Characterization and validation of low emission mechanisms in hydrogen micromix diffusion combustor

This paper proposes a novel hydrogen micromix diffusion combustor with an embedded vortex generator at the dome, specifically designed for micro turbojet engines with a thrust of 20 kgf. The low-emission mechanism of the combustor was characterized and validated through experimental and numerical investigations. The vortex generator produces the air streamwise vortex, which enhances the penetration capability of hydrogen and couples with the hydrogen jet vortex to strengthen mixing. The dome vortex system drives the expansion of the flame kernel in both axial and radial directions, promoting flame propagation and stability. Under the influence of the dilution jet, the dome vortex system undergoes fragmentation and reorganization, which enhances local turbulence intensity and improves the mixing efficiency. To minimize the OTDF, the design of experiment (DOE) method was employed to systematically evaluate the impacts of dilution hole parameters. It was found that smaller dilution holes would generate higher axial vorticity, leading to more intense and homogeneous mixing. An optimized configuration with an OTDF value of 0.19 was achieved. Experimental validation on a 20 kgf thrust micro turbojet engine confirmed NOx emissions below 20 ppm, with no thermal oscillation issues observed. Phase space reconstruction methods further confirmed the absence of oscillation, as phase trajectories displayed a spindle-like shape without forming a closed limit cycle. These findings offer valuable insights into the design of hydrogen micromix diffusion combustors.