LES and Experimental Study of Flow Features in Humid-Air Combustion Chamber With Non-Premixed Circular-Disc Stabilized Flames

Sydney/Sandia bluff-body flame series [1] has been world-widely studied based on a simple-geometry bluff-body. This study focuses on a turbulent piloted non-premixed methane jet flame with circular-disc which is used in a humid-air combustion chamber without a swirler. Large eddy simulation has been performed to investigate the flow features. Meanwhile, in order to validate the simulation results, an experimental study is also conducted, where the instantaneous velocity and temperature fields are measured using PIV and high temperature thermocouples, respectively. Compared to Sydney/Sandia flame series, the enlarged simulation area effectively eliminates the boundary effects on flow field. Comparisons with experimental data also show that for high resolution of grids, comparatively good agreement is obtained for the flow field. Unlike Sydney/Sandia flame series, central jet tends to break up early in this case because of the existence of the circular disc. It has also been found that the shear layer between the co-flow and the bluff-body wake is captured by LES as well as by PIV. Because of the difference in geometry between Sydney/Sandia and circular-disc bluff-bodies, it needs to be further studied how to apply the conclusions based on the former to the latter. However, current and future LES and experimental study can help to illustrate the tradeoffs among the degree of swirl and the choice of bluff-body shapes in devices such as industrial burners and gas turbines.

Experimental Study of Humid Air Diffusion Flames in HAT Cycle

Combustion with humid air is a key process of humid air turbine (HAT) cycles. Many studies have been undertaken to understand the influence of moisture in air on combustion fields. This study focuses on investigating the differences between the propane/humid air turbulent diffusion flame in a bluff-body burner and the same flame with normal dry air. The moisture levels were achieved by injecting steam into dry air. Particle image velocimetry was used to study the velocity fields experimentally in the humid reactive burner flow and the equivalent non-humid flow. The temperature fields of flames were measured using high temperature thermocouples, and the NO distributions were obtained with gas detection instruments. The results show that although humid air reactive flow fields are similar to the non-humid flow fields in general, there are some differences in the humid air combustion flow field comparing to the same combustion flow field with normal dry air: the center of the reversed-flow region goes forward; the dimension of the reversed-flow region is smaller. An analysis of NO formation revealed NO reduction of humid air flames due to the presence of steam. It is suggested that humid air combustion is helpful to shorten the axial length of combustor, and reduce the formation of pollution.