The 69-foot stainless steel shock tube will give AE researchers a rare opportunity to investigate nextgen combustors

To the untrained eye, it could easily be mistaken for an air duct running down the southern wall of the Ben T. Zinn Combustion lab. Its shiny stainless steel surface indicates only that it is new.

But for Prof. Wenting Sun, the 69-foot shock tube holds the promise of revolutionizing the efficiency of gas turbines and reducing carbon emissions from fossil fueled energy.

“This represents a new and very exciting capacity for Georgia Tech,” says Sun of the eight-ton, $500K tube, the centerpiece of a joint research endeavor with mechanical engineering professor Devesh Ranjan.

“There really isn’t one this large, doing this kind of research. And it really wouldn’t be possible in most other labs that I know about. It’s so large that no lab would have the room for it. The Zinn Combustion Lab is unique that way.”

Sun said the shock tube will allow AE researchers to obtain higher quality, more accurate data from their work in combustion kinetics at conditions which were not explored before.

“Using this, we can explore a combustor’s properties at new, more extreme, conditions – much higher pressure. We can experiment with different gases. And I will be able to isolate the conditions, which is important because I need to know the exact conditions to validate kinetic models for gas turbine combustors.”

The precision of the shock tube’s engineering is key to Sun’s research. Its structure and capacity allow Sun and his colleagues to extract information they can use to create and validate new models for combustors.

“The conditions we are targeting are around 300 atmospheres [atm], and between 800 and 2500 Kelvin,” said Sun.  “We want to mimic conditions for next generation of gas turbines because we want to have greater efficiency, and greater carbon sequestration. If we can capture the carbon, we can stop it from being emitted.“

Manufactured by Marine Technology, an Irish company, the AE shock tube has an outer diameter of 10 inches, two-inch walls, and a six-inch diameter passageway inside. It is comprised of 10 sections, each riveted to the next. The tube’s sturdy construction allows it to sustain blast waves that replicate actual explosions and their effects. Its smooth inner walls and the relatively large inner passageway give it a unique advantage over smaller, less sophisticated shock tubes.

“That surface is very important because when you initiate a shock wave, you don’t want any interference from the walls. We get more reliable data when we start out with a smooth inner surface,” said Sun. “And the six-inch diameter, inside, allows us to isolate conditions between the walls and the center. Normally, you’d have a one or two-inch diameter tube, and that doesn’t produce data that is reliable.”

Sun said several potential funders – both federal and private - have approached him about pursuing projects now that the shock tube is up and running.

“This will be a very well-used piece of equipment,” he said. “We will be running several experiments a day.”

Sun oversaw the installation of the mammoth tube as a part of a $1M grant  he received to pursue "Investigation of Autoignition and Combustion Stability of High Pressure Supercritical Carbon Dioxide Oxycombustion"-  a three-year study of oxy-combustion technologies capable of high-efficiency, low-cost carbon dioxide (CO2) capture from coal and natural gas-fired power plants. He has been working with two of his AE colleagues, professors Tim Lieuwen and Suresh Menon, and Prof. Devesh Ranjan from the School of Mechanical Engineering.

Oxy-combustion represents one of the most promising methods for removing carbon dioxide from gas and coal-fired power plant exhaust gases. Unlike conventional combustion processes that utilize air as the oxygen source, oxy-combustion utilizes pure oxygen for combustion.

The approach produces a flue gas stream consisting mainly of CO2 and water vapor, which allows the CO2 to be much more easily and more cost-effectively captured from exhaust gas than with conventional combustion methods where nitrogen is the dominant flue gas component.

While the use of pure oxygen eliminates the presence of pure nitrogen in the flue gas - which can react negatively with oxygen at combustion temperatures - the approach requires high-pressure, high temperature operating conditions that far exceed the capabilities of conventional gas turbine engines. In addition, little is known about how the extreme conditions or the higher bulk gas concentrations of CO2 in the oxy-combustion environment affect combustion properties and overall system performance.