Modified vitiation in a moderate or intense low-oxygen dilution (MILD) combustion furnace

This paper reports on the effects of various operational and geometric parameters on mixing and vitiation in a laboratory-scale furnace operating with natural gas and under the moderate or intense low-oxygen dilution (MILD) regime. The study is carried out through numerical modeling. Seven independent parameters are considered: i.e., mass fraction (f) of fuel diluents (CO 2 and N 2), air preheat temperature (T a), global equivalence ratio (φ), air nozzle exit diameter (D a), fuel nozzle exit diameter (D f), fuel-air nozzles separation distance (S), and fuel injection angle from the furnace floor (α). The modeling is initially verified through a comparison to measurements by Szegö et al. (Szegö, G. G., Dally, B. B., and Nathan, G. J.Combust. Flame 2008, 154, 281-295) in the same furnace geometry. It is shown that varying each of the parameters f, φ, D a, D f, S, and α can considerably influence the fuel-jet penetration distance and the recirculation rate of the exhaust gas, two important quantities for establishing the MILD combustion. Relatively, the geometric parameters D a, D f, S and α play more effective roles in controlling the vitiation rate and, hence, "flame" characteristics. Also, it is revealed that influences of all of the parameters, except S and α, can be represented by that of the ratio of the fuel injection momentum to the air injection momentum. © 2011 American Chemical Society.