No abstract

Transverse dilution jets are widely used in combustion systems. The current research provides a detailed study of the primary jets of a realistic annular combustion chamber sector. The combustor sector comprises an aerodynamic diffuser, inlet cowl, combustion dome, primary dilution jets, secondary dilution jets and cooling strips to provide convective cooling to the liner. The chamber contracts toward the end to fit the turbine nozzle ring. 2D PIV is employed at an atmospheric pressure drop of 4% (isothermal) to delineate the flow field characteristics. The laser is introduced to the sector through the exit flange. The interaction between the primary jets and the swirling flow as well as the sensitivity of the primary jets to perturbations is discussed. The perturbation study includes: effect of partially blocking the jets, one at a time, the effect of blocking the convective cooling holes, placed underneath the primary jets and shooting perpendicular to it. In addition, the effect of reducing the size of the primary jets as well as off-centering the primary jets is explained. Moreover, PIV is employed to study the flow field with and without fuel injection at four different fuel flow rates. The results show that the flow field is very sensitive to perturbations. The cooling air interacts with the primary jet and influences the flow field although the momentum ratio has a 100:1 order of magnitude. The results also show that the big primary jets dictate the flow field in the primary zone as well as the secondary zone. However, relatively smaller jets mainly influence the primary combustion zone because most of the jet is recirculated back to the CRZ. Also, the jet penetration is reduced with 25% and 11.5% corresponding to a 77% and 62% reduction of the jet’s area respectively. The study indicates the presence of a critical jet diameter beyond which the dilution jets have minimum impact on the secondary region. The jet off-centering shows significant effect on the flow field though it is in the order of 0.4 mm. The fuel injection is also shown to influence the flow field as well as the primary jets angle. High fuel flow rate is shown to have very strong impact on the flow field and thus results in a strong distortion of both the primary and secondary zones. The results provide useful methods to be used in the flow field structure control. Most of the effects shown are attributed to the difference in jet opposition. Hence, the results are applicable to reacting flow.

No abstract

Gas Turbine Combustor Flow Structure Control Tbrougb Modification of the Chamber GeometryAs combustors are put in ser\'ice, problems such as erosion, hot spots, and liner oxidation occur, and a solution based on lessons learned is essenticd to avoid similar problems in future combustor generations. In the present paper, a combustor flow structure control via combustor geometry alteration is investigated using laser Doppler vetocimetry. Mainly, three configurations are studied. The first configuration is that of a .swirl cup feeding a dump (rectangular cro.'is section) combustor. The rectangular chamber is configured with a width to breadth (w/b) ratio of 85%. The .-¡econd configuration is similar to the first one, but a combustion dome is installed. The dome is configured with a 9 deg difference in the expansion angle on both sides (asymmetric dome). The third configuration is that of a swirl cup and a combustion dome installed in a prototype comhustor (single cumular combustor (SAC) sector), with both primary and secimdary dilution jets blocked. The SAC is configured with a cross sectional area that decreases toward the exit through the tilting of the inner combustor liner. The results show that the combustion dome eliminates the comer recirculation zone and the low velocity region close to the combustor walls. The combustion dome asymmetry results in a significant asymmetry in the velocity magnitude, as well as the turbulence activities and the tilting of the central recirculation zone (CRZ) toward the surface with the higher expansion angle. The liner tilting results in a 40% reduction in the length of the CRZ. However once the primary jets are open, they define the termination point of the CRZ. The chamber w/b ratio results in a CRZ with the scmxe diameter ratio (85%) in all configurations. Interestingly, the maximum reverse flow velocity is roughly constant in all measurement plans and configurations up to a downstream distcmce of IR (R is the flare radius). However, with open primary jets, the CRZ strength increases appreciably. It appears that the confinement dictates both the flow field outside the CRZ and the size of the CRZ, white the swirl cup configuration mainly influences the strength of the CRZ. Regarding turbulence activities, the presence of the dome damps the fluctuations in the expanding swirling jet region. On the other hand, the primary jets increase the turbulence activities appreciably in the jet impingement region, as well as the upper portion of the CRZ (60% increase).

The current research provides the impact of hydrogen enrichment on gas turbine combustion characteristics. The uniqueness of this study is it isolates the hydrogen effects while minimizing the impact of other parameters that are known to influence combustion characteristics. Experiments are carried out under high operating pressure and a wide range of firing temperatures that extend from the Lean Blow Out (LBO) limit to beyond J class firing temperature. Aerodynamic effects are isolated by using a perforated plate burner to provide a simple flame structure. The study is conducted under perfectly premixed conditions to exclude the mixing effects from the problem under investigation. Air flow, residence time, pressure and temperature are all held constant to enable back to back comparison. Hydrogen enrichment is varied from 0 to 25 percent by volume while holding the combustor exit temperature constant. No cooling air or effusion air is used in the combustion zone to ensure that there is no impact on the problem under investigation and to focus the study on kinetics effects and flame shape variation. NOx, CO emissions, LBO limits as well as flame luminosity are reported. Oxygen and carbon dioxide are measured at the combustor exit and used to ensure test integrity and for confirmation of the exit temperature. A reactor network model is used to mimic the experimental work and study sensitivity. The effective residence time in the model is varied slightly to mimic the slight change observed in flame length with hydrogen addition. This basic research provides a key resolution to the contradictory results that are typically reported in the literature for the impact of hydrogen on NOx emissions.