पड़ने का स्तर था, द्धजस पर शुि ऑक्सीजन सह-र्ह आक्सीकारक के द्धर्ना वातगति के

द्धर्ना लौ लगी।

दफक्स्ड ईंधन और ऑक्सीडाइज़र गैस रचनाओं और सह-प्रवाह वेग के द्धलए जेट वेग र्ढ़ गया था, तो

लौ की लांर्ाई में उल्लेखनीय वृद्धि हुई लेदकन द्धलफ्ट-ऑफ की ऊांचाई और लौ की चौड़ाई र्हुत कम प्रवाह सीमाओं के अलावा द्धस्थर रही। जर् दफक्स्ड ईंधन और आक्सीकारक गैस रचनाओं और जेट वेग के द्धलए सह- प्रवाह वेग र्ढ़ता था, तो लौ की लांर्ाई, चौड़ाई और द्धलफ्ट-ऑफ ऊांचाई में महत्वपूणब पररवतबन नहीं दिखाए गए थे। लेदकन उच्च व्यापक तुल्यता अिुपात या कम सह-प्रवाह वेग (VCF ≤ 5 cm /s) पारस पर, लौ छोटे

क्षोभ के प्रद्धत सांवेिनशील हो गई और ऑक्सीद्धडजर की कमी के कारण लौ तापमान में कमी आने के र्ाि से

लांर्ी लौ की लांर्ाई दिखायी गयी। इसके अद्धतररक्त, कम ऑक्सीजन सांवधबन के स्तर (वातगति की सीमाओं के

करीर्) में, लौ ने सह-प्रवाह वेग र्ढ़ाने के साथ द्धलफ्ट-ऑफ प्रवृद्धत्त भी दिखायी। लौ द्धलफ्ट-ऑफ ऊांचाई को

द्धनधाबररत करने के द्धलए, यह पाया गया दक HO2 आईएसओ-समोच्च ज्वालामुखी के सामने की द्धस्थद्धत को

र्हुत अच्छी तरह से पररभाद्धषत करता है, जो दक 1000 K समताप रेखा की तुलना में अन्य शोधकताबओं द्वारा

उपयोग दकया गया था। LCVG-OEC ज्वालामुखीय गमी ररहाई िर, HO2 के द्रव्यमान अांश, स्टोइचीओमेरट्रक द्धमश्रण अांश और 1000 K समताप रेखा के आइसो-आकृद्धत के सांयोजन का प्रयोग करके लौ

दकनारों (आदिवासी) सांरचना का सांख्यात्मक अध्ययन दकया गया था।

प्रतुत अध्यि LCVG के दक्ष दहि एवं तकिीकी नवकास के अिुसन्धाि में मूलभूत ज्ञाि बढ़िे में

योगदाि प्रदाि करता है। अतः अवशेष गैस का उपयोग वैकनल्पक ुुऊजाि के रूप में कर ककसी निकाय की

दक्षता को बढ़ाया, ग्लोबल वार्मिंग एवं वातावरण प्रदुषण को काम ककया जा सक्ता है ।

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LIST OF FIGURES

Figure 2.1 Dead space above the rim ... 25

Figure 2.2 S-shape flame temperature response with Damköhler number, ... 30

Figure 2.3 Tri-brachial flame structure ... 31

Figure 3.1 Layout of the experimental set ... 52

Figure 3.2 Mixing unit for five gases ... 54

Figure 3.3 Mole Fraction of CH4- N2 gas mixing in the axial direction at the center of the tube (left side) and across radial direction at the exit of the mixing tube (right side) ... 55

Figure 3.4 Coaxial burner configuration ... 56

Figure 3.5 Honeycomb structure ... 57

Figure 3.6 Flame image capturing device ... 58

Figure 3.7 Temperature measuring device ... 59

Figure 3.8 Two types of thermocouple wire arrangements ... 60

Figure 3.9 General workflow chart ... 63

Figure 3.10 Flow chart for ignition process ... 65

Figure 3.11 Actual flame image captured by DSLR camera (A) and its red (B), green (C) and blue (D) intensity images ... 68

Figure 3.12 The intensity of red, green and blue colors for a typical flame across axial direction... 69

Figure 3.13 The intensity of red, green and blue colors of typical flame across radial direction ... 70

Figure 3.14 Radial (a) and axial (b) temperature measurement sequence ... 71

Figure 4.1 Flame length variation with oxygen concentration levels at a fixed Rv= 0.08 (V_CF= 5.4 cm/s and V_{jet mean}_, = 66.3 cm/s) for 15, 14, 13, 12 and 11 % by vol. CH4 in the fuel stream... 79

Figure 4.2 Flame length variation with oxygen concentration levels at different co-flow velocities (5.4, 33.3, 66.3, 99.7 cm/s) for fixed jet velocity (66.3 cm/s) and LCVG fuel composition (15 % CH4 – 85 % N2). ... 81

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xiv LIST OF FIGURES Figure 4.3 Variation of flame length with oxygen concentration levels at three

different jet velocities (66.3, 132.6, and 198.9 cm/s) for fixed co-flow velocity (33.3 cm/s) and fuel composition (15% CH4 – 85 % N2). ... 82 Figure 4.4 Flame length variation with oxygen concentration levels at two

different jet velocities (66.3 and 132.6 cm/s) and two co-flow

velocities (5.4 and 33.3 cm/s) for 15 % CH4 – 85 % N2 fuel. ... 83 Figure 4.5 Flame length variation with oxygen concentration level at two

different jet velocities (66.3 and 132.6 cm/s ) and two co-flow

velocities (33.3 and 66.6 cm/s) for 15% CH4 – 85 % N2 fuel. ... 84 Figure 4.6 Flame width variation with oxygen concentration levels at a fixed

co-flow (27 cm/s) and jet (66.3cm/s) velocities for 15, 14, 13, 12

and 11 % by vol. CH4 contains LCVG fuels. ... 87 Figure 4.7 Flame width variation with oxygen concentration levels at four

different co-flow velocities (5.4, 33.3, 66.3 and 99.7 cm/s) and fixed

jet velocity (33.3 cm/s) for 15 % CH4 – 85 % N2 fuel. ... 88 Figure 4.8 Flame width variation with oxygen concentration levels at three

different jet velocities (66.3, 132.6, 198.9 cm/s) for fixed co-flow

velocity (33.3 cm/s) and 15% CH4 -85 % N2 fuel. ... 89 Figure 4.9 Flame lift-off height variation with oxygen concentration levels at

fixed jet (66.3 cm/s) and co-flow (5.4 cm/s) velocities for 15, 14, 13,

12 and 11 % by vol. CH4 contains fules. ... 90 Figure 4.10 Flames of 15, 14, 13, 12, and 11 % by vol. of CH4 contains LCVG at

two O2 concentration levels; 100 % by vol. (left) and before blow-out (right), for fixed jet (66.3 cm/s) and co-flow (5.4 cm/s) velocities. ... 91 Figure 4.11 Variation of flame luminosity with oxygen enhancement levels for

fixed fuel composition (15 % CH4 -85 % N2), jet (66.3 cm/s) and

co-flow (33.3 cm/s) velocities... 93 Figure 4.12 Locations of a 3 mm diameter circular cells on 10 by 10 pixels

rectangular domain (100 cell points) for 40 % by vol. (left side) and

95 % by vol. (right side) of O2 enhanced flames ... 94

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LIST OF FIGURES xv Figure 4.13 Variation of average grayscale (left) and average intensity (right)

of flames of 95 % O2 by vol. (red) and 40 % O2 % by vol. (blue) ... 94 Figure 4.14 Flame length variation with fuel dilution levels at three jet velocities

(33.3, 66.3 and 132.6 cm/s) and two O2 concentration levels (100 and 50 % by vol.) for fixed co-flow velocity (13.4 cm/s). ... 96 Figure 4.15 Flame length variation with fuel dilution levels at lower (QCF = 0.5

and 1 LPM) and higher (QCF = 5 and 10 LPM) flow of co-flow for fixed jet flow (0.25 and 0.5 LPM) and O2 enrichment level (100 and

50 % by vol.) ... 98 Figure 4.16 Flame length variation with fuel dilution levels at two low range jet

velocities (13.3 and 26. 5 cm/s) for fixed co-flow velocity (13.4 cm/s) and two oxygen enhancement levels (50 and 100 % by vol.). ... 100 Figure 4.17 Flame width variations with fuel dilution levels at three different jet

velocities (33.3, 66.3 and 132.6 cm/s) for fixed co-flow velocity

(13.4 cm/s ) and two O2 enhancement levels (100 and 50 % by vol.). ... 101 Figure 4.18 Flame width variation with fuel dilution levels at four high range

co-flow velocities (13.3, 27, 33.3 and 43 cm/s) for fixed jet velocity

(66.3 cm/s ) and 50 % by vol. O2 enhancement level. ... 102 Figure 4.19 Flame width variations with fuel dilution levels at four low rang

co-flow velocities (1.3, 2, 2.7 and 13.4 cm/s) for fixed jet velocity

(33.3 cm/s) and 100 % by vol. O2 enhancement level. ... 103 Figure 4.20 Flame width variation with fuel dilution levels at two low range jet

velocities (13.3 and 26. 5 cm/s) for fixed co-flow velocity (13.4 cm/s) and two oxygen enhancement levels (50 and 100 % by vol.). ... 104 Figure 4.21 Stoichiometric mixture fraction (^Z^st) variation with fuel dilution

levels at 100 and 50 % by vol. O2 concentration levels in the

oxidizer stream. ... 105 Figure 4.22 Flame lift-off height variation with fuel dilution levels at three different

jet velocities (33.3, 66.3 and 132.6 cm/s) for fixed co-flow velocity

(13.4 cm/s ) and two O2 enrichment levels (100 and 50 % by vol.). ... 106

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xvi LIST OF FIGURES Figure 4.23 Flame lift-off height variation with fuel dilution levels at four high

range co-flow velocities (13.3, 27, 33.3 and 43 cm/s) for fixed jet

velocity (66.3 cm/s ) and 50 % by vol. O2 enhancement level. ... 108 Figure 4.24 Flame lift-off height variations with fuel dilution levels under the

influence of low co-flow Reynolds numbers (40, 60 and 80) and

fixed jet velocity (33.3 cm/s) and 100 % by vol. O2. ... 108 Figure 4.25 Flame lift-off height variation with fuel dilution levels at two low

range jet velocities (13.3 and 26. 5 cm/s) for fixed co-flow velocity (13.4 cm/s) and two oxygen enhancement levels (50 and 100 % by

vol.). ... 109 Figure 4.26 Flame pictures of varying fuel dilution (CH4 concentration) levels at low jet

velocity (13.3 cm/s) and medium co-flow velocity (13.4 cm/s) ranges for 100

% by vol. oxygen enhancement level. ... 110 Figure 4.27 The variation of flame luminosity with the fuel dilution levels at fixed

jet (66.3 cm/s) and co-flow (53.7 cm/s) velocities for 100 % by vol.

O2 enhancement level ... 111 Figure 4.28 Flames luminosity variation with three CH4 concentration levels

(20 %, 15 % and critical limit before blow-out) at three jet velocities (132.6, 66.3 and 27 cm/s) for fixed co-flow velocity (54 cm/s) and O2

enhancement level (50 % by vol.)... 111 Figure 4.29 The variation of average grayscale and intensity of 30% by vol. and

10 % by vol. CH4 flames at 100 cell locations across the flame regions .... 112 Figure 4.30 Calculated Flame temperature (T_F) and laminar burning velocity,

SL st for various CH4 concentration levels under pure and 50 % by vol.

O2 enhancement levels. ... 114 Figure 4.31 Flame length variation with the jet velocity at five fixed co-flow

velocities (5, 10, 20 and 40 cm/s) for 15 % CH4 – 85 % N2 fuel

burning with 100 % by vol. O2 oxidizer . ... 119 Figure 4.32 Normalized flame length variation with the velocity ratio at five

fixed co-flow velocities (5, 10, 20 and 40 cm/s) for 15 % CH4 –

85 % N2 fuel and 100 % by vol. O2 in the oxidizer stream... 120

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LIST OF FIGURES xvii Figure 4.33 Variation of flame lift-off height with the jet velocity at fixed

co-flow velocities (5, 10, 20, 30, and 40 cm/s) for 15 % CH4 –

85 % N2 fuel and 100 % by vol. O2 in the oxidizer stream... 120 Figure 4.34 Flame width variation with the jet velocity at five fixed co-flow

velocities (5, 10, 20 and 40 cm/s) for 15 % CH4 – 85 % N2 fuel and

100 % by vol. O2 in the oxidizer stream. ... 121 Figure 4.35 Variation of flame length (a), lift-off height (b) and flame width (c)

with the jet velocity for two fuels (15 and 12 % by vol. CH4) at fixed co-flow velocity (13.4 cm/s ) and two oxygen enhancement levels

(100 and 50 % by vol.). ... 123 Figure 4.36 Flames for various values of jet velocity for 15 % CH4 – 85 % N2

fuel and 100 % by vol. O2 in the oxidizer stream at a fixed co-flow

velocity of 27 cm/s. ... 124 Figure 4.37 Flames for various values of jet velocity for 15 % CH4 – 85 % N2

fuel and 50 % by vol. O2 in the oxidizer stream at a fixed co-flow

velocity of 27 cm/s. ... 124 Figure 4.38 The average grayscale and average intensity of four selected flames

at ^V^jet =199, 133, 66.3 and 13 cm/s for 200 selected cell points across 10 by 20 pixels domain ( 200 cells ). ... 125 Figure 4.39 Flame length variation with co-flow velocity at three fixed jet velocities

(26.5, 66.3, and 132.6 cm/s) for 15% CH4 – 85 % N2 fuel and 100 % by vol. oxygen in the oxidizer stream. ... 127 Figure 4.40 Flame length and lift-off height variation with the co-flow velocity at

fixed jet velocity of 132.6 cm/s for 15 % CH4 – 85 % N2 and 100 %

by vol. O2 in the oxidizer stream. ... 127 Figure 4.41 Variation of flame length (a), lift-off height (b) and flame width (c)

with the co-flow velocities for fuel stream containing 15 and 12 % by vol. CH4 and oxidizer stream containing 100 and 50 % by vol.

O2 at 66.3 and 132.6 cm/s jet velocities. ... 129

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xviii LIST OF FIGURES Figure 4.42 Minimum oxygen concentration level before blow-out at 66.3 and

132.6 cm/s jet velocities and 5.4 and 27 cm/s co-flow velocities for fuels containing 15, 14, 13, 12 and 11 % by vol. CH4 concentration level. ... 132 Figure 4.43 Flame stability zones (by determining the limiting CH4 concentration

level for a given oxygen enhancement levels) at 66.3 cm/s jet and

27 cm/s co-flow velocities. ... 134 Figure 4.44 Flames temperature profile at three flame heights (burner rim (a),

5 mm (b) and 20 mm (c)) for four O2 enhancement levels (100, 90, 80 and 60 % by vol.) and fixed fuel composition (15 % CH4 - 85 % N2), jet (132.6 cm/s) and co-flow (2.7 cm/s) velocities. And at three flame heights (burner rim (d), 5 mm (e) and 10 mm (f)) for CH4 contains fuels (15,14,13 and 12 % by vol) and fixed O2 enhancement level (60 %) jet (66.3cm/s) and co-flow (27 cm/s) velocities. ... 137 Figure 4.45 Flames temperature profiles for fuel (13 % CH4 - 85 % N2) at three

flame heights (burner rim (a), 5 mm (b) and 10 mm (c)) for two jet velocities (66.3 and 132.6 cm/s) and fixed co-flow velocity (27 cm/s) and O2 enhancement level (60 % by vol.). And for fuel (15 % CH4 - 85 % N2) at three flame heights (burner rim (d), 5mm (e) and 10 mm (f)) for two co-flow velocities (5.4 and 27 cm/s), fixed jet

velocity (66.3 cm/s) and O2 enhancement level (40 % by vol.). ... 139 Figure 4.46 Axial temperature profile for two fuel dilution levels (15 and 12

% by vol. CH4 contains LCVG) at fixed jet velocity (66.3 cm/s), two co-flow velocities (5.4 and 27 cm/s) and two O2 enhancement

levels (40 and 65 % by vol.). ... 141 Figure 4.47 Axial flame temperature profile when 10 % by vol. moles of N2

shifting from the oxidizer to fuel stream while maintaining the

unity global equivalence ratio ... 141 Figure 5.1 Two dimensional axisymmetric computational domain and boundaries. ... 155 Figure 5.2 A typically magnified view of mesh grid 100 𝜇𝑚 × 50 𝜇𝑚 finest

grid size for 120 mm × 100 mm computatioanl domain. ... 158

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LIST OF FIGURES xix Figure 5.3 Computational domain, boundary conditions and mesh used

for fluent... 162 Figure 5.4 Radial profiles of temperature and major species at two flame

heights (2.2 mm (left) and 7.6 mm (right)) using the current computational model (solid line) and experimental results

(dotted line) of Flame-3 reported by Bennett et al. ... 162 Figure 5.5 Parameters used to define lift-off height, H_L(left side), flame

length, L_f(middle) and flame width, W_f (right side) : maximum and 1000 K isotherms (red lines), contours of

HO2

Y and Y_CH (flooded zone)

and ^Z^stiso-contour (black line). ... 164 Figure 5.6 Converged temperature contours close to flame tip for grid

independence cheek (the initial grid (a) has smallest cell size of 100m50 m, (b) refined the cells 4× between 1500-2033.8 K iso-temperature flame region then (c) refined the cells 16× between

2000-2033.8 K iso-temperature flame regions). ... 166 Figure 5.7 Comparison of flame structure with OTA radiation model

(right-hand side) and without radiation model (left-hand side), (a) the temperature contour along above 500 K and^Z^st (b) peak and 1000 K isotherms, ^Y^HO²contour and ^Z^st iso-contour. for a

flame of 15 % CH4 – 85 % N2 fuel with 37 % O2 – 63 % N2 oxidizer

at jet velocity of 66.3 cm/s and co-flow velocity of 33.3 cm/s. ... 168 Figure 5.8 The mole Fraction HO2, reaction rate of R-9 and temperature variation

for a planar flame of (12 % CH4−88 % N2) fuel with (50 % O2−

50 % N2) oxidizer at unity equivalence ratio. ... 170 Figure 5.9 The sensitivity coefficients of temperature for ten most sensitive

reactions at 1000 K flame location, i.e., at 39.96 mm. ... 170 Figure 5.10 The rate of production and destruction of HO2 species (mole/cm³-

sec) from different reactions at 1000 K flame location. ... 172 Figure 5.11 The total rate of production and destruction of HO2 species and

temperature across the flame. ... 172

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xx LIST OF FIGURES

Figure 5.12 Isotherms between 300 - 1400 K (flooded zone), iso-contours of ^Y^HO² light blue lines) and ^Y^OH ( white broken lines) and ^Z^st iso-contour (dark blue line) at the flame base when 15 % CH4 - 85 % N2 fuel burned with 100 % by vol. O2 (a) and 50 % by vol. O2 (b) at

jet (66.3 cm/s) and co-flow (27 cm/s) velocities for ^d^jet = 4 mm burner. .. 173 Figure 5.13 1000k isoterm (black line), contours of

HO2

Y (flooded Zone) and YOH(White broken line) species and Z_st iso-contour (blue line) at fixed jet (26.5 cm/s) and co-flow (27 cm/s) velocities and

djet = 4 mm, when (a) 20 % by vol. CH4 and (b) 12 % by Vol.

CH4 burn with 50 % by vol. O2. ... 175 Figure 5.14 1000k isotherm (black line), contours of

HO2

Y (flooded Zone) and YOH (White broken line) species and Z_st iso-contour (blue line) at fixed jet (26.5 cm/s) and co-flow (27 cm/s) velocities and

djet = 4 mm, when 30 % by vol. CH4 burn with 21 % by vol. (air). ... 175 Figure 5.15 Contours of HRR (left) and Y_HCO (right) for combustion of 12 %

CH4 - 88 % N2 fuel with 50 % O2 - 50% N2 oxidizer at fixed jet

velocity of V_{jet mean}_, = 26.5 cm/s and Co-flow velocity of V_CF = 27 cm/s ... 177 Figure 5.16 Comparison of Predicted flame lift-off height by

HO2

Y and HRR/HCO

approaches for different fuel dilution levels at a fixed oxidizer enrichment (50 % O2 - 50 % N2), jet velocity of 26.5 cm/s and

co-flow velocity of 27 cm/s. ... 178 Figure 5.17 Flame lift-off height prediction based on volumetric heat release

rate (left), maximum YHO2 iso-contour (middle) compared with the experimentally determined value (right-hand side) for burning 15 % CH4 with 37 % O2 enhanced air at 66.3 cm/s jet and 33 cm/s co-flow velocities. Here 1000 K isotherm (black line), stoichiometric

mixture fraction, Z_st(yellow line) and YHO2 (flooded zone). ... 179

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LIST OF FIGURES xxi Figure 5.18 Effect of varying O2 enrichment levels from 100 to 37 % by vol.

for 15 % CH4, - 85 % N2 fuel at a fixed jet (66.3 cm/s), co-flow (33 cm/s) velocities and ^d^jet= 4 mm. The maximum and 1000 K isotherms (white lines), contour of

HO2

Y species (flooded zone)

and Z_st iso-contour (black line). ... 181 Figure 5.19 Comparison of experimental (circular shape dots) and numerical

(diamond shape dots) flame lift-off height variation with oxygen enhancement level for (15 % CH4 - 85 % N2) fuel at fixed jet

(66.3 cm/s) and co-flow (33 cm/s) velocities and d_jet= 4 mm. ... 182 Figure 5.20 Effect of varying oxygen enhancement from 100 to 50 % by vol.

for 10 % CH4 – 90 % N2 fuel at fixed jet (87.5 cm/s) and co-flow (66 cm/s) velocites and d_jet = 3.5 mm. The maximum and 1000 K isotherms (white lines), contour of

HO2

Y species (flooded zone) and

Zst iso-contour (black line) ... 183 Figure 5.21 Comparison of experimental (diamond dots) and numerical

(circular dots) flame length variation with oxygen enhancement levels for 15 % CH4 - 85 % N2 fuel at fixed jet (66.3 cm/s) and

co-flow (33 cm/s) velocities and d_jet = 4 mm. ... 184 Figure 5.22 Experimental (diamond dots) and numerical (circular dots) flame

width variation with oxygen concentration levels for 15 % CH4 – 85% N2 fuel at fixed jet (66.3 cm/s) and co-flow (33 cm/s) velocities

and d_jet = 4 mm. ... 186 Figure 5.23 Flame width varation with two O2 enrichment levels; 100 % (left side)

and 40 % by vol. (right side) for 15 % CH4- 85 % N2 fuel at fixed jet (66.3 cm/s) and co-flow (33 cm/s) velocities and d_jet= 4 mm.

The maximum and 1000 K isotherms (black lines), contour of

HO2

Y (flooded zone), maximum iso-contour of Y_CH(white lines) and

Zst iso-contour (red lines) ... 187

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xxii LIST OF FIGURES Figure 5.24 Effect of varying fuel dilution levels on flame length and lift-off height

for O2 enhancement level of 50 % by vol. at fixed jet (26.5 cm/s) and co-flow (27 cm/s) velocities and ^d^jet = 4 mm. The maximum and 1000 K isotherms (white lines), contour of

HO2

Y species

(flooded zone) and Z_st iso-contour (black line) ... 189 Figure 5.25 Effect of varying fuel dilution levels on flame length and lift-off

height for O2 enhancement level of 100 % by vol. at fixed jet (75 cm/s) and co-flow (50 cm/s) velocities and d_jet = 3.5 mm.

The maximum and 1000 K isotherms (white lines), contour of

HO2

Y species (flooded zone) and Z_stiso-contour (black line) ... 189 Figure 5.26 Comparison of predicted (circular dots) and experimental (diamond

dots) lift-off height variation with reduction of a fuel CH4 concentration levels for 50 % by vol. O2 enhanced oxidizer at fixed jet (26.5 cm/s)

and co-flow (27 cm/s) velocities and d_jet = 4 mm... 190 Figure 5.27 Comparison of predicted (circular dots) and experimental (diamond

dots) flame length variation with fuel dilution level for 50 % by vol.

oxygen enhancement level at fixed jet (26.5 cm/s) and co-flow (27 cm/s) velocities and d_jet= 4 mm. ... 191 Figure 5.28 Axial flame temperature profile along the symmetry axis at

100, 80, 60, 40 and 38 % by vol. O2 enhancement levels for fixed fuel composition (15 % CH4 - 85% N2), 66.3 cm/s jet and 33 cm/s

co-flow velocities and d_jet = 4 mm. ... 192 Figure 5.29 Axial flame temperature profile along the axis of symmetry line

for 20, 16.7,10, and 9 % by vol. methane contains LCVG at fixed oxygen concentration level (100% by vol.), 75 cm/s jet and 50 cm/s

co-flow velocities and ^d^jet = 4 mm. ... 192 Figure 5.30 Variation of laminar burning velocity, (cm/s) with methane and

oxygen concentration level for 100 % (red) and 50 % (green) by

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LIST OF FIGURES xxiii vol. oxygen enhancement levels and 15 % by vol. CH4 (blue)

contains LCVG fuel and d_jet = 4 mm.. ... 193 Figure 5.31 Effect of varying jet velocity when 15 % CH4 – 85 % N2 fuel burned

with 100 % by vol. O2 enhancement level at fixed co-flow velocity of 30 cm/s and d_jet = 4 mm. The maximum and 1000 K isotherms (white lines), contour of

HO2

Y species (flooded zone) and Z_st iso-

contour (black line) ... 195 Figure 5.32 Effect of varying jet velocity when 15 % CH4 – 85 %N2 fuel burned

with 50 % by vol. O2 enhancement level at fixed co-flow velocity of 50 cm/s and d_jet= 4 mm. The maximum and 1000 K isotherms (white lines), contour of

HO2

Y species (flooded zone) and 𝑍𝑠𝑡 iso-

contour (black line) ... 195 Figure 5.33 Non-dimensional flame length (L_f d_jet ) variation with the velocity

ratio, R_vfor fuel composition (15 % CH4 – 85 % N2) at two fixed co-velocities (30 and 50 cm/s) and two oxygen enhancement levels

(100 and 50 % by vol.) and d_jet = 4 mm ... 196 Figure 5.34 Effect of varying co-flow velocities when 15 % CH4 – 85 %N2 fuel

burned with 100 % O2 enrichment levels at fixed jet velocity of 66.3 cm/s and d_jet = 4 mm. The maximum and 1000 K isotherms (white lines), contour of

HO2

Y species (flooded zone) and ^Z^st iso-contour

(black line) ... 198 Figure 5.35 Effect of varying co-flow velocities when 15 % CH4 – 85 %N2

fuel burned with 40 % O2 enrichment levels at fixed jet velocity of 66.3 cm/s and d_jet = 4 mm. The maximum and 1000 K isotherms (white lines), contour of

HO2

Y species (flooded zone) and ^Z^st iso-contour (black line) ... 198 Figure 5.36 Radial profiles of temperature and mole fraction of major species at

two flame heights ( 0.3 (a) and  1.1 (b)) for LCVG fuel

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xxiv LIST OF FIGURES (15 % CH4 - 85% N2) with 38 % by vol. O2 enhancement level

at fixed jet (66.3 cm/s) and Co-flow (33 cm/s) velocities... 200 Figure 5.37 Radial flame profiles of temperature and mole fraction of major

Species at two flame heights ( _0.3 or _x_3.1_mm (Left) and

 1.1 or x11.2mm (Right)) for LCVG fuel (15 % CH4-85

% N2) with 100 % O2 enhancement level at fixed jet (66.3 cm/s)

and co-flow (33 cm/s) velocities. ... 200 Figure 5.38 Radial flame profiles of temperature and mole fraction of major

species at two flame heights ( 0.3 or x₁1.3mm (a) and  1.1 or

2 4.8

x  mm (b)) for LCVG fuel (12 % CH4 – 88 % N2) with 50 % O2

enhancement level at a fixed jet (26.5 cm/s) and co-flow (27 cm/s)

velocities and d_jet = 3.5 mm. ... 202 Figure 5.39 Radial flame profiles of temperature and mole fraction of major

species at two flame heights ( 0.3 or x₁1.8mm (a) and  1.1 or

2 4.63

x  mm (b)) for LCVG fuel (20 % CH4 – 88 % N2) with 50 % O2

enhancement level at a fixed jet (26.5 cm/s) and co-flow (27 cm/s)

velocities and d_jet= 3.5 mm. ... 202 Figure 5.40 Volumetric HRR, (left side), 1000 K isotherms, contours of

HO2

Y (Right side) and iso-contour of Z_st (left and right side) for two fuels

containing 20 % (a) and (b) 12 % by vol. CH4 burned with 50 % by vol. O2 at a fixed jet (26.5 cm/s) m/s and co-flow (27 cm/s) velocities ... 204 Figure 5.41 Volumetric HRR, (left side), 1000 K isotherms, contours of

HO2

Y (Right side) and iso-contour of Z_st (left and right side) when 15 % by vol., CH4 fuel burned with two O2 enhancement levels 100 % (a) and 37 % by vol. (b) O2 burned with 50 % by vol. O2 at a fixed jet

(66.3 cm/s) m/s and co-flow (33 cm/s) velocities. ... 205 Figure 5.42 Volumetric HRR, (left side), 1000 K isotherm, contours of

HO2

Y (Right side) and iso-contour of Z_st (left and right side) at two jet

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LIST OF FIGURES xxv velocities of 10 cm/s (a) and 400 cm/s (b)when 15% CH4-85% N2

fuel burned with 50 % vol. O2 at a fixed co-flow velocity of 50 cm/s. ... 205 Figure 5.43 Volumetric HRR, (left side), 1000 K isotherm, contours of

HO2

Y (Right side) and iso-contour of Z_st (left and right side) at two co-flow velocities of 1cm/s (a) and 55 cm/s (b) when 15% CH4-85% N2 fuel

burned with 40 % vol. O2 at a fixed mean jet velocity of 66.3 cm/s ... 206 Figure 5.44 Iso-contour of 1000 K, (red line), Z_st , (black line), axial velocities

(blue lines),

HO2

Y (flooded zone, left-hand side) and Y_HCO (flooded zone, right-hand side) for combustion of 15 % CH4- 85% N2 fuel with 40 %-O2-60 % N2 oxidizer at fixed jet (V_{jet mean}_, = 66.3 cm/s)

and co-flow (V_CF= 55 cm/s ) Velocities. ... 207 Figure A. 1 Flame length (a), flame width (b) and Lift-off Height (c) variation

with O2 concentration level for fuel (15 % CH4- 885% N2) at Vjet,mean = 66.3cm/s and VCF = 5.4 cm/s ... 228 Figure A.2 Radial flame temperature profiles for fuel contains 12 % by vol. CH4,

and O2 enhancement level of 75 % by vol. at jet (0.5 LPM) and

co-flow (4 LPM) flow rates ... 229 Figure A. 3 Effect of changing the purity of oxygen gas on flame length (left) and

lift-off height (right) variation with CH4 concentration level at 100 % by vol. O2 concentration, ^Q^jet =1 and ^Q^CF=10 LPM ... 230 Figure A.4 4 Effect of seasonal (ambient temperature) change on flame length

(left) and lift-off height (right) with variation of methane concentration at 100 % O2 concentration, ^Q^jet = 0.2 and ^Q^CF = 5 LPM ... 230 Figure A. 5 Effect of reversing the order of varying parameter (O2 con.) on flame

length (left) and lift-off height (right) at 12 % by vol. methane

concentration, ^Q^jet = 0.56 and ^Q^CF=10 LPM ... 230

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LIST OF TABLES

Table 2.1 LCVG gas compositions ... 12

Table 2.2 Adiabatic flame temperature (K) ... 13

Table 2.3 Upper and lower flammability limits (% by volume) ... 13

Table 2.4 Maximum laminar burning velocity (cm/s) ... 14

Table 2.5 Molar stoichiometric ratio (𝑆) ... 20

Table 3.1 Test matrix and flame length measurement for validation of experiments setup... 73

Table 4.1 Experimental parameters for varying oxygen enrichment level at fixed velocity ratio ... 78

Table 4.2 Calculated _g and Z_st at two O2 concentration levels (100 % by vol. and the corresponding blow-out limit) ... 79

Table 4.3 Experimental conditions for varying R_v values by changing Co-flow Velocity,V_CF ... 80

Table 4.4 Experimental conditions for varying R_v by Changing jet velocity ... 81

Table 4.5 AFT, laminar burning velocity, density ratio, approximated maximum propagation speed for combustion of 15 % CH4 – 85 % N2 fuel at different oxygen enactment levels ... 92

Table 4.6 Experimental conditions for varying fuel dilution levels at different jet velocities ... 95

Table 4.7 Experimental parameters for varying fuel dilution levels at different co-flow velocities ... 97

Table 4.8 Experimental parameters for varying fuel dilution levels at very low jet velocities ... 98

Table 4.9 ... Experimental parameters for combustion of highly diluted fuel with pure oxygen. ... 110

Table 4.10 Richardson number calculation for various fuel dilution levels at fixed oxygen enhancement level (100 % by vol. O2), jet velocity (Vjet, mean = 13.3 cm/s ) and djet = 4 mm ... 113

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xxviii LIST OF TABLES Table 4.11 The maximum and minimum calculated 𝑅𝑖 at 20 and 8 % by vol.

CH4 concentration level for selected jet velocities and djet = 4 mm ... 113 Table 4.12 Minimum amount of fuel dilution required to equate the calculated

laminar burning velocity with jet exit velocity at two O2 enrichment

levels (100 and 50 % by vol.) ... 115 Table 4.13 Experimental parameters for varying jet velocity at different fixed

co-flow velocities for LCVG fuel (15 % CH4 – 85 % N2) and 100 %

by vol. O2 enhancement level ... 119 Table 4.14 Experimental parameters for varying jet velocity at different fuel

composition, oxygen ehacment and co-flow velocity ... 122 Table 4.15 Experimental conditions for varying co-flow velocity at different

fixed jet velocities for the given fuel dilution and O2 enhancement

level ... 126 Table 4.16 Experiential conditions of varying the co-flow velocities under

different fuel dilution and O2 enhancement level and fixed jet velocity .... 128 Table 4.17 Experimental parameters for identifying flame stability zones for

various fuel dilution levels at two fixed jet (0.5 and 1 LPM) and

co-flow (10 LPM) velocities ... 131 Table 4.18 Experimental parameters for identifying flame stability zones for

various fuels dilution levels at two fixed jet (0.5 and 1 LPM) and

co-flow (2 LPM) velocities ... 131 Table 4.19 Experimental conditions for identifying flame stability zones of

oxidizer contains various O2 enhancement levels at a fixed jet

(0.5 LPM) and co-flow (10 LPM) velocities ... 133 Table 4.20 Experimental parameters for radial flame temperature profile

measurement at two jet and co-flow velocities ... 135 Table 4.21 Experimental parameters for radial flame temperature profile

measurement at two jet and two co-flow velocities for fixed fuel

dilution and O2 enhancement levels ... 138 Table 4.22 Experimental conditions for axial temperature measurement ... 140 Table 4.23 Summary of Experimental Results ... 142

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LIST OF TABLES xxix

Table 5.1 Curve fit polynomial coefficients of H2O and CO2 to find plank absorpation cofficent ... 154

Table 5.2 Curve fit polynomial coefficients of CH4 and COto find plank absorpation cofficent ... 154

Table 5.3 The boundary conditions at the jet and co-flow exit plane ... 157

Table 5.4 The boundary conditions at the jet and co-flow walls ... 157

Table 5.5 The boundary conditions at the two pressure inlets planes ... 157

Table 5.6 The boundary conditions at the pressure outlet plane ... 158

Table 5.7 The boundary conditions at the axis symmetry plane ... 158

Table 5.8 Comparison of the present simulation result with experimental and numerical results of Flame -3 from Bennett et al. ... 163

Table 5.9 Comparison of numerical prediction of T_max with optically thin radiation model and without radiation model for selected flames. ... 167

Table 5.10 Simulation parameters for the effect of varying the oxygen enhancement level ... 180

Table 5.11 Simulation parameters for varying fuel dilution level. ... 188

Table 5.12 Simulation parameters for varying jet velocity ... 194

Table 5.13 Simulation parameters for variation of co-flow velocity ... 197

Table A. 1 Sample calculation of uncertainty of number of pixels per unit length ... 226

Table A. 2 Sample calculation of uncertainty of flame length ... 226

Table A. 3 Sample calculation of uncertainty of flame width ... 227

Table A. 4 Sample Calculation of uncertainty of flame lift-off height ... 227

Table B. 1 35-steps Skeletal methane-air chemical reaction mechanisms, ... 231

Table B. 2 43-steps Skeletal methane-air chemical reaction mechanisms, ... 232

Table C. 1 Thermo-Physical properties of various fuel compositions. ... 233

Table C. 2 Thermo-Physical properties of various oxidizer compositions ... 233

Table C. 3 Stoichiometric laminar burning velocity (cm/s) ... 234

Table C. 4 Adiabatic flame temperature (k) ... 234

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xxx LIST OF TABLES

Table C. 5 Burn gas density (kg/m³) ... 235 Table C. 6 Stoichiometric mixture fraction,^Z^st ... 235 Table C. 7 Maximum flame propagation speed,^S^e^,max (cm/s) ... 235 Table C. 8 Sample calculation of Richardson number, ^Ri or ^V^{jet mean}^, = 66.3 cm/s,

djet

= 4 mm and g = 9.81 cm/s². ... 236

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NOMENCLATURE

Abbreviations

BO Blow-out LPF Lean Premix Flame

CV Calorific value MFC Mass Flow Controller

DF Diffusion flame OEC Oxygen-enhanced Combustion

GER Global Equivalence Ratio OTA Optically Thin Approximation LCVG Low calorific value Gas RPF Rich Premixed Flame

LER Local Equivalence Ratio UDF User Defined Function Symbols

Ai Chemical symbol for species 𝑖 Ns Number of chemical species Ak Pre-Exponential Factor of reaction k p Static pressure

cp Specific heat capacity for mixture q Heat flux field

Da Damköhler number Q Volumetric heat release rate Di Diffusion coefficient of species 𝑖 Qk Heat of combustion of reaction 𝑘 Dij Binary diffusion coefficient Q_F /Q_jet Volume flow rate of fuel/jet Ea Activation energy Q_CF Volume flow rate of co-flow

Fr Froude number r Radial coordinates

g Gravitational acceleration R Radius

g Critical velocity gradient Re Reynolds number

h Sensible enthalpy Ri Richardson number

HL Lift-off height R_v Velocity ratio

k Flame stretch R_u Universal gas constant

K Reaction rate coefficient s Mass stoichiometric ratio

Le Lewis number S Molar stoichiometric ratio

Lf Flame length Sc Schmidt number

m Molar mass S_d Flame displacement speed

m Mass flow rate (mass Flux) S_e Edge flame propagation speed Mw Molecular weight S_L Laminar burning velocity

Investigation of flame structure and stability for oxygen-enhanced combustion of low calorific value gases

INVESTIGATION OF FLAME STRUCTURE AND

STABILITY FOR OXYGEN-ENHANCED COMBUSTION OF LOW CALORIFIC VALUE GASES

BISRAT YOSEPH GEBREYESUS

DEPARTMENT OF MECHANICAL ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY DELHI

OCTOBER – 2017

INVESTIGATION OF FLAME STRUCTURE AND

STABILITY FOR OXYGEN-ENHANCED COMBUSTION OF LOW CALORIFIC VALUE GASES

BISRAT YOSEPH GEBREYESUS Department of Mechanical Engineering

Submitted

in fulfillment of the requirements of the degree of Doctor of Philosophy to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI NEW DELHI, INDIA

OCTOBER - 2017

CERTIFICATE

ACKNOWLEDGMENTS

ABSTRACT

सार

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

NOMENCLATURE