Combustion exhaust measurements using a diode-laser-based ultraviolet absorption sensor for nitric oxide
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abstract
A diode-laser-based sensor has been developed for ultraviolet absorption measurements of the nitric oxide (NO) molecule. The sensor is based on the sum-frequency-mixing (SFM) of the output of a tunable, 395 nm external cavity diode laser (ECDL) and a 532 nm diode pumped, frequency-doubled Nd:YAG laser in a beta-barium-borate (BBO) crystal. The sum frequency mixing process generates 250 nW of ultraviolet radiation at 226.8 nm, corresponding to the (v'=0, v"=0) band of the A2+-X2{square cap} electronic transition of NO. Results from initial laboratory experiments in a gas cell are briefly discussed, followed by results from field demonstrations of the sensor on a gas turbine engine and a well-stirred reactor. Results indicate that the sensor is capable of fully resolving the absorption spectra and accurately measuring the NO concentration in actual combustion environments. The sensitivity of the current system is estimated at 0.23%, which corresponds to a detection limit of 0.8 ppm of NO per meter path length for 1000 K gas. Future system modifications to enhance sensitivity are discussed.
