## 2 Materials and Methods
### Research Stand, Plan, and Procedure for Conducting the Experiments  
The experimental setup consisted of a tractor with its exhaust system tightly connected to a vertically mounted ultrasonic exhaust gas purification unit. The smoke density was measured at the outlet of the system using an exhaust gas analyzer (Brand: Infrakar, Model: M-1.01, manufactured by Alfa-Dinamika LLC, Moscow, Russia) (Figure 2). The experimental studies were carried out on the diesel engine of the MTZ-80 tractor, a model commonly used in agricultural machinery. This choice was made due to the engine's widespread application, making the reduction in its emissions both practical and highly relevant. \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline Base machine & MTZ-80 (Minsk Tractor Works) \\ Manufacturer city and country & Minsk, Belarus (then part of the USSR) \\ Model of backhoe loader & Self-propelled machine based on MTZ-80 \\ Year of manufacture & Approximately 1986–1990 \\ Type of machine & Multifunctional backhoe loader \\ Purpose & Earthquworks, material handling, \\  & laboratory testing \\ Operating weight & \(\sim\)6500–7500 kg (depending on \\  & attachments) \\ Transmission type & Manual transmission with \\ Maximum speed & low-speed gears \\  & \(\sim\)30 km/h \\  & Front bucket \\  & (width \(\sim\)1.9 m, capacity \(\sim\)0.8 m\({}^{3}\)) \\ Additional equipment & Capability for rear excavator \\  & arm installation \\ Measurement equipment installed & Gas analyzer, power supply units, \\  & ultrasonic emitters, data acquisition units \\ Design features & Modified into a laboratory stand for \\  & exhaust gas treatment experiments \\ \hline \end{tabular}
\end{table} 
Table 3: Technical data of the tested backhoe loader. \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline Year of manufacture & 1986 (test sample) \\ Engine type & Diesel, 4-stroke, naturally aspirated \\ Configuration & Inline, 4 cylinders \\ Displacement & 4750 cm\({}^{3}\) \\ Bore \(\times\) stroke & 110 \(\times\) 125 mm \\ Power output & 59 kW (80 hp) at 2200 rpm \\ Torque & Up to 290 Nm at 1400–1600 rpm \\ Cooling system & Liquid-cooled \\ Fuel & Diesel \\ Emission standard & Non-compliant with modern standards \\  & (no DPF, EGR, etc.) \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._Experimental studies on the developed stand were conducted as follows. The methodology of the experiment involved evaluating the effectiveness of ultrasonic influence on the exhaust gas smoke level of a diesel engine under different operating modes. For this, a comparative measurement of smoke levels was carried out both without ultrasonic influence and with its application, taking into account various combinations of ultrasonic emitter connections and changes in engine crankshaft speed. The experiments were conducted in two stages:  
* The first stage involved determining the baseline values of the exhaust gas smoke without ultrasonic influence, establishing the initial level of pollutant emissions. * The second stage involved conducting measurements with activated ultrasonic emitters, varying their configurations and connection order to identify the most effective operating mode. The frequency and power of the ultrasonic emitters remained fixed. The measurements were conducted in real time at various engine operating modes (1000, 1500, and 2000 rpm), under no-load (idle) conditions, which provided an objective assessment of the impact of the ultrasonic treatment on exhaust emissions. The experimental research on the developed ultrasonic muffler stand was carried out according to a pre-prepared plan, as presented in Figure 3.  
The experimental plan included step-by-step connection of the ultrasonic emitters in various combinations, which allowed for the identification of their impact on the exhaust gas smoke levels of a diesel engine:  
1. Baseline stage (control measurement): Initially, the exhaust gas smoke levels were measured without ultrasonic exposure (experiment 1).