Multiangular Absorption Diagnostics of a Turbulent Argon-Methane Jet

Absorption techniques are being applied to three-dimensional combustion diagnostics. Convolution, Fourier transforms, and iterative algorithms have already been proven in x-ray absorption tomography and interferometric applications. They are currently being tested and compared on their ability to determine typical pollutant and radical concentrations as they appear in flames or exhausts. The effect of the number of scans is analyzed for parallel beams. A tradeoff exists between accuracy and the number of viewing angles. A five-angle procedure gives 10% accuracy with a moderately filtered convolution algorithm. An experiment feasibility study shows that the near time-continuous three-dimensional maps of concentration as low as 1 ppm can be obtained at repetition rates up to 20 KHz. The potential of this method was demonstrated in the laboratory. A diluted methane jet was observed at several sections along its axis. Time-averaged two-dimensional profiles were reconstructed from the absorption scans effected from six and twelve angles. The theoretically predicted dependence of the accuracy on the number of observation angles was verified. Real-time experiments are now being prepared.