Original Design
12" Coflow, 1" Jet
Second Design
4" Coflow, 1/8" Jet
Current Design
8" Coflow, 1/4" Jet
Design Evolution
In order to arrive at the current design, several design iterations were made. The design modifications were influenced by experimental, economical and model capatability issues.
Several design candidates were considered prior to selecting the perforated plate to provide a stable source of vitiated coflow. These candidates included catalysts, porous ceramic media and tube bundles. The decision to use the perforated plate is a result of a need to have a turbulent, stable coflow.
Initially, it was the goal of the team to have the largest coflow possible. The larger the coflow, the larger the target volume. This target volume consists of the expanding central jet that is isolated from the outer quiescent air. The original combustor design, that had a 12" diameter, perforated area proved to require high fuel and air flowrates. Subsequently, this design would generate an extremely high amount of thermal energy. (On the order of 1 MW) The picture below shows the original design.
Original Design |
Second Design |
Current Design |
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Next, the notion of having a stable, high velocity jet flame was investigated. A second, much smaller, (4" perforated area diameter) combustor was designed and built. A 1/8" diameter jet was installed and the burner was operated under many conditions. The observations from this research was presented at the 4th International Workshop on Measurement and Computation of Turbulent Nonpremixed Flames in Darmstadt, Germany in June 1999.
Aside from the gaseous jet, several spray nozzles have been considered. This spray research is an ongoing collaboration with research groups in Germany and Japan.
A common concern expressed by the group and fellow researchers is the severity of a possible blackflash through the perforated plate. It could be assumed that any flame would be quenched as it attempts to pass through the plate. (Plate Thickness to hole diameter ratio is 8) Even so, an intentional light off within the mixing chamber was studied. This was done by producing a spark in the center of the mixing chamber while a methane-air, stoichiometric mixture was passing through. The result was a sudden pressure pulse and rapid flash that reached thru the plate and about 2' above the surface. This was followed by the stabilization of a premixed flame on one of the thin, aluminum perforated sheets (flow straighteners) within the chamber. The rapid flash did not harm the system but the stabilized internal flame began to burn the inside walls of the PVC mixing chamber. Therefore a safety system should be in place such that an increase of temperature or pressure would result in the immediate shutoff of fuel.
Perforated Plate:
.... more to follow... 11/23/99
Mixing Chamber and Combustor Setup:
Current Combustor Setup, 8" |
Second Setup, 4" |
Mixing Chamber Evolution |
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