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| Thesis Name： |
Nitric oxide concentration and fluorescence lifetime in non-premixedatmospheric pressure flames. |
| Usage： |
chemistry |
| Keyword： |
Nitric oxide, fluorescence, non-premixedatmospheric |
| Remarks： |
Abstract:
Nitric oxide (NO) is an important combustion pollutant, and understanding NOformation and destruction chemistry requires accurate concentration measurements in geometricallysimple flames. The increasing importance of combustion in non-premixed and partially premixed modesfor power generation and transportation places additional emphasis on experiments under non-premixedconditions.; Nitric oxide concentration profiles along the stagnation streamline were measured withlaser induced fluorescence (LIF) in non-premixed, atmospheric-pressure counterflow flamesstabilized under a semi-cylindrical burner (Tsuji-type). Concentration profiles were measured inpure methane/air flames and flames with NO seeded into the fuel flow at 100- to 600-ppm levels.Several air flow-rates were examined to study the effect of flame stretch. A picosecond-pulsetunable dye laser and microchannel plate photomultiplier tube were used to provide time-resolved LIFsignal under linear (non-saturated) excitation, and fluorescence lifetimes and quenching rates weredetermined by de-convolving the temporal fluorescence signals. Coherent anti-Stokes Ramanspectroscopy was used to measure temperature profiles in the flames; this information was used toextract quantitative species concentration data from the LIF measurements and provide a boundarycondition for kinetic modeling.; Measured peak NO concentrations were between 84 ± 12-ppm(low flame stretch) and 50 ± 8-ppm (high stretch). To evaluate the kinetic mechanisms, theflames were modeled computationally and NO concentrations were calculated. Absolute concentrationpredictions in seeded and unseeded flames were accurate to within the error imposed by uncertaintyin the “prompt” NO production pathway rate (CH + N2 → HCN + N). However,the models over-predicted the decline in NO concentration with increasing air flow velocity.;Calculated flame species concentrations were coupled with model estimations for collisionalquenching cross sections, and these predicted fluorescence lifetimes were compared to directlymeasured LIF lifetimes. The predictions were accurate within experimental error in the fuel-lean andhigh-temperature regions of the flame. However, the model error in the fuel-rich region of theflame exceeded uncertainty limits; erroneously low model quenching cross sections for H2Oand CO2 could explain the discrepancy, but this possibility has not been fully explored.
Author:Driscoll, James Joshua.
Unit:University of Michigan. |
| Original file： |
No File
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