NOx emission characteristics of CH4 versus O2/CO2 counterflow non-premixed flames at various pressures up to 300 atm

Abstract

The characteristics of NOx emission of oxy-methane combustor operating over a wide range of pressure (1-300 atm) are investigated by performing one-dimensional numerical simulations of CH4 versus O-2/CO2 counterflow non-premixed flames. The amount of NOx emission is estimated by varying the pressure, oxygen mole fraction, strain rate, and N-2 amount in the fuel and oxidizer streams. It is found that N-2 ingress in the oxidizer stream is more critical to the NOx emission than that in the fuel stream because the reaction zone for NOx formation develops in the oxidizer side. It is also found that the amount of NOx emission non-monotonically varies with the increase of pressure at relatively-low oxygen mole fraction. The NOx reaction pathway analysis demonstrates that such a non-monotonic behavior of NOx emission is mainly attributed to reduction in NOx formation via prompt NOx and NOx reburn pathways at high pressure. The sensitivity of NOx emission to several chemical kinetic mechanisms is examined under various combustion conditions, which reveals important reaction pathways for NOx formation/consumption.