Against the backdrop of increasingly severe global energy and environmental problems, hydrogen fuel is garnering significant attention as a pivotal component of the future sustainable energy landscape by all countries in the world. The advantages of hydrogen are manifold, including its diverse production sources and crucially, the potential to enable carbon-free combustion with low nitrogen oxide emissions when utilized in advanced combustion systems such as micro-mix combustors. The stability and pollutant performance of a micro-mix combustor depend critically on the fuel-air mixing characteristics and the consequent combustion behavior. Given this critical dependence, it is necessary to study the mixing characteristics of micro-mix combustors.

This study is based on the self-designed single-stage micro-mixing combustor, and employs numerical simulation to investigate the mixing and flow characteristics of the single-stage micro-mix combustor, exploring its working principle and studying the effects of different offset distances, mixing distances, air hole shapes and momentum flux ratios on the flow field structure and mixing characteristics at low power.

The numerical simulation results show that increasing both the offset distance and mixing distance contributes to improved mixing uniformity. With the increase of the offset distance, the influence of the equivalence ratio on the mixing effect becomes more significant: increasing the equivalence ratio accelerates the merger of internal vortices, while the contraction of external vortices leads to an increase in vorticity magnitude. As the mixing distance increases to a certain distance, the uniformity index growth gradually decelerates, while hydrogen diffusion becomes severe, making it difficult to ensure complete mixing is confined within the mixing zone. When fuel jet depth is low, air holes with small aspect ratios and small upper-lower area ratios achieve better mixing performance. At a low equivalent ratio, the internal vortex of triangular air holes exerts a strong entrainment effect on the fuel. Furthermore, the mixing uniformity is affected by the combined action of the momentum flux ratio and the vorticity magnitude. The momentum flux ratio in the small-scale jet in cross flow has a more significant and pronounced effect on mixing than the vorticity magnitude. When the air hole is smaller under the same momentum flux ratio, the mixing effect is better. With the increase of momentum flux ratio, the fuel distribution shows a trend changing from semicircle to water droplet shape and then to horseshoe shape.

The research provides valuable references for the optimized design and application of micro-mix combustion technology in micro gas turbines.