Although transport electrification is increasingly seen as the future, the reality is different—diesel engines remain widely used and are expected to stay in service for at least the next decade. Along with them persists a major challenge: ultrafine particulate matter emissions that pass through conventional diesel particulate filters and contribute to air pollution associated with an increased risk of premature deaths.
A Direct Threat to Human Health
In Lithuania, the transport sector accounts for nearly 15% of fine particulate matter emissions, posing the greatest risk to residents of major cities such as Vilnius and Kaunas.
According to Dr. Sai Manoj Rayapureddy, a researcher at the VILNIUS TECH Faculty of Transport Engineering, the greatest concern comes from particles that are too small to be captured by conventional diesel particulate filters. These particles escape into the environment and eventually enter the human body, where they easily interact with the skin and respiratory system, posing a direct threat to human health.
Dr. Sai Manoj Rayapureddy
To address this issue, Dr. Rayapureddy conducted research and prepared his doctoral dissertation, Investigation of Acoustic Agglomeration Phenomenon in Compression Ignition Engines Fuelled with Alternative Fuels for Reducing Particulate Matter Emissions.
„In a world where pollution continues to increase, diesel vehicles are still widely used, while efforts are being made to reduce dependence on fossil fuels. This research proposes a solution by combining alternative fuel blends that produce lower emissions with the principle of acoustic agglomeration. In this process, sound waves cause ultrafine particles to interact and merge into larger clusters that can then be captured by conventional diesel particulate filters,“ explains Dr. Sai Manoj Rayapureddy, researcher at VILNIUS TECH.
Results Exceeded Expectations
Dr. Rayapureddy carried out his research in three stages, combining theoretical analysis, numerical calculations, and laboratory experiments. The experiments were conducted using a well-known 1.9-litre Audi-VW diesel engine installed in a VILNIUS TECH laboratory.
To investigate how fuel properties affect particulate formation, he tested specially prepared fuel blends with different carbon-to-hydrogen ratios and oxygen content, comparing the resulting emissions with those of conventional diesel fuel. Finally, particulate emissions were measured both with and without the application of sound waves.
The results exceeded expectations. The study found that applying acoustic waves reduced particulate emissions from conventional diesel fuel by 17–44%. When alternative fuel blends were used, the reduction increased to an impressive 24–80%. Dr. Rayapureddy also demonstrated that the higher oxygen content and improved surface characteristics of alternative fuels increased particle agglomeration efficiency by as much as 100–190%.
„Applying acoustic agglomeration to diesel engine particles is still a relatively new and underexplored research field. I wanted to demonstrate its importance and potential for reducing engine emissions. What surprised and delighted me most was how effectively a long-established theoretical principle worked in practice. My research proved that this method significantly improves the ability of conventional particulate filters to remove harmful particles,“ says the Faculty of Transport Engineering researcher.
According to Dr. Rayapureddy, while the future undoubtedly belongs to electric mobility, the present requires an intermediate solution. As the complete electrification of the transport sector is unrealistic within at least the next decade, improving today’s technologies and reducing emissions from existing diesel-powered vehicles remains essential.
„Implementing this concept could significantly improve the efficiency of existing diesel particulate filters. It would allow us to substantially reduce the fine particulate pollution generated by the diesel engines that are already on our roads and will continue to be used for years to come,“ he adds.
A PhD Is Not a Sprint, but a Marathon
Dr. Rayapureddy began his academic journey in India, where he earned a Bachelor’s degree in Mechanical Engineering. He later moved to Lithuania to complete a Master’s degree in Automotive Engineering at VILNIUS TECH before continuing with doctoral studies at the university. Throughout his academic career, he remained focused on making steady progress toward his goals, improving year after year.
According to the researcher, writing the dissertation itself was not the most challenging part, as publishing several scientific papers during his doctoral studies helped him develop a clear research structure.
„The most difficult part was justifying, revising, or even removing certain parts of the research during the peer-review process. In the end, however, everything worked out wonderfully. Thanks to the guidance of my supervisor and the valuable feedback from reviewers, my dissertation was awarded second place in Lithuania’s Best Doctoral Dissertation Competition.
I consider my PhD studies—during which I also completed a second Master’s degree in Engineering Economics and Management at VILNIUS TECH—to be the first step toward an academic career. Pursuing a doctorate requires curiosity, hard work, and patience. To everyone considering a career in research, I would like to say this: a PhD is not a sprint, but a marathon.“
