Methane–air mixtures ignited by CW laser-heated targets on optical fiber tips: Comparison of targets, optical fibers, and ignition delays

Dubaniewicz, Thomas H.

doi:10.1016/j.jlp.2005.10.004

Cited by 8 publications

(1 citation statement)

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“…However, while having a detector as part of the interrogation cell improves tolerance to beam deviation and dispersion due to the larger target area on a photodiode versus a collimating optic, eliminating the photodetector from an interrogation region placed in situ reduces the need for electrical components and cabling, and more importantly for this application, removes the flammability risk by ensuring the remote sensor head is intrinsically safe. In principle, this might be implemented by centralizing of the expensive and sensitive base TDLAS system within an intrinsically safe environment, and multiplexing the laser signal to many sensor heads located hundreds of meters away using fiber optics (Dubaniewicz, 2006;Stewart et al, 1998a;Stewart et al, 2004).…”

Section: Current State Of Tdlasmentioning

confidence: 99%

Design of an Optical Fiber-Coupled Sensor for Ambient Methane Measurement

Schoonbaert¹

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A tunable diode laser system was developed for remote monitoring of ambient methane using fiber optically connected all-optical sensor heads. Experiments were performed to quantitatively evaluate the influence of selected system hardware and software configurations, with the further goal of enabling measurements of ambient methane concentrations over an intrinsically-safe fiber optic network at sufficient precision and sensitivity to detect unknown fugitive emission sources. The designed system could switch between the sweep integration (SI) and wavelength modulation spectroscopy (WMS) detection methods, which inferred the methane volume mixing ratio from an absorption or second-harmonic (2f) feature respectively. Signals controlling the laser injection current were optimized to balance trade-offs between measurement precision and system sensitivity, and fiber optic components were thermally stabilized to reduce system drift. Starting from this base system, experiments were performed to evaluate the effectiveness of theory-based and experimental calibration methods, software and dual laser approaches to estimating the absorption-free intensity, different signal processing approaches to suppress effects of residual amplitude modulation (RAM) of the laser output intensity, and methods to reduce system drift. Tests also considered effects of varying fiber lengths between the central laser control hardware and the remotely located optical sensor heads. Finally, long-term stability was evaluated by quantifying bias (drift) and precision uncertainty in tests up to 16 months after initial calibration. The best measurement performance was achieved using the WMS method with thermally stabilized optical components within the central control hardware combined with a theory-based calibration, automated daily calibration supported by concurrent softwarebased estimation of the absorption-free intensity, and pair-wise averaging of the 2f feature maxima in each sweep period to suppress effects of RAM. At an averaging time of 1 s and methane concentrations between 1.0 and 50 ppm v , the system implementing the 2f-WMS method surpassed the methane volume mixing ratio measurement targets with a precision of 1.6 ppm v (absorbance of 6.57×10 -7 cm -1 ) and lower detection limit (LDL) of 1.5 ppm v (6.13×10 -7 cm -1 ). In achieving these values, thermal stabilization was responsible for a 93% reduction in the precision uncertainty; adding the concurrent software-based absorption-free intensity estimate netted a further reduction of 73%; and implementing RAM suppression via pair-wise averaging of the resolved 2f features within each sweep period technique allowed a further reduction of 9%.3

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Section: Current State Of Tdlasmentioning

confidence: 99%