The unsteady characteristic of the pressure-swirl atomization system was studied experimentally in this paper. It was found that the fluctuations of the spray can be divided into two modes: high and low frequency mode, among which the frequency of the high mode is within the range of 500-1100Hz, and the low mode is 100-400Hz. The low mode depends on the turbulent exchange of momentum between the liquid and the surrounding stagnant gas. While the high mode depends on the comprehensive effect of the turbulent vortex generated by the liquid flowing through the atomizer and the natural frequency of the atomizer.

In this paper, a high speed camera is used to film the spray produced by different working conditions and different atomizer geometry. Then automatic identification of spray cone angle by Matlab programming. Finally, the discrete Fourier transform method is used to process the data, and the spectrum diagram of spray cone angle fluctuations is obtained to study the unsteady characteristics of the pressure swirl atomization system. The following conclusions are obtained:

\(1\) The pressure swirl atomization system has both steady state and non-steady state characteristics during operation.

\(2\) The non-steady state characteristics are mainly reflected in the fluctuations of the spray at a certain frequency. The variation of spray cone angle with time is observed and the result is obtained by discrete Fourier transform. It is found that the spray fluctuations contain two modes, among which the high mode ranges from 500 to 1100Hz and the low mode ranges from 100 to 400Hz.

\(3\) By changing the operating condition of the atomizer and the size parameters of the atomizer, it is found that when the pressure drop of the atomizer increases, the peak frequency of the low mode increases and the peak frequency of the high mode decreases; When the atomizer outlet area size is changed, the larger the area size is, the lower the peak frequency of the two modes are; When the deflection angle of the swirl chamber increases, the peak frequency of the low mode increases, while the high mode decreases first and then increases, reaching the minimum at 60°, and the difference between 45° and 80° is very small.

\(4\) From the above analysis, it is inferred that the generation mechanisms of the low mode and the high mode are different. The low mode fluctuation is caused by the exchange of momentum between the liquid and the surrounding still air. But the high mode fluctuation is the result of the combined action of the turbulent vortex and the natural frequency of the object. Therefore, the surrounding stationary gas induces and promotes the low mode fluctuations, but inhibits the high mode fluctuations.

In summary, both high mode and low mode fluctuations have predictable periodic properties, which provides the possibility of adjusting the unsteady characteristics of spray to control the complex combustion process.


Investigation on the Fluctuations of the Spray Angle Generated From Pressure-Swirl Atomizers

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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