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Army researchers conduct first combustion experiment with X-rays

The US Army Research Laboratory’s Center for Unmanned Aircraft Systems Propulsion has, for the first time, used X-rays with its experiment in a gas turbine combustor using X-rays. The data will help advance gas turbine engine designs for higher power density and efficiency, scientists said.

Dr. Tonghun Lee, an associate professor in the Department of Mechanical Science and Engineering University of Illinois at Urbana-Champaign, which recently joined forces with ARL, and his graduate students, along with partners from the ARL Center for UAS Propulsion, set up shop in the US Department of Energy’s Advanced Photon Source at Argonne National Laboratory.

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Inside a gas turbine engine’s combustor, scientists use the world’s strongest X-ray source at the Advanced Photon Source at Argonne National Laboratory to peer inside formally unseen processes. Credit: US Army photo by David McNally. Click to enlarge.

Lee said their experiment mimicked what happens inside a typical Army helicopter gas turbine engine.

Inside a gas turbine engine, a combustor is fed high pressure air that is heated by constant pressure. After heating, the air passes from the combustor through the nozzle guide vanes to the turbine, producing thrust. Combustors play a crucial role in determining many of an engine’s operating characteristics, such as power density, fuel efficiency and levels of emissions.

We had a combustion going on, which is done for the first time ever at APS and we are imaging the spray breakup at the very tip of the injector using an X-Ray source. Typically that region where the liquid breaks up is very dense and it’s difficult to image anything inside there.

—Dr. Tonghun Lee

By using the world’s most powerful X-Ray source, the team was able to penetrate and understand how the ligaments, or strands of burning fuel, break up into small droplets. The data gathered during this experiment will become the initial conditions for numerical simulations that will further understanding of gas turbine combustors.

We are trying to understand exactly what occurs inside the gas turbine combustor to understand how it responds to different operating conditions. We’re trying to get an understanding of the physics, which to this day we have been speculating, we can really visualize using this X-Ray source. We want to understand what we’re doing right now, understanding the fuel impact. When Soldiers are off in a different location and they have different types of fuels, how will it impact the combustor they have?

—Dr. Tonghun Lee

Lee said that in the slightly longer term, he hopes the data from the experiment will allow researchers to design more optimized combustor systems for the future.

The Advance Photon Source has spent a lot of effort over the last decade or so looking at spray-droplet breakup. And never has it been done in a live combusting environment. So we made the hardware to make it happen and this is actually this first time it’s ever been done live with a combusting flow in a combustor.

—Dr. Tonghun Lee

Lee, while remaining a faculty member at UIUC, recently accepted an additional position as a researcher on the laboratory’s regional office in Illinois, ARL Central. The Army established ARL Central in November 2017, as an extension of its Maryland-based headquarters with the goal of leveraging regional science and technology talent.

The experiment was the first accomplishment of the lab’s new Center for UAS Propulsion, which kicked off a partnership between academia and industry. ARL held a ribbon cutting for the center 2 April.

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