Effects of H{sub 2} enrichment on the propagation characteristics of CH{sub 4}-air triple flames

Journal Article · Thu May 15 00:00:00 EDT 2008 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2008.02.005· OSTI ID:21036808

Briones, Alejandro M; Aggarwal, Suresh K ^[1]; Katta, Viswanath R ^[2]

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1. Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL 60607 (United States)
2. Innovative Scientific Solutions, Inc., 2766 Indian Ripple Road, Dayton, OH 45440 (United States)

The effects of H{sub 2} enrichment on the propagation of laminar CH{sub 4}-air triple flames in axisymmetric coflowing jets are numerically investigated. A comprehensive, time-dependent computational model, which employs a detailed description of chemistry and transport, is used to simulate the transient ignition and flame propagation phenomena. Flames are ignited in a jet-mixing layer far downstream of the burner. Following ignition, a well-defined triple flame is formed that propagates upstream along the stoichiometric mixture fraction line with a nearly constant displacement velocity. As the flame approaches the burner, it transitions to a double flame, and subsequently to a burner-stabilized nonpremixed flame. Predictions are validated using measurements of the displacement flame velocity. As the H{sub 2} concentration in the fuel blend is increased, the displacement flame velocity and local triple flame speed increase progressively due to the enhanced chemical reactivity, diffusivity, and preferential diffusion caused by H{sub 2} addition. In addition, the flammability limits associated with the triple flames are progressively extended with the increase in H{sub 2} concentration. The flame structure and flame dynamics are also markedly modified by H{sub 2} enrichment, which substantially increases the flame curvature and mixture fraction gradient, as well as the hydrodynamic and curvature-induced stretch near the triple point. For all the H{sub 2}-enriched methane-air flames investigated in this study, there is a negative correlation between flame speed and stretch, with the flame speed decreasing almost linearly with stretch, consistent with previous studies. The H{sub 2} addition also modifies the flame sensitivity to stretch, as it decreases the Markstein number (Ma), implying an increased tendency toward diffusive-thermal instability (i.e. Ma {yields} 0). These results are consistent with the previously reported experimental results for outwardly propagating spherical flames burning a mixture of natural gas and hydrogen. (author)

• OSTI ID: 21036808
• Journal Information: Combustion and Flame, Vol. 153, Issue 3; 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
METHANE
HYDROGEN
AIR
LAMINAR FLAMES
VELOCITY
MIXTURES
ENRICHMENT
AXIAL SYMMETRY
TIME DEPENDENCE
DIFFUSION
MATHEMATICAL MODELS
FLAMMABILITY
IGNITION
INSTABILITY
FLAME PROPAGATION
CORRELATIONS
MIXING
COMPUTERIZED SIMULATION
ABUNDANCE
SENSITIVITY
STOICHIOMETRY
TRANSIENTS
COMBUSTION KINETICS
Hydrogen-methane blends
Propagating triple flames
Diffusive-thermal instability
Preferential diffusion
Stretch-flame speed interactions