Tiny Cavitation Bubbles Enhance Energy Conversion in Fuel Injectors’ Jets

Ultrafast X-ray imaging created with new technology offers insights into improving the energy efficiency of combustion engines.

The Science

Cavitation is the formation of vapor bubbles that occurs when an area in a liquid is quickly accelerated to high speeds. This can damage equipment such as ship propellers. Scientists know little about how cavitation affects microscopic devices. In this research, scientists took high-speed images of microscale cavitating fuel jets. This allowed them to capture the motion of liquid jets moving at the speed of sound from high-pressure fuel injectors like those used in vehicle engines. Analysis of the results showed that previously invisible flow dynamics depend on cavitation in a wide range of pressures and temperatures. This cavitation enhances the energy conversion efficiency of the fuel injection.

The Impact

Scientists used X-ray imaging to determine the role of cavitation in fuel injection performance. The results show that these bubbles can be harnessed to improve energy conversion efficiency when the fuel is injected directly into engine cylinders, an approach that improves combustion efficiency. The results will help researchers optimize these effects to design more efficient combustion engines. This, in turn, will help vehicles use petroleum fuels more efficiently while we move to alternative fuels.

Summary

Liquid fuel spray dynamics are hard to study because the flow is highly transient and optically opaque. The ultra-intense X-ray beams delivered by the unique superconducting helical undulator (SCHU) provide an ideal tool to visualize fast liquid-fuel dynamics. The SCHU is located at the Advanced Photon Source, a Department of Energy (DOE) Office of Science user facility operated by Argonne National Laboratory. The research team demonstrated that the SCHU source enabled high-speed imaging at 65,000 frames per second with exposure time as short as 100 billionths of a second, with 1-micrometer spatial resolution. The unprecedented spatiotemporal resolution is made possible by the unique radiation properties of the SCHU device.

Facilitated by highly quantitative analysis, the images reveal detailed fluid dynamics that are not only sensitive to hydrodynamic parameters such as injection pressure, surprisingly, but also their interplay with the fluid temperature, an important but often overlooked thermodynamic parameter. For the first time, the scientists found that the flow dynamics related to the fluid velocity can be perfectly scaled by a single dimensionless parameter, cavitation number, in the extended pressure and temperature range. The researchers found that cavitation at high pressure and temperature promotes the liquid jet to reach 90% of the ideal values, significantly improving energy conversion during the atomization process in modern engines.

Contact

Funding

The research was partially supported by the DOE Office of Science, Office of Basic Energy Sciences, Scientific User Facilities Division and Argonne National Laboratory. The research used resources at the Advanced Photon Source, a DOE Office of Science user facility operated by Argonne National Laboratory.

Publications

Zhang, Q., et al., Enhanced energy conversion efficiency promoted by cavitation in gasoline direct injection. Energy 265, 126117 (2023). [DOI: 10.1016/j.energy.2022.126117]

Highlight Categories

Program: BES , SUF

Performer: University , DOE Laboratory , APS