O2 Coflow Jet Diffusion Flames

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9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK 9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK

Chemiluminescence and Structure Characteristics in CH4/O2 Coflow The 15th International Symposium on District Heating in andCH Cooling Chemiluminescence andJet Structure Characteristics 4/O2 Coflow Diffusion Flames Jet Diffusion Flames a,b a,b a,b the heat demand-outdoor Assessing the feasibility ofGuo using Yan Gong , Chonghe Hu , Qinghua , Xiaoxiang Wu a,b, Guangsuo Yu a,b,* a,b a,b a,b Yan Gong , Chonghe Hu for , Qinghua Guo , Xiaoxiang Wu a,bdemand , Guangsuoforecast Yu a,b,* temperature function a long-term district heat Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and a

a Technology, P. O. Box 272, Shanghai 200237,ofPR. China East China University of Science and Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry Education, a Gasification, aEast China University b of Science and Technology, c P. O. Box 272, Shanghai c Shanghai Engineeringa,b,c Research CenterTechnology, of Coal P. O. Box 272, Shanghai 200237, PR. China b 200237, PR. China Shanghai Engineering Research Center of Coal Gasification, East China University of Science and Technology, P. O. Box 272, Shanghai

I. Andrić

b

a

*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre

IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal 200237, PR. China

b Abstract Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract The chemiluminescence characteristics of the excited state radicals are significant for spectrum-based diagnostics of practical diffusion flames. The detailed spatial profiles OH* and radicals in diffusionfor flames are investigated, and theofeffects of The chemiluminescence characteristics of the of excited stateCH* radicals are significant spectrum-based diagnostics practical different ondetailed the chemiluminescence andOH* structure are studied. emissions are obtained by the UVand imaging system, diffusion conditions flames. The spatial profiles of and CH* radicalsOH* in diffusion flames are investigated, the effects of while CH* emissions by a novel high-spatial-resolution line-scan hyperspectral camera. by Thethe results show that there different conditions onare thecaptured chemiluminescence and structure are studied. OH* emissions are obtained UV imaging system, Abstract are three structure types laminarby flame along the flame propagatingline-scan direction: jet core region, jet transition region jet while CH* emissions areincaptured a novel high-spatial-resolution hyperspectral camera. The results showand thatthe there fully developed region. However, the turbulent flame only has jet core region and transition region. Moreover, the twoare three structure types in laminar flame along the flame propagating direction: jet transition and the jet District heating networks are commonly addressed in the literature as one of jet thecore mostregion, effective solutions region for decreasing the also feature different characteristics. dimensional distributions offrom OH* the andthe CH* under different equivalent ratios e) and fully developed region. However, turbulent flame only has jet core([O/C] region transition region. Moreover, thethetwogreenhouse gas emissions building sector. These systems require high investments which are returned through heat © 2017 Due The Authors. Published byand Elsevier Ltd. different different dimensional distributions of OH* CH* under equivalent ratios ([O/C] sales. to the changed climate conditions and building renovation policies,) also heatfeature demand in the characteristics. future could decrease, © 2017 The Authors. Published by Elsevier Ltd. committee of the 9th InternationaleConference on Applied Energy. Peer-review under responsibility ofperiod. the scientific © 2017 The Authors. Published by Elsevier Ltd. prolonging the investment return Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. Keywords: flame; flame is state; chemiluminescence; equivalent ratio Peer-review underofresponsibility of scientific committee of the 9thheat International on Applied Energy.for heat demand The mainDiffusion scope this paper to the assess the feasibility of using the demand –Conference outdoor temperature function Keywords: flame;offlame state; chemiluminescence; equivalent ratio was used as a case study. The district is consisted of 665 forecast. Diffusion The district Alvalade, located in Lisbon (Portugal), buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district 1.Introduction renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were 1.Introduction compared with results from a dynamic heat demand model, previously developed and validated by the authors. From theshowed detailed chemistry mechanisms, reacting species/intermediates will be for produced during The results that when only weather change is many considered, the margin of error could be acceptable some applications [1-3] (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation . Three phenomena make combustion. Some intermediates are related to the pollutant emission and heat release From the detailed chemistry mechanisms, many reacting species/intermediates will be produced during [1-3] scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). flame to spontaneously emit electromagnetic radiation: black-body spectrum produced by solid bodies (e.g., char . Three phenomena make combustion. Some intermediates are related to the pollutant emission and heat release [4] corresponds to the The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that . Flame spectral particles), rotation-emission bands of high temperature gas molecules and chemiluminescence flame to spontaneously emit electromagnetic radiation: black-body spectrum produced by solid bodies (e.g., char decrease in the number of heating hours of 22-139h during the heating season (depending on flame the combination of[5]weather and [4] . Detailed visualization based on chemiluminescence intermediates an important for diagnosis . Flame spectral particles), rotation-emission bands of highoftemperature gasismolecules andmethod chemiluminescence renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on [6the [5] two-dimensional spatial distribution of radical radiation can directly characterize the shape and structure of flames visualization based on chemiluminescence of intermediates is an important method for flame diagnosis . Detailed coupled scenarios). The values [12] suggested could be used to modify the function parameters for the scenarios considered, and 11] [6. Study from Marchese showsofthat the OH* distribution yield a rational the indication of structure flame-front position, two-dimensional spatial distribution radical radiation can directly characterize shape and of flames improve the accuracy of heat demand estimations. [13] [12] 11]

indicates that position, the twosince the maximum OH* emission near maximum flame temperature. . Study from Marchese shows isthat thethe OH* distribution yield a rational Walsha indication of flame-front [13] indicates that the twosince theThe maximum OH* emission is near © 2017 Authors. Published by Elsevier Ltd. the maximum flame temperature. Walsha Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

* Corresponding author. Tel.: +86 2164252974; Fax: +86 2164251312. E-mail address: (G. Yu).change Keywords: Heat [email protected] demand; Forecast; Climate * Corresponding author. Tel.: +86 2164252974; Fax: +86 2164251312. E-mail address: [email protected] (G. Yu). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review©under the scientific committee 1876-6102 2017responsibility The Authors. of Published by Elsevier Ltd. of the 9th International Conference on Applied Energy.

Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. 10.1016/j.egypro.2017.12.356

Yan Gong et al. / Energy Procedia 142 (2017) 1059–1064 Yan Gong, Chonghe Hu, Qinghua Guo, Xiaoxiang Wu, Guangsuo Yu* / Energy Procedia 00 (2017) 000–000

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dimensional distribution of OH* could reflect the lift-off heights and flame shapes by analyzing both normal gravity and reduced gravity CH4-N2/air flames. Compared with laminar flames, turbulent flames are less stable [14,15]. It’s hard to determine the structure of the turbulent flame due to massive wrinkle and vortex in the flame downstream. Nada [16] reports that the three-dimensional flame structure caused by strong fine scale eddies in turbulence appears even in laminar flamelet regime in the turbulent combustion diagram. There are significant differences between diffusion flames and premixed flames [4]. In this study, the distributions of OH* and CH* chemiluminescence are measured and discussed in CH4/O2 co-flowing jet diffusion flames by employing hyperspectral and ultraviolet cameras. The influence of different gas velocities on the structures and the radiation characteristics for laminar and turbulent flames are also studied. 2.Experimental Setups Fig. 1 shows the spectral diagnostics experimental platform for jet diffusion flames which consisting of four parts: the combustion system, CCD camera system and the detection apparatuses for OH* and CH*. The visible flame images are recorded by a high resolution CCD camera (JAI Inc., BB-500CL).

Fig. 1. The schematic diagram of the spectroscopic diagnostic system.

Fig. 2 Components of UV imaging system

2.1. Burner and operating conditions The coaxial three-channel non-premixed nozzle is applied in this study. As shown in Fig. 1, fuel is pumped through the central channel, oxidant goes through the intermediate annulus and nitrogen isolates the flame from the environment at outer annulus. Pure methane (>99.9%) is used as fuel, and pure oxygen (>99.9%) is used as oxidizer. Both of them are measured and controlled by mass flow meters. Four velocity conditions range from fuel-rich combustion to fuel-lean combustion are chosen to discuss the influence of velocity on flame. The O/C equivalence ratio ([O/C]e) varies in a range of 0.70 to 1.20, defined by the following equation: [O/C]e=[O/C]a/[O/C]s

(1)

where [O/C]a is the actual O/C molar ratio calculated from the feeding flows of fuel and oxygen, and [O/C]s the stoichiometric O/C molar ratio. Table 1 lists the experimental conditions. Reynolds number (Re) in Table 1 is calculated by the following formulas: Re 

De u 

(2)



  2( mc  ma ) De  [  (Gc  Ga )]1/ 2



yM yM i

i

i

1/ 2 i 1/ 2 i

(3) (4)



Yan Gong et al. / Energy Procedia 142 (2017) 1059–1064 Yan Gong, Chonghe Hu, Qinghua Guo, Xiaoxiang Wu, Guangsuo Yu* / Energy Procedia 00 (2017) 000–000

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Formula (3) has been given by Beér and Chigier [17], where De is the equivalent nozzle diameter, m is the gas mass flow rate, G is the momentum flux, and ρ is the average density of fuel and oxidizer. The subscripts c and a refer to the central tube and the annular tube, respectively. u is the average velocity, and μ is the average viscosity of fuel and oxidizer. As calculated by formula (4), yi is the mole fraction of component i, Mi is the molar mass of component i. Table 1. Experimental conditions.

1 vCH4 (L/min) uCH4 (m/s) vO2 (L/min) uO2 (m/s) [O/C] e Re

2

3

4

5

6

7

8

9

10

11

12

13

14

0.50

1.00

1.50

2.00

15.79

31.58

47.37

63.16

15

16

0.70

0.80

0.90

1.00

1.10

1.20

1.40

2.40

2.10

3.60

2.80

3.20

3.60

4.00

4.40

4.80

2.15

2.46

2.77

3.07

3.37

3.69

4.30

7.40

6.45

11.10

8.60

9.84

11.08

12.32

13.56

14.80

0.70

0.80

0.90

1.00

1.10

1.20

0.70

1.20

0.70

1.20

0.70

0.80

0.90

1.00

1.10

1.20

1155

1184

1212

1241

1269

1299

2310

2599

3465

3898

4620

4737

4850

4964

5079

5198

2.2. OH* and CH* measurement approach The main OH* radiation exists in the UV region (280-350nm), with the most intense radiation occurring at 309nm [18]. In this study, the OH* emission (A2∑+-X2Π) is obtained by a high-spatial-resolution UV imaging system (EX-3011B, Isuzu Optics) consisting of three parts: bandpass filter, UV quartz lens and UV cameras, as shown in Fig. 2. The CCD panel consists of 1024×255 pixels with 14bit output. The spatial resolution in image is about 0.175 mm, and the exposure time of each image is set to 1000ms in this study. The CH* radiation exists in the visible region, with the most intense emission occurring at 431 nm [19]. In this study, EMCCD line-scan hyperspectral camera (V8E-EMCCD-RS, Isuzu Optics) is used to detect the twodimensional emission distribution of CH*(C2 ∑+-X2Π). The spectral transmission technology and CCD image acquisition technology are combined to integrate a EMCCD which can quickly obtain spectral images. This imaging system consists of three parts: objective lens, spectrometer and camera. The target light passes through the objective lens and the entrance slit successively. The slit allows only a single linear array of light entering into the detection system. The spectral range of EMCCD is 380-800nm, and the spectral resolution is 2nm (FWHM), with the maximum image size of 1004(H)×1002 pixels(V). 3. Results and Analysis 3.1. Two-dimensional distributions of OH* and CH* with different velocities 3.1.1. OH* distributions

a. condition 6

b. condition 8 c. condition 10 Fig. 3 OH* 2-D profile

d. condition 16

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Yan Gong et al. / Energy Procedia 142 (2017) 1059–1064 Yan Gong, Chonghe Hu, Qinghua Guo, Xiaoxiang Wu, Guangsuo Yu* / Energy Procedia 00 (2017) 000–000

Fig. 3 shows the OH* 2-D profiles at different velocities at [O/C]e =1.20. With the increase of velocity, the flame height increases and then decreases. The flame shape is very clear at low velocity. When the velocity increases to a critical value, the flame becomes unstable. The OH* distribution of the downstream is inhomogeneous. The flame shape becomes illegibility, indicating the flame changes from laminar flow to turbulence [20,21]. The increase of velocity enlarges the relative velocity between the fuel and oxidant. The increased relative velocity intensifies the shearing action of the two streams and enhances the mixing. It can be seen clearly that the core reaction area of the flame shrinks to the exit of the burner gradually with the increase of velocity, as shown in Fig. 3. Comparing with the steady laminar flames, the change of concentration gradient for the turbulent flames is more remarkable while the reaction is more intense.

a. condition 6

b. condition 8 c. condition 10 Fig. 4 OH* radial distribution

d. condition 16

The radial distributions of OH* in different axial positions of the steady laminar flow have been analyzed in the previous section, and three distribution types are classified: the bimodal distribution, the uniform distribution and the normal distribution. With the increase of gas velocity, the flame changes from laminar flow (condition 6) to turbulence flow (condition 16), and the OH* radial distribution also changes. When 0 ≤ L ≤ 9De, the OH* distribution is consistent with bimodal distribution, and a clear flame front is formed where reactions take place. No matter it is laminar or turbulent flame, the position of the main reactions does not change and an OH* peak occurs at L=3De. With the propagation of flame, the OH* gradually approaches the normal distribution in laminar flow while the uniform distribution in turbulent flow. The OH* concentration gradient in laminar flow is higher than that in turbulent flow. 3.1.2. CH* distributions

a. condition 6

b. condition 16

Fig. 5 CH* 2-D profile

a. condition 6 Fig. 6 CH* radial distribution

b. condition 16

In diffusion flame, CH* appears at the initial region of the fuel side which is closer to the central axis. Fig. 5 shows the CH* distributions in laminar and turbulent flames. The CH* distribution has minor difference between laminar and turbulent flames than that of OH* distribution. The generation range of CH* has a tendency to expand to the downstream in turbulent flame. The CH* would not directly reveal the contour of flame but it does indicate the internal structure clearly. As the gas velocity increases, the variation gradient of CH* from the central axis to the flame front increases significantly, which indicates that reaction in the core zone is intensified. Fig. 6 shows the CH* radial distributions at different axial positions in laminar and turbulent flame. The CH* peak takes place at the position of 0.5 De, and the radial position does not change with the change of velocity.



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3.2. Two-dimensional distributions of OH* and CH* with different [O/C]e The two-dimensional OH* distribution of different [O/C]e in laminar flame is shown in Fig. 7. When [O/C]e increases to 0.80, the generation of OH* extends along the axis of flame as well as the reaction zone. Similarly, the variation of OH * radial distribution can be divided into three parts: I. the bimodal distribution (L＜7De), II. the uniform distribution (7De≤L<9De) and III. the normal distribution (L≥9De). Compared with [O/C]e=0.70, the change is mainly in Part III which extends about 10De in the downstream of flame. When the [O/C]e increases to 0.90, the flame changes from fuel-rich to fuel-lean gradually, and the increase of [O/C]e has little influence on the overall distribution of OH*. The distance from axial boundary to the burner maintains a length of 15De.

Fig. 7 Comparison of OH* two-dimensional distribution with different [O/C]e (laminar flame)

It indicates that the transitional region shrinks with the increase of [O/C]e. The transitional section fades away when [O/C]e>1.00 , and the flame transforms from core region to fully developed region. In addition the proportion of fully developed region increases. The two-dimensional OH* distribution at different [O/C]e can further indicate that the difference between fuel-rich and fuel-lean flames occurs in the downstream. The structure of fuel-rich flame consists of three parts: the core region, the transition region and the fully developed region. Compared with fuel-rich flame, the core region of fuel-lean flame does not change, while the fully developed region extends to the transition region which fades away gradually.

Fig. 8 Comparison of CH* two-dimensional distribution with different [O/C]e (laminar flame)

The comparison of CH* two-dimensional distribution with different [O/C]e is shown in Fig. 8. The CH* distribution doesn’t change with the flame changing from fuel-rich condition to fuel-lean condition, the distance from axial boundary to the nozzle is about 6De, and the radial boundary is 1.3mm from the central axis of the flame. In the flame, the CH* generates near the fuel side which is also close to the central axis, and CH* mainly concentrate in the flame front. According to the results of OH* distribution above, the difference between fuel-rich condition and fuel-lean condition mainly occurs at the downstream of the flame, thus the differences between CH* two-dimensional distributions at different [O/C]e is small. 4. Conclusions The two-dimensional OH* and CH* distribution and the structure of coaxial jet diffusion flames at different velocities are studied by hyperspectral and ultraviolet cameras. OH* radial distributions at different axial positions are mainly classified as three forms: the bimodal distribution, the horizontal distribution and the nearly normal distribution. The distribution area of CH* is smaller than that of OH* and OH* mainly distributes in the area which is about ±1.5De away from the central axis. CH* only exists in the area where is about ±0.5De away from the central axis. The CH* distribution is basically uniform, and the

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Yan Gong et al. / Energy Procedia 142 (2017) 1059–1064 Yan Gong, Chonghe Hu, Qinghua Guo, Xiaoxiang Wu, Guangsuo Yu* / Energy Procedia 00 (2017) 000–000

double peak distribution exists at all conditions. The structural changes in the flame propagation process can be obtained according to the radial distribution of OH* at different axial positions: the jet core section with OH* radial bimodal-distribution, the jet transition section with OH* radial uniform-distribution and the jet fully developed section with OH* radial normal-distribution. The flame fades away before the fully developed region forms in turbulence. The OH* bimodal region doesn’t change with the increase of [O/C]e. The OH* axial distribution changes from the bimodal to normal distribution when [O/C]e>1.00, and the uniform distribution region no longer exists. The transition region is shrinks and vanishes with the increase of [O/C]e. Fuel-rich and fuel-lean flame make differences only in the downstream of flame. Acknowledgements This work has been supported by the National Natural Science Foundation of China (51406056; U1604252) and the Fundamental Research Funds for the Central Universities (222201717004). References [1] Dong H, Zhang Y, Guo ZZ. Effects of diluents on NO x formation in coflow CH4/air diffusion flames. Korean J Chem Eng 2014; 31; 1002-8. [2] Lee C, Kil HG. Effects of nitrogen dilution for coal synthetic gas fuel on the flame stability and NOx formation. Korean J Chem Eng 2009; 26; 862-74. [3] Chhiti Y, Peyrot M, Salvadorc S. Soot formation and oxidation during bio-oil gasification: experiments and modelling. J Energ Chem 2013; 22; 701-9. [4] Gaydon AG, Wolfhard HG. Flames: their structure, radiation and temperture. London: Chapman and Hall; 1960. [5] Hwang CH, Lee S, Kim JH, Lee CE. An experimental study on flame stability and pollutant emission in a cyclone jet hybrid combustor. Appl Energy 2009; 86; 1154-60. [6] Ballester J, Hernández R, Sanz A, Somlarz A, Barroso J, Pina A. Chemiluminescence monitoring in premixed flames of natural gas and its blends with hydrogen. Proc Combust Inst 2009; 32; 2983-91. [7] Rieker GB, Jeffries JB, Hanson RK, Mathur T, Gruber MR, Carter CD. Diode laser-based detection of combustor instabilities with application to a scramjet engine. Proc Combust Inst 2009; 32; 831-8. [8] Li ZS, Li B, Sun ZW, Aldén M. Turbulence and combustion interaction: High resolution local flame front structure visualization using simultaneous single-shot PLIF imaging of CH, OH, and CH2O in a piloted premixed jet flame. Combust Flame 2010; 157; 1087-96. [9] Khalil AE, Gupta AK. Hydrogen addition effects on high intensity distributed combustion. Appl Energy 2013; 104; 74-81. [10] Kothnur PS, Tsurikov MS, Clemens NT, Donbar JM, Carter CD. Planar imaging of CH, OH, and velocity in turbulent non-premixed jet flames. Proc Combust Inst 2002; 29; 1921-7. [11] Oh J, Noh D, Lee E. Planar imaging of CH, OH, and velocity in turbulent non-premixed jet flames. Appl Energy 2013; 112; 350-7. [12] Marchese AJ, Dryer FL, Nayagam V, Colantonio RO. Hydroxyl radical chemiluminescence imaging and the structure of microgravity droplet flames,” Symp Combust 1996; 26; 1219–26. [13] Walsha KT, Fieldinga J, Smooke MD, Longa M, Linan A. A comparison of computational and experimental lift-off heights of coflow laminar diffusion flames. Proc Combust Inst 2005; 30; 357-65. [14] Shimura M, Ueda T, Choi GM, Mamoru T, Toshio M. Simultaneous dual-plane CH PLIF, single-plane OH PLIF and dual-plane stereoscopic PIV measurements in methane-air turbulent premixed flames. Proc Combust Inst 2011; 33; 775-82. [15] Tanahashi M, Murakami S, Choi GM, Yuichi F, Toshio M. Simultaneous dual-plane CH PLIF, single-plane OH PLIF and dual-plane stereoscopic PIV measurements in methane-air turbulent premixed flames. Proc Combust Inst 2005; 30; 1665-770. [16] Nada Y, Tanahashi M, Miyauchi T. Effect of turbulence characteristics on local flame structure of H2-air premixed flames. Jour Turbul 2004; 16; 21-2. [17] Beér J, Chigier NA. Combustion aerodynamics. London: Applied Science Publishers Ltd; 1972. [18] Zhang T, Guo QH, Lang QF, Dai ZH, Yu GS. Distribution Characteristics of OH*, CH*, and C2* Luminescence in CH4/O2 Co-flow Diffusion Flames. Energy Fuel 2012; 26; 5503-8. [19] Tripathi MM, Krishnan SR, Srinivasan KK, Yueh FY, Singh JP. Chemiluminescence-based multivariate sensing of local equivalence ratios in premixed atmospheric methane–air flames. Fuel 2012; 93; 684-91. [20] Tamir A. Impinging-Stream Reactors: Fundamentals and Applications. Amsterdam: Elsevier; 1994. [21] Benvenutti LH, Marques CST, Bertran CA. Chemiluminescent emission data for kinetic modelling of ethanol combustion. Combust Sci Technol 2004;177; 26-9.