## 3 Results and Discussion  
### Results of Experimental Studies  
During the experiments, quantitative measurements of the exhaust smoke density were obtained at different engine speeds (1000, 1500, and 2000 rpm), both without ultrasonic exposure and under various ultrasonic emitter operating modes. The results of the experimental studies are presented in Figure 4. The obtained experimental results confirm that the use of ultrasound had a positive effect on reducing the smoke opacity levels of the exhaust gases, indicating the potential effectiveness of this cleaning method. Although the reduction in smoke opacity is less pronounced with increasing engine speed, this was due to the higher gas flow velocity and the need to establish the optimal configuration of ultrasonic emitters and their power levels. The highest smoke density was observed when the engine operated without ultrasonic influence, confirming the high level of pollutant emissions in the absence of ultrasonic particle coagulation. When individual emitters (experiments 2, 3, and 4) were connected, a slight reduction in smoke density was observed, but the effect remained insignificant. This is attributed to the localized nature of ultrasonic influence--certain areas in the gas flow are not subjected to coagulation.  
Figure 3: Experimental plan.  
A significant reduction in smoke density was observed when two or more emitters were activated simultaneously. The configurations used in experiments 5, 6, and 7 show a pronounced decrease in smoke levels, indicating a more uniform distribution of ultrasonic impact within the gas flow. However, even with three active emitters (1, 3, and 6) in experiment 8, a noticeable level of smoke density remained, suggesting the need for further optimization of the acoustic treatment to achieve optimal results.  
The lowest level of pollution was recorded when all ultrasonic emitters were activated simultaneously (experiment 9). In this mode, a uniform ultrasonic field was created, encompassing the entire exhaust gas stream and ensuring maximum coagulation of PM particles and their effective deposition.  
It should also be noted that at low engine speeds of 1000 rpm, the slower gas flow increased the residence time of the ultrasonic waves on the particles, promoting their effective coagulation.  
At medium engine speeds of around 1500 rpm, the flow velocity increased, reducing the time that particles were in contact with the ultrasonic field. At the same time, the turbulence increased, which, on the one hand, contributed to the mixing of the gas and increased the likelihood of particle interaction with ultrasonic waves, but, on the other hand, may have hindered their coagulation. Despite this, when all emitters were fully activated, a significant reduction in smoke density was observed, although the effect was less pronounced compared to that at low engine speeds.  
Figure 4: Changes in the smoke density indicators depending on the combination of ultrasonic emitter connections and rotational speed engine.  
At high engine speeds of around 2000 rpm, the gas flow became very fast, substantially reducing the residence time for ultrasonic exposure. Under these conditions, the turbulence intensified, resulting in chaotic particle movement, which can both facilitate coagulation and break up already formed aggregates. The maximum reduction in smoke density was again achieved when all emitters were activated, as this provided the most powerful and uniform coverage by the ultrasonic field.  
Therefore, to improve the gas cleaning efficiency at high engine speeds, it is recommended to increase the power of the emitters, optimize their placement or the distance between them, and consider the implementation of multi-stage gas treatment.