Sensors for high-pressure, harsh combustion environments using wavelength-agile diode lasers
✍ Scribed by Scott T. Sanders; Daniel W. Mattison; Jay B. Jeffries; Ronald K. Hanson
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 446 KB
- Volume
- 29
- Category
- Article
- ISSN
- 1540-7489
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✦ Synopsis
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 10 cm 1מ spectral window at megahertz ratesroughly 10 times the scanning range and 1000 times the scanning rate of a conventional diode laser. The VCSEL probes absorption line shapes of the ϳ852 nm D 2 transition of atomic Cs, seeded at ϳ5 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 lm, 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 01מ to 05ם ЊC (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.