Infrared laser-absorption sensing for combustion gases

Recent advances in understanding of flammability characteristics of hydrogen

Recent advances in laser absorption and shock tube methods for studies of combustion chemistry

Measurement and modelling of the laminar burning velocity of methane-ammonia-air flames at high pressures using a reduced reaction mechanism

Tomographic absorption spectroscopy for the study of gas dynamics and reactive flows

A novel strategy has been developed for analysis of wavelength-scanned, wavelength modulation spectroscopy (WMS) with tunable diode lasers (TDLs). The method simulates WMS signals to compare with measurements to determine gas properties (e.g., temperature, pressure and concentration of the absorbing species). Injection-current-tuned TDLs have simultaneous wavelength and intensity variation, which severely complicates the Fourier expansion of the simulated WMS signal into harmonics of the modulation frequency (fm). The new method differs from previous WMS analysis strategies in two significant ways: (1) the measured laser intensity is used to simulate the transmitted laser intensity and (2) digital lock-in and low-pass filter software is used to expand both simulated and measured transmitted laser intensities into harmonics of the modulation frequency, WMS-nfm (n = 1, 2, 3,...), avoiding the need for an analytic model of intensity modulation or Fourier expansion of the simulated WMS harmonics. This analysis scheme is valid at any optical depth, modulation index, and at all values of scanned-laser wavelength. The method is demonstrated and validated with WMS of H2O dilute in air (1 atm, 296 K, near 1392 nm). WMS-nfm harmonics for n = 1 to 6 are extracted and the simulation and measurements are found in good agreement for the entire WMS lineshape. The use of 1f-normalization strategies to realize calibration-free wavelength-scanned WMS is also discussed.

http://iopscience.iop.org/article/10.1088/0957-0233/24/12/125203/pdf

Analysis of calibration-free wavelength-scanned wavelength modulation spectroscopy for practical gas sensing using tunable diode lasers

Scanned-wavelength-modulation-spectroscopy sensor for CO, CO2, CH4 and H2O in a high-pressure engineering-scale transport-reactor coal gasifier

Hydrogen peroxide (H 2 O 2 ) and hydroperoxy (HO 2 ) reactions present in the H 2 O 2 thermal decomposition system are important in combustion kinetics H 2 O 2 thermal decomposition has been studied behind reflected shock waves using H 2 O and OH diagnostics in previous studies (Hong et al (2009) [9] and Hong et al (2010) [6,8]) to determine the rate constants of two major reactions: H 2 O 2  + M → 2OH + M ( k 1 ) and OH + H 2 O 2  → H 2 O + HO 2 ( k 2 ) With the addition of a third diagnostic for HO 2 at 227 nm, the H 2 O 2 thermal decomposition system can be comprehensively characterized for the first time Specifically, the rate constants of two remaining major reactions in the system, OH + HO 2  → H 2 O + O 2 ( k 3 ) and HO 2  + HO 2  → H 2 O 2  + O 2 ( k 4 ) can be determined with high-fidelity No strong temperature dependency was found between 1072 and 1283 K for the rate constant of OH + HO 2  → H 2 O + O 2 , which can be expressed by the combination of two Arrhenius forms: k 3  = 70 × 10 12  exp(550/ T ) + 45 × 10 14  exp(−5500/ T ) [cm 3  mol −1  s −1 ] The rate constants of reaction HO 2  + HO 2  → H 2 O 2  + O 2 determined agree very well with those reported by Kappel et al (2002) [5]; the recommendation therefore remains unchanged: k 4  = 10 × 10 14  exp(−5556/ T ) + 19 × 10 11+ exp(709/ T ) [cm 3  mol −1  s −1 ] All the tests were performed near 17 atm

On the rate constants of OH + HO2 and HO2 + HO2: A comprehensive study of H2O2 thermal decomposition using multi-species laser absorption

We report the first tunable diode laser (TDL) absorption measurements for gas temperature and species concentrations in a pilot-scale, high-pressure, entrained-flow, oxygen-blown, slagging coal gasifier with pressures up to 18 atm and temperatures to 1800 K. Three locations in the gasifier flow were investigated: (1) the reactor core, (2) the exit of the reactor where a water spray quenches the reaction products (pre-quench), and (3) in the gasifier product stream before particulate clean-up (post-quench). Gas temperature was measured by three pairs of H2O transitions with distinct temperature dependence at all three locations using five distributed feedback (DFB) lasers near 1.4 μm. CO, CO2 and H2O concentrations were measured at the post-quench location using DFB lasers near 2.3 μm, 2.0 μm and 1.4 μm, respectively. Fixed-wavelength, 1f-normalized, wavelength-modulation-spectroscopy with second-harmonic detection (WMS-2f) was used for all the measurements. Usable signal-to-noise ratio (SNR) > 10 was achieved with one second averaging even at gasifier conditions with large particulate loading where the non-absorption transmission loss was >99.99% from light scattering and the thermal emission was intense. The work demonstrates the capability of TDL sensors to monitor transient changes in gas temperature providing a potentially valuable control sensor for gasifier performance. In addition, measurements of CO, CO2 and H2O in the gasifier product stream showed good promise for monitoring the syngas heating value. The potential advantages of using higher WMS harmonics under high-pressure conditions were also investigated.

TDL absorption sensors for gas temperature and concentrations in a high-pressure entrained-flow coal gasifier

Tunable diode laser absorption spectroscopy based in situ sensors for CO (2.33 μm), CO2 (2.02 μm), CH4 (2.29 μm) and H2O (1.35 μm) were deployed in a pilot-scale (1 ton/day), high-pressure (up to 18 atm), entrained flow, oxygen-blown, slagging coal gasifier at the University of Utah. Measurements of species mole fraction with 3-s time resolution were taken at the pre- and post-filtration stages of the gasifier synthesis gas (called here syngas) output flow. Although particulate scattering makes pre-filter measurements more difficult, this location avoids the time delay of flow through the filtration devices. With the measured species and known N2 concentrations, the H2 content was obtained via balance. The lower heating value and the Wobbe index of the gas mixture were estimated using the measured gas composition. The sensors demonstrated here show promise for monitoring and control of the gasification process.

Ritobrata Sur

Papers

Analysis of calibration-free wavelength-scanned wavelength modulation spectroscopy for practical gas sensing using tunable diode lasers

Scanned-wavelength-modulation-spectroscopy sensor for CO, CO2, CH4 and H2O in a high-pressure engineering-scale transport-reactor coal gasifier

On the rate constants of OH + HO2 and HO2 + HO2: A comprehensive study of H2O2 thermal decomposition using multi-species laser absorption

TDL absorption sensors for gas temperature and concentrations in a high-pressure entrained-flow coal gasifier

TDLAS-based sensors for in situ measurement of syngas composition in a pressurized, oxygen-blown, entrained flow coal gasifier