Abstract
The purpose of this study is to critically review and generalize theoretical and experimental research on ultrasonic coagulation of aerosol and soot particles as a promising approach to reducing the smoke opacity and toxicity of exhaust gases from internal combustion engines. The scope of the work encompasses both classical diffusion-based coagulation theories and contemporary studies of acoustic agglomeration in stationary aerosols, flow channels, and automotive mufflers. The research methodology is based on a systematic analysis and comparison of existing models and experimental results, with an emphasis on their relevance to real exhaust-system operating conditions. The analysis demonstrates that most diffusion and acoustic coagulation models are formulated under idealized assumptions, such as stationary and isothermal media and negligible turbulence. These assumptions significantly restrict their applicability to real exhaust flows, which are characterized by high temperatures, turbulent and pulsating motion, variable composition, and limited particle residence time. A synthesis of experimental data shows that ultrasonic exposure enhances soot particle growth and promotes their subsequent sedimentation in flowing gases. The effectiveness of ultrasonic purification is determined by several interrelated factors, including turbulence intensity, pressure pulsations, residence time of particles in the active zone, acoustic field configuration, muffler geometry, and the polydisperse structure of soot. The study also identifies the main shortcomings of existing theoretical and experimental approaches, such as the widespread use of batch-type accumulation chambers, simplified test-bench designs, and the lack of reliable experimental data under high-temperature exhaust conditions. Based on the obtained results, the main conclusions highlight the necessity of optimizing ultrasonic muffler geometry, developing adaptive and multi-frequency acoustic fields, and implementing control algorithms for ultrasonic emitters. The revealed regularities form a scientific basis for the rational design of ultrasonic mufflers and confirm their potential to improve analytical modeling accuracy, reduce experimental workload, and enhance exhaust gas purification efficiency.