OCR Text |
Show performed. The following conclusions may be drawn from this investigation: 1. Two-stage burning in a porous media burner results in lower average axial temperature compared to singlestage combustion; 2. Two-stage burning, in which the first stage is lean and the second stage is fuel-rich, results in lower NOx and CO emissions than single-stage burning at the same overall equivalence ratio; 3. Two-stage burning, in which the first stage is fuelrich and the second stage is lean, does not offer a significant advantage over single-stage combustion at the same equivalence ratios; and 4. Two-stage burning, in which the first stage is lean and the second stage is fuel-rich, results in very low NOx and CO emissions even at overall stoichiometric fuel:air ratios and, as such, affords maximum fuel efficiency with minimum emissions. These preliminary results demonstrate proof-of-concept that NOx emissions can be minimized by two-stage burner operation in a porous media burner as discussed in this paper. Further optimization of the burner is required to determine the effects of varying radiant heat transfer rates, which should reduce the operating temperature further and result in even lower NOx emissions. Another area of concern is the selection of an optimum material for the porous matrix. The material used in this study was partially stabilized zirconia which exhibited excellent high temperature properties, but was subject to thermal shock from temperature cycling. Further studies were proposed to investigate other ceramic materials, such as mullite, zirconia oxide, and silicon carbide. The work described in this paper was performed at the University of Texas at Austin and funded, in part, by Radian corporation. A patent is currently pending for staging techniques to reduce NOx from a porous media burner, while achieving high radiant heat transfer. -14- |