A DIODE-LASER ABSORPTION SENSOR SYSTEM FOR COMBUSTION EMISSION MEASUREMENTS

A diode-laser sensor system has been developed to measure the concentr ations of NO, N2O, CO, CO2 and O-2 in combustion gases using absorptio n spectroscopy and fast-extraction sampling techniques. Measured surve y spectra of the NO 3 nu band (the R branch) and H2O lines from the nu (2) + nu(3) band in the spectral region from 5556 to 5572 cm(-1) were recorded and compared with calculated spectra to select optimum transi tions for detection of NO. Similarly, measured survey spectra of the N 2O 3 nu(3) band from 6535 to 6600 cm(-1) were used to identify optimum transitions for detection of N2O. High-resolution NO absorption measu rements (R-2(7.5) and R-1(7.5) lines) were recorded in a fast-flow mul tipass cell containing probe-sampled combustion gases to determine NO concentrations in a laminar, premixed CH4-air flame, seeded with NH3. For fuel-lean conditions, the measured NO mole fractions corresponded to 68% of the injected NH3. For fuel-rich conditions, the fraction of NH3 converted to NO decreased with increasing equivalence ratio. In ad ditional experiments, CO, CO2 and O-2 absorption measurements (the R(1 3) line of the 3 nu band, the R(16) line of the 2 nu(1) + 2 nu(2)(0) nu(3) band and the RQ(7, 8) line of the b(1) Sigma(g)(+)(nu' = 0) <-- X-3 Sigma(g)(-)(nu '' = 0) band, respectively) were used to determine species concentrations above a laminar, premixed CH4-air flame. Good agreement was found between measured CO, CO2 and O-2 concentrations an d calculated chemical equilibrium values.