Fueling the Fire: Studying Flame Behavior to Improve Combustion Systems

underside of aircraft in flight
Photo courtesy of Pixabay.

The power you feel underneath you when you’re on a plane as it takes off is tremendous. The physics that enable the remarkable feat of lifting a 175,000-pound midsize commercial aircraft into the sky and keeping it there are just as incredible – and complicated.

There are four components to a commercial aircraft gas turbine engine: the fan that produces most of the thrust, the compressor, which compresses the incoming air, the combustor which burns the fuel to create high-energy gas, and the turbine that produces work from that gas to power the fan and exhaust to produce additional thrust.

The challenge in this system is keeping the flame in the combustor burning. Flame blowoff can occur when the air flow speed is very high, or the fuel-air mixture is weak so that the flame cannot be stabilized, so it moves downstream and eventually extinguishes itself.

University of Connecticut professor of mechanical engineering, Baki Cetegen has received $320,000 from the National Science Foundation to study this problem by investigating how different fuels and high levels of flow turbulence affect the occurrence of flame blowoff.

There are a couple variables engineers can experiment with to create the best-performing engine. The fuel the flame is fed can be either initially premixed with air at the inlet of the combustor or mix the fuel with air gradually in the combustor. Premixing fuel with air and controlling the mixture composition has advantages for pollution control, particularly for nitrogen-oxide emissions.

In these high-speed, high-intensity combustion systems like gas turbine combustors, flame stabilization is achieved by creating a recirculating flow near the combustor inlet.  One way to achieve this is by inserting a bluff body, which creates a flow re-circulation zone in the combustor, into the high-speed combustible flow or aerodynamically swirling the flow to create what is known as vortex breakdown. This region acts as a continuous source of ignition for the oncoming fuel-air mixture thereby keeping the flame burning inside the combustor.

There has been a great deal of research on various modes of combustion in a wide range of configurations, yet there has not been a comprehensive and systematic investigation of the effects of high levels of turbulence encountered in these devices interacting with flames fueled with different types of fuels in a canonical experimental configuration.

“Better understanding of flame behavior at conditions that are encountered in practical systems is important to come up with better design and operation of combustion systems,” Cetegen says.

Cetegen will study flames fueled by different gaseous and pre-vaporized liquid fuels under high flow turbulence using state-of-the-art laser based diagnostics to unveil new and important combustion physics that have not been explored fully before. This will provide valuable information about the effects of fuel type on flame stability under different turbulent flow conditions.

Cetegen has been a faculty member at UConn since 1987. Prior to joining UConn, he was a research fellow at the University of California, Irvine and research group leader at Energy and Environmental Research Corporation. He received his Ph.D. from the California Institute of Technology in 1982 and M.S. from UC, Berkeley in 1979, both in mechanical engineering. In addition to this project, Cetegen is currently studying reacting jets in cross flow for new staged combustion systems and heat transfer in gas turbine combustors.

This project is NSF Grant No.: 1842545

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