Minute Concentration Measurements of Simple Hydrocarbon Species Using Supercontinuum Laser Absorption Spectroscopy

Abstract

Minute concentration measurements of simple hydrocarbon gases are demonstrated using near-infrared supercontinuum laser absorption spectroscopy. Absorption-based gas sensors, particularly when combined with optical fiber components, can significantly enhance diagnostic capabilities to unprecedented levels. However, these diagnostic techniques are subject to limitations under certain gas sensing applications where interference and harsh conditions dominate. Supercontinuum laser absorption spectroscopy is a novel laser-based diagnostic technique that can exceed the above-mentioned limitations and provide accurate and quantitative concentration measurement of simple hydrocarbon species while maintaining compatibility with telecommunications-grade optical fiber components. Supercontinuum radiation generated using a highly nonlinear photonic crystal fiber is used to probe rovibrational absorption bands of four hydrocarbon species using full-spectral absorption diagnostics. Absorption spectra of methane (CH4), acetylene (C2H2), and ethylene (C2H4) were measured in the near-infrared spectrum at various pressures and concentrations to determine the accuracy and feasibility of the diagnostic strategy. Absorption spectra of propane (C3H8) were subsequently probed between 1650 nm and 1700 nm, to demonstrate the applicability of the strategy. Measurements agreed very well with simulated spectra generated using the HITRAN database as well as with previous experimental results. Absorption spectra of CH4, C2H2, and C2H4 were then analyzed to determine their respective measurement accuracy and detection limit. Concentration measurements integrated from experimental results were in very good agreement with independent concentration measurements. Calculated detection limits of CH4, C2H2, and C2H4 at room temperature and atmospheric pressure are 0.1%, 0.09%, and 0.17%, respectively.

Tunable Diode Laser Absorption Spectroscopy- Based Detection of Propane for Explosion Early Warning by Using a Vertical Cavity Surface Enhanced Laser Source and Principle Component Analysis Approach

“…A broad absorption feature can be observed in the region from 1680nm to 1740nm, with an absorption peak superimposed on the spectral band at a wavelength near 1684nm. These results show good agreement with the work of Chan et al [22] and Yoo et al [23].…”

“…However, a scheme using near-infrared for the detection of propane would be much more practical, given the considerably lower cost of the optical fiber needed for that spectral region. Propane has an absorption feature in the wavelength region near 1684nm (Chan et al [22] and Yoo et al [23]) and therefore such a scheme could be practical given a suitable source. However, unlike methane, ethylene and acetylene, for example, there is no simple absorption peak in the wavelength region near 1684nm -the spectrum mainly consists of a spectral band with a peak superimposed upon it.…”

TDLAS Detection of Propane/Butane Gas Mixture by Using Reference Gas Absorption Cells and Partial Least Square Approach

“…Using the near-infrared wavelength band allows the much greater variety of lasers, optical fiber and components operating in that spectral region to be used. However, comparing with the absorption feature at ~3.3μm, the near-infrared absorption spectral features of propane and butane (seen in the region from 1680nm to 1690nm) mainly consist of multiple spectral bands which overlap with each other, in the case of propane and butane, combined with an absorbance level in the near infrared that is not as strong as that at ~3.3μm [23]- [24]). Thus while it is difficult to find obvious 'standalone' absorption peaks to allow calculation of the individual component concentrations (which would follow the usual approach to TDLAS spectral analysis) from across the total absorption spectrum, what is worse is that for a propane/butane gas mixture, the absorption spectra of propane and butane severely overlap with each other in that near infrared region.…”

“…Thus, according to equations (19) - (24), the concentration vector, Cdetect, which involves the concentrations of the propane and the butane components in the sample mixture to be detected can be given by:…”

Simultaneous Measurements of Light Hydrocarbons Using Supercontinuum Laser Absorption Spectroscopy

“…The minimum detection limit of SCLAS for several hydrocarbons can be found in the literature. 9 SCLAS is a novel diagnostic technique that combines the measurement versatility of broadband absorption diagnostic techniques and the measurement sensitivity of narrow line width absorption diagnostic techniques. Supercontinuum generation (SC) is a nonlinear phenomena in which a single wavelength pump laser is converted to a continuous spectrum that often extends well over thousands of wavenumbers, in the UV, 10 visible, 11 and IR wavelength regions.…”