Ultrasound Vegetable Glycerin homogenization

We are trying to homogenize VG (USP) with propylene-glycol using ultrasonic homogenizer with titanium probe, but we are experiencing very strange - bad odor from the emulsion after sonication. 
We tried different amplitudes, different time settings, different power settings. We can control amplitude for 2 modes only, I believe they are 50% and 100%.
Also if I am sonicating pure vegetable oil for just 5-10 sec I can smell that strange odor, it is very similar to that, I am getting with VG.
I just want to know, what this smell can come from? From our probe? No it is clean, we can sonicate water well.




Depending on intensity, ultrasound can produce *intense* heat at some locations. In fact, [cavitation can induce temperatures far exceeding **5,000 K**.](https://www.hielscher.com/ultrasonic-cavitation-in-liquids-2.htm) Even a small ultrasonic room humidifier can burn through a plastic comb held in the upwelling stream. The sound intensity is decomposing the oil and/or propylene glycol.


Try lower frequencies and lower sound intensity. You might experiment with different shape containers, as well, to avoid focusing the sound into a high-intensity spot.


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