Effect of H2 and Jet-A1 fuel split on flame stability and pollutant emissions from low-swirl burner

Abstract

Hydrogen combustion is emerging as a promising solution for future aircraft engines, offering a shift from fossil fuels to sustainable alternatives and the potential for reduced pollutant emissions. While the complete transition to ${\text{H}}_2$ presents a significant challenge due to its low volumetric energy density, limited availability, and infrastructure and aircraft redesign constraints, fuel-flexible burner technologies that allow ${\text{H}}_2$ blending with Jet-A1 offer a viable alternative. These technologies provide additional benefits such as an enhanced stability range and can contribute to achieving near-term decarbonization goals. This study explores the capabilities of a novel dual-fuel burner developed as part of the European project FFLECS (Novel Fuel-Flexible ultra-Low Emissions Combustion systems for Sustainable aviation). Flame stabilization in a lean lifted flame combustor operating under atmospheric conditions and fueled by Jet-A1 and ${\text{H}}_2$ is experimentally investigated. A new fuel-flexible nozzle, based on the “low swirl” lean lifted flame concept, is developed to enable high premixing, significantly reducing ${\text{NO}}_{\text{x}}$ emissions and minimizing flashback risk compared to conventional swirl-stabilized flames. The ${\text{H}}_2$ injection for the investigated nozzle was optimized for part load conditions, but can still be operated up to $100\text{\%}{\text{H}}_2$. The flame shape and lift-off height were studied at elevated air inlet temperature and ${\text{H}}_2$ blending ratios up to 100% of the total thermal power. Moreover, the lean blowout limits remain similar for ${\text{H}}_2$ blending ratios up to 30% across various air inlet temperatures but change significantly at higher blends. Finally, switching from Jet-A1 to ${\text{H}}_2$ lowers ${\mathrm{NO}}_x$ emission at low air inlet temperatures and increases it at higher temperatures, with a pronounced rise across all air inlet temperatures at blends above 75% ${\text{H}}_2$ under elevated specific thermal power. In contrast, the ${\text{NO}}_{\text{x}}$ emissions remain consistently very low at low specific power close to the lean blowout limit. Additionally, even a modest ${\text{H}}_2$ fuel split of 15% significantly reduces CO emissions. These findings highlight the potential of ${\text{H}}_2$ addition to lean lifted spray flame utilizing Jet-A1, facilitating the future development and optimization of fuel-flexible combustors for aircraft engines.