A sensor system for fast gas composition analysis is presented. Using linear Raman scattering the simultaneous detection of virtually all components of fuel gas mixtures such as natural gas and biogas can be achieved. The system consists of commercially available hardware components, in detail a frequency doubled continuous wave laser at 532 nm and a compact spectrometer with an embedded charge coupled device chip. For the evaluation of the Raman spectra a fast software module based on a contour fit algorithm is developed. Moreover, modules for controlling the hardware components are implemented in the sensor software ensuring simple operability of the entire system. In this paper the sensor is characterized in terms of, e.g., accuracy, reproducibility, detection limits and temporal performance. Finally its application for natural gas analysis in a gas turbine power plant is demonstrated, and the results obtained are compared to gas chromatography results.

The simultaneous application of pure rotational coherent anti-Stokes Raman spectroscopy (CARS) and vibrational linear Raman spectroscopy (LRS) for the measurement of temperature and species concentrations in combustion systems is demonstrated. In addition to the standard rotational CARS experimental setup, only one detection system (spectrometer and intensified CCD camera) for the collection of the LRS signals was applied. The emission of the broadband dye laser used for CARS was shifted to the deep red to avoid interferences with the LRS signals located in the visible region. First experimental results from a vaporizing propane spray using an engine injection system are shown.

This paper describes the characterization of a combined Coherent anti-Stokes Raman Spectroscopy and Interferometric Rayleigh Scattering (CARS-IRS) system by reporting the accuracy and precision of the measurements of temperature, species mole fraction of N 2 , O 2 , and H 2 , and two-components of velocity. A near-adiabatic H 2 -air Hencken burner flame was used to provide known properties for measurements made with the system. The measurement system is also demonstrated in a small-scale Mach 1.6 H 2 -air combustionheated supersonic jet with a co-flow of H 2 . The system is found to have a precision that is sufficient to resolve fluctuations of flow properties in the mixing layer of the jet.

Abstract:For the first time laser-induced gratings (LIGs) have been used for the investigation of a non-stationary pulse-repetitive injection process of gaseous propane, C 3 H 8 , into air. By recording and evaluating single-shot LIG signals it was possible to determine, on a cycle-averaged basis, the temporal evolution of the local (within a probe volume 300 μm in diameter and 10 mm in length) equivalence ratio and by this the fuel-air ratio. Two different data treatment strategies, subject to C 3 H 8 concentration range, were first tested at stationary conditions and then used to evaluate the LIG signals obtained during the injection process. The relative standard deviation of single-shot measurements were estimated to be 0.14 and 0.32 at 0.8 % and 10 % of propane concentration, respectively.

The acetylene-nitrogen system is investigated in a combined theoretical and experimental effort in view of its thermometry applications. Accurate values of the rotational Raman linewidths of acetylene are of crucial importance for the computation of spectra from rotational coherent anti-Stokes Raman scattering (CARS) used for temperature and concentration evaluations. Since the direct measurements of these linewidths are not available, they are rigorously calculated by a semi-classical Robert-Bonamy formalism employing exact trajectories. The computed linewidths are used as input parameters in the theoretical spectra simulation, which is also improved by the inclusion of an interbranch interference with coherent Stokes Raman scattering (CSRS). These theoretical spectra are used to evaluate the temperature from experimental CARS spectra of acetylene-nitrogen mixtures recorded in the pressure range 0.1-0.6 MPa. The new linewidths (NLWs) and the CSRS interference inclusion result in a clear improvement of spectral fitting as well as in reasonable values of evaluated temperatures.