On the characteristics of laminar lifted flames in a nonpremixed jet
- Dept. of Mechanical Engineering, Seoul National Univ., Seoul 151-742 (KR)
This paper reports on characteristics of laminar lifted flames stabilized in a nonpremixed jet issuing from a small nozzle into ambient air that have been studied experimentally. Results show that near the flame base the lifted flame has a tribrachial structure composed of a lean premixed flame, a rich premixed flame, and a diffusion flame extending downstream from the same point. A simple theoretical formula for the liftoff height of nonpremixed jet flames based on a boundary layer type of jet theory predicts that the liftoff height increases with increasing flow rate for Schmidt numbers in the range Sc {gt} 1 of Sc {lt} 0.5, while it decreases for 0.5 {lt} Sc {lt} 1, which is physically unrealistic. This is consistent with the experimental observation that propane and n-butane jets (Sc {gt} 1) have lifted flames while methane and ethane (0.5 {lt} Sc {lt} 1) exhibit blowout directly from the attached flames. A correlation for the explicit dependence of the liftoff height on the flow rate and the nozzle diameter was derived from the experiments for propane and butane and shown to agree well with the theory. This finding emphasizes the importance of the tribrachial flame, approximated as a stoichiometric premixed flame, in determining the characteristics of lifted laminar nonpremixed jet flames.
- OSTI ID:
- 5728073
- Journal Information:
- Combustion and Flame; (United States), Journal Name: Combustion and Flame; (United States) Vol. 86:1; ISSN 0010-2180; ISSN CBFMA
- Country of Publication:
- United States
- Language:
- English
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092000 -- Biomass Fuels-- Combustion-- (1990-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
42 ENGINEERING
420400 -- Engineering-- Heat Transfer & Fluid Flow
ALKANES
BOUNDARY LAYERS
BUTANE
CALCULATION METHODS
DESIGN
DISPERSIONS
FLAMES
FLOW RATE
FLUID FLOW
HYDROCARBONS
JETS
LAMINAR FLOW
LAYERS
MIXTURES
NOZZLES
ORGANIC COMPOUNDS
PROPANE