Experimental assessment of O2 interferences on laser-induced fluorescence measurements of NO in high-pressure, lean premixed flames by use of narrow-band and broadband detection
William P. Partridge, Michael S. Klassen, D. Douglas Thomsen, and Normand M. Laurendeau
William P. Partridge, Michael S. Klassen, D. Douglas Thomsen, and Normand M. Laurendeau, "Experimental assessment of O2 interferences on laser-induced fluorescence measurements of NO in high-pressure, lean premixed flames by use of narrow-band and broadband detection," Appl. Opt. 35, 4890-4904 (1996)
We experimentally investigate the influence of O2 interferences on laser-induced fluorescence measurements of NO in lean methane-fueled flames at a range of pressures for both narrow-band and broadband fluorescence detection. We identify NO excitation schemes that minimize O2 interferences. From detection scans we obtain interference spectra for the different NO excitation schemes. We then identify optimum excitation–detection schemes for narrow-band detection measurements of NO. To simulate broadband detection experiments, we numerically apply five different filter combinations to the experimentally obtained detection scans. We develop filter-assessment parameters to judge the effectiveness of the different filtering schemes, and we establish a methodology for evaluating broadband excitation–detection strategies. From this research we identify optimum excitation–detection schemes for broadband detection measurements of NO.
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The O2 line specification notation is as described by Ref. 11. The R2,4(23) and P2,4(21) lines are apparent in the excitation scans that use broadband detection; the R4,4(51) and R4,5(15) lines are the O2 excitation pathways that produce potential interferences with Q2(25.5) excitation of NO, as is the R4,5(13) line for Q2(26.5) excitation of NO. However, these three O2 lines are not apparent in the excitation scans. All other O2 line positions are apparent in the detection scans of Figs. 7, 8, or 9.
Table 2
Description of Five Filters Investigated for Reducing O2 Interferences
All bandpass filters were applied in conjunction with a varying number of 1-mm UG5 CG filters.
The base bandwidth refers to the FWHM bandwidth of each bandpass filter without UG5 application.
Table 3
VALUE- and PST-Based Rank of the Candidate Excitation and Broadband Filtering Schemes at 1.0 atm for Three Experimentally Feasible Levels of ST at the Pump Wavelength
A higher VALUE-based rank indicates better interference rejection.
The initial number in the notation refers to the filter as defined in Table 2.
A higher PST-based rank indicates a greater NO-attributable signal level.
Table 4
VALUE- and PST-based Rank of the Candidate Excitation and Broadband Filtering Schemes at 6.1 atm for Three Experimentally Feasible Levels of ST at the Pump Wavelength
A higher VALUE-based rank indicates better interference rejection.
The initial number in the notation refers to the filter as defined in Table 2.
A higher PST-based rank indicates a greater NO-attributable signal level.
Tables (4)
Table 1
Line Positions of the Different O2 Lines Encountered Either in Absorption or Emission
The O2 line specification notation is as described by Ref. 11. The R2,4(23) and P2,4(21) lines are apparent in the excitation scans that use broadband detection; the R4,4(51) and R4,5(15) lines are the O2 excitation pathways that produce potential interferences with Q2(25.5) excitation of NO, as is the R4,5(13) line for Q2(26.5) excitation of NO. However, these three O2 lines are not apparent in the excitation scans. All other O2 line positions are apparent in the detection scans of Figs. 7, 8, or 9.
Table 2
Description of Five Filters Investigated for Reducing O2 Interferences
All bandpass filters were applied in conjunction with a varying number of 1-mm UG5 CG filters.
The base bandwidth refers to the FWHM bandwidth of each bandpass filter without UG5 application.
Table 3
VALUE- and PST-Based Rank of the Candidate Excitation and Broadband Filtering Schemes at 1.0 atm for Three Experimentally Feasible Levels of ST at the Pump Wavelength
A higher VALUE-based rank indicates better interference rejection.
The initial number in the notation refers to the filter as defined in Table 2.
A higher PST-based rank indicates a greater NO-attributable signal level.
Table 4
VALUE- and PST-based Rank of the Candidate Excitation and Broadband Filtering Schemes at 6.1 atm for Three Experimentally Feasible Levels of ST at the Pump Wavelength
A higher VALUE-based rank indicates better interference rejection.
The initial number in the notation refers to the filter as defined in Table 2.
A higher PST-based rank indicates a greater NO-attributable signal level.