A novel airblast injector is designed for gas turbine combustors. Unlike standard pressure swirl and prefilming/non-prefilming air blast atomizers, the novel injector is designed to improve the fuel injection delivery to the injector and improve atomization of the fuel by using a porous stainless steel tube. There are three swirling air streams in the injector. The liquid fuel is injected through the porous tube, with 7 micron porosity, between the swirling air streams, viz. an inner swirling air through the tube and the other two swirling air streams merging downstream of the tube. The swirl vane angles and the air split ratio are selected to increase the amount of air through the injector and facilitate the atomization process. The liquid fuel is injected through the outer surface of the porous tube, due to the permeability of the tube, produces a thin liquid sheet on the inner surface of the tube. The atomization occurs by surface stripping of the liquid sheet. The advantage of such an injector is that it produces a liquid sheet with uniform thickness around the circumference of the tube under all liquid loading. The porous tube also increases the surface area of contact between the fuel and air and produces a fine spray at engine idle conditions. An experimental approach is adopted in the present study to characterize the spray and aerodynamics of the injector for Jet-A and Gas-To-Liquid (GTL) fuels at atmospheric conditions. The effect of flare height on the Sauter Mean Diameter (SMD) is also studied. Spray characterization, droplet size and volume flux are investigated with PDI measurements. The effect of pressure drop and fuel properties on SMD distribution is analyzed. Velocity profiles at downstream of the injector are obtained from LDV measurements, and the velocity profile at the exit of the injector is also analyzed. A central toroidal recirculation zone (CTRZ) is observed at the exit of the injector. The effect of different configurations of the injector on spray characteristics is studied. A correlation for SMD is obtained.
In the present investigation, a novel fuel injection concept is developed for Dry Low NOx combustors. A multi-injector block is used for fuel-air mixing and flame stabilization. The injectors in the multi-injector block are equally spaced in a rectangular grid of 3×3. Each injector of the multi-injector block has a porous concentric tube through which fuel is injected into the annular space around the porous tube. The porous tube is made up of stainless steel with 30 μm porosity. Air enters the annular space around the porous tube through eight tubes that surround the porous tube. The fuel and air mix in the annular space between the injector wall and the porous tube. A CO2 mixing technique is adopted to investigate the fuel-air mixing quality under non-reacting atmospheric conditions. CO2 is used to simulate the fuel. The CO2 concentrations are converted to fuel mass fractions for comparison. The experiments are carried out at pressure drop of 4% across the injector. The fuel mass fraction contours show an annular ring of low fuel concentration downstream of the individual injectors with a high concentration in the Central Toroidal Recirculation zone (CTRZ). Furthermore, PIV measurements are conducted to study the injector aerodynamics under the same operating conditions. The PIV measurements also show CTRZ downstream of the individual injector. The jet emanating from the injectors expands gradually downstream. An outer weak recirculation zone (ORZ) is also observed between the jets. Preliminary combustion experiments are carried out to observe the flame shape and heat release distribution. The flame shape follows the velocity contours. The combustion studies show that the flame length is longer. The long flame length is due to the high velocities at the exit of the injector. A probability density function (pdf) is generated for the fuel mixture fraction. The pdf is based on the mixture fraction and velocity data obtained at the exit of the injector block. Chemkin analysis is carried out to estimate the emissions based on the experimentally obtained pdfs.
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