Georgia Tech Researchers Create a Low-Emission, Fuel-Flexible Combustion System

Researchers at the Ben T. Zinn Combustion Lab (left to right): George Widmer, Srujan Gubbi, Ruhani Prasad, Ishan Gupta, Maksim Kvetny, Benjamin Emerson, Shivam Patel, Cristian D. Avila Jimenez.

“There are a lot of people out there who assume the need for combustion will go away as our society decarbonizes,” said Ben Emerson, a principal research engineer in Georgia Tech’s Daniel Guggenheim School of Aerospace Engineering.

Combustion is a chemical process in which fuel reacts with oxygen to produce energy (or heat). Combustors make the world run. From powering jets to heating houses, they are vital to everyday life and responsible for 95% of the world’s energy. But current combustors still run mostly on carbon-based fuels and emit a troubling amount of carbon dioxide.

Fast forward to 2050: In the decarbonized world of the future, most of our energy will come from renewable sources — but the way we move that energy around and store it will come from a mix of technologies. Energy analysts expect that electricity will be responsible for moving roughly 50% of that energy and the other half will still come from fuel to meet net-zero carbon emission goals. Yet, many of these fuels, such as hydrogen, ammonia, or sustainable aviation fuels, will be manufactured rather than derived from fossil energy sources.

Benjamin Emerson inspects a high-pressure combustion test rig.

“These zero-carbon fuels provide energy density, they’re easy to move, and there are trillions of dollars of existing infrastructure in production and transportation,” explained Tim Lieuwen, interim executive vice president for Research, Regents’ Professor, and David S. Lewis Jr. Chair in the Guggenheim School.

These sustainable fuels have their own issues, though. The power plant or aircraft engine must still operate efficiently even with alternative fuels. While they might not cause carbon dioxide emissions, any device that uses air (which is composed of nitrogen, N₂, and oxygen, O₂) without proper engineering can still release harmful gases like nitric oxide (NOx). Keeping any type of harmful gas emissions low is part of attaining net-zero emissions. And while modern combustion technology is already built to reduce emissions, it also often makes these systems less accommodating to diverse fuel types.

“As we’ve dramatically decreased pollutant emissions, we've essentially made these systems pickier,” Lieuwen said. “It's like moving from an old truck to a super sporty race car. You can’t just put any fuel in a highly optimized racing engine.”

Current low-NOx technologies premix air and fuel before they enter the combustion chamber, which enables the fuel to be clean, low-emission, and low-particulate. But this premixed solution is not hazard-free; it can ignite at the wrong time or in the wrong environment, leading to catastrophic consequences.

Shivam Patel installs an igniter on a high pressure combustion test rig.

Lieuwen and his research group are developing a new type of all-purpose combustor that can use any type of fuel while still maintaining low emission standards. Their non-premixed, rich, relaxation, lean (NRRL) combustor works just as well as current mixed-fuel type combustors — but without instability.

This non-premixed technology keeps the fuel and oxygen separate the entire time and dramatically expands the tolerance for a variety of fuels.

To determine if the technology works under various real-world conditions, like changing temperatures and elevations, the researchers are currently developing a prototype NRRL combustor. They will fabricate the combustor on campus, and then test and analyze the data.

The technology is promising: NASA is funding the work, and the researchers have already applied for a patent. They are contributing to a significant reimagining of our energy systems for a carbon-zero future and envisioning the potential use of this combustor in aviation or even space travel.