An asymptotic and numerical investigation of homogeneous ignition in catalytically stabilized channel flow combustion
The combustion of fuel-lean gaseous premixtures with increased flame stability and very low NO{sub x} emissions is an issue of prime interest in many practical applications, such as gas-fired turbines and burners. Catalytically stabilized thermal combustion (CST) is an alternative to the widely employed conventional lean premixed gaseous combustion. In CST partial--and less frequently, complete--fuel conversion is accomplished via heterogeneous (surface) oxidation reactions in burners with a suitably large surface-to-volume ratio. Complete fuel conversion is achieved with subsequent homogeneous (gaseous) combustion either in the catalytic burner itself or in a postcatalyst staged gaseous burner. This process leads to substantial reduction of NO{sub x} emissions as NO{sub x} is produced almost exclusively from the gaseous reaction path. The gas-phase ignition of a fuel-lean premixed combustible gas is investigated in a forced convection two-dimensional laminar channel flow configuration established by two catalytically-active parallel plates placed at a distance 2b apart. A close form ignition criterion is obtained for the gas-phase ignition distance in terms of nondimensional groups that are relevant to confined flows. Numerical simulations are performed for channel flow catalytic combustion of a fuel-lean (equivalence ratio 0.32) propane-oxygen-nitrogen mixture using the same underlying chemistry assumptions as in the analytical asymptotic approach. The analytically calculated ignition distances are in good agreement with those numerically predicted. The effect of flow confinement (finite b) on gaseous ignition is examined by comparing ignition distances with the corresponding ones of the unconfined (flat plate) case. Flow confinement (decreasing b) increases the ignition distances due to the resulting increase in the channel surface-to-volume ratio.
- Research Organization:
- Paul Scherrer Inst., Villigen-PSI (CH)
- OSTI ID:
- 20006275
- Journal Information:
- Combustion and Flame, Vol. 119, Issue 4; Other Information: PBD: Dec 1999; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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