DNS predictions of NO_x production in developing turbulent mixing layers with non-premixed hydrogen–air combustion

ABSTRACT

Direct numerical simulations of three-dimensional compressible mixing layers with non-premixed hydrogen–air combustion were performed using a detailed chemical reaction mechanism with $\mathrm{N}{\mathrm{O}}_{\mathrm{x}}$ production. Flow fields with three types of initial disturbances were simulated to investigate the relationship between developing vortical structures and $\mathrm{N}{\mathrm{O}}_{\mathrm{x}}$ formation. The amounts of $\mathrm{N}\mathrm{O}$ and $\mathrm{N}{\mathrm{O}}_2$ produced in the simple shear layer were smaller than those in the two- and three-dimensional mixing layers with vortical structures. In the mixing layers, the formation and expansion of the combustion region by the roller vortices and the baroclinic torque had a significant impact on $\mathrm{N}\mathrm{O}$ production, while the relatively low-temperature combustion region formed by the three-dimensional developed rib vortices in the blade regions between the roller vortices had a large effect on the $\mathrm{N}{\mathrm{O}}_2$ production. It was found that a two-dimensional simulation can estimate the $\mathrm{N}\mathrm{O}$ production, while the information on a three-dimensional mixing layer is necessary to predict the $\mathrm{N}{\mathrm{O}}_2$ production.

KEYWORDS:

• Non-premixed hydrogen–air combustion
• mixing layer
• NOx production
• turbulence vortex
• direct numerical simulation

Acknowledgements

This research was performed using the supercomputer of the Academic Centre for Computing and Media Studies, Kyoto University.

Disclosure statement

The authors report there are no competing interests to declare.

Additional information

Funding

The use of the supercomputer was funded by the Centre for Information Initiative, University of Fukui.