In situ measurement of oscillation frequency of self-excited sweeping fuel nozzle based on laser self-mixing interference effect

As a novel type of aero engine fuel nozzle, the self-excited sweeping nozzle (SSN) can effectively improve the atomization effect and combustion efficiency in the combustion chamber due to its unique fluid oscillation phenomenon, but the high-speed swing behavior during SSN working is still challenging for characterization, thus a compact, accurate, and low-cost measuring tool is desired greatly. To solve this problem, in this paper based on Laser self-mixing interferometry (LSMI) we developed a sensitive, compact, and portable optoelectronic system to measure the SSN oscillation frequency. Based on the theory of LSMI effect, a coupling relationship model between the sweeping oscillation and the optical phase of the liquid flow is established. In the model, the VMD algorithm successfully extracted the low frequency part caused by liquid swing motion and the high frequency part resulting from interference due the stream surface fluctuation. Comparing the oscillation frequency measurement results by LSMI method and high-speed camera, the overall error is less than 0.5 % in useable measurement range from 200 Hz to 5000 Hz, satisfying the realistic requirement. The experimental results prove our LSMI method can be a promising tool in SNN jetting characterization.