Climate change and global warming are major challenges that society must address. Hydrogen (H2) will play an important role as an energy carrier because hydrogen combustion does not produce carbon dioxide (CO₂). However, it produces more nitrogen oxides (NOx) than fossil fuel combustion. A redesign of the hydrogen combustion process with reduced NOx production is necessary; rapidly applicable solutions are required.

In an internal research project, the FH Aachen, the Fraunhofer IPT and the company Präwest GmbH have developed a plug-in solution for existing systems. Together, they have additively manufactured a prototype of a hydrogen combustion chamber.

MicroMix: Lower NOx emissions thanks to many small flames

The hydrogen combustion chamber features the patented MicroMix design, which uses many small flames compared to conventional combustion processes with a few large flames. This reduces nitrogen oxide emissions to the level of fossil combustion. The MMX combustion chamber allows the gas to flow optimally, and there are almost no dead water areas. The external geometry further supports the flow behavior of the flame rings.

The MMX design has already proven itself in initial operating tests. However, the production of MMX combustion chambers places high demands on manufacturing tolerances, subsequent tightness and the distribution of the hydrogen, and is very expensive using subtractive processes.

Simpler and more cost-effective production of a denser combustion chamber

In the joint research project, the partners use Laser Powder Bed Fusion (LPBF), an additive manufacturing process, to produce the combustion chamber. With LPBF, the combustion chamber can be manufactured as an integral component and all functional elements, such as the air baffles, are already fully aligned with each other. In addition, the effort required for subsequent drilling of the spoke centering is significantly lower with LPBF.

Simulations have shown that LPBF can reduce the cost and assembly time of such a combustion chamber by up to 90 percent. In the next steps, the project partners plan to further elaborate the manufacturing process to achieve further synergistic effects.

Synergetic manufacturing chain combines additive and subtractive processes

After the combustion chamber is manufactured additively and separated from the platform on which it was built, the component is processed further: For example, the filigree, movable air baffles and the holes for the hydrogen outlet are produced in a milling process.

In the cooperation, the three partners have succeeded in overcoming the deficits of the existing manufacturing methods and in synergistically combining the different manufacturing processes into an improved process chain. The subtractive manufacturing processes, such as milling or drilling, are designed in such a way that they can be used along the entire process chain, if required. All these measures mean that, in addition to the ecologically and economically more favorable use of the combustion chamber, the manufacturing process is also more sustainable and involves a minimum use of resources.

Partners

• Fraunhofer Institute for Production Technology IPT
• FH Aachen University of Applied Sciences
• Präwest Precision Workshops Dr.-Ing. Heinz-Rudolf Jung GmbH & Co. KG, Bremen