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

In this paper, the effect of H 2 addition to CH 4 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 H 2 added to CH 4 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 H 2 prevents flame extinction that often occurs under MILD conditions when CO 2 replaces N 2. Reaction pathway analysis displays that dominant routes of NO emission in the H 2 -lean are N 2 O-intermediate for the air-fuel and oxygen-enriched conditions and NNH for the oxy-fuel MILD regime. In the H 2 -rich condition, the NNH mechanism plays the most important role in the NO production. • X H2,cr is known that in the higher values of it, NO emission increases dramatically. • H 2 added to CH 4 prevents flame extinction due to the replacement of CO 2 with N 2. • Change of diluent form N 2 to CO 2 reduces significantly NO emission under MILD regime. • H 2 -lean shows N 2 O-intermediate as main NO mechanism of air-fuel and oxygen-enriched. • NNH is the main route in the NO emission of CH 4 /H 2 -rich MILD regime. [ABSTRACT FROM AUTHOR]