UCI Conducts Combustion Research aboard the International Space Station

June 18, 2018 - When SpaceX launched a resupply mission to the International Space Station last summer, two UC Irvine scientists watched with more than just passing curiosity. Among the nearly 6,000 pounds of scientific research, supplies and hardware hurtling toward space aboard the Falcon 9 rocket was equipment integral to a UCI-designed-and-run combustion experiment nearly 20 years in the making.

Mechanical and aerospace engineering professor Derek Dunn-Rankin and project scientist Yu-Chien (Alice) Chien watched as their gear headed toward the ISS. Their E-FIELD Flames (Electric-Field Effects on Laminar Diffusion Flames) is a part of NASA’s ACME (Advanced Combustion via Microgravity Experiments) program, a suite of six experiments designed to enhance understanding of combustion by studying flames in a microgravity environment.

The E-FIELD Flames research is the culmination of Dunn-Rankin’s ongoing efforts – since 1998, with a succession of doctoral students – to design the ultimate electric-field and flame interaction experiment to take place in space.

About 85 percent of the energy used on Earth comes from combustion – the burning of some sort of fuel. Combustion heat is used to process materials, create fertilizer for food, and power cars and airplanes. Scientists hope that by learning more about the process, they can develop new and less-polluting combustion methods.

The problem is, it is difficult on Earth to try to understand how combustion works, because gravity and the resulting buoyancy affect the way flames behave. So scientists look to zero-gravity or microgravity environments to get an unadulterated view of the process.

“Humans have been trying to control fire since the beginning of their existence,” Dunn-Rankin says. “Experiments on Earth are complicated by gravity, and buoyancy flows can make it difficult to understand what is going on in the flame. We want to understand what is happening when gravity is not affecting it.”

There is a miniscule amount of gravity at the altitude of the ISS, which orbits approximately 250 miles above Earth. By conducting flame experiments in that environment, researchers can better understand the chemistry of a flame, why it behaves as it does and how to better control it. E-FIELD Flames focuses specifically on examining the effects of electric fields on the burning behavior of two fuel gases: methane and ethylene. Flames naturally create charged particles called chemi-ions, which can be manipulated and rearranged when moderate electricity is applied to them. “Our project is to see if we can get a better feel for where these ions are coming from and how we can pull on them to make flames more efficient and less polluting,” says Dunn-Rankin.

The experiment includes applying both positive and negative electric fields in varying strengths and at varying intervals to burners operating with different concentrations of the two fuels. The first of two phases began on March 14 of this year (Pi Day, Chien notes with a smile), and ended on May 17. Phase II is scheduled for later this year.

Eleven non-consecutive trial days were conducted aboard the ISS, and Chien and Dunn-Rankin had to set up all the parameters for multiple test runs on those days – including flow combinations, electric field strengths, camera settings, ignition conditions and size of the flame – and submit them to NASA 48 hours in advance of each day. There were only 999 seconds of fuel available each test day, which supported around eight to 12 different tests in an average eight-hour test period.

NASA scientists and NASA contractors are critical to the operation as modifications and unplanned outcomes are the norm in zero-gravity science. Compromise is a constant companion. “We had to plan and calculate everything … it’s a little bit of a struggle,” Chien says. “And sometimes things fail. Everything is not nice and smooth all the time.”

While the astronauts set up the experiment’s components and kept watch on its progress, the experiment itself was completely automated, running remotely from the NASA Glenn Center in Cleveland, Ohio. Under the primary direction of NASA scientist Dennis Stocker, UCI’s test parameters guided the experiment. Each day of testing, a conference call link to NASA Glenn and live video streaming from the ISS brought the research directly into Chien and Dunn-Rankin’s lab.

As the experiments proceeded, one screen in their lab displayed the live video feed while another displayed processing data. “We pull the raw data right away but we cannot get all the images because those files are really, really large,” Chien explains. It is generally a day or two later, after downlinking from the ISS, that the full set of data arrives at UCI.

Are the results of Phase I what Dunn-Rankin and Chien expected? No. “We were expecting to see what we might see on Earth,” says Chien, who ran similar experiments on terra firma during her doctoral studies at UCI. “But from the Space Station, we actually are seeing soot eliminated in some cases under the influences of the electric field.”

Dunn Rankin explains that ideally, combustion systems can be tuned using ions generated by flame to keep them operating at their highest efficiency. “When a flame is burning properly, it emits the fewest pollutants,” he says, adding that incandescent soot in the flame can be controlled by burning it at exactly the right temperature for a specific amount of time in the right region of the flame. “One of our datasets shows quite clearly that you can eliminate soot in some flames by changing the electric field.”

Changes in earthly combustion systems based on electric field technology are many years down the road, however. For now, the research is focused on contributing to fundamental knowledge about how flames react to various stimuli. Datasets generated by the trials contain unique information that will allow modelers to develop simulations; one day those simulations may inform design tools for combustion systems of the future.

Additionally, understanding how gravity, or the lack thereof, affects a flame, Dunn-Rankin adds, could have implications for fire safety in futuristic space environments. Fires burn differently in space; some materials that burn in space do not burn on Earth, and vice-versa.

“It’s the capability for tuning the environment and controlling the flame that makes the electric body force an interesting one for us to pursue,” he says. “Gravity gets in the way of understanding, and we had to get into an environment where we could study only the effects of these electric fields on the flames. That’s why I got really excited to have the opportunity to be part of the ACME suite of experiments.”  

Editor’s note: The E-FIELD Flames experiment traces its roots to 1998, when Dunn-Rankin and Professor Felix Weinberg from Imperial College, London, conceived the idea of a space-based electric-field and flame interaction experiment. Over the ensuing 20 years, a succession of doctoral students – including Ben Strayer, Ph.D. 2001; Mike Papac, Ph.D. 2005; Sunny Karnani, Ph.D. 2011; Yu-Chien Chien, Ph.D. 2015; and Jesse Tinajero, Ph.D. 2017 – along with other graduate and undergraduate students have contributed to the project. Tinajero, currently a postdoctoral scholar at Yale University, is working on another ACME experiment using the same burner aboard the ISS. “This brings a cohesive team collaboration and greatly supports both experiments,” Dunn-Rankin says.

- Anna Lynn Spitzer