A numerical study on the influence of airstream dilution and jet velocity on NO emission characteristics of CH4 and DME bluff-body flames

In this paper, a bluff-body flame structure has been modeled using conditional moment closure model (CMC) to study the effect of airstream dilution with CO2 and H2O on nitric oxide (NO) production. This scenario would mimic the effect of exhaust gas recirculation (EGR) in an internal combustion (IC) engine or in a gas turbine. A 2D in-house code, employing a k-ε turbulence model with modified constant Cε1, has been used to calculate the flow and mixing field. Methane (CH4) and di-methyl-ether (DME) have been separately used as fuels to assess the performance. Fuel jet velocities are varied to investigate the effectiveness of these dilutions at different levels of turbulence-chemistry interactions. The presence of both CO2 and H2O in the airstream reduced the NO quantity for both the fuels. The effectiveness of the H2O diluent on mass basis is more prominent in reducing NO. With the increased fuel velocity, a situation similar to increased injection pressure in IC engines, higher amounts of diluents caused near extinction of the flame. For the same amount of diluents, global NO reduction in DME is higher compared to that for methane.