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A major design challenge, however, is injecting the gases so that near-ideal mixing is achieved, because uneven concentrations of air and fuel will substantially increase emissions levels and reduce combustion efficiency. The fuel is brought into the mixing chamber in pipes arranged in a radial pattern, and holes are provided to inject the fuel into the chamber. The holes need to be arranged to provide as close a uniform fuel air mixture throughout the mixing chamber as possible.

Astec engineers addressed this and other design issues by modeling the burner using FLUENT CFD software from Fluent Inc., Lebanon, NH. The initial concept design was generated using the SolidWorks computer aided design system. Engineers imported the geometry into the ICEM CFD preprocessor where they generated separate CFD models for the blower, mixing chamber, and nose. They created separate models of different sections of the burner in order to focus on one part of the design at a time while reducing CFD solution times.

Several models were run in succession. The results of one were used as boundary conditions for the next.

The goal of the fan simulation was to obtain an even velocity distribution over the output cross-section. This goal was accomplished by adding directional vanes.

In the mixing chamber simulation, engineers moved the injection holes in order to achieve a swirling flow pattern that provided excellent mixing while also controlling the size of the flame to avoid damage to the drum. In simulations of the nose, engineers focused on generating small recirculation zones to hold the flame in place to maintain stability.