Effects of H{sub 2} or CO{sub 2} addition, equivalence ratio, and turbulent straining on turbulent burning velocities for lean premixed methane combustion

Journal Article · Sun Jun 15 00:00:00 EDT 2008 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2008.03.014· OSTI ID:21044860

Shy, S S; Chen, Y C; Yang, C H; Liu, C C; Huang, C M ^[1]

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1. Department of Mechanical Engineering, Institute of Energy Engineering, National Central University, Jhong-li, Tao-yuan 32001 (China)

Using hydrogen or carbon dioxide as an additive, we investigate the bending effect of turbulent burning velocities (S{sub T}/S{sub L}) over a wide range of turbulent intensities (u{sup '}/S{sub L}) up to 40 for lean premixed methane combustion at various equivalence ratios ({phi}), where S{sub L} is the laminar burning velocity. Experiments are carried out in a cruciform burner, in which a sizable downward-propagating premixed CH{sub 4}/diluent/air flame interacts with intense isotropic turbulence in the central region without influences of ignition and unwanted turbulence from walls. Simultaneous measurements using the pressure transducer and pairs of ion-probe sensors at various positions of the burner show that effects of gas velocities and pressure rise due to turbulent combustion on S{sub T} of lean CH{sub 4}/H{sub 2}/air flames can be neglected, confirming the accuracy of the S{sub T} data. Results with increasing hydrogen additions ({delta}=10, 20, and 30% in volume) show that the bending of S{sub T}/S{sub L} vs u{sup '}/S{sub L} plots is diminished when compared to data with {delta}=0, revealing that high reactivity and diffusivity of hydrogen additives help the reaction zone remaining thin even at high u{sup '}/S{sub L}. In contrast, the bending effect is strongly promoted when CO{sub 2} is added due to radiation heat losses. This leads to lower values of S{sub T}/S{sub L} at fixed u{sup '}/S{sub L} and {phi}, where the slope n can change signs from positive to negative at sufficiently large u{sup '}/S{sub L}, suggesting that the reaction zone is no longer thin. All S{sub T} data with various {delta} can be well approximated by a general correlation (S{sub T}-S{sub L})/u{sup '}=0.17Da{sup 0.43}, covering both corrugated flamelet and distributed regimes with very small data scatter, where Da is the turbulent Damkoehler number. These results are useful in better understanding how turbulence and diluents can influence the canonical structures of turbulent premixed flames and thus turbulent burning rates. (author)

• OSTI ID: 21044860
• Journal Information: Combustion and Flame, Vol. 153, Issue 4; Other Information: Elsevier Ltd. All rights reserved; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
03 NATURAL GAS
METHANE
CARBON DIOXIDE
HYDROGEN
COMBUSTION
AIR
VELOCITY
FLAMES
TURBULENCE
REYNOLDS NUMBER
ADDITIVES
PRESSURE DEPENDENCE
ACCURACY
CORRELATIONS
RADIATIVE COOLING
COMBUSTION KINETICS
SOLVENTS
Lean methane combustion
Turbulent burning velocities
Bending effect