NO emission characteristics for the HTC and MILD combustion regimes with N2, N2/CO2 and CO2 diluents: effect of H2 addition to CH4

Abstract

In this paper, the effect of H2 addition to CH4 on the NO emission of oxy-fuel, oxygen-enriched, and air-fuel MILD combustion is studied by numerical and chemical calculations. In the CFD section, the University of Lisbon MILD furnace is modeled. The results show that H2 added to CH4 is associated with a higher NO emission in the same oxidant composition. It is due to higher NO formation by NNH and thermal mechanisms. It can be found that by transformation from air-fuel to oxy-fuel MILD regimes, NO emission is reduced significantly. Moreover, the addition of H2 prevents flame extinction that often occurs under MILD conditions when CO2 replaces N2. Reaction pathway analysis displays that dominant routes of NO emission in the H2-lean are N2O-intermediate for the air-fuel and oxygen-enriched conditions and NNH for the oxy-fuel MILD regime. In the H2-rich condition, the NNH mechanism plays the most important role in the NO production.