Yixiang Yuan

Aiming at the problem of the narrow combustion stability boundary, a conical swirler was designed and constructed based on the concept of fuel distribution. The blowout performance was studied at specified low operating conditions by a combination of experimental testing and numerical simulations. Research results indicate that the technique of the fuel distribution can enhance the combustion stability and widen the boundary of flameout within the range of testing conditions. The increase of the fuel distribution ratio improves the combustion stability but leads to an increase in NOx emission simultaneously. The simulation results show the increase of the fuel distribution ratio causes contact ratio increase in the area of lower reference velocity and gas temperature increase. The increased contact ratio and temperature contribute to the blowout performance enhancement, which is identical to the analysis result of the Damkohler number. The reported work in this paper has potential application value for the development of an industrial burner and combustor with high stability and low NOx emission, especially when the combustion system is required to be stable and efficient at low working conditions.

Transverse jets in crossflow are widely used in energy systems, especially as dilution air jets, fuel/air mixers, and combustion equipment, and have received extensive attention and plenty of research. However, the studies of the circular transverse jet issued from a circular gap at the circumferential direction of a tube in crossflow are very limited. This paper studies a relatively new jet: the circular transverse jet. Firstly, numerical calculations are conducted under different turbulence models but with the same boundary conditions. By comparing the numerical results of different turbulence models with the existing experimental data, the turbulence model which is most suitable for the numerical calculation of the circular transverse jet is selected. Then, this turbulence model is used to calculate and analyze the flow field structure and its characteristics. It is found that due to the aerodynamic barrier effect of the high-velocity jet, a negative pressure zone is formed behind the jet trajectory; the existence of the negative pressure zone causes the formation of a vortex structure and a recirculation zone downstream the circular transverse jet; and the length/width ratio of the recirculation zone does not change with the changes of the crossflow and the jet parameters. It means that the recirculation zone is a fixed shape for a definite device. This would be fundamental references for the studying of fuel/air mixing characteristics and combustion efficiency when the circular transverse jet is used as a fuel/air mixer and stable combustion system.

The multihole tube is an important component used for lean premixed prevaporized low-emission combustion in micro gas turbines, as it plays a key role in establishing uniform fuel-air mixture before flowing into the combustor. Recognizing that poor fuel-air mixing leads to increased emissions, it is therefore imperative to characterize the extent of fuel-air mixing at the exit of the multihole tube. In the present investigation, mixing characterization experiments were conducted by mapping the distribution of fuel-air equivalence ratios at the tube exit with gas analysis technique. Two different multihole tube configurations were tested and compared using aviation kerosene. Experiments were performed under atmospheric pressure, with an inlet air temperature of 480 K and an overall fuel-air equivalence ratio of 0.6. While the baseline configuration yielded the maximum magnitude of equivalence ratio deviation close to 35% at the tube exit, the modified configuration demonstrated much improved mixing uniformity with the maximum extent of equivalence ratio deviation being reduced to ∼10%. A three-dimensional computational fluid dynamics simulation was also carried out to illustrate the resulting flow field associated with the baseline configuration and suggest the needed configuration modifications for performance improvement. Experimental and computational results indicate that the matching of fuel atomization and flow field is the primary factor affecting fuel-air mixture uniformity. By optimizing the flow rate ratio of the axial jet air in the nozzle section to the swirling jet air in the tube section as well as the axial jet momentum, enhanced fuel-air mixture uniformity can be achieved.