New UAS ignition-assist spray research project takes flight at CoMFRE

Center for Multiphase Flow Research and Education (CoMFRE) researchers Song-Charng Kong and James Michael are answering key questions about UAS engine ignition in a new project funded by the Army Research Laboratory (ARL).

Kong, professor of mechanical engineering, and Michael, assistant professor of mechanical engineering, will characterize the interaction of high-speed fuel spray and the ignition plug in unmanned aircraft systems (UAS) engines to better understand their interaction – at the high altitudes and low temperatures UAS operate in.

“Right now, most fundamental knowledge about fuel-spray and ignition plug physics is based on standard ‘glow’ plugs on standard engines, but UAS conditions are unique and extreme, so we must know more about the conditions most relevant to UAS to ensure that future UAS ignition-assist systems are highly reliable,” said Kong.

Mission-driven spray investigation

The new project builds upon Kong and Michael’s previous success studying and modeling fuel droplet impact on heated surfaces for the ARL.

Now, the team will extend capabilities to investigate small (less than 100 micrometers in diameter), high-speed (about 100 meters/second) fuel sprays on a heated ignition plug (approximately 1000 Kelvin) with realistic geometries and materials. The physical phenomena that will be investigated include fluid-structure interactions at UAS engine-relevant temperatures and pressures, effects of ignition plug geometry and materials, temperature distributions and thermal stresses.

“Our work in this project is considerably more complex than our previous work, accounting for the impact of many consecutive fuel drops on a heated ceramic plate, with a temperature that will change due to drop impact. These new simulations will also span a longer timeframe, and will take into account fuel vaporization and properties of a liquid fuel film that may develop,” said Michael.


Collaboration speeds tech advancements

Even with so many variables in play, Kong and Michael will work with ARL researchers to narrow their focus to simulation conditions that most closely mimic those faced by UAS in the sky. The team will do the same when they turn their attention to conducting experimental studies to validate their simulations in Iowa State’s drop-wall interaction instrumentation.

“Collaborating with the ARL every step of the way will ensure we can make the maximum contribution to the Army’s mission,” said Kong. “UAS engine design is a new area and designs vary widely, depending on the nature of the mission. This work is tailored to the Army’s UAS applications, but we expect our discoveries to be useful in the future to other types of UAS’ ignition and other types of ignition in extreme conditions.”

This project is part of the large effort in reinventing the next-generation UAS propulsion systems under the direction of Mike Kweon at the ARL. Iowa State researchers have been collaborating with those at University of Wisconsin-Madison, University of Illinois at Urbana-Champaign, and Argonne National Laboratory on determining the operating conditions.

“Song-Charng and James’ project is an excellent example of the purpose of CoMFRE: To bring together expertise across disciplines and organizations so we can solve complex multiphase flow engineering problems,” said Ted Heindel, director of CoMFRE, University Professor of mechanical engineering and Bergles Professor of Thermal Science. “CoMFRE faculty are among the world leaders in their areas of expertise. By working hand-in-hand with military, industry and other partners, we speed up the transfer of our discoveries to those who can use them in applications.”