In situ laser measurement of oxygen concentration and flue gas temperature utilizing chemical reaction kinetics

Combustion research requires detailed localized information on the dynamic combustion conditions to improve the accuracy of the simulations and, hence, improve the performance of the combustion processes. We have applied chemical reaction kinetics of potassium to measure the local temperature and O2 concentration in flue gas. An excess of free atomic potassium is created in the measurement volume by a photofragmenting precursor molecule such as potassium chloride or KOH which are widely released from solid fuels. The decay of the induced potassium concentration is followed with an absorption measurement using a narrow-linewidth diode laser. The temperature and O2 concentration are solved from the decay curve features using equations obtained from calibration measurements in a temperature range of 800°C–1000°C and in O2 concentrations of 0.1%–21%. The local flue gas temperature and O2 concentration were recorded in real time during devolatilization, char burning, and ash cooking phases of combustion in a single-particle reactor with a 5 Hz repetition rate. The method can be further extended to other target species and applications where the chemical dynamics can be disturbed with photofragmentation.acceptedVersionPeer reviewe

Wavelength modulation waveforms in laser photoacoustic spectroscopy

Different wavelength modulation waveforms were studied comprehensively in tunable diode laser photoacoustic spectroscopy. The generation of the photoacoustic signal was studied by way of simulations and experiments. A cantilever-enhanced photoacoustic detector and CO2 sample gas were used in the experiments. The modulation waveforms compared in this study were sinusoidal, triangular, shaped, and quasi-square waves. All four waveforms allow background-free detection of trace gases. Compared to the conventionally used sinusoidal modulation, the triangular, shaped, and quasi-square waves enhanced the photoacoustic signal by factors of 1.12, 1.42, and 1.57, respectively.Peer reviewe

Electromechanical films as a photoacoustic transducer

An electromechanical film, EMFi, is utilized as a transducer in a photoacoustic (PA) gas sensor. The film is a sensitive acoustic transducer, it is easily formable, and it exhibits a wide frequency response regardless of its large surface area. As a demonstration of its capabilities, the EMFi-based PA detector is used to measure NO2 with pulsed excitation at 436 and 473 nm. The minimum detectable absorption coefficient is extrapolated to be 5•10−7 cm−1. Improvements for EMFi-based PA detector are discussed.Peer reviewe

Optical detection of the anesthetic agent propofol in the gas phase.

The anesthetic agent propofol (2,6-diisopropylphenol) is the most widely used intravenously administered drug in general anesthesia. However, a viable online capability to monitor metabolized levels of propofol in patients does not currently exist. Here we show for the first time that optical spectroscopy has good potential to detect metabolized propofol from patients' exhaled breath. We present quantitative absorption measurements of gas phase propofol both in the ultraviolet and middle-infrared spectral regions. We demonstrate that a detection limit in the subparts-per-billion concentration range can be reached with photoacoustic spectroscopy in the UV spectral region, paving the way for the development of future optical monitors

An analysis of factors affecting the market price of electricity: the case of Phelix index

The addition reaction of potassium atoms with oxygen has been studied using the collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) method. KCl vapor was photolyzed with 266 nm pulses and the absorbance by K atoms at 766.5 nm was measured at various delay times with a narrow line width diode laser. Experiments were carried out with O₂/N₂ mixtures at a total pressure of 1 bar, over 748–1323 K. At the lower temperatures single exponential decays of [K] yielded the third-order rate constant for addition, <i>k</i>_R1, whereas at higher temperatures equilibration was observed in the form of double exponential decays of [K], which yielded both <i>k</i>_R1 and the equilibrium constant for KO₂ formation. <i>k</i>_R1 can be summarized as 1.07 × 10^–30(<i>T</i>/1000 K)^−0.733 cm⁶ molecule^–2 s^–1. Combination with literature values leads to a recommended <i>k</i>_R1 of 5.5 × 10^–26<i>T</i>^–1.55 exp­(−10/<i>T</i>) cm⁶ molecule^–2 s^–1 over 250–1320 K, with an error limit of a factor of 1.5. A van’t Hoff analysis constrained to fit the computed Δ<i>S</i>₂₉₈ yields a K–O₂ bond dissociation enthalpy of 184.2 ± 4.0 kJ mol^–1 at 298 K and Δ_f<i>H</i>₂₉₈(KO₂) = −95.2 ± 4.1 kJ mol^–1. The corresponding <i>D</i>₀ is 181.5 ± 4.0 kJ mol^–1. This value compares well with a CCSD­(T) extrapolation to the complete basis set limit, with all electrons correlated, of 177.9 kJ mol^–1