The effects of steam and water spray on NO formation in a methane–air counterflow diffusion flame

Abstract

This paper presents a numerical investigation of the effects of steam and water mist/spray addition on NO formation in a methane–air counterflow diffusion flame. A detailed chemical mechanism (Glarborg et al. Modeling nitrogen chemistry in combustion, Prog. Energy Combust. Sci. 67 (2018), pp. 31–68) which contains 1397 reactions and 151 species has been employed to investigate the NO formation in a counterflow diffusion flame for a wide range of strain rates (50–400 s) in OPPDIF. The water spray/mist evaporation is represented as a first-order dynamic process with Arrhenius type dependence on temperature that can be expressed in a form similar to a first-order chemical reaction. Instead the process is represented as a first-order dynamic process by invoking a hypothetical chemical species and a surrogate reaction . This approach allows handling detail chemistry and droplet evaporation at a reasonable computational cost. This model is validated with CFD simulation results where droplets are modelled using the Discrete Phase Modelling approach. The effects of steam and water mist on the flame temperature and NO formation have been examined. It is found that steam/water mist inhibits NO formation by affecting both thermal and prompt pathways. It is seen that the percentage contribution of prompt NO in overall NO production significantly decreases with increasing steam dilution. Water mist causes an additional evaporative heat loss and results in a drop in percentage contribution of thermal NO in overall NO formation.