Georgia Tech's combustor injects the fuel and air separately into the combustor while its shape forces them to mix with one another and with combustion products before ignition.

Researchers Ben Zinn (left) and Yedidia Neumeier (right) look up at a mirror placed above the Georgia Tech combustor to demonstrate how few emissions its exhaust produces.

The device, the researchers say, has a simpler design than present state-oftheart combustors and could be manufactured and maintained at a much lower cost.

The Georgia Tech design contrasts with that of existing combustors where fuel mixes with a large amount of swirling airflow prior to injection into the combustor. Unfortunately, the combustion process often excites instabilities that are counterproductive to clean emissions.

Georgia Tech's design eliminates this problem by injecting fuel and air separately into the combustor. The shape of the combustor forces them to mix with one another and with combustion products before ignition. To keep emissions low, the injection path and chamber geometry are complex.

The combustor burns fuel in low-temperature reactions throughout the combustor. This avoids acoustic instabilities of current low-emissions combustors. It does this by eliminating all high-temperature pockets of combustion through better control of the flow of reactants and combustion products in the combustor.

Called the Stagnation Point Reverse Flow Combustor, the Georgia Tech device is designed for aircraft engines and gas turbines. It burns fuel with NOx emissions below 1 part per million (ppm) and CO emissions lower than 10 ppm.

"The combustion community is working hard to find ways of burning fuel completely, deriving all its energy while minimizing emissions," says Dr. Ben Zinn, a professor at Georgia Tech's Guggenheim School of Aerospace Engineering and a key collaborator on the project. Attaining ultralow emissions has become a top priority for combustion researchers as federal and state restrictions on pollution continuously reduce the allowable levels of emitted NOx and CO.

Researchers initially wanted to develop a low-emissions combustor that would burn large amounts of fuel in a small volume over a wide range of power settings (or fuel flow rates). But the design adapts to a variety of applications, from small home water heaters to large power-generating gas turbines.

The project was funded by the NASA University Research Engineering Technology Institute Center on Aeropropulsion and Power and Georgia Tech.