Sensors for high-pressure, harsh combustion environments using wavelength-agile diode lasers

Autor: Scott T. Sanders, Ronald K. Hanson, Jay B. Jeffries, D. W. Mattison
Rok vydání: 2002
Předmět:
Zdroj: Proceedings of the Combustion Institute. 29:2661-2667
ISSN: 1540-7489
Popis: Practical combustors often produce a hostile environment for optical sensors, owing to elevated pressures, multiple phases, and unsteady behavior. Fortunately, new lasers and wavelength-tuning strategies have produced a class of wavelength-agile diode-laser sensors appropriate for such environments. Here, we demonstrate the extended capabilities of wavelength-agile sensors by applying a vertical cavity surface-emitting laser (VCSEL) to monitor gas temperature and pressure in a pulse detonation engine (PDE). Using aggressive injection current modulation, the VCSEL is scanned through a 10cm −1 spectral window at megahertz rates—roughly 10 times the scanning range and 1000 times the scanning rate of a conventional diode laser. The VCSEL probes absorption line shapes of the ∼852 nm D 2 transition of atomic Cs, seeded at ∼5 ppm into the feedstock gases of a PDE. Using these line shapes, detonated-gas temperature and pressure histories, spanning 2000–4000 K and 0.5–30 atm, respectively, are recorded with microsecond time response. To facilitate similar measurements using traditional spectroscopic targets such as H 2 O near 1.4 μm, where wavelength-agile lasers are not yet commercially available, we demonstrate a novel wavelength-tuning strategy. A standard distributed-feedback diode laser is thermally cycled from −10 to +50°C (scanning the output from 1399 to 1403 nm) at kilohertz rates by pulsed heating with an auxiliary 532 nm laser. Such 4 nm scans represent a 10-fold increase in the wavelength-scanning range offered by standard current-tuning techniques. Measurements of H 2 O in a static cell at 10 atm provide the groundwork for future measurements in aeropropulsion and piston engines.
Databáze: OpenAIRE
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