Conventional combustors that employ air-blast and pressure-swirl injection technologies are very sensitive to fuel properties, especially viscosity, limiting their ability to utilize certain classes of fuels and blends, including bio-based fuels. The new swirl-burst (SB) fuel-injector technology developed at Baylor University (Waco, Tex.; www.baylor.edu) by mechanical engineering professor Lulin Jiang and her research team leverages an advanced atomization process that enables combustion of very viscous oils without any preheating. “The SB injector, with its unique geometry, generates internal two-phase flow to immediately create a fine fuel spray at the injector exit. Conversely, traditional injectors will first discharge a liquid jet core or film, which will very gradually disintegrate into ligaments, then large droplets and then, finally, finer droplets, even for conventional low-viscosity fuels,” explains Jiang. Easily creating fine spray is key when dealing with liquid fuels because larger droplets will result in pollutant emissions. For viscous liquids, such as glycerol, those conventional injectors lead to even coarser sprays that are difficult to ignite without further increasing emissions.
Mechanical engineering professor Lulin Jiang, Ph.D., and her research team on the novel Swirl Burst injector inside the Cornerstone Atomization and Combustion Lab at Baylor University. (Robert Rogers/Baylor University)
Additionally, at higher flowrates, other injection methods using two-phase flows may experience internal gas voids, which can cause pulsating fuel spray, paralyzing the flame stability. “With the new SB injector, the integrated swirls help to overcome that hindrance — even with higher flowrates, it does not generate gas voids internally. It also generates more uniform droplet-size distribution compared to other technologies, which can generate many large droplets or ligaments at the periphery, increasing emissions,” she adds. The team has tested the SB injector with many different fuel blends, covering a wide range of fuel properties, including glycerol, methanol, diesel, vegetable oil, SAF and even straight algae oil. “I believe we were the first team to directly burn algae oil without preheating the fuel or the air,” notes Jiang.
Now, in a project funded by the U.S. Dept. of Energy and the National Science Foundation, the technology is set to be deployed in a waste-to-energy process at a landfill near Waco. This pilot system will begin testing in early 2025 and will help to reduce methane emissions and other pollutants from the site, while producing resilient energy. Beyond combustion, the atomization technology of the SB injector could provide value in medical, agricultural and spray-coating applications.