Diode laser measurements of ammonia and carbon dioxide for combustion and bioreactor applications

Diode laser sensors based on absorption spectroscopy techniques were designed and demonstrated for three applications: (1) in situ NH₃ monitoring for combustion emissions using laser sources near 1.5 μm; (2) in situ CO₂ monitoring in combustion zones using lasers near 2 μm; and (3) field measurements of NH₃ and CO₂ near 2 μm in the vent gases of a spacecraft bioreactor.; Ammonia spectroscopy near 1.5 μm was investigated to select transitions appropriate for trace ammonia detection in air-quality and combustion emissions-monitoring applications using diode lasers. Six ammonia features were selected for these trace-gas detection applications based on their transition strengths and isolation from interfering species. Ammonia slip was measured in the exhaust above an atmospheric pressure premixed ethylene-air burner to demonstrate the feasibility of the in situ diode laser sensor for Thermal DeNO _x or Selective Catalytic Reduction applications.; High-resolution absorption measurements of CO₂ were made in a heated static cell and in the combustion region above a flat-flame burner for the development of an in situ CO₂ combustion diagnostic based on a diode laser operating near 2.0 μm. Measurements of spectroscopic parameters such as the linestrength, self-broadening coefficient and line position were made for the R(50) transition, and an improved value for the linestrength is reported. The combustion product mole fractions of CO₂ above a flat-flame burner were determined in situ to verify the measured spectroscopic parameters and to demonstrate the feasibility of the diode laser sensor.; Ammonia spectra near 2 μm were studied with external cavity diode lasers to select appropriate transitions for monitoring trace species concentration in the vent gases of a bioreactor. The fundamental spectroscopic parameters of the selected and neighboring transitions were measured to confirm the spectroscopic database using a DFB diode laser. The 2 μm laser was aligned into a sampling sensor system designed at Rice University to measure NH₃ concentration in the vent gases of a groundtest bioreactor at NASA-JSC and to monitor the potential toxicity of space cabin indoor air quality. The same laser probed CO₂'s R(50) transition to assess overall bioreactor health and carbon conversion efficiency. The measurements demonstrated the sensor's ability to track changes in NH₃ and CO₂ concentration due to different bioreactor events.; All three projects in this work have led to improvements in the published spectroscopic database for NH₃ or CO₂, and have established the optimum wavelengths to be employed by diode-laser based sensors for different industrial applications.