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Title: Effects of CO addition on the characteristics of laminar premixed CH{sub 4}/air opposed-jet flames

Abstract

The effects of CO addition on the characteristics of premixed CH{sub 4}/air opposed-jet flames are investigated experimentally and numerically. Experimental measurements and numerical simulations of the flame front position, temperature, and velocity are performed in stoichiometric CH{sub 4}/CO/air opposed-jet flames with various CO contents in the fuel. Thermocouple is used for the determination of flame temperature, velocity measurement is made using particle image velocimetry (PIV), and the flame front position is measured by direct photograph as well as with laser-induced predissociative fluorescence (LIPF) of OH imaging techniques. The laminar burning velocity is calculated using the PREMIX code of Chemkin collection 3.5. The flame structures of the premixed stoichiometric CH{sub 4}/CO/air opposed-jet flames are simulated using the OPPDIF package with GRI-Mech 3.0 chemical kinetic mechanisms and detailed transport properties. The measured flame front position, temperature, and velocity of the stoichiometric CH{sub 4}/CO/air flames are closely predicted by the numerical calculations. Detailed analysis of the calculated chemical kinetic structures reveals that as the CO content in the fuel is increased from 0% to 80%, CO oxidation (R99) increases significantly and contributes to a significant level of heat-release rate. It is also shown that the laminar burning velocity reaches a maximum value (57.5more » cm/s) at the condition of 80% of CO in the fuel. Based on the results of sensitivity analysis, the chemistry of CO consumption shifts to the dry oxidation kinetics when CO content is further increased over 80%. Comparison between the results of computed laminar burning velocity, flame temperature, CO consumption rate, and sensitivity analysis reveals that the effect of CO addition on the laminar burning velocity of the stoichiometric CH{sub 4}/CO/air flames is due mostly to the transition of the dominant chemical kinetic steps. (author)« less

Authors:
 [1]; ; ;  [2];  [3]
  1. Advanced Engine Research Center, Kao Yuan University, Kaohsiung County, 821 (China)
  2. Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan, 701 (China)
  3. Department of Mechanical Engineering, Chung Hua University, Hsinchu, 300 (China)
Publication Date:
OSTI Identifier:
21137921
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 156; Journal Issue: 2; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CARBON MONOXIDE; METHANE; AIR; LAMINAR FLAMES; VELOCITY; JETS; STOICHIOMETRY; OXIDATION; SIMULATION; COMBUSTION PROPERTIES; COMPARATIVE EVALUATIONS; SENSITIVITY ANALYSIS; HEAT LOSSES; CONSUMPTION RATES; COMBUSTION KINETICS; Blended fuels; Premixed opposed-jet flames; Numerical simulation

Citation Formats

Wu, C.-Y., Chao, Y.-C., Chen, C.-P., Ho, C.-T., and Cheng, T.S. Effects of CO addition on the characteristics of laminar premixed CH{sub 4}/air opposed-jet flames. United States: N. p., 2009. Web. doi:10.1016/J.COMBUSTFLAME.2008.10.028.
Wu, C.-Y., Chao, Y.-C., Chen, C.-P., Ho, C.-T., & Cheng, T.S. Effects of CO addition on the characteristics of laminar premixed CH{sub 4}/air opposed-jet flames. United States. doi:10.1016/J.COMBUSTFLAME.2008.10.028.
Wu, C.-Y., Chao, Y.-C., Chen, C.-P., Ho, C.-T., and Cheng, T.S. Sun . "Effects of CO addition on the characteristics of laminar premixed CH{sub 4}/air opposed-jet flames". United States. doi:10.1016/J.COMBUSTFLAME.2008.10.028.
@article{osti_21137921,
title = {Effects of CO addition on the characteristics of laminar premixed CH{sub 4}/air opposed-jet flames},
author = {Wu, C.-Y. and Chao, Y.-C. and Chen, C.-P. and Ho, C.-T. and Cheng, T.S.},
abstractNote = {The effects of CO addition on the characteristics of premixed CH{sub 4}/air opposed-jet flames are investigated experimentally and numerically. Experimental measurements and numerical simulations of the flame front position, temperature, and velocity are performed in stoichiometric CH{sub 4}/CO/air opposed-jet flames with various CO contents in the fuel. Thermocouple is used for the determination of flame temperature, velocity measurement is made using particle image velocimetry (PIV), and the flame front position is measured by direct photograph as well as with laser-induced predissociative fluorescence (LIPF) of OH imaging techniques. The laminar burning velocity is calculated using the PREMIX code of Chemkin collection 3.5. The flame structures of the premixed stoichiometric CH{sub 4}/CO/air opposed-jet flames are simulated using the OPPDIF package with GRI-Mech 3.0 chemical kinetic mechanisms and detailed transport properties. The measured flame front position, temperature, and velocity of the stoichiometric CH{sub 4}/CO/air flames are closely predicted by the numerical calculations. Detailed analysis of the calculated chemical kinetic structures reveals that as the CO content in the fuel is increased from 0% to 80%, CO oxidation (R99) increases significantly and contributes to a significant level of heat-release rate. It is also shown that the laminar burning velocity reaches a maximum value (57.5 cm/s) at the condition of 80% of CO in the fuel. Based on the results of sensitivity analysis, the chemistry of CO consumption shifts to the dry oxidation kinetics when CO content is further increased over 80%. Comparison between the results of computed laminar burning velocity, flame temperature, CO consumption rate, and sensitivity analysis reveals that the effect of CO addition on the laminar burning velocity of the stoichiometric CH{sub 4}/CO/air flames is due mostly to the transition of the dominant chemical kinetic steps. (author)},
doi = {10.1016/J.COMBUSTFLAME.2008.10.028},
journal = {Combustion and Flame},
number = 2,
volume = 156,
place = {United States},
year = {Sun Feb 15 00:00:00 EST 2009},
month = {Sun Feb 15 00:00:00 EST 2009}
}
  • Experimental measurements of adiabatic burning velocity and NO formation in (CH{sub 4} + H{sub 2}) + (O{sub 2} + N{sub 2}) flames are presented. The hydrogen content in the fuel was varied from 0 to 35% and the oxygen content in the air from 20.9 to 16%. Nonstretched flames were stabilized on a perforated plate burner at 1 atm. The heat flux method was used to determine burning velocities under conditions when the net heat loss of the flame is zero. Adiabatic burning velocities of methane + hydrogen + nitrogen + oxygen mixtures were found in satisfactory agreement with themore » modeling. The NO concentrations in these flames were measured in the burnt gases at a fixed distance from the burner using probe sampling. In lean flames, enrichment by hydrogen has little effect on [NO], while in rich flames, the concentration of nitric oxide decreases significantly. Dilution by nitrogen decreases [NO] at any equivalence ratio. Numerical predictions and trends were found in good agreement with the experiments. Different responses of stretched and nonstretched flames to enrichment by hydrogen are demonstrated and discussed. (author)« less
  • An experimental study was performed to investigate the effects of partially premixing, varying the equivalence ratios from 0.79 to 9.52, on OH*, CH* and C{sub 2}* in laminar partially premixed flames. The signals from the electronically excited states of OH*, CH* and C{sub 2}* were detected through interference filters using a photo multiplier tube, which were processed to the intensity ratios (C{sub 2}*/CH*, C{sub 2}*/OH* and CH*/OH*) to determine a correlation with the local equivalence ratios. Furthermore, the consistency between the results of the tomographic reconstruction; Abel inversion technique, image with CCD (Couple Charged Detector) camera and the local radicalmore » intensity with PMT was investigated. The results demonstrated that (1) the flames at F=<1.36 exhibited classical double flame structure, at F>=4.76, the flames exhibited non-premixed-like flame structure and the intermediate flames at 1.36<F<4.76 merged, (2) the peak intensities of OH*, CH* and C{sub 2}* were maximal at F=0.86, 0.91 and 1.06, (3) the intensity ratio of CH*/OH* was nearly proportional to 1/F for the 1 dimensional results with PMT, with a correlation coefficient of 0.99 at the equivalence ratios of 0.79-9.52. These results are in good agreement with those obtained from the two dimensional results with ICCD. However, it is difficult to predict the relationships between the equivalence ratios and intensity ratios of C{sub 2}*/CH* and C{sub 2}*/OH*. (author)« less
  • Effects of pressure on NO formation in CH{sub 4}/air flames at a fixed equivalence ratio of 1.3 are investigated. The axial profiles of temperature, OH, CH, and NO mole fractions are measured using laser-induced fluorescence and compared with one-dimensional flame calculations. The measured and calculated temperature, CH, and NO profiles in free flames are observed to vary upon increasing the pressure from 40 to 75 Torr, following a scaling law derived for a chemical mechanism containing only second-order reactions. At pressures 300-760 Torr, the measurements and calculations in burner-stabilized flames show increasing flame temperature and NO mole fractions when themore » mass flux is increased linearly with pressure, while the CH profiles remain unchanged. The observed deviation from the scaling law in the temperature profiles arises from the increasing contribution of three-body reactions to the flame front propagation velocity, leading to a decrease in the degree of burner stabilization. The deviation from the pressure scaling law for the NO mole fractions is due to the temperature dependence of the rate coefficient for the reaction between CH and N{sub 2} and the fact that the temperature profiles themselves do not scale. In contrast, the surprisingly good scaling of the CH mole fractions with pressure indicates the dominant role of two-body reactions participating in the chain of chemical reactions leading to CH formation. The calculations using GRI-Mech 3.0 substantially overpredict (up to 50%) the measured nitric oxide concentrations for all pressures studied. The observed differences in the NO mole fraction may be addressed by improving the CH prediction. (author)« less
  • Measurements of visible flame heights, global radiative heat loss fractions, distributions of mole fractions of stable gas species, and pollutant emission indices in laminar partially premixed flames burning various fuel-rich mixtures of CH{sub 4} and air in an overventilating co-flow of air are reported. Mole fractions of CO{sub 2}, CO, H{sub 2}, O{sub 2}, N{sub 2} CH{sub 4}, C{sub 2}H{sub 4} and C{sub 2}H{sub 2} were measured, using sampling and gas chromatography, at several radial locations at three different heights above the fuel tube for a fixed fuel flow rate and six different fuel tube equivalence ratios. Mole fractions ofmore » H{sub 2}O were inferred from the dry based measurements. With increasing levels of partial premixing following effects are observed: (1) the visible flame height decreases and the overall flame color changes from yellow to blue; (2) the radiative heat loss fraction first decreases and then reaches a constant value; (3) the mole fractions of CO decrease and those of CO{sub 2} and H{sub 2}O increase in the lean parts of the flame; (4) mole fractions of C{sub 2}H{sub 2} decrease and those of C{sub 2}H{sub 4} first increase and then decrease in the rick parts of the flame; (5) mole fractions of CO and H{sub 2} first decrease slightly and then increase in the rich parts of the flame; and (6) the O{sub 2} mole fractions at the point of negligible CH{sub 4} mole fraction decrease. Measurements of emission indices for NO, NO{sub x}, CO and HC show that, for a fixed fuel flow rate and overall equivalence ratio, an optimum level of partial premixing exists.« less