Development of All-Solid-State Sensors for Measurement of Nitric Oxide and Ammonia Concentrations by Optical Absorption in Particle-Laden Combustion Exhaust Streams
An all-solid-state continuous-wave (cw) laser system for ultraviolet absorption measurements of the nitric oxide (NO) molecule has been developed and demonstrated. For the NO sensor, 250 nW of tunable cw ultraviolet radiation is produced by sum-frequency-mixing of 532-nm radiation from a diode-pumped Nd:YAG laser and tunable 395-nm radiation from an external cavity diode laser (ECDL). The sum-frequency-mixing process occurs in a beta-barium borate crystal. The nitric oxide absorption measurements are performed by tuning the ECDL and scanning the sum-frequency-mixed radiation over strong nitric oxide absorption lines near 226 nm. In Year 1 of the research, the nitric oxide sensor was used for measurements in the exhaust of a coal-fired laboratory combustion facility. The Texas A&M University boiler burner facility is a 30 kW (100,000 Btu/hr) downward-fired furnace with a steel shell encasing ceramic insulation. Measurements of nitric oxide concentration in the exhaust stream were performed after modification of the facility for laser based NOx diagnostics. The diode-laser-based ultraviolet absorption measurements were successful even when the beam was severely attenuated by particulate in the exhaust stream and window fouling. Single-laser-sweep measurements were demonstrated with an effective time resolution of 100 msec, limited at this time by the scan rate of our mechanically tuned ECDL system. In Year 2, the Toptica ECDL in the original system was replaced with a Sacher Lasers ECDL. The mode-hop-free tuning range and tuning rate of the Toptica ECDL were 25 GHz and a few Hz, respectively. The mode-hop-free tuning range and tuning rate of the Sacher Lasers ECDL were 90 GHz and a few hundred Hz, respectively. The Sacher Lasers ECDL thus allows us to scan over the entire NO absorption line and to determine the absorption baseline with increased accuracy and precision. The increased tuning rate is an advantage in that data can be acquired much more rapidly and the absorption measurements are less susceptible to the effects of transient fluctuations in the properties of the coal combustor exhaust stream. Gas cell measurements were performed using the NO sensor with the new ECDL, and a few spectra were acquired from the coal exhaust stream. However, the laser diode in the new ECDL failed during the coal combustor tests. In Year 3, however, we obtained a new GaN laser diode for our ECDL system, installed it, and completed an extensive series of measurements in the Texas A&M coal-fired laboratory combustion facility. The combustor was operated with coal and coal/biomass as fuels, with and without reburn, and with and without ammonia injection. Several different fuel equivalence ratios were investigated for each operating condition. A series of spectral simulations was performed using the HITRAN code to investigate the potential sensitivity of absorption measurements of ammonia in different spectral regions. It was concluded that ammonia absorption features in the 3000-nm spectral region would be hard to measure due to water vapor interferences. We will concentrate on the spectral region near 1530 nm, where other researchers have had some success in measuring ammonia.
- Research Organization:
- Texas A & M Univ., College Station, TX (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG26-02NT41535
- OSTI ID:
- 881865
- Country of Publication:
- United States
- Language:
- English
Similar Records
Development of All-Solid-State Sensors for Measurement of Nitric Oxide and Ammonia Concentrations by Optical Absorption in Particle-Laden Combustion Exhaust Streams
Development of All-Solid-State Sensors for Measurement of Nitric Oxide and Ammonia Concentrations by Optical Absorption in Particle-Laden Combusion Exhaust Streams