Laser-Induced Fluorescence Measurements in Venturi-Cascaded Propane Gas Jet Flames

Venturi-cascading is a technique to control pollutant emissions from diffusion flames by modifying air infusion and fuel-air mixing rates through changing the flow dynamics in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at a burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi-cascading technique resulted in a decrease of 33 percent in NO emission index along with a 24-percent decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). In order to understand the mechanism behind these results, laser-induced fluorescence (LIF) spectroscopy was employed to study the concentration field of the radicals (OH, CH, and CN) in the baseline and venturi-cascaded flames. The LIF measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18, 24 and 12 percent in the concentrations of OH, CH, and CN radicals, respectively, from their baseline values. However, in the midflame region, a 40-percent average increase in OH from its baseline value was observed. In this region, CH or CN radicals were not detected. The OH radical concentration in the downstream locations was mostly affected by soot rather than by temperature.

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Laser-Induced Fluorescence Measurements in Venturi-Cascaded Propane Gas Jet Flames

10.1115/imece1999-1115 ◽

1999 ◽

Author(s):

Ala R. Qubbaj ◽

S. R. Gollahalli

Keyword(s):

Diffusion Flames ◽

Concentration Field ◽

Laser Induced Fluorescence ◽

Pollutant Emissions ◽

Average Decrease ◽

Burner Exit ◽

Fluorescence Measurements ◽

Air Mixing ◽

Flame Region ◽

Lif Spectroscopy

Abstract “Venturi-cascading” technique is a means to control pollutant emissions of diffusion flames by modifying air infusion and fuel-air mixing rates through changing the flow dynamics in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at a burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi-cascading technique resulted in a decrease of 33% in NO emission index along with a 24% decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). In order to understand the mechanism behind these results, Laser Induced Fluorescence (LIF) spectroscopy was employed to study the concentration field of the radicals (OH, CH and CN) in the baseline and venturi-cascaded flames. The LIF measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18%, 24% and 12% in the concentrations of OH, CH and CN radical, respectively, from their baseline values. However, in the mid-flame region, a 40% average increase in OH, from its baseline value, was observed. In this region, CH or CN radicals were not detected. The OH radical, in the downstream locations, was mostly affected by soot rather than by temperature. In addition, prompt-NO mechanism appeared to play a significant role besides the conventional thermal-NO mechanism.

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Laser-induced fluorescence measurements of oh· concentrations in the oxidation region of laminar, hydrocarbon diffusion flames

Symposium (International) on Combustion ◽

10.1016/s0082-0784(06)80120-7 ◽

1992 ◽

Vol 24 (1) ◽

pp. 1015-1022 ◽

Cited By ~ 13

Author(s):

Rahul Puri ◽

Marlow Moser ◽

Robert J. Santoro ◽

Kermit C. Smyth

Keyword(s):

Diffusion Flames ◽

Laser Induced Fluorescence ◽

Fluorescence Measurements

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A Numerical Simulation of Gas Jet Diffusion Flames Enveloped by a Cascade of Venturis

Volume 2: 19th Computers and Information in Engineering Conference ◽

10.1115/detc99/cie-9046 ◽

1999 ◽

Author(s):

Ala R. Qubbaj ◽

S. R. Gollahalli

Keyword(s):

Diffusion Flames ◽

Co2 Concentration ◽

Reaction Model ◽

Numerical Results ◽

Pollutant Emissions ◽

Gas Jet ◽

University Of Oklahoma ◽

Burner Exit ◽

Baseline Case ◽

O2 Concentration

Abstract “Venturi-cascading” technique has been developed in the Combustion Laboratory at the University of Oklahoma. The goal was to control the pollutant emissions of diffusion flames by modifying the air infusion rate into the flame. The modification was achieved by installing a cascade of venturis around the burning gas jet. The basic idea behind this technique is controlling the stoichiometry of the flame through changing the flow dynamics and rates of mixing in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The thermal and composition fields of the baseline and venturi-cascaded flames were numerically simulated using CFD-ACE+, an advanced computational environment software package. The instantaneous chemistry model was used as the reaction model. The concentration of NO was determined through CFD-POST, a post processing utility program for CFD-ACE+. The numerical results showed that, in the near-burner, mid-flame and far-burner regions, the venturi-cascaded flame had lower temperature by an average of 13%, 19% and 17%, respectively, and lower CO2 concentration by 35%, 37%. and 32%, respectively, than the baseline flame. An opposite trend was noticed for O2 concentration; the cascaded flame has higher O2 concentration by 7%, 26% and 44%, in average values, in the near-burner, mid-flame and far-burner regions, respectively, than in the baseline case. The results also showed that, in the near-burner, mid-flame, and far-burner regions, the venturi-cascaded flame has lower NO concentrations by 89%, 70% and 70%, in average values, respectively, compared to the baseline case. The simulated results were compared with the experimental data. Good agreement was found in the near-burner region. However, the agreement was poor in the downstream regions. The numerical results substantiate the conclusion, which was drawn in the experimental part of this study, that venturi-cascading is a feasible method for controlling the pollutant emissions of a burning gas jet. In addition, the numerical results were useful to interpret the experimental measurements and understand the thermo-chemical processes involved. The results showed that the prompt-NO mechanism plays an important role besides the conventional thermal-NO mechanism.

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