RESUMEN
A sensor for the rapid (10-ms response time) measurement of vapors from the hydrocarbon-based fuels JP-8, DF-2, and gasoline is described. The sensor is based on a previously reported laser-mixing technique that uses two tunable diode lasers emitting in the near-infrared spectral region [Appl. Opt. 39, 5006 (2000)] to measure concentrations of gases that have unstructured absorption spectra. The fiber-mixed laser beam consists of two wavelengths: one that is absorbed by the fuel vapor and one that is not absorbed. Sinusoidally modulating the power of the two lasers at the same frequency but 180 degrees out of phase allows a sinusoidal signal to be generated at the detector (when the target gas is present in the line of sight). The signal amplitude, measured by use of standard phase-sensitive detection techniques, is proportional to the fuel-vapor concentration. Limits of detection at room temperature are reported for the vapors of the three fuels studied. Improvements to be incorporated into the next generation of the sensor are discussed.
RESUMEN
We describe the development and characterization of a near-infrared diode-laser-based sensor to measure the vapor from trace gases having unstructured absorption spectra. The technique uses two equal amplitude-modulated laser beams, with the modulation of the two lasers differing in phase by 180 deg. One of the laser beams is at a wavelength absorbed by the gas [for these experiments, vapor is from pyridine (C(5)H(5)N)], and the second laser beam is at a wavelength at which no absorption occurs. The two laser beams are launched onto near-coincident paths by graded-index lens-tipped optical fibers. The mixed laser beam signal is detected by use of a single photodiode and is demodulated with standard phase-sensitive detection. Data are presented for the detection and measurement of vapor from pyridine (C(5)H(5)N) by use of the mixed laser technique. The discussion focuses on experimental determination of whether a compound exhibits unstructured absorption spectra (referred to here as a broadband absorber) and methods used to maximize sensitivity.
RESUMEN
Laser-induced breakdown spectroscopy is evaluated as a means of detecting the fire suppressants CF(3)Br, C(3)F(7)H, and CF(4) and the refrigerant C(2)F(4)H(2). The feasibility of employing laser-induced breakdown spectroscopy for time- and space-resolved measurement of these agents during use, storage, and recharge is discussed. Data are presented that demonstrate the conditions necessary for optimal detection of these chemicals.
RESUMEN
Fourier-transform infrared spectroscopy is used to monitor gases generated during chemical inhibition of JP-8 fuel pool fires burning in air. Gas samples are taken from a location that approximates the position of an individual who is using a handheld extinguisher to subdue the fire. These gas samples are flowed through a 10-m path-length multipass optical cell placed in the sample beam of a Fourier-transform infrared spectrometer. Gas samples are analyzed before and during application of C(3)F(7)H (trade name FM200) and CF(3)Br (Halon 1301) to the fire. It is shown that application of these halogenated hydrocarbons to JP-8 pool fires produces significant quantities of acid gases (HF and HBr) and of CF(2)O. A calculation of the concentrations (in parts in 10(6)) of these gases and other gaseous combustion products, based on observed absorbances, is presented. We believe this is the first quantitative simultaneous measurement of HF, HBr, HCl, and CF(2)O production during chemical inhibition of real fires.
RESUMEN
We have employed tunable diode laser absorption spectroscopy (TDLAS) to characterize low-pressure premixed CH(4)/O(2)/Ar flames inhibited with Halon 1301 (CF(3)Br) and the candidate Halon alternative compounds FE-13 (CF(3)H) and HFC-125 (C(2)F(5)H). This work is part of a larger program designed to help identify replacement fire-suppression compounds for the currently used Halon 1301. We have used CO two-line thermometry to profile the temperature in low-pressure laminar flames and have determined concentration profiles for a large number of flame species, including reactive intermediates. To date, we have detected 12 flame species by using TDLAS in our laboratory and report on seven of them here: CH(4), H(2)O, CO, CF(2)O, CF(2)H(2), CF(3)H, and CF(4). To the best of our knowledge, this is the first time the last four species have been observed in flame by the use of TDLAS. Our data are important for validating the detailed kinetic mechanisms of chemical flame inhibition. Our results indicate that TDLAS is a versatile and powerful diagnostic technique for studying combustion processes.
RESUMEN
Tomographic analysis is used to provide a correction to low-pressure stoichiometric premixed CH(4)/O(2) flame temperatures measured with tunable diode laser absorption spectroscopy employing CO two-line thermometry. It is shown that flame temperatures measured with line-of-sight-based two-line thermometry are always too low and that the correction to the observed temperature is a nonlinear function of the height above the burner surface. It is also shown that, at a given height in the flame, a constant temperature across the flame does not imply that vibrational populations are constant and that, at low pressures (<20 Torr), the flame spreads radially beyond the burner diameter and so may no longer be approximated by a one-dimensional model.
RESUMEN
We have developed an approximation that provides a fast reasonably accurate estimate of the halfwidth at half-height of a single pressure-broadened line.