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Laser scattering patternator for liquid flow measurement of industrial sprays

Exploitable results

The laser scattering patternator (LSP) project grew out of the need to monitor the fuel sprayed from the injectors in gas turbines. The injectors must be set correctly to maximize efficiency yet produce the minimum pollution. An array of collection tubes is normally used to sample a spray, but this is time-consuming, intrusive and inaccurate. The project exploits non-intrusive laser optics to produce phase-Doppler measurements of fuel particle size and velocity. Scattered light signals are at the same time computer processed to produce, in conjunction with the phase-Doppler, accurate flow-rate readings, relatively quickly. The project was based on the phase-Doppler interferometry technique that is well-known in the laboratory for measuring sprays. By firing a laser at a spray and measuring the change in phase and frequency of the reflected signal, the size and velocity of droplets can be determined. Using the phase-Doppler technique to calculate fuel flow rates, however, produces unreliable results when the sprays are optically dense and turbulent, such as from gas turbine fuel injectors. It was thought that the flow-rate inadequacies of the phase-Doppler technique could be overcome by exploiting latest optics and the rapid processing power of today's computers. An off-axis laser light-scattering system is also used to obtain readings of the spray activity at different points within the spray. Specifically developed correction algorithms are applied both to the scattering and the phase-Doppler information. By combining the phase-Doppler and the light-scattering data, the LSP can calculate the volume flux of the spray. One of the big attractions of the LSP system is the ability to produce flow-rate readings of much greater accuracy than those produced using the phase-Doppler system. The time needed may also be as little as a tenth of that required for the phase-Doppler technique.