An experimental and numerical investigation into the effects of nozzle scale was undertaken at the U.S. Federal Energy Technology Center in conjunction with the United Technologies Research Center. Experiments were conducted at operating pressures from 6.8 to 27.2 atm., and at primary zone equivalence ratios from 0.4 to 0.75. Results reported herein summarize tests at 6.8 atm., and with zero and 4% piloting levels (expressed as mass fractions of total fuel). Computations used to compare to the experimental data were made using the GRI Mech 2.11 kinetics and thermodynamics database for flame chemistry modeling. A perfectly stirred reactor network (PSR) was used to create a network of PSRs to simulate the flame. From these investigations, concentrations of NOx and CO expressed in parts per million (ppm) were seen to increase and remain virtually unchanged, respectively, when comparing a Quarter to Full Scale Bluff-Body (Tangential Entry) nozzle. Simple heat transfer modeling and CO emissions refuted that any variations in thermal characteristics within the combustors were solely responsible for the observed NOx variations. Using PSR network modeling, the NOx trends were explained due to variations in macroscopic mixing scales which increased with nozzle size, thereby creating progressively less uniform mixing, and hence higher NOx levels.

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