Solid waste presents a very large problem in the developed world. Waste plastics, which make up a large part of solid waste, have high energy value, which is discarded if they are not treated properly. Most of the plastic found in solid waste is produced from petrochemical material, so it can be used in resource recovery processes to produce various materials. One promising resource recovery process is the pyrolysis process, from which pyrolytic oil, gas, and solid residue are obtained. Pyrolytic oils have properties that are similar to conventional fossil fuels, and are promising fuels for use in heat engines or heating applications. In the present work, HDPE plastic in the form of plastic bottles caps was collected from solid waste and used in a thermal pyrolysis process for the production of pyrolytic oil. The obtained oil was characterised, and the obtained results were compared to conventional fuels. The obtained oil was used further in an oil burner fuel injection application, in which the spray breakup characteristics were monitored and analysed using VisiSize particle characterisation systems. The obtained results were compared to those of conventional fuel. The results indicate that the difference in fuel properties influences the spray breakup process slightly, but the differences are rather small. This indicates that from a spray development perspective, pyrolytic oil can be used as a substitute for conventional fuels in oil burners.

Flow in fluid machinery can include multiphase phenomena such as cavitation due to energy exchange between the machinery and flow of a liquid, which, in turn, produces local drops in pressure and, therefore, evaporation. When vapor structures are subjected to increased pressure, they collapse during the process of condensation. These collapses are driven by high ambient pressure and can, over time, induce damage to the fluid machinery solid walls—a process termed cavitation erosion. In addition, fluid machinery such as water turbines and pumps often operate in water that is not pure. In this water, solid particles can be present, for example, river sediment, which can also produce erosion. In the past, these causes of erosion were mostly investigated separately; however, as they sometimes occur simultaneously, studies that replicate these conditions are necessary. In the present work, we investigated the erosion of a Venturi channel surface with several different divergent angles using CFD simulations, which were validated experimentally using the soft paint method. Results showing the cavitation and particle erosion were obtained for different flow conditions (specifically with different vortical structures) that are expected to occur in fluid machinery. The results suggest that cavitation modifies the flow field in a manner that affects particle-induced erosion, leading to different macroscopic erosion patterns.

The rising instability in global energy markets and fuel supply challenges in 2026 have intensified the search for sustainable alternative fuels. Since most plastics originate from petrochemical sources, they represent a valuable feedstock for energy recovery once they become waste. In this study, high-density polyethylene plastic waste was processed via pyrolysis to produce pyrolytic oil, which was characterized and compared with conventional extra-light heating oil. Evaluating the atomization performance of high-density polyethylene pyrolytic oil represents an important technical step toward assessing its potential for more sustainable plastic waste valorization and alternative heating applications. The atomization behavior of both fuels was investigated through a combined experimental and numerical approach. The spray characteristics were measured using the VISISIZE 60N droplet characterization system, enabling detailed analysis of the droplet size distribution. In parallel, CFD simulations were conducted in Ansys FLUENT using the Euler–Lagrange framework. The pressure-swirl atomizer was modeled with a Linear Instability Sheet Atomization model to describe the primary breakup, with emphasis on the influence of the model constants. The results show that the pyrolytic oil exhibits spray characteristics comparable to heating oil, with only minor differences in the droplet size distribution and breakup behavior. The CFD simulations captured the droplet size distribution trends successfully, confirming the predictive capability of the Euler–Lagrange framework. These findings indicate that pyrolytic oil is a viable alternative fuel for pressure-swirl atomization systems, contributing to both waste valorization and mitigation of the current energy challenges.

Cavitation erosion is a major concern in water turbines and hydraulic machinery, where bubble collapse near solid surfaces leads to material degradation and reduced efficiency. In this study, ultrasonic cavitation tests were conducted using a Sonics VCX-750 ultrasonic vibratory apparatus operating at 20 kHz to investigate erosion behaviour of aluminium and steel specimens under identical conditions. The sonotrode tip was submerged 30 mm below the water surface, with amplitude of 30 µm and fluid temperature maintained at 17 °C. High-speed imaging at 100,000 frames per second captured bubble dynamics. After 3 hours of exposure, surface photographs revealed significantly more extensive erosion on aluminium compared to steel, demonstrating higher resistance of the latter to cavitation. The results highlight the importance of material selection in hydraulic applications and provide insights into cavitation mechanisms relevant to the durability and performance of water turbines.