Semiempirical Correlation for Predicting Laminar Flame Speed of

Verhelst , S.; Woolley , R.; Lawes , M.; Sierens , R. Laminar and unstable burning velocities and Markstein lengths of hydrogen–air mixtures at engi...
0 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/EF

Semiempirical Correlation for Predicting Laminar Flame Speed of H2/ CO/Air Flames with CO2 and N2 Dilution Rongxue Shang,†,‡ Yang Zhang,*,†,§ Mingming Zhu,† Zhezi Zhang,† and Dongke Zhang† †

Centre for Energy (M473), The University of Western Australia, 35 Stirling Highway, Perth, Western Australia 6009, Australia Fire & Explosion Protection Laboratory, Northeastern University, Shenyang 110004, China § Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China ‡

ABSTRACT: A semiempirical correlation was developed for predicting the laminar flame speed of H2/CO/air flames with N2 and CO2 dilution without solving the detailed governing equations, detailed chemical kinetics, and molecular mass transport. The correlation, derived through an asymptotic analysis, comprised a theoretically based expression with a series of experimentally fitted parameters. New experimental measurements were conducted using the Bunsen flame method over broad ranges of unburned mixture temperature (300−600 K), H2 ratio in the H2/CO blends (0.25−0.75), CO2 or N2 dilution ratio (0−0.67), and equivalence ratio (0.8−4.0) to comprehensively validate the performance of the proposed correlation. Detailed numerical simulation and sensitivity analysis using CHEMKIN-Pro were also carried out to gain an insightful understanding of the experimental observations. Results showed that the proposed correlation was able to satisfactorily predict the laminar flame speed, with error < 15%, of a wide range of H2/CO/N2/CO2/air mixtures covering H2 ratios in the H2/CO blends from 0.25 to 1.0, N2 and CO2 dilution ratios from 0 to 0.25, equivalence ratios from 0.8 to 4.0, unburned gas temperatures from 300 to 500 K, and pressures from 1 to 2 atm. When the unburned gas temperature was raised to >500 K or the mixture was highly diluted (dilution ratio up to 0.67), the proposed correlation could be conditionally applied since the prediction error would reach 15− 30%. The sensitivity analysis demonstrated that the relatively poor prediction of the proposed correlation under high unburned temperature or high dilution conditions was mainly due to the variation of the chemical kinetics. The proposed correlation generally provided a much simpler and more convenient approach to estimating the laminar flame speed of H2/CO/N2/CO2/air flames with an acceptable accuracy, especially suitable for applications in the engineering computations.

1. INTRODUCTION Synthesis gas (or syngas), produced from gasification of various unconventional feedstocks and comprising H2, CO, N2, CO2, and a small amount of hydrocarbons and water, is an attractive alternative fuel in the future energy mix.1 The design of a safe and efficient syngasfuelled combustion device requires insightful knowledge of the fundamental combustion characteristics of syngas. The highly variable nature of syngas composition results in diverse combustion characteristics, bringing difficulties to the syngas utilization. Thus, investigations into the fundamental combustion properties of syngas fuels with varying composition have become popular, and a number of studies have been reported, as reviewed in 2. Laminar flame speed (Su0) is among the most important fundamental combustion characteristic as it indicates the burning rate and thereby the heat release rate during the combustion of a fuel. Su0 of syngas has been extensively experimentally studied under atmospheric conditions,3−7 at elevated pressures or elevated temperatures,8−13 with a vast amount of inert diluents,5,14−17 and with impurities.8,11,18,19 Meanwhile, accurate numerical prediction of Su0’s is also aspired. Recently, comprehensive H2/CO combustion kinetic mechanisms 10,20−25 have been developed, and detailed simulations using CHEMKIN or other commercial software have satisfactorily predicted Su0 of syngas.26 Detailed simulations using CHEMKIN involve advanced mathematical algorithms such as iterative solution of a set of © XXXX American Chemical Society

differential equations with detailed kinetic mechanism and molecular mass transport. Although detailed simulations can accurately predict Su0 of syngas, this approach to Su0 estimation is time consuming and only limited within the community of qualified experts. In a more general situation for engineering calculations, a simple, prompt, and sometimes by-hand method for Su0 estimation with acceptable accuracy is considered of practical significance. Consequently, polynomial fitting of Su0 experimental data was carried out in a series of studies,5,7,15 and the fitted equations were used to calculate Su0 of syngas if the conditions match. However, these empirically fitted correlations lack theoretical basis and are not applicable under wider conditions. On the other hand, mixing models were also developed in some other studies27−31 to estimate Su0 of binary fuel mixtures. However, as summarized in ref 32, none of these existing mixing models works for H2/CO mixtures, especially when the H2 ratio (xH2, defined as xH2 = moles of H2/(moles of H2 + moles of CO)) varies considerably. Recently, Zhang et al.32 proposed a semiempirical correlation, developed based on an asymptotic analysis with the optimization of the key coefficients using experimental data. This semiempirical correlation has been shown to offer satisfactory predictions of Su0 of H2/CO/air mixtures (from stoichiometric to lean) Received: February 18, 2017 Revised: July 4, 2017 Published: July 24, 2017 A

DOI: 10.1021/acs.energyfuels.7b00494 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels without solving the differential equations, detailed chemistry, and mass transport. However, this correlation is not applicable under the fuel-rich conditions as its estimation significantly deviates from the experimental data when the equivalence ratio (ϕ) is greater than 1.2 (details to be shown in Figures 1 and 2).

Figure 1. Experimental, computed, and estimated laminar flame speed of H2/air mixtures: (squares) ref 41; (circles) ref 42; (triangles up) ref 43; (triangles down) ref 44; (diamonds) ref 45; (left pointing triangles, ref 46); (solid line) present correlation; (dashed line) Zhang’s correlation;32 (dashed dotted line) Davis-Mech.

Systematic experimental data over a broad range of experimental conditions are crucial for developing and validating the models and correlations of Su0 of syngas. Although numerous experimental data have been reported in the literature, the data obtained at elevated temperatures8,9,11 only covers a very limited H2/CO ratio range, especially on the fuel-rich side where data is only available for H2/CO mole ratio = 1:1 (shown in Figure 3). Besides H2 and CO, syngas inevitably contains inert diluents such as N2 and CO2. Experimental data of Su0 of N2 or CO2 diluted H2/CO/air mixtures at elevated temperatures are rare in the literature. In view of the above considerations, a systematic experimental study of Su0 of H2/CO/air mixtures over a wide range of H2 molar ratio in the H2/CO mixture (xH2 = 0.25− 0.75) with N2 (0−66.7 vol %) and CO2 (0−66.7 vol %) dilutions was first conducted at elevated initial temperatures (Tu = 300−600 K). The dilution ratio (xdilution) was defined as xdilution = moles of dilution/(moles of H2 + moles of CO) in the unburned fresh mixture. Corresponding detailed numerical simulations were also carried out to help obtain an in-depth understanding of the physical and chemical processes that control the combustion. On the basis of the new experimental data as well as the experimental data available in the literature, a new semiempirical correlation for predicting the laminar flame speed of H2/CO/air flames with CO2 and N2 dilutions was developed. The validity of the newly proposed correlation was further discussed under various conditions.

Figure 2. Experimental, computed, and estimated laminar flame speed of H2/CO/air mixtures at different initial temperatures: (solid circle) experimental data; (open circles) ref 33; (solid line) present correlation; (dashed line) Zhang’s correlation;32 (dashed dotted line) Davis-Mech.

Figure 3. Experimental laminar flame speeds of H2/CO/air mixtures at different initial temperatures: (solid circle) present work; (triangles up) ref 8; (open squares) ref 9; (triangles down) ref 11.

2. EXPERIMENTAL AND NUMERICAL APPROACHES The well-known Bunsen flame method was used to measure the Su0 of syngas at elevated temperatures in the present study. The detailed description of the experimental configuration can be found elsewhere.33 In brief, the inner diameter of the Bunsen burner exit was 4.44 mm, and the length of the burner was at least 50 times its diameter in order to ensure that the flow was laminar and fully

developed at the burner exit.9 A Z-type two-mirror Schlieren system was employed to obtain the Schlieren images, captured using a digital CMOS camera. Meanwhile, the other CMOS camera was used to capture the colored flame images. B

DOI: 10.1021/acs.energyfuels.7b00494 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels The fuels used in the present study were mixtures of pure H2 (>99.99%) and CO (>99.5%). Diluents were pure N2 (>99.9%) and CO2 (>99.99%). The oxidizer was compressed air, predried with a desiccator. The flow rates of H2, CO, N2, CO2, and air streams were separately controlled using sonic-nozzle type flowmeters. According to the basic principles of fluid dynamics,34 the flow velocity at the narrow neck of the sonic nozzle is the sound velocity for an ideal gas when the upstream pressure (p1) of the sonic nozzle is greater than 1/0.528 times of the downstream pressure (p2) of the sonic nozzle. When p1 > p2/0.528 holds, the volumetric flow rate passing through the sonic nozzle is independent of p2 and is only a function of p1.34 Thus, a linear relation of flow rate with p1 was established through calibration and so as to control the flow rate easily by simply adjusting p1 using a regulator integrated with a high-accuracy digital pressure gauge. All experimental runs were carried out at atmospheric pressure (1 atm). In order to obtain the experimental data at elevated unburned mixture temperatures Tu, the gas mixture was preheated using a thermal resistance heating furnace and a series of electrical heating tapes to maintain the temperature variation of the mixture along the tubing below 20 K. The temperature along the gas tubing was monitored using 5 K-type thermocouples and controlled using 5 PID feedback controlling units. The temperature of the gas mixture at the burner exit was measured using a K-type thermocouple (Omega CHAL-010-BW) with a diameter (d) of the welding joint being 0.254 mm (0.01 in.). This thermocouple was placed inside the burner nozzle along the stream line facing toward the upstream. The length (l) of this thermocouple inside the burner was ∼10 mm. The section of this thermocouple outside the burner was also heated to a temperature very close to the burner wall temperature and thus also very close to the flow temperature (ΔT < 7K). The measurements were taken in steady state. In the present study, Tu = 300, 400, 500, and 600 K. Similar to a previous study,33 Su0 was experimentally determined using the nonlinear extrapolation approach. Theoretically, Su0 and Su (method-dependent flame speed) meet 0 0 ⎧ ⎪ ln Su = ln Su + Ma Ka ⎨ ⎪ ⎩ Ka = 1 − A b /A u

Figure 4. Colored image and the corresponding gray scale Schlieren image of a Bunsen flame: (left) colored image; (right) Schlieren image. thermocouple wire, (2) thermal radiation to the burner wall, and (3) flow-induced kinematic temperature. In this experimental setup, since l/d > 25 and the temperature difference along the thermocouple wire was quite low ( 1, H2 will not be completely consumed and YH2 will need to be calculated as

(6)

The present semiempirical correlation is an extension of that in ref 32 for H2/CO blends over a broader range of conditions. Compared to solving differential equations and detailed chemistry and molecular mass transport, this correlation will significantly save computation time and even make the calculation solvable by hand.

where Wi denotes the molecular weight of species i. Tb can be calculated from the constant pressure adiabatic flame temperature, and Lei = λmix/(ρmixDi,N2Cp,mix) can be estimated from the transport parameters of species i at Tu. Tc only depends on the pressure p. The constants (F, G, l, m, and n) were obtained through the empirical correlation of the experimental Su0 data, and k was expressed as an equation in order to better predict the temperature dependence of the laminar flame speed in the present study. The empirical correlation was obtained by solving the nonlinear data-fitting problems using a MATLAB program based on the “Isqcurefit” function. Considering the significant differences in the chemical kinetics over such a large ϕ range (0.8−3.0), the fitting parameters are separately provided for ϕ ≤ 1.65 and ϕ ≥ 1.73. Within the narrow range of 1.65 < ϕ < 1.73, the Su0 value needs to be calculated from the linear interpolation of the values at ϕ = 1.65 and 1.73 in order to maintain the continuity of the entire fitting curve. The semiempirical correlation of Su0 for H2/CO/ air flames and the detailed calculation method for each involved parameters are shown in Table 1.

4. RESULTS AND DISCUSSION 4.1. Validation of the Proposed Semiempirical Correlation. The performance of the newly proposed correlation was first validated using the Su0 data of H2/air flames41−46 since the data is abundant in the literature and the fuel is the simplest. The estimations using Zhang’s previous correlation32 and CHEMKIN computation were provided as well for comparison. Figure 1 shows that Zhang’s correlation accurately predicted Su0 of lean H2/air flames but underpredicted Su0 by up to 35% when ϕ > 1.2. The predictions using the new correlation agreed with the experimental data under fuel-rich conditions well, and under ultrafuel-rich conditions (ϕ > 3.5), it only slightly overpredicted the experimental data by 1.5, confirming that Zhang’s correlation was not applicable for those fuel-rich mixtures. Generally, the new correlation gave satisfactory predictions of Su0 of H2/CO/air flames at Tu = 300, 400, and 500 K over ϕ = 0.6−4.0, while slightly overpredicted Su0 at Tu = 600 K, and the overprediction was greater when xH2 was larger. For instance, for those cases at Tu = 600 K with ϕ > 3.0, the predictions using the new correlation were 15−18% lower than the corresponding experimental values. The new correlation was also validated for H2/CO/air flames with high N2 and CO2 dilutions, and the results are presented in Figures 5 and 6. The predictions using the new correlation agreed well with the experimental data and the detailed computation results when H2/CO was diluted by 25% (xdilution = 0.25) of N2 or CO2 at Tu = 300 and 500 K (Figures 5a and 6a). When xdilution increased to 0.67, the new correlation still performed satisfactorily for N2-diluted H2/CO at Tu = 300 K (Figure 5b) but considerably overpredicted Su0 at Tu = 500 K, especially for CO2-diluted fuel-rich mixtures (Figure 6b). Clearly, further improvement to the correlation is needed if it is to be applied to the syngas mixtures with extremely high dilutions. The validity of the new correlation was also verified at an elevated pressure (p = 2 atm) against the literature data,10 as shown in Figure 7. In general, the predictions using the new correlation showed good agreement with the experimental Su0

Figure 7. Experimental, computed, and estimated laminar flame speed of H2/CO/air mixtures under elevated pressure: (solid symbols) experimental data,10 (solid line) present correlation, (dashed line) Davis-Mech.

of H2/CO/air flames at xH2 values of 0.25 and 0.5 as well as the detailed CHEMKIN computation results. Further validation of the new correlation under even higher pressures will be a future task once the experimental data are available. F

DOI: 10.1021/acs.energyfuels.7b00494 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

where z denotes an object parameter concerned in the calculation. The results of the sensitivity analysis are shown in Figure 9. The predicted Su0 value was extremely sensitive to

In summary, the predicted data (ordinate) were compared with the experimental measurements (abscissa) covering xH2 = 0.25−1.0, xdilution = 0−0.25, ϕ = 0.6−4.0, Tu = 300−600 K, and p = 1−2 atm from both the present work and the literature,3−5,7−11,13,14,18,33,41,42,44−48 as shown in Figure 8.

Figure 9. Sensitivity of the predicted laminar flame speed of syngas mixtures using the new correlation to each fitting parameter (H2/CO/ air, xH2 = 0.5, Tu = 300 K, p = 1 atm).

Figure 8. Predicted laminar flame speed of syngas mixtures using the present semiempirical correlation against experimental data: (symbols) experimental data; (solid line) unity; (dashed line) ±10 error lines; (dotted line) ±15 error lines.

the minor disturbance of the parameter l, the exponent of YH2. For instance, only 1% disturbance to l resulted in ∼7.6% decrease in Su0 on the lean side and ∼4.1% on the rich side. This result also echoes the conscientious determination of YH2 in section 3. In addition, parameter G also had a large sensitivity factor, which logically indicates that the chemical kinetics played an important role. As aforementioned (section 3), the chemical kinetics in the correlation was simply represented by a constant “activation energy”, G, which may introduce inaccuracy and thereby partially contribute to the overall prediction deviation. In order to further evaluate the effect of chemical kinetics at different Tu’s or xdilution’s, sensitivity analysis of Su0 to each elementary reaction was also carried out using CHEMKIN, and the sensitivity coefficients of the key reactions are shown in Figures 10 and 11. As expected, the H2/O2 chemistry dominated the overall chemical kinetics, and the key reactions were quite similar under the tested conditions, implying that it is reasonable to use quite limited parameters (only G and Tc in the new correlation) to describe the overall kinetics. However, as Tu increased from 300 to 600 K, the sensitivity coefficients of some key reactions, such as CO + OH = CO2 + H, H + O2 = O + OH, and H + O2 (+M) = HO2 (+M), considerably changed and even altered their orders (Figure 10b). The effect was more significant when xdilution changed from 0 to 0.67 (Figure 11), especially for those three-body reactions, such as H + O2 (+M) = HO2 (+M). This observation implies that G and Tc at Tu = 600 K and under high dilution conditions may deviate from those used in the new correlation, explaining the relatively poor prediction of the correlation under high-temperature or highdilution conditions. Similarly, the new correlation may overpredict Su0 of H2/ CO/air at xH2 < 0.1 by up to 34%, as the previous study32 confirmed the significantly varied effect of chemical kinetics. However, the H2 ratio ( 500 K if the acceptable uncertainty is defined. Compared to detailed numerical simulations, this correlation provides a more convenient, effective means to estimate Su0 in the engineering computations.

from 0.25 to 1.0, N2 and CO2 dilution ratio from 0 to 0.25, equivalence ratio from 0.8 to 4.0, unburned gas temperature from 300 to 500 K, and pressure from 1 to 2 atm, without solving the detailed governing equations, chemical kinetics, and molecular mass transport. When the unburned gas temperature was raised to greater than 500 K or the mixture was highly diluted (dilution ratio up to 0.67), the proposed correlation could be conditionally applied since the prediction error might reach 15−30%. The relatively poor predictions of the proposed correlation under high-unburned-temperature or high-dilution conditions were mainly due to the variation of the chemical kinetics. In general, the proposed correlation provided a more convenient, effective approach to estimating the laminar flame speed of H2/CO/N2/CO2/air flames with acceptable accuracy compared to the detailed numerical simulation, especially suitable for applications in the engineering computations.

5. CONCLUSIONS A semiempirical correlation for the prediction of the laminar flame speed of H2/CO/N2/CO2/air flames was proposed and evaluated. The performance of the proposed correlation was validated using a broad range of experimental data from both the literature and new measurements. Results showed that the proposed correlation was able to satisfactorily (error < 15%) predict the laminar flame speed of a wide range of H2/CO/N2/ CO2/air mixtures covering the H2 ratio in the H2/CO mixture H

DOI: 10.1021/acs.energyfuels.7b00494 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

■

(5) Prathap, C.; Ray, A.; Ravi, M. R. Effects of dilution with carbon dioxide on the laminar burning velocity and flame stability of H2−CO mixtures at atmospheric condition. Combust. Flame 2012, 159 (2), 482−492. (6) Zhang, Y.; Shen, W.; Fan, M.; Zhang, H.; Li, S. Laminar flame speed studies of lean premixed H2/CO/air flames. Combust. Flame 2014, 161 (10), 2492−2495. (7) Dong, C.; Zhou, Q.; Zhao, Q.; Zhang, Y.; Xu, T.; Hui, S. Experimental study on the laminar flame speed of hydrogen/carbon monoxide/air mixtures. Fuel 2009, 88 (10), 1858−1863. (8) Lapalme, D.; Seers, P. Influence of CO2, CH4, and initial temperature on H2/CO laminar flame speed. Int. J. Hydrogen Energy 2014, 39 (7), 3477−3486. (9) Natarajan, J.; Lieuwen, T.; Seitzman, J. Laminar flame speeds of H2/CO mixtures: Effect of CO2 dilution, preheat temperature, and pressure. Combust. Flame 2007, 151 (1−2), 104−119. (10) Sun, H.; Yang, S.; Jomaas, G.; Law, C. High-pressure laminar flame speeds and kinetic modeling of carbon monoxide/hydrogen combustion. Proc. Combust. Inst. 2007, 31 (1), 439−446. (11) Singh, D.; Nishiie, T.; Tanvir, S.; Qiao, L. An experimental and kinetic study of syngas/air combustion at elevated temperatures and the effect of water addition. Fuel 2012, 94, 448−456. (12) Zhang, W.; Gou, X.; Kong, W.; Chen, Z. Laminar flame speeds of lean high-hydrogen syngas at normal and elevated pressures. Fuel 2016, 181, 958−963. (13) Han, M.; Ai, Y.; Chen, Z.; Kong, W. Laminar flame speeds of H2/CO with CO2 dilution at normal and elevated pressures and temperatures. Fuel 2015, 148, 32−38. (14) Burbano, H. J.; Pareja, J.; Amell, A. A. Laminar burning velocities and flame stability analysis of H2/CO/air mixtures with dilution of N2 and CO2. Int. J. Hydrogen Energy 2011, 36 (4), 3232− 3242. (15) Weng, W.; Wang, Z.; He, Y.; Whiddon, R.; Zhou, Y.; Li, Z.; Cen, K. Effect of N2/CO2 dilution on laminar burning velocity of H2−CO− O2 oxy-fuel premixed flame. Int. J. Hydrogen Energy 2015, 40 (2), 1203−1211. (16) Zhang, Y.; Shen, W.; Zhang, H.; Wu, Y.; Lu, J. Effects of inert dilution on the propagation and extinction of lean premixed syngas/air flames. Fuel 2015, 157, 115−121. (17) Zhang, Y.; Zhu, M.; Zhang, Z.; Shang, R.; Zhang, D. Ozone effect on the flammability limit and near-limit combustion of syngas/ air flames with N2, CO2, and H2O dilutions. Fuel 2016, 186, 414−421. (18) Cheng, T. S.; Chang, Y. C.; Chao, Y. C.; Chen, G. B.; Li, Y. H.; Wu, C. Y. An experimental and numerical study on characteristics of laminar premixed H2/CO/CH4/air flames. Int. J. Hydrogen Energy 2011, 36 (20), 13207−13217. (19) Meng, S.; Sun, S.; Xu, H.; Guo, Y.; Feng, D.; Zhao, Y.; Wang, P.; Qin, Y. The effects of water addition on the laminar flame speeds of CO/H2/O2/H2O mixtures. Int. J. Hydrogen Energy 2016, 41 (25), 10976−10985. (20) Davis, S. G.; Joshi, A. V.; Wang, H.; Egolfopoulos, F. An optimized kinetic model of H2/CO combustion. Proc. Combust. Inst. 2005, 30 (1), 1283−1292. (21) Li, J.; Zhao, Z.; Kazakov, A.; Chaos, M.; Dryer, F. L.; Scire, J. J. A comprehensive kinetic mechanism for CO, CH2O, and CH3OH combustion. Int. J. Chem. Kinet. 2007, 39 (3), 109−136. (22) Frassoldati, A.; Faravelli, T.; Ranzi, E. The ignition, combustion and flame structure of carbon monoxide/hydrogen mixtures. Note 1: Detailed kinetic modeling of syngas combustion also in presence of nitrogen compounds. Int. J. Hydrogen Energy 2007, 32 (15), 3471− 3485. (23) Kéromnès, A.; Metcalfe, W. K.; Heufer, K. A.; Donohoe, N.; Das, A. K.; Sung, C.-J.; Herzler, J.; Naumann, C.; Griebel, P.; Mathieu, O.; Krejci, M. C.; Petersen, E. L.; Pitz, W. J.; Curran, H. J. An experimental and detailed chemical kinetic modeling study of hydrogen and syngas mixture oxidation at elevated pressures. Combust. Flame 2013, 160 (6), 995−1011. (24) Wang, Q. D. An updated detailed reaction mechanism for syngas combustion. RSC Adv. 2014, 4 (9), 4564−4585.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +61 8 6488 7600. Fax: +61 8 6488 7622. ORCID

Yang Zhang: 0000-0003-3297-7433 Mingming Zhu: 0000-0002-3643-1799 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Partial financial supports has been received for this work from the Australian Commonwealth Government under the Australian Research Council’s ARC Linkage Projects Scheme (LP100200135), Australia−India Strategic Research Fund Grand Challenge Projects Scheme (GCF020010). R.S. received a study-abroad scholarship from the China Scholarships Council.

■

NOMENCLATURE

Roman Letters

Ab = burned flame surface area, cm2 Au = unburned flame surface area, cm2 Ka = Karlovitz number Le = Lewis number Ma0 = flow-independent Markstein number Mach = Mach number p = pressure, atm Q̇ = total volumetric flow rate, mL·s−1 Su0 = laminar flame speed, cm·s−1 Su = method-dependent flame propagation speed, cm·s−1 T = temperature, K xH2 = H2 ratio in H2/CO mixtures, moles of H2/(moles of H2 + moles of CO) xdilution = dilution ratio, moles of dilution/(moles of H2 + moles of CO) YH2,u = mass fraction of consumed H2 in the overall fresh mixture

Greek Letters

ρu = unburned gas density, g·cm−3 ϕ = equivalence ratio Φ,H2 = reference H2 equivalence ratio σ = standard derivation

Subscripts

b = burned gas property c = inner layer property t = thermocouple g = gas u = unburned gas property

■

REFERENCES

(1) Lieuwen, T.; Yang, V.; Yetter, R. Synthesis gas combustion: fundamentals and applications; CRC Press: 2009. (2) Chaos, M.; Dryer, F. L. Syngas Combustion Kinetics and Applications. Combust. Sci. Technol. 2008, 180 (6), 1053−1096. (3) Bouvet, N.; Chauveau, C.; Gökalp, I.; Halter, F. Experimental studies of the fundamental flame speeds of syngas (H2/CO)/air mixtures. Proc. Combust. Inst. 2011, 33 (1), 913−920. (4) Fu, J.; Tang, C.; Jin, W.; Thi, L. D.; Huang, Z.; Zhang, Y. Study on laminar flame speed and flame structure of syngas with varied compositions using OH-PLIF and spectrograph. Int. J. Hydrogen Energy 2013, 38 (3), 1636−1643. I

DOI: 10.1021/acs.energyfuels.7b00494 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels (25) Healy, D.; Kalitan, D. M.; Aul, C. J.; Petersen, E. L.; Bourque, G.; Curran, H. J. Oxidation of C1-C5 Alkane Quinternary Natural Gas Mixtures at High Pressures. Energy Fuels 2010, 24, 1521−1528. (26) Kee, R. J.; Grcar, J. F.; Smooke, M.; Miller, J.; Meeks, E. CHEMKIN; Sandia National Laboratories, 1985. (27) Yu, G.; Law, C.; Wu, C. Laminar flame speeds of hydrocarbon +air mixtures with hydrogen addition. Combust. Flame 1986, 63 (3), 339−347. (28) Tang, C.; Huang, Z.; Law, C. Determination, correlation, and mechanistic interpretation of effects of hydrogen addition on laminar flame speeds of hydrocarbon−air mixtures. Proc. Combust. Inst. 2011, 33 (1), 921−928. (29) Di Sarli, V.; Benedetto, A. D. Laminar burning velocity of hydrogen−methane/air premixed flames. Int. J. Hydrogen Energy 2007, 32 (5), 637−646. (30) Ji, C.; Egolfopoulos, F. N. Flame propagation of mixtures of air with binary liquid fuel mixtures. Proc. Combust. Inst. 2011, 33 (1), 955−961. (31) Chen, Z.; Dai, P.; Chen, S. A model for the laminar flame speed of binary fuel blends and its application to methane/hydrogen mixtures. Int. J. Hydrogen Energy 2012, 37 (13), 10390−10396. (32) Zhang, Y.; Yang, Y.; Miao, Z.; Zhang, H.; Wu, Y.; Liu, Q. A mixing model for laminar flame speed calculation of lean H2/CO/air mixtures based on asymptotic analyses. Fuel 2014, 134, 400−405. (33) Shang, R.; Zhang, Y.; Zhu, M.; Zhang, Z.; Zhang, D.; Li, G. Laminar flame speed of CO2 and N2 diluted H2/CO/air flames. Int. J. Hydrogen Energy 2016, 41 (33), 15056−15067. (34) Prandtl, L. The Essentials of Fluid Dynamics; Blackie and Son, 1963. (35) Dunn-Rankin, D.; Weinberg, F. Location of the schlieren image in premixed flames: axially symmetrical refractive index fields. Combust. Flame 1998, 113 (3), 303−311. (36) Moffat, R. J. Describing the uncertainties in experimental results. Exp. Therm. Fluid Sci. 1988, 1 (1), 3−17. (37) Zhang, Y.; Shang, R.; Shen, W.; Zhu, M.; Zhang, Z.; Zhang, H.; Zhang, D. Extinction limit and near-limit kinetics of lean premixed stretched H2-CO-air flames. Int. J. Hydrogen Energy 2016, 41 (39), 17687−17694. (38) Göttgens, J.; Mauss, F.; Peters, N. In Analytic approximations of burning velocities and flame thicknesses of lean hydrogen, methane, ethylene, ethane, acetylene, and propane flames. Symp. Combust., [Proc.] 1992, 24 (1), 129−135. (39) Seshadri, K. Multistep asymptotic analyses of flame structures. Symp. Combust., [Proc.] 1996, 26 (1), 831−46. (40) Müller, U. C.; Bollig, M.; Peters, N. Approximations for burning velocities and markstein numbers for lean hydrocarbon and methanol flames. Combust. Flame 1997, 108 (3), 349−56. (41) Krejci, M. C.; Mathieu, O.; Vissotski, A. J.; Curran, H. J. Laminar flame speed and ignition delay time data for the kinetic modeling of hydrogen and syngas fuel blends. J. Eng. Gas Turbines Power 2013, 135, 021503. (42) Egolfopoulos, F. N.; Law, C. K. An experimental and computational study of the burning rates of ultra-lean to moderately-rich H2/O2/N2 laminar flames with pressure variations. Symp. Combust., [Proc.] 1991, 23 (1), 333−340. (43) Vagelopoulos, C. M.; Egolfopoulos, F. N. Laminar flame speeds and extinction strain rates of mixtures of carbon monoxide with hydrogen, methane, and air. Symp. Combust., [Proc.] 1994, 25 (1), 1317−1323. (44) Tse, S. D.; Zhu, D. L.; Law, C. K. Morphology and burning rates of expanding spherical flames in H2/O2/inert mixtures up to 60 atm. Proc. Combust. Inst. 2000, 28 (2), 1793−1800. (45) Kwon, O. C.; Faeth, G. M. Flame/stretch interactions of premixed hydrogen-fueled flames: measurements and predictions. Combust. Flame 2001, 124 (4), 590−610. (46) Verhelst, S.; Woolley, R.; Lawes, M.; Sierens, R. Laminar and unstable burning velocities and Markstein lengths of hydrogen−air mixtures at engine-like conditions. Proc. Combust. Inst. 2005, 30 (1), 209−216.

(47) Vagelopoulos, C. M.; Egolfopoulos, F. N. Laminar flame speeds and extinction strain rates of mixtures of carbon monoxide with hydrogen, methane, and air. Symp. Combust., [Proc.] 1994, 25, 1317− 1323. (48) Hu, E.; Fu, J.; Pan, L.; Jiang, X.; Huang, Z.; Zhang, Y. Experimental and numerical study on the effect of composition on laminar burning velocities of H2/CO/N2/CO2/air mixtures. Int. J. Hydrogen Energy 2012, 37 (23), 18509−18519.

J

DOI: 10.1021/acs.energyfuels.7b00494 Energy Fuels XXXX, XXX, XXX−XXX