Pengshuai Sun

Simultaneous detection of multiple gas concentrations with multi-frequency wavelength modulation spectroscopy

A multi-frequency wavelength modulation spectroscopy (MF-WMS) method for simultaneous monitoring multiple gas concentrations is reported. Two wavelength lasers are selected and scanned at the same sawtooth waveform and different sinusoidal modulation frequencies. Also, a 2-in-1 coupler is used to collect laser beams into a single-mode fiber to deliver the combined beams to a same optical path. The outputs from the same InGaAs detector are demodulated by a set of homemade digital lock-in-amplifiers to obtain the harmonic signals, accordingly. The new multi-pass cell was designed and filled with five different concentrations of H2S and HCl gas mixtures for further analysis. In addition, an digital filter and a data running means method were used to further improve the stability. The results show that the signal-to-noise ratio and the anti-interference ability had been improved and the MF-WMS system gives a good performance in terms of reproducibility and feasibility.

Reconstruction of combustion temperature and gas concentration distributions using line-of-sight tunable diode laser absorption spectroscopy

Abstract. Spatial temperature and gas concentration distributions are crucial for combustion studies to characterize the combustion position and to evaluate the combustion regime and the released heat quantity. Optical computer tomography (CT) enables the reconstruction of temperature and gas concentration fields in a flame on the basis of line-of-sight tunable diode laser absorption spectroscopy (LOS-TDLAS). A pair of H2O absorption lines at wavelengths 1395.51 and 1395.69 nm is selected. Temperature and H2O concentration distributions for a flat flame furnace are calculated by superimposing two absorption peaks with a discrete algebraic iterative algorithm and a mathematical fitting algorithm. By comparison, direct absorption spectroscopy measurements agree well with the thermocouple measurements and yield a good correlation. The CT reconstruction data of different air-to-fuel ratio combustion conditions (incomplete combustion and full combustion) and three different types of burners (one, two, and three flat flame furnaces) demonstrate that TDLAS has the potential of short response time and enables real-time temperature and gas concentration distribution measurements for combustion diagnosis.

Development of a tunable diode laser absorption sensor for online monitoring of industrial gas total emissions based on optical scintillation cross-correlation technique.

We report the first application of gas total emission using a DFB diode laser for gas concentration measurements combined with two LEDs for gas velocity measurements. In situ gas total emissions and particle density measurements in an industrial pipeline using simultaneous tunable diode laser absorption spectroscopy (TDLAS) and optical scintillation cross-correlation technique (OSCC) are presented. Velocity mean values obtained are 7.59 m/s (OSCC, standard deviation is 1.37 m/s) and 8.20 m/s (Pitot tube, standard deviation is 1.47 m/s) in a steel plant pipeline for comparison. Our experiments demonstrate that the combined system of TDLAS and OSCC provides a new versatile tool for accurate measurements of total gas emissions.

Detection of gas temperature using a distributed feedback laser at O 2 absorption wavelength 760 nm

Direct absorption spectroscopy for gas temperature monitoring in a tube furnace is proposed over the temperature range 300–900 K with intervals of 100 K. This detecting technique is based on the relationship between two lines’ absorption strength and temperature. The gas temperature can be inferred from the ratio of the integrated spectral area of the oxygen absorption features measured with a distributed feedback diode laser near 760 nm. Compared with the thermocouple measured results, the direct absorption spectroscopy approach also provides a temporal resolution. The results show that the accuracy is better at low temperatures than at high temperatures. In the future, we hope to improve the detection accuracy and demonstrate the utility of the diode laser absorption sensors operating for active combustion diagnostics and optimizations, simultaneously.