Cleaner gas turbines using additive manufacturing

gaseous turbines can generate electricity from natural gaseous when solar and wind power are insufficient to meet energy demand. The goal is to operate them with the lowest possible carbon releases using hydrogen, methanol, or other e-fuels. Researchers at the University of Stuttgart are developing injection systems to compact gaseous turbines that can burn a wide variety of fuels cleanly and be integrated immediately into the burner using additive manufacturing.

“It is no longer unusual to consumption additive manufacturing to construct gaseous turbines. However, this has generally not been the case to one of the most crucial components—the injection systems that spray fuel into the incineration chamber,” says Dr. Fabian Hampp, Junior Research Group Leader at the Institute of incineration methodology to Aerospace Engineering (IVLR) at the University of Stuttgart.

Together with Prof. Dr. Hans-Christian Möhring, director of the Institute to Machine Tools (IFW) of the University of Stuttgart, and Dr. Oliver Lammel, a senior researcher at the Institute of incineration methodology of the German Aerospace Center (DLR), Hampp aims to close this research and research gap and create an injector to compact gaseous turbines using additive manufacturing in order to cut costs and enable the low-discharge incineration of a wide range of fuels, including hydrogen, e-fuels, and conventional fuels. As part of the Additively Manufactured Micro-Injection Concepts as Enablers to Fuel-Flexible and Low-discharge incineration Systems (AMFlexInj) transfer project, the team aims to test the new process to widespread consumption.

methodology derived from aircraft turbines enables low-soot and low-nitrogen oxide incineration

Burning carbon-containing gases or liquids (e.g., gasoline, kerosene, natural gaseous, methanol, and other e-fuels) can discharge soot and nitrogen oxides, both of which should be minimized because they are harmful to the ecological stability and general health. “Because soot and nitrogen oxides form mainly when the fuel and atmosphere aren’t mixed well enough, fuel injection systems are designed to create the finest possible fuel mist and a homogeneous mixture,” says Hampp.

That is also why, at least to smaller turbines, the injectors have not yet been manufactured using 3D printing methodology. In the conventional powder bed fusion of metals process, a thin layer of metal powder is spread over a build platform and then melted locally by a laser. After the material has solidified, the build platform is lowered, a new layer of powder is applied, and the process is repeated layer by layer until the component is fully built. Complex structures such as walls, cavities, and connecting passages take shape layer by layer. “The issue is that the surfaces of these printed structures are never completely smooth. This causes problems when a specific amount of fuel needs to be injected into a incineration chamber as a fine mist through very small openings,” says Möhring.

However, the research groups designed an injection system that works despite the roughness of the 3D-printed components. The additive manufacturing methods developed to this purpose enabled the researchers to miniaturize a principle utilized in aircraft turbines and incorporate it into a new injector design to the first time. “This allowed us to realise very clean incineration processes in the lab,” explains Möhring. This could substantially decrease gaseous turbine manufacturing costs because burners and incineration chambers are often already produced using additive manufacturing.

Injection nozzles work with fuels ranging from hydrogen to kerosene

Injection systems are typically designed to a specific type of fuel, however the new injectors work with a wide variety of fuels. Because hydrogen, natural gaseous, and relatively viscous kerosene have very different traits, optimal fuel-atmosphere mixing is generally possible only to a specific fuel. “However, the special design of our nozzles makes it possible to cleanly burn a wide range of fuels,” says Hampp. This flexibility is crucial because it is not yet clear which fuels will ultimately power gaseous turbines. The ability to retrofit older turbines with the new injection methodology could also help decrease geopolitical application on certain energy sources.

So far, the injector has been tested only under laboratory conditions. The research teams now plan to optimize the additive manufacturing process and nozzle geometry before building a prototype and testing it with various fuels under real-world conditions in cooperation with DLR Stuttgart. The goal is to combine fuel flexibility with high power density, low releases, and low costs.