Numerical investigation on the dry low NOx of hydrogen combustion

Abstract Globally, energy is predominantly generated through the combustion of fossil fuels. However, the emissions from these fuels severely impact the ecological balance and environment. As a result, there is a growing emphasis on clean and renewable energy sources as alternatives. Hydrogen is a promising and clean energy source for gas turbines, transportation, and industrial applications. Nevertheless, due to significant differences in hydrogen’s thermophysical properties, it cannot be directly integrated into conventional combustion systems. Therefore, a specialized micromix combustion model must be developed to achieve stable combustion with low dry NOx emissions. In this study, a novel micromix combustor is developed based on the cross-flow mixing of air and injected hydrogen fuel. Under this concept, hydrogen combustion occurs through diffusion-type flames, with the reaction taking place in a very short time. This micromix combustor design ensures inherently stable combustion, resistant to flashback while maintaining low dry NOx emissions. The results indicate that the stability of the flame structure and thermal NOx emissions are controlled by the operating equivalence ratios. A stable hydrogen flame was particularly formed in the shear regions between the two vortices. Thermal NOx generation was strongly influenced by the flame front temperature, with measurements ranging from approximately 0.66 to 11.14 ppm (at 15% oxygen concentration). Consequently, thermal NOx emissions increased by up to 16 times under an equivalence ratio of 0.5.